Power conversion device and control method for same

Abstract

The present invention achieves a power conversion device capable of handling a wide input / output voltage ratio and operating with high efficiency. A power conversion device (1) comprises: first through fourth switches (AH to BL) connected to the primary side of a transformer (T1), and fifth to eighth switches (CH to DL) connected to the secondary side thereof; and a control circuit (10). The control circuit (10) repeats the following control. The first switch (AH) and the fourth switch (BL) and the fifth switch (CH) and the eighth switch (DL) are turned on, the fifth switch (CH) and the eighth switch (DL) are turned off, the first switch (AH) and the fourth switch (BL) are turned off, the second switch (AL) and the third switch (BH) and the sixth switch (CL) and the seventh switch (DH) are turned on, the sixth switch (CL) and the seventh switch (DH) are turned off, and the second switch (AL) and the third switch (BH) are turned off.

Description

Power conversion device and control method thereof

[0001] The present disclosure relates to a power conversion device and a control method thereof.

[0002] Patent Document 1 discloses a power conversion device having a phase-shift full-bridge configuration in which a secondary-side transistor is controlled in synchronization with a primary-side transistor.

[0003] Japanese Patent No. 6849373

[0004] However, in the power conversion device disclosed in Patent Document 1, the operating conditions (specifically, the operating conditions related to the switching frequency and the phase shift amount of the power conversion device) change to accommodate a wide input / output voltage ratio, and depending on the operating conditions, there is a problem that the secondary-side transistor turns off when a large current is flowing, resulting in a decrease in efficiency.

[0005] Therefore, the present disclosure provides a power conversion device capable of operating with high efficiency while accommodating a wide input / output voltage ratio, and a control method thereof.

[0006] A power conversion device according to the present disclosure includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, a seventh switch, an eighth switch, and a control circuit. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. The isolation transformer has a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The fifth switch is provided on a third path connecting the first output terminal and the second output terminal. The sixth switch is provided on the third path and connected in series with the fifth switch. The seventh switch is provided on a fourth path different from the third path connecting the first output terminal and the second output terminal. The eighth switch is provided on the fourth path and connected in series with the seventh switch. The control circuit controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch. The isolation transformer further has a secondary winding connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. The control circuit sequentially repeats the following controls (1) to (6) to control the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is lower than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor.(1) Turn on one of the first and second switch groups and the fifth and eighth switches. (2) Turn off the fifth and eighth switches. (3) Turn off the one of the switch groups. (4) Turn on the other of the first and second switch groups and the sixth and seventh switches. (5) Turn off the sixth and seventh switches. (6) Turn off the other of the switch groups.

[0007] A power conversion device according to the present disclosure includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, a seventh switch, an eighth switch, and a control circuit. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. The isolation transformer has a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The fifth switch is provided on a third path connecting the first output terminal and the second output terminal. The sixth switch is provided on the third path and connected in series with the fifth switch. The seventh switch is provided on a fourth path different from the third path connecting the first output terminal and the second output terminal. The eighth switch is provided on the fourth path and connected in series with the seventh switch. The control circuit controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch. The isolation transformer further has a secondary winding connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. The control circuit sequentially repeats the following controls (1) to (6) to control the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor.(1) Turn on one of the first and second switch groups, and the fifth and eighth switches. (2) Turn off one of the switch groups. (3) Turn off the fifth and eighth switches. (4) Turn on the other of the first and second switch groups, and the sixth and seventh switches. (5) Turn off the other switch group. (6) Turn off the sixth and seventh switches.

[0008] A power conversion device according to the present disclosure includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, a seventh switch, an eighth switch, and a control circuit. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. The isolation transformer has a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The fifth switch is provided on a third path connecting the first output terminal and the second output terminal. The sixth switch is provided on the third path and connected in series with the fifth switch. The seventh switch is provided on a fourth path different from the third path connecting the first output terminal and the second output terminal. The eighth switch is provided on the fourth path and connected in series with the seventh switch. The control circuit controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch. The secondary winding of the isolation transformer is further connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch.The control circuit controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, by sequentially repeating the following controls (1) to (8): (1) Turn off the sixth switch and the seventh switch, and turn on the first switch; (2) Turn on the fourth switch, the fifth switch, and the eighth switch; (3) Turn off the first switch; (4) Turn off the fourth switch; (5) Turn off the fifth switch and the eighth switch, and turn on the second switch; (6) Turn on the third switch, the sixth switch, and the seventh switch; and (7) Turn off the second switch. (8) Turn off the third switch. Furthermore, the control circuit sequentially repeats the following controls (9) to (16) to control the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, so that the switching phase of the first switch lags behind the switching phase of the fourth switch, and so that the switching phase of the second switch lags behind the switching phase of the third switch. (9) Turn off the sixth switch and the seventh switch, and turn on the third switch. (10) Turn on the second switch, the fifth switch, and the eighth switch. (11) Turn off the third switch. (12) Turn off the second switch. (13) Turn off the fifth switch and the eighth switch. Turn on the fourth switch. (14) Turn on the first switch, the sixth switch, and the seventh switch. (15) Turn off the fourth switch. (16) Turn off the first switch.

[0009] A power conversion device according to the present disclosure includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, a seventh switch, an eighth switch, and a control circuit. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. The isolation transformer has a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The fifth switch is provided on a third path connecting the first output terminal and the second output terminal. The sixth switch is provided on the third path and connected in series with the fifth switch. The seventh switch is provided on a fourth path different from the third path connecting the first output terminal and the second output terminal. The eighth switch is provided on the fourth path and connected in series with the seventh switch. The control circuit controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch. The isolation transformer has a secondary winding connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. The control circuit controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, by sequentially repeating the following controls (1) to (10):(1) Turn on the first switch. (2) Turn off the sixth and seventh switches. (3) Turn off the third switch. (4) Turn on the fourth, fifth, and eighth switches. (5) Turn off the first switch. (6) Turn on the second switch. (7) Turn off the fifth and eighth switches. (8) Turn off the fourth switch. (9) Turn on the third, sixth, and seventh switches. (10) Turn off the second switch. The control circuit further controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch, by sequentially repeating the following controls (11) to (20): (11) Turn on the third switch; (12) Turn off the sixth switch and the seventh switch; (13) Turn off the first switch; (14) Turn on the second switch, the fifth switch, and the eighth switch; (15) Turn off the third switch; (16) Turn on the fourth switch; (17) Turn off the fifth switch and the eighth switch; and (18) Turn off the second switch. (19) Turn on the first switch, the sixth switch, and the seventh switch. (20) Turn off the fourth switch.

[0010] A power conversion device according to the present disclosure includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, and a control circuit. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. The isolation transformer has a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The control circuit controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch. The isolation transformer further has a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to the first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other end of the fifth switch and the other end of the sixth switch are connected to the second output terminal. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. The control circuit controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is lower than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, by sequentially repeating the following controls (1) to (6): (1) Turn on one of the first and second switch groups and the fifth switch, (2) Turn off the fifth switch, (3) Turn off one of the switch groups, and (4) Turn on the other of the first and second switch groups and the sixth switch.(5) Turn off the sixth switch. (6) Turn off the other switch group.

[0011] A power conversion device according to the present disclosure includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, and a control circuit. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. The isolation transformer has a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The control circuit controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch. The isolation transformer further has a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to the first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other end of the fifth switch and the other end of the sixth switch are connected to the second output terminal. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. The control circuit controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, by sequentially repeating the following controls (1) to (6): (1) Turn on one of the first and second switch groups and the fifth switch, (2) turn off one of the switch groups, (3) turn off the fifth switch, and (4) turn on the other of the first and second switch groups and the sixth switch.(5) Turn off the other switch group. (6) Turn off the sixth switch.

[0012] A power conversion device according to the present disclosure includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, and a control circuit. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. The isolation transformer has a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The control circuit controls the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch. The isolation transformer further has a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to the first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other end of the fifth switch and the other end of the sixth switch are connected to the second output terminal. The control circuit sequentially repeats controls (1) to (8) to control the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch. (1) Turn off the sixth switch and turn on the first switch, (2) Turn on the fourth and fifth switches, (3) Turn off the first switch, and (4) Turn off the fourth switch.(5) Turn off the fifth switch and turn on the second switch. (6) Turn on the third switch and the sixth switch. (7) Turn off the second switch. (8) Turn off the third switch. The control circuit further repeats the following controls (9) to (16) in order to control the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch. (9) Turn off the sixth switch and turn on the third switch. (10) Turn on the second switch and the fifth switch. (11) Turn off the third switch. (12) Turn off the second switch. (13) Turn off the fifth switch and turn on the fourth switch. (14) Turn on the first switch and the sixth switch. (15) Turn off the fourth switch. (16) Turn off the first switch.

[0013] A power conversion device according to the present disclosure includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, and a control circuit. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. The isolation transformer has a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The control circuit controls the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch. The isolation transformer further has a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to the first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other end of the fifth switch and the other end of the sixth switch are connected to the second output terminal. The control circuit controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch. The control circuit sequentially repeats the following controls (1) to (10) to control the switching of the first switch, the second switch, the third switch, and the fourth switch. (1) Turn on the first switch. (2) Turn off the sixth switch. (3) Turn off the third switch. (4) Turn on the fourth and fifth switches. (5) Turn off the first switch.(6) Turn on the second switch. (7) Turn off the fifth switch. (8) Turn off the fourth switch. (9) Turn on the third switch and the sixth switch. (10) Turn off the second switch. The control circuit further repeats the following controls (11) to (20) in order to control the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch. (11) Turn on the third switch. (12) Turn off the sixth switch. (13) Turn off the first switch. (14) Turn on the second switch and the fifth switch. (15) Turn off the third switch. (16) Turn on the fourth switch. (17) Turn off the fifth switch. (18) Turn off the second switch. (19) Turn on the first switch and the sixth switch. (20) Turn off the fourth switch.

[0014] A control method according to the present disclosure is a control method for a power conversion apparatus as follows. The power conversion apparatus includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, a seventh switch, and an eighth switch. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. A primary winding of the isolation transformer is connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between a second node and the primary winding. The fifth switch is provided on a third path connecting the first output terminal and the second output terminal. The sixth switch is provided on the third path and connected in series with the fifth switch. The seventh switch is provided on a fourth path different from the third path connecting the first output terminal and the second output terminal. The eighth switch is provided on the fourth path and connected in series with the seventh switch. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. The control method controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are lower than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and in this case, the following controls (1) to (6) are repeated in order: (1) Turn on one of the first switch group and the second switch group, and the fifth switch and the eighth switch; (2) Turn off the fifth switch and the eighth switch. (3) Turn off one of the switch groups, (4) turn on the other of the first and second switch groups, the sixth switch, and the seventh switch.(5) Turn off the sixth switch and the seventh switch. (6) Turn off the other switch group.

[0015] A control method according to the present disclosure is a control method for a power conversion apparatus. The power conversion apparatus includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, a seventh switch, and an eighth switch. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path connecting the first input terminal and the second input terminal, which is different from the first path. The fourth switch is provided on the second path and connected in series with the third switch. A primary winding of the isolation transformer is connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The fifth switch is provided on a third path connecting the first output terminal and the second output terminal. The sixth switch is provided on the third path and connected in series with the fifth switch. The seventh switch is provided on a fourth path different from the third path connecting the first output terminal and the second output terminal. The eighth switch is provided on the fourth path and connected in series with the seventh switch. The isolation transformer further has a secondary winding connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. In the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and in this case, the following controls (1) to (6) are repeated in order. (1) Turn on one of the first and second switch groups and the fifth and eighth switches, and (2) turn off one of the switch groups.(3) Turn off the fifth switch and the eighth switch. (4) Turn on the other switch group of the first switch group and the second switch group and the sixth switch and the seventh switch. (5) Turn off the other switch group. (6) Turn off the sixth switch and the seventh switch.

[0016] A control method according to the present disclosure is a control method for a power conversion apparatus. The power conversion apparatus includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, a seventh switch, and an eighth switch. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path connecting the first input terminal and the second input terminal, which is different from the first path. The fourth switch is provided on the second path and connected in series with the third switch. A primary winding of the isolation transformer is connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The fifth switch is provided on a third path connecting the first output terminal and the second output terminal. The sixth switch is provided on the third path and connected in series with the fifth switch. The seventh switch is provided on a fourth path different from the third path connecting the first output terminal and the second output terminal. The eighth switch is provided on the fourth path and connected in series with the seventh switch. The isolation transformer further has a secondary winding connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. In the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, and in this case, the following controls (1) to (8) are repeated in order: (1) Turn off the sixth switch and the seventh switch, and turn on the first switch.(2) Turn on the fourth switch, the fifth switch, and the eighth switch. (3) Turn off the first switch. (4) Turn off the fourth switch. (5) Turn off the fifth switch and the eighth switch, and turn on the second switch. (6) Turn on the third switch, the sixth switch, and the seventh switch. (7) Turn off the second switch. (8) Turn off the third switch. The control method further controls the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch, and in this case, the following controls (9) to (16) are repeated in order. (9) Turn off the sixth switch and the seventh switch. (10) Turn on the third switch. (11) Turn on the second switch, the fifth switch, and the eighth switch. (12) Turn off the third switch. (13) Turn off the fifth switch and the eighth switch, and turn on the fourth switch. (14) Turn on the first switch, the sixth switch, and the seventh switch. (15) Turn off the fourth switch. (16) Turn off the first switch.

[0017] A control method according to the present disclosure is a method for controlling a power conversion apparatus. The power conversion apparatus includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, a sixth switch, a seventh switch, and an eighth switch. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path different from the first path connecting the first input terminal and the second input terminal. The fourth switch is provided on the second path and connected in series with the third switch. A primary winding of the isolation transformer is connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The fifth switch is provided on a third path connecting the first output terminal and the second output terminal. The sixth switch is provided on the third path and connected in series with the fifth switch. The seventh switch is provided on a fourth path different from the third path connecting the first output terminal and the second output terminal. The eighth switch is provided on the fourth path and connected in series with the seventh switch. The isolation transformer further has a secondary winding connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. In the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, and in this case, the following controls (1) to (10) are repeated in order: (1) Turn on the first switch; (2) Turn off the sixth switch and the seventh switch;(3) Turn off the third switch. (4) Turn on the fourth switch, the fifth switch, and the eighth switch. (5) Turn off the first switch. (6) Turn on the second switch. (7) Turn off the fifth switch and the eighth switch. (8) Turn off the fourth switch. (9) Turn on the third switch, the sixth switch, and the seventh switch. (10) Turn off the second switch. The control method further controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch, and in this case, the following controls (11) to (20) are repeated in order. (11) Turn on the third switch. (12) Turn off the sixth and seventh switches. (13) Turn off the first switch. (14) Turn on the second, fifth, and eighth switches. (15) Turn off the third switch. (16) Turn on the fourth switch. (17) Turn off the fifth and eighth switches. (18) Turn off the second switch. (19) Turn on the first, sixth, and seventh switches. (20) Turn off the fourth switch.

[0018] A control method according to the present disclosure is a method for controlling a power conversion apparatus. The power conversion apparatus includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, and a sixth switch. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path connecting the first input terminal and the second input terminal, which is different from the first path. The fourth switch is provided on the second path and connected in series with the third switch. A primary winding of the isolation transformer is connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The isolation transformer further includes a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of a fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of a sixth switch. The other end of the fifth switch and the other end of the sixth switch are connected to a second output terminal. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. In the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are lower than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor. In this case, the following controls (1) to (6) are repeated in order: (1) Turn on one of the first switch group and the second switch group, and the fifth switch; (2) Turn off the fifth switch. (3) Turn off one of the switch groups. (4) Turn on the other of the first and second switch groups and the sixth switch. (5) Turn off the sixth switch. (6) Turn off the other switch group.

[0019] A control method according to the present disclosure is a method for controlling a power conversion apparatus. The power conversion apparatus includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, and a sixth switch. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path connecting the first input terminal and the second input terminal, which is different from the first path. The fourth switch is provided on the second path and connected in series with the third switch. A primary winding of the isolation transformer is connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The isolation transformer further includes a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of a fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of a sixth switch. The other end of the fifth switch and the other end of the sixth switch are connected to a second output terminal. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. In the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor. In this case, the following controls (1) to (6) are repeated in order: (1) Turn on one of the first switch group and the second switch group, and the fifth switch; (2) Turn off one of the switch groups. (3) Turn off the fifth switch. (4) Turn on the other switch group of the first switch group and the second switch group and the sixth switch. (5) Turn off the other switch group. (6) Turn off the sixth switch.

[0020] A control method according to the present disclosure is a method for controlling a power conversion apparatus. The power conversion apparatus includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, and a sixth switch. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path connecting the first input terminal and the second input terminal, which is different from the first path. The fourth switch is provided on the second path and connected in series with the third switch. A primary winding of the isolation transformer is connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The isolation transformer further has a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of a fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of a sixth switch. In the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch. In this case, the following controls (1) to (8) are repeated in order: (1) Turn off the sixth switch and turn on the first switch; (2) Turn on the fourth switch and the fifth switch; and (3) Turn off the first switch. (4) Turn off the fourth switch. (5) Turn off the fifth switch and turn on the second switch. (6) Turn on the third switch and the sixth switch. (7) Turn off the second switch.(8) Turn off the third switch. Furthermore, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch. In this case, the following controls (9) to (16) are repeated in order. (9) Turn off the sixth switch and turn on the third switch. (10) Turn on the second switch and the fifth switch. (11) Turn off the third switch. (12) Turn off the second switch. (13) Turn off the fifth switch and turn on the fourth switch. (14) Turn on the first switch and the sixth switch. (15) Turn off the fourth switch. (16) Turn off the first switch.

[0021] A control method according to the present disclosure is a method for controlling a power conversion apparatus. The power conversion apparatus includes a first switch, a second switch, a third switch, a fourth switch, an isolation transformer, a resonant capacitor, a resonant inductor, a fifth switch, and a sixth switch. The first switch is provided on a first path connecting a first input terminal and a second input terminal. The second switch is provided on the first path and connected in series with the first switch. The third switch is provided on a second path connecting the first input terminal and the second input terminal, which is different from the first path. The fourth switch is provided on the second path and connected in series with the third switch. A primary winding of the isolation transformer is connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch. The resonant capacitor and the resonant inductor are connected between the first node and the primary winding or between the second node and the primary winding. The isolation transformer further has a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of a fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of a sixth switch. The other end of the fifth switch and the other end of the sixth switch are connected to a second output terminal. In the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch. In this case, the following controls (1) to (10) are repeated in order: (1) Turn on the first switch; (2) Turn off the sixth switch. (3) Turn off the third switch. (4) Turn on the fourth and fifth switches. (5) Turn off the first switch. (6) Turn on the second switch. (7) Turn off the fifth switch.(8) Turn off the fourth switch. (9) Turn on the third switch and the sixth switch. (10) Turn off the second switch. Furthermore, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch. In this case, the following controls (11) to (20) are repeated in order. (11) Turn on the third switch. (12) Turn off the sixth switch. (13) Turn off the first switch. (14) Turn on the second switch and the fifth switch. (15) Turn off the third switch. (16) Turn on the fourth switch. (17) Turn off the fifth switch. (18) Turn off the second switch. (19) Turn on the first switch and the sixth switch. (20) Turn off the fourth switch.

[0022] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0023] According to a power conversion device according to an aspect of the present disclosure, it is possible to operate with high efficiency while accommodating a wide input / output voltage ratio.

[0024] 1 is a circuit configuration diagram showing an example of a power conversion device according to a first embodiment. FIG. 1 is a timing chart showing a case where optimization control is not performed on each switch in the first control mode. FIG. 2 is a timing chart showing a case where optimization control is performed on each switch in the first control mode. FIG. 3 is a timing chart showing a case where optimization control is not performed on each switch in the second control mode. FIG. 4 is a timing chart showing a case where optimization control is performed on each switch in the second control mode. FIG. 5 is a timing chart showing a case where optimization control is not performed on each switch in the third control mode. FIG. 6 is a timing chart showing a case where optimization control is performed on each switch in the third control mode. FIG. 7 is a timing chart showing a case where optimization control is not performed on each switch in the fourth control mode. FIG. 8 is a timing chart showing a case where optimization control is performed on each switch in the fourth control mode. 10 is a flowchart showing an example of a control method according to another embodiment.

[0025] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0026] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0027] (First embodiment) Hereinafter, a power conversion device according to a first embodiment will be described.

[0028] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device 1 according to the first embodiment.

[0029] The power conversion device 1 is an isolated DC-DC converter that boosts or bucks an input voltage to a predetermined voltage and outputs it. For example, the power conversion device 1 is an LLC converter that utilizes LLC resonance due to the leakage inductance, excitation inductance, and resonant capacitor of a transformer. The LLC converter performs frequency control to change the switching frequency of each switch on the primary side and phase shift control to change the phase difference between the switching of each switch on the primary side, thereby changing the input / output voltage ratio (Gain), and thereby enabling the desired power output.

[0030] The power conversion device 1 has terminals t1, t2, t3, and t4. Terminal t1 is an example of a first input terminal. Terminal t2 is an example of a second input terminal, specifically a ground terminal. Terminal t3 is an example of a first output terminal. Terminal t4 is an example of a second output terminal, specifically a ground terminal. Note that, since the power conversion device 1 is an isolated DC-DC converter, terminals t2 and t4 are electrically isolated. An input voltage and an input current are input to terminal t1. The input voltage is the voltage between terminals t1 and t2. An output voltage and an output current are output from terminal t3. The output voltage is the voltage between terminals t3 and t4.

[0031] For example, the power conversion device 1 is mounted on a vehicle and applied to an electric vehicle system that drives auxiliary equipment. For example, a high-voltage lithium-ion battery or the like is connected to terminals t1 and t2, and a low-voltage lead-acid battery and auxiliary equipment are connected to terminals t3 and t4. For example, the voltage of a lithium-ion battery is 250 V to 450 V, and the voltage of a lead-acid battery is 10 V to 16 V. For example, to convert a high voltage of 250 V to 450 V to a low voltage of 10 V to 16 V, a power conversion device 1 such as an LLC converter that supports a wide input / output voltage ratio is used.

[0032] The power conversion device 1 includes switches AH, AL, BH, BL, CH, CL, DH, and DL, a transformer T1, a capacitor Cr, an inductor Lr, and a control circuit 10.

[0033] The switch AH is a switch provided on the path P1 connecting the terminal t1 and the terminal t2. The switch AH is an example of a first switch. The path P1 is an example of a first path. The switch AH is, for example, an N-channel metal oxide semiconductor field effect transistor (MOSFET). The drain of the switch AH is connected to the terminal t1, and the source of the switch AH is connected to the drain of the switch AL.

[0034] The switch AL is provided on the path P1 and is connected in series with the switch AH. The switch AL is an example of a second switch. The switch AL is, for example, an N-channel MOSFET. The drain of the switch AL is connected to the source of the switch AH, and the source of the switch AL is connected to the terminal t2.

[0035] The switches AH and AL are also referred to as the A phase.

[0036] The switch BH is a switch provided on a path P2 that connects the terminal t1 and the terminal t2 and is different from the path P1. The switch BH is an example of a third switch. The path P2 is an example of a second path. The switch BH is, for example, an N-channel MOSFET. The drain of the switch BH is connected to the terminal t1, and the source of the switch BH is connected to the drain of the switch BL.

[0037] The switch BL is provided on the path P2 and is connected in series with the switch BH. The switch BL is an example of a fourth switch. The switch BL is, for example, an N-channel MOSFET. The drain of the switch BL is connected to the source of the switch BH, and the source of the switch BL is connected to the terminal t2.

[0038] The switches BH and BL are also referred to as the B phase.

[0039] The transformer T1 is an example of an isolation transformer, and has a primary winding and a secondary winding that are insulated from each other.

[0040] The primary winding of the transformer T1 is connected between a node N1 on the path P1 between the switch AH and the switch AL, and a node N2 on the path P2 between the switch BH and the switch BL. The node N1 is an example of a first node, and the node N2 is an example of a second node.

[0041] The capacitor Cr and the inductor Lr are connected between the node N1 and the primary winding of the transformer T1 or between the node N2 and the primary winding of the transformer T1. The capacitor Cr is an example of a resonant capacitor, and the inductor Lr is an example of a resonant inductor. For example, the capacitor Cr is connected to the node N1, the inductor Lr is connected to the node N1 via the capacitor Cr, and the capacitor Cr and the inductor Lr are connected in series. The inductor Lr may be provided as a separate inductor, or may be provided by utilizing the leakage inductance of the transformer T1.

[0042] The capacitor Cr and the inductor Lr may be connected to the node N2. In this case, one end of the primary winding of the transformer T1 is connected to the node N1, and the other end of the primary winding of the transformer T1 is connected to the node N2 via the capacitor Cr and the inductor Lr. Although the example in which the capacitor Cr is connected to the transformer T1 via the inductor Lr has been shown, the inductor Lr may be connected to the transformer T1 via the capacitor Cr. For example, the capacitor Cr and the inductor Lr shown in FIG. 1 may be interchanged. However, if the inductor Lr is provided by utilizing the leakage inductance of the transformer T1, the inductor Lr is placed closer to the transformer T1 than the capacitor Cr (in other words, the capacitor Cr is connected to the transformer T1 via the inductor Lr).

[0043] In FIG. 1, the excitation inductance of the transformer T1 is indicated by an inductor Lm.

[0044] The switch CH is a switch provided on the path P3 connecting the terminal t3 and the terminal t4. The switch CH is an example of a fifth switch. The path P3 is an example of a third path. The switch CH is, for example, an N-channel MOSFET. The drain of the switch CH is connected to the terminal t3, and the source of the switch CH is connected to the drain of the switch CL.

[0045] The switch CL is provided on the path P3 and is connected in series with the switch CH. The switch CL is an example of a sixth switch. The switch CL is, for example, an N-channel MOSFET. The drain of the switch CL is connected to the source of the switch CH, and the source of the switch CL is connected to the terminal t4.

[0046] The switch DH is a switch provided on a path P4 that connects the terminal t3 and the terminal t4 and is different from the path P3. The switch DH is an example of a seventh switch. The path P4 is an example of a fourth path. The switch DH is, for example, an N-channel MOSFET. The drain of the switch DH is connected to the terminal t3, and the source of the switch DH is connected to the drain of the switch DL.

[0047] The switch DL is provided on the path P4 and is connected in series with the switch DH. The switch DL is an example of an eighth switch. The switch DL is, for example, an N-channel MOSFET. The drain of the switch DL is connected to the source of the switch DH, and the source of the switch DL is connected to the terminal t4.

[0048] The secondary winding of the transformer T1 is connected between a node N3 on the path P3 between the switch CH and the switch CL and a node N4 on the path P4 between the switch DH and the switch DL. The node N3 is an example of a third node, and the node N4 is an example of a fourth node.

[0049] 1 shows the parasitic capacitance of each switch, and each parasitic capacitance is connected in parallel to the corresponding switch in the equivalent circuit. Also, FIG. 1 shows the body diode of each switch, and each body diode is connected in parallel to the corresponding switch in the equivalent circuit. Specifically, the anode of each body diode is connected to the source of the corresponding switch in the equivalent circuit, and the cathode is connected to the drain of the corresponding switch.

[0050] The control circuit 10 controls the switching of the switches AH, AL, BH, BL, CH, CL, DH, and DL. For example, the control circuit 10 controls the switching of the switches AH, AL, BH, BL, CH, CL, DH, and DL by controlling gate drive circuits (not shown) connected to the gates of the switches AH, AL, BH, BL, CH, CL, DH, and DL via a PWM generator (not shown) or the like.

[0051] The control circuit 10 is realized by, for example, a computer including a processor (microprocessor) and a memory. The memory may be a read-only memory (ROM) or a random access memory (RAM), and can store programs executed by the processor. For example, the control circuit 10 is realized by a microcontroller.

[0052] Because the current value flowing on the secondary side is very large, if diodes are provided instead of the switches CH, CL, DH, and DL, conduction loss due to the forward voltage of the diodes will be large. For this reason, in the power conversion device 1, the switches CH, CL, DH, and DL are provided on the secondary side of the transformer T1, and the control circuit 10 performs synchronous rectification control by controlling the switches CH, CL, DH, and DL on the secondary side.

[0053] The control circuit 10 has four control modes, for example, a first control mode to a fourth control mode, for controlling the switches AH, AL, BH, and BL on the primary side.

[0054] In the first control mode, the control circuit 10 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is lower than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr. When the input / output voltage ratio is made larger than 1, the control circuit 10 operates in the first control mode.

[0055] In the second control mode, the control circuit 10 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr. When the input / output voltage ratio is made smaller than 1, the control circuit 10 operates in the second control mode.

[0056] In the third control mode and the fourth control mode, the control circuit 10 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, and so that the switching phase of the switch BL lags behind the switching phase of the switch AH and the switching phase of the switch BH lags behind the switching phase of the switch AL. Alternatively, in the third control mode and the fourth control mode, the control circuit 10 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, and so that the switching phase of the switch AH lags behind the switching phase of the switch BL and the switching phase of the switch AL lags behind the switching phase of the switch BH. Note that the amount of phase shift is larger in the fourth control mode than in the third control mode. When the input / output voltage ratio is made smaller than the input / output voltage ratio in the second control mode, the control circuit 10 operates in the third control mode. When the input / output voltage ratio is made smaller than the input / output voltage ratio in the third control mode, the control circuit 10 operates in the fourth control mode.

[0057] Next, the operation of the control circuit 10 in the first control mode will be described with reference to FIGS.

[0058] Figure 2 is a timing chart showing the first control mode without optimization control of the switches AH, AL, BH, BL, CH, CL, DH, and DL. From top to bottom, Figure 2 shows the current flowing through the primary winding of the transformer T1 (primary current), the current flowing through the secondary winding of the transformer T1 (secondary current), the gate voltages (secondary gate voltages) applied to the secondary switches CH, CL, DH, and DL, the gate voltages (primary B-phase gate voltages) applied to the primary switches BH and BL, and the gate voltages (primary A-phase gate voltages) applied to the primary switches AH and AL. The solid line in the graph of the primary current represents the total primary current, which is the sum of the resonant current and the excitation current, and the dashed line represents the excitation current. The solid line in the graph of the secondary gate voltage represents the gate voltages of the switches CH and DL, and the dashed line represents the gate voltages of the switches CL and DH. The solid line in the graph of the primary side B-phase gate voltage represents the gate voltage of switch BL, and the dashed line represents the gate voltage of switch BH. The solid line in the graph of the primary side A-phase gate voltage represents the gate voltage of switch AH, and the dashed line represents the gate voltage of switch AL. The same applies to the following Figures 3 to 9.

[0059] In Fig. 2, the control circuit 10 controls the secondary-side switches CH, CL, DH, and DL in synchronization with the primary-side switches AH, AL, BH, and BL. Specifically, the control circuit 10 synchronizes the switches CH and DL with the switches AH and BL, and synchronizes the switches CL and DH with the switches AL and BH. In this case, as shown in Fig. 2, it can be seen that the secondary-side switches CH, CL, DH, and DL are turned off at times when the secondary-side current is large. Therefore, in this case, the efficiency of the power conversion device 1 decreases.

[0060] Therefore, when the control circuit 10 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is lower than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, that is, when operating in the first control mode, the control circuit 10 performs the optimization control described in FIG. 3 .

[0061] 3 is a timing chart showing the case where optimization control is performed on the switches AH, AL, BH, BL, CH, CL, DH, and DL in the first control mode. The switches AH and BL are defined as a first switch group, and the switches AL and BH are defined as a second switch group.

[0062] In the first control mode, the control circuit 10 repeats the following controls (1) to (6) in order.

[0063] The control circuit 10 (1) turns on one of the first and second switch groups, as well as the switches CH and DL. In the example shown in Figure 3, the one switch group is the first switch group, i.e., the switches AH and BL, and the control circuit 10 (1) turns on the switches AH and BL and the switches CH and DL.

[0064] The control circuit 10 (2) turns off the switches CH and DL.

[0065] The control circuit 10 (3) turns off one of the switch groups. In the example shown in Figure 3, the control circuit 10 (3) turns off the switches AH and BL.

[0066] The control circuit 10 (4) turns on the other switch group of the first switch group and the second switch group and the switches CL and DH. In the example shown in Figure 3, the other switch group is the second switch group, that is, the switches AL and BH, and the control circuit 10 (4) turns on the switches AL and BH and the switches CL and DH.

[0067] The control circuit 10 (5) turns off the switches CL and DH.

[0068] The control circuit 10 (6) turns off the other switch group. In the example shown in Figure 3, the control circuit 10 (6) turns off the switches AL and BH.

[0069] When the switching frequency of the primary-side switches AH, AL, BH, and BL is set lower than the resonant frequency to achieve the target output voltage, the above-described controls (1) through (6) are repeated for the primary-side and secondary-side switches AH, AL, BH, BL, CH, CL, DH, and DL, thereby enabling the secondary-side switches CH, CL, DH, and DL to be turned off at a timing when the current flowing on the secondary side is small. Thus, high-efficiency operation is possible under the operating condition (i.e., the first control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is set lower than the resonant frequency, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0070] In the above (1), the control circuit 10 may turn on one switch group (e.g., switches AH and BL) and then turn on switches CH and DL. In the above (4), the control circuit 10 may turn on the other switch group (e.g., switches AL and BH) and then turn on switches CL and DH.

[0071] In this way, in (1) above, it is not necessary to synchronize the turn-on of one of the switch groups with the switches CH and DL, and in (4) above, it is not necessary to synchronize the turn-on of the other switch group with the switches CL and DH.

[0072] In the above (2), the control circuit 10 may turn off one of the switches CH and DL, and then turn off the other of the switches CH and DL. In the above (5), the control circuit 10 may turn off one of the switches CL and DH, and then turn off the other of the switches CL and DH.

[0073] In (2) above, one of the switches CH and DL is turned off earlier than the other switch, and in (5) above, one of the switches CL and DH is turned off earlier than the other switch, thereby preventing negative current from flowing through the secondary side path, reducing conduction loss and switching loss, and enabling even more efficient operation.

[0074] The control circuit 10 may simultaneously turn off the other of the switches CH and DL (the switch that turns off after the one switch) in (2) above and the one group of switches in (3) above. The control circuit 10 may also simultaneously turn off the other of the switches CL and DH (the switch that turns off after the one switch) in (5) above and the other group of switches in (6) above.

[0075] As long as one of switches CH and DL is turned off, it does not matter if the other of switches CH and DL is turned on for a relatively long time. Also, as long as one of switches CL and DH is turned off, it does not matter if the other of switches CL and DH is turned on for a relatively long time. Therefore, the turning off of the other of switches CH and DL in (2) above and the turning off of one of the switch groups in (3) above may be performed simultaneously, and the turning off of the other of switches CL and DH in (5) above and the turning off of the other of the switch groups in (6) above may be performed simultaneously.

[0076] In the above (1), the control circuit 10 may simultaneously turn on the switches CH and DL. In the above (4), the control circuit 10 may simultaneously turn on the switches CL and DH.

[0077] This makes it possible to balance the currents flowing through the switches CH and DL, and also to balance the currents flowing through the switches CL and DH, thereby suppressing variations in loss between the switches. By suppressing variations in loss between the switches, for example, it is possible to optimize thermal design or device selection, and reduce costs.

[0078] Although an example has been described in which one of the first and second switch groups is the first switch group, i.e., the switches AH and BL, and the other of the first and second switch groups is the second switch group, i.e., the switches AL and BH, this is not limiting. For example, in the above description, one of the switch groups may be replaced with the second switch group, i.e., the switches AL and BH, and the other switch group may be replaced with the first switch group, i.e., the switches AH and BL. This is because the winding of the transformer T1 may be reversed.

[0079] Next, the operation of the control circuit 10 in the second control mode will be described with reference to FIGS.

[0080] FIG. 4 is a timing chart when optimization control is not performed on the switches AH, AL, BH, BL, CH, CL, DH, and DL in the second control mode.

[0081] In Fig. 4, the control circuit 10 controls the secondary-side switches CH, CL, DH, and DL in synchronization with the primary-side switches AH, AL, BH, and BL. Specifically, the control circuit 10 synchronizes the switches CH and DL with the switches AH and BL, and synchronizes the switches CL and DH with the switches AL and BH. In this case, as shown in Fig. 4, the secondary-side switches CH, CL, DH, and DL are turned off at times when the secondary-side current is large. Therefore, the efficiency of the power conversion device 1 decreases in this case.

[0082] Therefore, when the control circuit 10 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, that is, when operating in the second control mode, the control circuit 10 performs the optimization control described in FIG. 5 .

[0083] 5 is a timing chart showing the case where optimization control is performed on the switches AH, AL, BH, BL, CH, CL, DH, and DL in the second control mode. The switches AH and BL are defined as a first switch group, and the switches AL and BH are defined as a second switch group.

[0084] In the second control mode, the control circuit 10 sequentially repeats the following controls (1) to (6).

[0085] The control circuit 10 (1) turns on one of the first and second switch groups and the switches CH and DL. In the example shown in Fig. 5, the one switch group is the first switch group, i.e., the switches AH and BL, and the control circuit 10 (1) turns on the switches AH and BL and the switches CH and DL.

[0086] The control circuit 10 (2) turns off one of the switch groups. In the example shown in Figure 5, the control circuit 10 (2) turns off the switches AH and BL.

[0087] The control circuit 10 (3) turns off the switches CH and DL.

[0088] The control circuit 10 (4) turns on the other switch group of the first switch group and the second switch group and the switches CL and DH. In the example shown in Figure 5, the other switch group is the second switch group, that is, the switches AL and BH, and the control circuit 10 (4) turns on the switches AL and BH and the switches CL and DH.

[0089] The control circuit 10 (5) turns off the other switch group. In the example shown in Figure 5, the control circuit 10 (5) turns off the switches AL and BH.

[0090] The control circuit 10 (6) turns off the switches CL and DH.

[0091] When the switching frequency of the primary-side switches AH, AL, BH, and BL is set higher than the resonant frequency to achieve the target output voltage, the above-described controls (1) through (6) are repeated for the primary-side and secondary-side switches AH, AL, BH, BL, CH, CL, DH, and DL, thereby enabling the secondary-side switches CH, CL, DH, and DL to be turned off at a timing when the current flowing on the secondary side is small. Thus, high-efficiency operation is possible under the operating condition (i.e., the second control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is set higher than the resonant frequency, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0092] In the above (1), the control circuit 10 may turn on one switch group (e.g., switches AH and BL) and then turn on switches CH and DL. In the above (4), the control circuit 10 may turn on the other switch group (e.g., switches AL and BH) and then turn on switches CL and DH.

[0093] In this way, in (1) above, it is not necessary to synchronize the turn-on of one of the switch groups with the switches CH and DL, and in (4) above, it is not necessary to synchronize the turn-on of the other switch group with the switches CL and DH.

[0094] In the above (3), the control circuit 10 may turn off one of the switches CH and DL, and then turn off the other of the switches CH and DL. In the above (6), the control circuit 10 may turn off one of the switches CL and DH, and then turn off the other of the switches CL and DH.

[0095] In the above (3), one of the switches CH and DL is turned off earlier than the other switch, and in the above (6), one of the switches CL and DH is turned off earlier than the other switch, thereby preventing negative current from flowing through the secondary side path, reducing conduction loss and switching loss, and enabling even more efficient operation.

[0096] In the above (1), the control circuit 10 may simultaneously turn on the switches CH and DL. In the above (4), the control circuit 10 may simultaneously turn on the switches CL and DH.

[0097] This makes it possible to balance the currents flowing through the switches CH and DL, and also to balance the currents flowing through the switches CL and DH, thereby suppressing variations in loss between the switches. By suppressing variations in loss between the switches, for example, it is possible to optimize thermal design or device selection, and reduce costs.

[0098] Although an example has been described in which one of the first and second switch groups is the first switch group, i.e., the switches AH and BL, and the other of the first and second switch groups is the second switch group, i.e., the switches AL and BH, this is not limiting. For example, in the above description, one of the switch groups may be replaced with the second switch group, i.e., the switches AL and BH, and the other switch group may be replaced with the first switch group, i.e., the switches AH and BL. This is because the winding of the transformer T1 may be reversed.

[0099] Next, the operation of the control circuit 10 in the third control mode will be described with reference to FIGS.

[0100] FIG. 6 is a timing chart showing a case where optimization control is not performed on the switches AH, AL, BH, BL, CH, CL, DH, and DL in the third control mode.

[0101] In Fig. 6, the control circuit 10 controls the secondary-side switches CH, CL, DH, and DL in synchronization with the primary-side switches BH and BL. Specifically, the control circuit 10 synchronizes the switches CH and DL with the switch BL, and synchronizes the switches CL and DH with the switch BH. In this case, as shown in Fig. 6, it can be seen that the secondary-side switches CH, CL, DH, and DL are turned off at times when the secondary-side current is large. Therefore, in this case, the efficiency of the power conversion device 1 decreases.

[0102] Therefore, when the control circuit 10 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, and so that the switching phase of the switch BL lags behind the switching phase of the switch AH and so that the switching phase of the switch BH lags behind the switching phase of the switch AL, that is, when operating in the third control mode, the control circuit 10 performs the optimization control described in FIG. 7 .

[0103] FIG. 7 is a timing chart when optimization control is performed on the switches AH, AL, BH, BL, CH, CL, DH, and DL in the third control mode.

[0104] In the third control mode, the control circuit 10 sequentially repeats the following controls (1) to (8).

[0105] Control circuit 10 (1) turns off switches CL and DH and turns on switch AH.

[0106] The control circuit 10 (2) turns on the switches BL, CH, and DL.

[0107] The control circuit 10 (3) turns off the switch AH.

[0108] The control circuit 10 (4) turns off the switch BL.

[0109] Control circuit 10 (5) turns off switches CH and DL and turns on switch AL.

[0110] Control circuit 10 (6) turns on switches BH, CL and DH.

[0111] The control circuit 10 (7) turns off the switch AL.

[0112] The control circuit 10 (8) turns off the switch BH.

[0113] To achieve a target output voltage, the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency, and the switching phase of the switches BH and BL is delayed relative to the switching phase of the switches AH and AL. By repeating the above-described control procedures (1) through (8) for the primary-side and secondary-side switches AH, AL, BH, BL, CH, CL, DH, and DL in sequence, the secondary-side switches CH, CL, DH, and DL can be turned off at a timing when the current flowing through the secondary side is small. Thus, high-efficiency operation is possible under the operating condition (i.e., the third control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency and the switching phase of the primary-side switches BH and BL is shifted, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0114] In the above (2), the control circuit 10 may turn on the switches CH and DL after turning on the switch BL. In the above (6), the control circuit 10 may turn on the switches CL and DH after turning on the switch BH.

[0115] In this way, in (2) above, the turn-on of switch BL does not have to be synchronized with that of switches CH and DL, and in (6) above, the turn-on of switch BH does not have to be synchronized with that of switches CL and DH.

[0116] In the above (1), the control circuit 10 may turn on the switch AH after turning off the switches CL and DH, or may turn on the switch AH before turning off the switches CL and DH. In the above (5), the control circuit 10 may turn on the switch AL after turning off the switches CH and DL, or may turn on the switch AL before turning off the switches CH and DL.

[0117] In this way, in (1) above, it is not necessary to synchronize the turning off of switches CL and DH with the turning on of switch AH, and in (5) above, it is not necessary to synchronize the turning off of switches CH and DL with the turning on of switch AL.

[0118] In the above (1), the control circuit 10 may turn off one of the switches CL and DH, and then turn off the other of the switches CL and DH. In the above (5), the control circuit 10 may turn off one of the switches CH and DL, and then turn off the other of the switches CH and DL.

[0119] As a result, in (1) above, one of the switches CL and DH is turned off earlier than the other switch, and in (5) above, one of the switches CH and DL is turned off earlier than the other switch, thereby preventing negative current from flowing through the secondary side path, reducing conduction loss and switching loss, and enabling even more efficient operation.

[0120] In the above (1), the control circuit 10 may turn off the switch DH after turning off the switch CL, and turn on the switch AH after turning off the switch DH, or may turn off the switch CL and turn on the switch AH, and turn on the switch AH and turn off the switch DH, or may turn on the switch AH and turn off the switch CL, and turn off the switch DH after turning off the switch CL. In the above (5), the control circuit 10 may turn off the switch DL after turning off the switch DL, or may turn on the switch AL after turning off the switch CH, and turn on the switch AL after turning on the switch AL, or may turn on the switch AL after turning off the switch CH, and turn off the switch CH and then turn off the switch DL.

[0121] As described above, the turn-off of switch CL, the turn-off of switch DH, and the turn-on of switch AH do not need to be synchronized in (1) above, and the turn-off of switch CH, the turn-off of switch DL, and the turn-on of switch AL do not need to be synchronized in (5) above. The on-time of switch CH may be approximately zero. Therefore, the control circuit 10 may simultaneously turn off switch AH in (3) above or switch BL in (4) above and turn off switch CH in (5) above. Alternatively, the control circuit 10 may turn off switch CH in (5) above before turning off switch AH in (3) above and switch BL in (4) above.

[0122] The on-time of switch CL may be substantially zero. Therefore, control circuit 10 may simultaneously turn off switch AL in (7) above or switch BH in (8) above and switch CL in (1) above. Alternatively, control circuit 10 may turn off switch CL in (1) above before turning off switch AL in (7) above and switch BH in (8) above.

[0123] Note that the transformer T1 may be wound in the opposite direction, in which case the switching phase of the switches AH and AL lags behind the switching phase of the switches BH and BL. In this case, in the third control mode, the control circuit 10 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, and so that the switching phase of the switch AH lags behind the switching phase of the switch BL and so that the switching phase of the switch AL lags behind the switching phase of the switch BH. In the third control mode, the control circuit 10 sequentially repeats the following controls (9) to (16).

[0124] Control circuit 10 (9) turns off switches CL and DH and turns on switch BH.

[0125] The control circuit 10 (10) turns on the switches AL, CH and DL.

[0126] The control circuit 10 (11) turns off the switch BH.

[0127] The control circuit 10 (12) turns off the switch AL, and the control circuit 10 (13) turns off the switches CH and DL and turns on the switch BL.

[0128] The control circuit 10 (14) turns on the switches AH, CL and DH.

[0129] The control circuit 10 (15) turns off the switch BL.

[0130] The control circuit 10 (16) turns off the switch AH.

[0131] To achieve a target output voltage, the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency, and the switching phase of the switches AH and AL is delayed relative to the switching phase of the switches BH and BL. By repeating the above controls (9) through (16) for the primary-side and secondary-side switches AH, AL, BH, BL, CH, CL, DH, and DL in sequence, the secondary-side switches CH, CL, DH, and DL can be turned off when the current flowing through the secondary side is small. Thus, high-efficiency operation is possible under the operating condition (i.e., the third control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency and the switching phase of the primary-side switches AH and AL is shifted, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0132] In the above (10), the control circuit 10 may turn on the switches CH and DL after turning on the switch AL. In the above (14), the control circuit 10 may turn on the switches CL and DH after turning on the switch AH.

[0133] In this way, in (10) above, the turn-on of switch AL does not have to be synchronized with that of switches CH and DL, and in (14) above, the turn-on of switch AH does not have to be synchronized with that of switches CL and DH.

[0134] In the above (9), the control circuit 10 may turn on the switch BH after turning off the switches CL and DH, or may turn on the switch BH before turning off the switches CL and DH. In the above (13), the control circuit 10 may turn on the switch BL after turning off the switches CH and DL, or may turn on the switch BL before turning off the switches CH and DL.

[0135] In this way, in (9) above, it is not necessary to synchronize the turning off of switches CL and DH with the turning on of switch BH, and in (13) above, it is not necessary to synchronize the turning off of switches CH and DL with the turning on of switch BL.

[0136] In the above (9), the control circuit 10 may turn off one of the switches CL and DH, and then turn off the other of the switches CL and DH. In the above (13), the control circuit 10 may turn off one of the switches CH and DL, and then turn off the other of the switches CH and DL.

[0137] As a result, by turning off one of the switches CL and DH earlier than the other switch in (9) above, and by turning off one of the switches CH and DL earlier than the other switch in (13) above, it is possible to prevent negative current from flowing through the secondary side path, thereby reducing conduction loss and switching loss and enabling even more efficient operation.

[0138] In the above (9), the control circuit 10 may turn off the switch DH after turning off the switch CL, and turn on the switch BH after turning off the switch DH, or turn off the switch CL after turning on the switch BH, and turn on the switch BH and turn off the switch DH, or turn on the switch BH and turn off the switch CL, and turn off the switch DH after turning off the switch CL. In the above (13), the control circuit 10 may turn off the switch DL after turning off the switch DL, or turn on the switch BL after turning off the switch CH, and turn on the switch BL after turning on the switch BL, or turn on the switch BL after turning off the switch CH, and turn off the switch CH and turn off the switch DL.

[0139] In this way, in the above (9), it is not necessary to synchronize the turning off of switch CL, the turning off of switch DH, and the turning on of switch BH, and in the above (13), it is not necessary to synchronize the turning off of switch CH, the turning off of switch DL, and the turning on of switch BL.

[0140] The on-time of switch CH may be substantially zero. Therefore, control circuit 10 may simultaneously turn off switch BH in (11) or switch AL in (12) and switch CH in (13). Alternatively, control circuit 10 may turn off switch CH in (13) before turning off switch BH in (11) and switch AL in (12).

[0141] The on-time of switch CL may be substantially zero. Therefore, control circuit 10 may simultaneously turn off switch BL in (15) or switch AH in (16) and switch CL in (9). Alternatively, control circuit 10 may turn off switch CL in (9) before turning off switch BL in (15) and switch AH in (16).

[0142] Next, the operation of the control circuit 10 in the fourth control mode will be described with reference to FIGS.

[0143] FIG. 8 is a timing chart showing a case where optimization control is not performed on the switches AH, AL, BH, BL, CH, CL, DH, and DL in the fourth control mode.

[0144] In Fig. 8, the control circuit 10 controls the secondary-side switches CH, CL, DH, and DL in synchronization with the primary-side switches BH and BL. Specifically, the control circuit 10 synchronizes the switches CH and DL with the switch BL, and synchronizes the switches CL and DH with the switch BH. In this case, as shown in Fig. 8, it can be seen that the secondary-side switches CH, CL, DH, and DL are turned off at times when the secondary-side current is large. Therefore, in this case, the efficiency of the power conversion device 1 decreases.

[0145] Therefore, the control circuit 10 performs optimization control described in Fig. 9 when controlling the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, and so that the switching phase of the switch BL lags behind the switching phase of the switch AH and the switching phase of the switch BH lags behind the switching phase of the switch AL, that is, when operating in the fourth control mode. Note that, as shown in Figs. 6 and 8, and 7 and 9, it can be seen that the amount of phase shift is larger in the fourth control mode than in the third control mode.

[0146] FIG. 9 is a timing chart when optimization control is performed on the switches AH, AL, BH, BL, CH, CL, DH, and DL in the fourth control mode.

[0147] In the fourth control mode, the control circuit 10 sequentially repeats the following controls (1) to (10).

[0148] The control circuit 10 (1) turns on the switch AH.

[0149] The control circuit 10 (2) turns off the switches CL and DH.

[0150] The control circuit 10 (3) turns off the switch BH.

[0151] The control circuit 10 (4) turns on the switches BL, CH, and DL.

[0152] The control circuit 10 (5) turns off the switch AH.

[0153] The control circuit 10 (6) turns on the switch AL.

[0154] The control circuit 10 (7) turns off the switches CH and DL.

[0155] The control circuit 10 (8) turns off the switch BL.

[0156] The control circuit 10 (9) turns on the switches BH, CL and DH.

[0157] The control circuit 10 (10) turns off the switch AL.

[0158] To achieve a target output voltage, the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency, and the switching phase of the switches BH and BL is delayed relative to the switching phase of the switches AH and AL. By repeating the above control procedures (1) through (10) for the primary-side and secondary-side switches AH, AL, BH, BL, CH, CL, DH, and DL in sequence, the secondary-side switches CH, CL, DH, and DL can be turned off when the current flowing through the secondary side is small. Thus, high-efficiency operation is possible under an operating condition (i.e., the fourth control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency and the switching phase of the primary-side switches BH and BL is shifted (specifically, shifted more than in the third control mode), which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0159] In the above (4), the control circuit 10 may turn on the switches CH and DL after turning on the switch BL. In the above (9), the control circuit 10 may turn on the switches CL and DH after turning on the switch BH.

[0160] In this way, in (4) above, the turn-on of switch BL does not have to be synchronized with that of switches CH and DL, and in (9) above, the turn-on of switch BH does not have to be synchronized with that of switches CL and DH.

[0161] In the above (2), the control circuit 10 may turn off one of the switches CL and DH, and then turn off the other of the switches CL and DH. In the above (7), the control circuit 10 may turn off one of the switches CH and DL, and then turn off the other of the switches CH and DL.

[0162] As a result, in (2) above, one of the switches CL and DH is turned off earlier than the other switch, and in (7) above, one of the switches CH and DL is turned off earlier than the other switch, thereby preventing negative current from flowing through the secondary side path, reducing conduction loss and switching loss, and enabling even more efficient operation.

[0163] The on-time of switch CH may be substantially zero. Therefore, control circuit 10 may simultaneously turn off switch AH in (5) or switch AL in (6) and switch CH in (7). Alternatively, control circuit 10 may turn off switch CH in (7) before turning off switch AH in (5) and switch AL in (6).

[0164] The on-time of switch CL may be substantially zero. Therefore, control circuit 10 may simultaneously turn off switch AL in (10) or switch AH in (1) and switch CL in (2). Alternatively, control circuit 10 may turn off switch CL in (2) before turning off switch AL in (10) and switch AH in (1).

[0165] Note that the transformer T1 may be wound in the opposite direction, in which case the switching phase of the switches AH and AL lags behind the switching phase of the switches BH and BL. In this case, in the fourth control mode, the control circuit 10 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, and so that the switching phase of the switch AH lags behind the switching phase of the switch BL and so that the switching phase of the switch AL lags behind the switching phase of the switch BH. In the fourth control mode, the control circuit 10 sequentially repeats the following controls (11) to (20).

[0166] The control circuit 10 (11) turns on the switch BH.

[0167] The control circuit 10 (12) turns off the switches CL and DH.

[0168] The control circuit 10 (13) turns off the switch AH.

[0169] The control circuit 10 (14) turns on the switches AL, CH and DL.

[0170] The control circuit 10 (15) turns off the switch BH.

[0171] The control circuit 10 (16) turns on the switch BL.

[0172] The control circuit 10 (17) turns off the switches CH and DL.

[0173] The control circuit 10 (18) turns off the switch AL.

[0174] The control circuit 10 (19) turns on the switches AH, CL and DH.

[0175] The control circuit 10 (20) turns off the switch BL.

[0176] To achieve a target output voltage, the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency, and the switching phase of the switches AH and AL is delayed relative to the switching phase of the switches BH and BL. By repeating the above-described control procedures (11) through (20) for the primary-side and secondary-side switches AH, AL, BH, BL, CH, CL, DH, and DL in sequence, the secondary-side switches CH, CL, DH, and DL can be turned off at a timing when the current flowing through the secondary side is small. Thus, high-efficiency operation is possible under an operating condition (i.e., the fourth control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency and the switching phase of the primary-side switches AH and AL is shifted (specifically, shifted more than in the third control mode), which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0177] In the above (14), the control circuit 10 may turn on the switches CH and DL after turning on the switch AL. In the above (19), the control circuit 10 may turn on the switches CL and DH after turning on the switch AH.

[0178] In this way, in (14) above, the turn-on of switch AL does not have to be synchronized with that of switches CH and DL, and in (19) above, the turn-on of switch AH does not have to be synchronized with that of switches CL and DH.

[0179] In the above (12), the control circuit 10 may turn off one of the switches CL and DH, and then turn off the other of the switches CL and DH. In the above (17), the control circuit 10 may turn off one of the switches CH and DL, and then turn off the other of the switches CH and DL.

[0180] As a result, by turning off one of the switches CL and DH earlier than the other switch in (12) above, and by turning off one of the switches CH and DL earlier than the other switch in (17) above, it is possible to prevent negative current from flowing through the secondary side path, thereby reducing conduction loss and switching loss and enabling even more efficient operation.

[0181] The on-time of switch CH may be approximately zero. Therefore, control circuit 10 may simultaneously turn off switch BH in (15) or switch BL in (16) and switch CH in (17). Alternatively, control circuit 10 may turn off switch CH in (17) before turning off switch BH in (15) and switch BL in (16).

[0182] The on-time of switch CL may be substantially zero. Therefore, the control circuit 10 may simultaneously turn off switch BL in (20) or switch BH in (11) and switch CL in (12). Alternatively, the control circuit 10 may turn off switch CL in (12) before turning off switch BL in (20) and switch BH in (11).

[0183] As described above, in each of the first to fourth control modes for accommodating a wide input / output voltage ratio, the secondary-side switches CH, CL, DH, and DL are controlled so that they turn off when the current flowing on the secondary side is small, thereby enabling highly efficient operation while accommodating a wide input / output voltage ratio.

[0184] Second Embodiment A power conversion device according to a second embodiment will be described below.

[0185] FIG. 10 is a circuit configuration diagram showing an example of a power conversion device 2 according to the second embodiment.

[0186] The power conversion device 2 according to the second embodiment differs from the power conversion device 1 according to the first embodiment in that it includes a transformer T2 instead of the transformer T1, a control circuit 20 instead of the control circuit 10, and the circuit configuration on the secondary side of the transformer T2 is different from the circuit configuration on the secondary side of the transformer T1. The following description will focus on the differences from the first embodiment, and a description of the same points will basically be omitted.

[0187] The power conversion device 2 includes terminals t1, t2, t3, and t4, switches AH, AL, BH, BL, EH, and EL, a transformer T2, a capacitor Cr, an inductor Lr, and a control circuit 20. Description of the terminals t1, t2, t3, and t4, the switches AH, AL, BH, and BL, the capacitor Cr, and the inductor Lr will be omitted.

[0188] The transformer T2 is an example of an isolation transformer, and has a primary winding and a secondary winding that are insulated from each other.

[0189] The primary winding of the transformer T2 is the same as the primary winding of the transformer T1 according to the first embodiment, and therefore a description thereof will be omitted.

[0190] The transformer T2 has a first winding L1 and a second winding L2 connected in series as a secondary winding.

[0191] One end of the first winding L1 (the upper side of the first winding L1 in FIG. 10) is connected to one end of the switch EH. The other end of the first winding L1 (the lower side of the first winding L1 in FIG. 10) and one end of the second winding L2 (the upper side of the second winding L2 in FIG. 10) are connected to a terminal t3. The other end of the second winding L2 (the lower side of the second winding L2 in FIG. 10) is connected to one end of the switch EL. The other ends of the switches EH and EL are connected to a terminal t4.

[0192] The switch EH is an example of a fifth switch. The switch EH is, for example, an N-channel MOSFET. The drain of the switch EH (one end of the switch EH) is connected to one end of the first winding L1, and the source of the switch EH (the other end of the switch EH) is connected to the terminal t4.

[0193] The switch EL is an example of a sixth switch. The switch EL is, for example, an N-channel MOSFET. The drain of the switch EL (one end of the switch EL) is connected to the other end of the second winding L2, and the source of the switch EL (the other end of the switch EL) is connected to the terminal t4.

[0194] As described above, in the power conversion device 2 according to the second embodiment, the secondary-side circuit is a center tap circuit. While Fig. 10 shows an example in which the power conversion device 2 is provided with one switch EH and one switch EL, the power conversion device 2 may also include a plurality of switches EH connected in parallel with each other and a plurality of switches EL connected in parallel with each other. By providing a plurality of switches EH and a plurality of switches EL, the on-resistance can be reduced.

[0195] 10 shows the parasitic capacitance of each switch, and each parasitic capacitance is connected in parallel to the corresponding switch in the equivalent circuit. Also, FIG. 10 shows the body diode of each switch, and each body diode is connected in parallel to the corresponding switch in the equivalent circuit. Specifically, the anode of each body diode is connected to the source of the corresponding switch in the equivalent circuit, and the cathode is connected to the drain of the corresponding switch.

[0196] The control circuit 20 controls the switching of the switches AH, AL, BH, BL, EH, and EL. For example, the control circuit 20 controls the switching of the switches AH, AL, BH, BL, EH, and EL by controlling gate drive circuits (not shown) connected to the gates of the switches AH, AL, BH, BL, EH, and EL via a PWM generator (not shown) or the like.

[0197] The control circuit 20 is realized by, for example, a computer including a processor (microprocessor) and a memory. The memory may be a ROM or RAM, and can store a program to be executed by the processor. For example, the control circuit 20 is realized by a microcontroller.

[0198] The operation of control circuit 20 is basically the same as the operation of control circuit 10 according to embodiment 1, and the operation of control circuit 20 will be described by replacing switches CH and DL with switches EH and switches CL and DH with switches EL in the description of control circuit 10 according to embodiment 1. The operation of control circuit 20 will be described below with reference to Figures 3, 5, 7, and 9, but in Figures 3, 5, 7, and 9 used in the description of the operation of control circuit 20, switches CH and DL are replaced with switches EH, and switches CL and DH are replaced with switches EL.

[0199] In the first control mode, the control circuit 20 repeats the following controls (1) to (6) in order.

[0200] The control circuit 20 (1) turns on one of the first and second switch groups and the switch EH. In the example shown in Figure 3, the one switch group is the first switch group, that is, the switches AH and BL, and the control circuit 20 (1) turns on the switches AH and BL and the switch EH.

[0201] The control circuit 20 (2) turns off the switch EH.

[0202] The control circuit 20 (3) turns off one of the switch groups. In the example shown in Figure 3, the control circuit 20 (3) turns off the switches AH and BL.

[0203] The control circuit 20 (4) turns on the other switch group of the first switch group and the second switch group and the switch EL. In the example shown in Figure 3, the other switch group is the second switch group, that is, the switches AL and BH, and the control circuit 20 (4) turns on the switches AL and BH and the switch EL.

[0204] The control circuit 20 (5) turns off the switch EL.

[0205] The control circuit 20 (6) turns off the other switch group. In the example shown in Figure 3, the control circuit 20 (6) turns off the switches AL and BH.

[0206] When the switching frequency of the primary-side switches AH, AL, BH, and BL is set lower than the resonant frequency to achieve the target output voltage, the above-described controls (1) through (6) are repeated for the primary-side and secondary-side switches AH, AL, BH, BL, EH, and EL in order, thereby enabling the secondary-side switches EH and EL to be turned off at a timing when the current flowing through the secondary side is small. Thus, high-efficiency operation is possible under the operating condition (i.e., the first control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is set lower than the resonant frequency, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0207] In the above (1), the control circuit 20 may turn on one switch group (e.g., switches AH and BL) and then turn on switch EH. In the above (4), the control circuit 20 may turn on the other switch group (e.g., switches AL and BH) and then turn on switch EL.

[0208] In this way, in (1) above, it is not necessary to synchronize the turn-on of one of the switch groups with switch EH, and in (4) above, it is not necessary to synchronize the turn-on of the other switch group with switch EL.

[0209] In the second control mode, the control circuit 20 repeats the following controls (1) to (6) in order.

[0210] The control circuit 20 (1) turns on one of the first and second switch groups and the switch EH. In the example shown in Fig. 5, the one switch group is the first switch group, that is, the switches AH and BL, and the control circuit 20 (1) turns on the switches AH and BL and the switch EH.

[0211] The control circuit 20 (2) turns off one of the switch groups. In the example shown in Figure 5, the control circuit 20 (2) turns off the switches AH and BL.

[0212] The control circuit 20 (3) turns off the switch EH.

[0213] The control circuit 20 (4) turns on the other switch group of the first switch group and the second switch group and the switch EL. In the example shown in Fig. 5, the other switch group is the second switch group, that is, the switches AL and BH, and the control circuit 20 (4) turns on the switches AL and BH and the switch EL.

[0214] The control circuit 20 (5) turns off the other switch group. In the example shown in Figure 5, the control circuit 20 (5) turns off the switches AL and BH.

[0215] The control circuit 20 (6) turns off the switch EL.

[0216] When the switching frequency of the primary-side switches AH, AL, BH, and BL is set higher than the resonant frequency to achieve the target output voltage, the above-described controls (1) through (6) are repeated for the primary-side and secondary-side switches AH, AL, BH, BL, EH, and EL in order, thereby enabling the secondary-side switches EH and EL to be turned off at a timing when the current flowing on the secondary side is small. Thus, high-efficiency operation is possible under the operating condition (i.e., the second control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is set higher than the resonant frequency, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0217] In the above (1), the control circuit 20 may turn on one switch group (e.g., switches AH and BL) and then turn on switch EH. In the above (4), the control circuit 20 may turn on the other switch group (e.g., switches AL and BH) and then turn on switch EL.

[0218] In this way, in (1) above, it is not necessary to synchronize the turn-on of one of the switch groups with switch EH, and in (4) above, it is not necessary to synchronize the turn-on of the other switch group with switch EL.

[0219] In the third control mode, the control circuit 20 repeats the following controls (1) to (8) in order.

[0220] The control circuit 20 (1) turns off the switch EL and turns on the switch AH.

[0221] Control circuit 20 (2) turns on switches BL and EH.

[0222] The control circuit 20 (3) turns off the switch AH.

[0223] The control circuit 20 (4) turns off the switch BL.

[0224] The control circuit 20 (5) turns off the switch EH and turns on the switch AL.

[0225] Control circuit 20 (6) turns on switches BH and EL.

[0226] The control circuit 20 (7) turns off the switch AL.

[0227] The control circuit 20 (8) turns off the switch BH.

[0228] To achieve a target output voltage, the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency, and the switching phase of the switches BH and BL is delayed relative to the switching phase of the switches AH and AL. By repeating the above-described control procedures (1) through (8) for the primary-side and secondary-side switches AH, AL, BH, BL, EH, and EL in sequence, the secondary-side switches EH and EL can be turned off at a timing when the current flowing through the secondary side is small. Thus, high-efficiency operation is possible under the operating condition (i.e., the third control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency and the switching phase of the primary-side switches BH and BL is shifted, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0229] In the above (2), the control circuit 20 may turn on the switch EH after turning on the switch BL. In the above (6), the control circuit 20 may turn on the switch EL after turning on the switch BH.

[0230] In this way, in the above (2), the switches BL and EH do not need to be turned on in synchronization, and in the above (6), the switches BH and EL do not need to be turned on in synchronization.

[0231] In the above (1), the control circuit 20 may turn on the switch AH after turning off the switch EL, or may turn on the switch AH and then turn off the switch EL. In the above (5), the control circuit 20 may turn on the switch AL after turning off the switch EH, or may turn on the switch AL and then turn off the switch EH.

[0232] In this way, in (1) above, the turning off of switch EL and the turning on of switch AH do not need to be synchronized, and in (5) above, the turning off of switch EH and the turning on of switch AL do not need to be synchronized.

[0233] Note that the transformer T1 may be wound in the opposite direction, in which case the switching phase of the switches AH and AL lags behind the switching phase of the switches BH and BL. In this case, in the third control mode, the control circuit 20 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, and so that the switching phase of the switch AH lags behind the switching phase of the switch BL and so that the switching phase of the switch AL lags behind the switching phase of the switch BH. In the third control mode, the control circuit 20 sequentially repeats the following controls (9) to (16).

[0234] The control circuit 20 (9) turns off the switch EL and turns on the switch BH.

[0235] The control circuit 20 (10) turns on the switches AL and EH.

[0236] The control circuit 20 (11) turns off the switch BH.

[0237] The control circuit 20 (12) turns off the switch AL, and the control circuit 20 (13) turns off the switch EH and turns on the switch BL.

[0238] The control circuit 20 (14) turns on the switches AH and EL.

[0239] The control circuit 20 (15) turns off the switch BL.

[0240] The control circuit 20 (16) turns off the switch AH.

[0241] To achieve a target output voltage, the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency and the switching phase of the switches AH and AL is delayed relative to the switching phase of the switches BH and BL. By repeating the above controls (9) through (16) for the primary-side and secondary-side switches AH, AL, BH, BL, EH, and EL in sequence, the secondary-side switches EH and EL can be turned off at a timing when the current flowing through the secondary side is small. Thus, high-efficiency operation is possible under the operating condition (i.e., the third control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency and the switching phase of the primary-side switches AH and AL is shifted, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0242] In the above (10), the control circuit 20 may turn on the switch EH after turning on the switch AL. In the above (14), the control circuit 20 may turn on the switch EL after turning on the switch AH.

[0243] In this way, in the above (10), the switches AL and EH do not need to be turned on in synchronization, and in the above (14), the switches AH and EL do not need to be turned on in synchronization.

[0244] In the above (9), the control circuit 20 may turn on the switch BH after turning off the switch EL, or may turn on the switch BH before turning off the switch EL. In the above (13), the control circuit 20 may turn on the switch BL after turning off the switch EH, or may turn on the switch BL before turning off the switch EH.

[0245] In this way, in (9) above, the turning off of switch EL and the turning on of switch BH do not have to be synchronized, and in (13) above, the turning off of switch EH and the turning on of switch BL do not have to be synchronized.

[0246] In the fourth control mode, the control circuit 20 sequentially repeats the following controls (1) to (10).

[0247] The control circuit 20 (1) turns on the switch AH.

[0248] The control circuit 20 (2) turns off the switch EL.

[0249] The control circuit 20 (3) turns off the switch BH.

[0250] The control circuit 20 (4) turns on the switches BL and EH.

[0251] The control circuit 20 (5) turns off the switch AH.

[0252] The control circuit 20 (6) turns on the switch AL.

[0253] The control circuit 20 (7) turns off the switch EH.

[0254] The control circuit 20 (8) turns off the switch BL.

[0255] Control circuit 20 (9) turns on switches BH and EL.

[0256] The control circuit 20 (10) turns off the switch AL.

[0257] To achieve a target output voltage, the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency, and the switching phase of the switches BH and BL is delayed relative to the switching phase of the switches AH and AL. By repeating the above-described control procedures (1) through (10) for the primary-side and secondary-side switches AH, AL, BH, BL, EH, and EL in sequence, the secondary-side switches EH and EL can be turned off at a timing when the current flowing through the secondary side is small. Thus, high-efficiency operation is possible under an operating condition (i.e., the fourth control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency and the switching phase of the primary-side switches BH and BL is shifted (specifically, shifted more than in the third control mode), which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0258] In the above (4), the control circuit 20 may turn on the switch EH after turning on the switch BL. In the above (9), the control circuit 20 may turn on the switch EL after turning on the switch BH.

[0259] In this way, in the above (4), the switches BL and EH do not need to be turned on in synchronization, and in the above (9), the switches BH and EL do not need to be turned on in synchronization.

[0260] Note that the transformer T1 may be wound in the opposite direction, in which case the switching phase of the switches AH and AL lags behind the switching phase of the switches BH and BL. In this case, in the fourth control mode, the control circuit 20 controls the switching of the switches AH, AL, BH, and BL so that the switching frequency of the switches AH, AL, BH, and BL is higher than the resonant frequency of the resonance generated by the capacitor Cr and the inductor Lr, and so that the switching phase of the switch AH lags behind the switching phase of the switch BL and so that the switching phase of the switch AL lags behind the switching phase of the switch BH. In the fourth control mode, the control circuit 20 sequentially repeats the following controls (11) to (20).

[0261] The control circuit 20 (11) turns on the switch BH.

[0262] The control circuit 20 (12) turns off the switch EL.

[0263] The control circuit 20 (13) turns off the switch AH.

[0264] The control circuit 20 (14) turns on the switches AL and EH.

[0265] The control circuit 20 (15) turns off the switch BH.

[0266] The control circuit 20 (16) turns on the switch BL.

[0267] The control circuit 20 (17) turns off the switch EH.

[0268] The control circuit 20 (18) turns off the switch AL.

[0269] Control circuit 20 (19) turns on switches AH and EL.

[0270] The control circuit 20 (20) turns off the switch BL.

[0271] To achieve a target output voltage, the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency, and the switching phase of the switches AH and AL is delayed relative to the switching phase of the switches BH and BL. By repeating the above-described control procedures (11) through (20) for the primary-side and secondary-side switches AH, AL, BH, BL, EH, and EL in sequence, the secondary-side switches EH and EL can be turned off at a timing when the current flowing through the secondary side is small. Thus, high-efficiency operation is possible under an operating condition (i.e., the fourth control mode) in which the switching frequency of the primary-side switches AH, AL, BH, and BL is increased above the resonant frequency and the switching phase of the primary-side switches AH and AL is shifted (specifically, shifted more than in the third control mode), which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0272] In addition, the control circuit 20 may turn on the switch EH after turning on the switch AL in the above (14). Also, in the above (19), the control circuit 20 may turn on the switch EL after turning on the switch AH.

[0273] In this way, in the above (14), the switches AL and EH do not need to be turned on in synchronization, and in the above (19), the switches AH and EL do not need to be turned on in synchronization.

[0274] As described above, in each of the first to fourth control modes for accommodating a wide input / output voltage ratio, the secondary-side switches EH and EL are controlled so that they are turned off at a timing when the current flowing on the secondary side is small, thereby enabling high-efficiency operation while accommodating a wide input / output voltage ratio.

[0275] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0276] For example, in the first and second embodiments, the control circuit may further determine the on-periods of a plurality of switches (switches CH, CL, DH, and DL in the first embodiment, and switches EH and EL in the second embodiment) connected to the secondary winding of the transformer based on detection results indicating whether the switches are operating as diodes and passing current. Hereinafter, the plurality of switches connected to the secondary winding of the transformer refer to switches CH, CL, DH, and DL in the first embodiment, and switches EH and EL in the second embodiment. Furthermore, diode operation refers to an operation in which a current flows from the source to the drain when the switch is in an off state, that is, a state in which the current from the drain to the source is blocked. For example, this corresponds to an operation in which a forward current flows through the body diode of a Si or SiC MOSFET when the switch is off.

[0277] This allows the on-period of each secondary-side switch to be determined so that the period during which each secondary-side switch operates as a diode and passes current is shortened (for example, so that the period during which the detection result indicates that current is passing as a diode is shortened), thereby reducing losses caused by each secondary-side switch operating as a diode and enabling even more efficient operation.

[0278] For example, in the first and second embodiments, the control circuit may further turn off the multiple switches connected to the secondary winding in synchronization with the timing at which the current flowing through the multiple switches becomes 0 A.

[0279] By turning off each switch on the secondary side when the current flowing through it becomes 0 A, it is possible to prevent current from flowing through the diode operation of each switch on the secondary side when it is off. This makes it possible to suppress losses caused by current flowing through each switch in diode operation, enabling even more efficient operation.

[0280] For example, in the above-mentioned first and second embodiments, the control circuit may further turn off the multiple switches connected to the secondary winding in synchronization with a timing that is a predetermined time earlier than the timing at which the current flowing through the multiple switches becomes 0 A.

[0281] There is a delay between when a control signal is sent to each switch on the secondary side and when the switch actually turns off. Therefore, by sending a control signal to turn off each switch on the secondary side at a timing that is a predetermined time earlier than the delay, that is, by sending a control signal to turn off each switch on the secondary side at a timing that is a predetermined time earlier than the delay, it is possible to turn off each switch on the secondary side at a timing when the current flowing through each switch on the secondary side becomes 0 A.

[0282] For example, the present disclosure can be realized not only as a power conversion device, but also as a control method including steps (processing) performed by components (for example, a control circuit) that make up the power conversion device.

[0283] 11 to 18B are flowcharts showing examples of control methods according to other embodiments.

[0284] The control method is a control method for the power conversion device 1, and in the case where the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is lower than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, as shown in FIG. 11 , (1) one of the first switch group and the second switch group and the fifth switch and the eighth switch are turned on (step S101), (2) the fifth switch and the eighth switch are turned off (step S102), (3) one of the switch groups is turned off (step S103), (4) the other of the first switch group and the second switch group and the sixth switch and the seventh switch are turned on (step S104), (5) the sixth switch and the seventh switch are turned off (step S105), and (6) the other switch group is turned off (step S106), and the controls from (1) to (6) above are repeated in order.

[0285] The control method is a control method for the power conversion device 1, and in the case where the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, as shown in FIG. 12 , (1) one of the first switch group and the second switch group and the fifth switch and the eighth switch are turned on (step S201), (2) one of the switch groups is turned off (step S202), (3) the fifth switch and the eighth switch are turned off (step S203), (4) the other of the first switch group and the second switch group and the sixth switch and the seventh switch are turned on (step S204), (5) the other switch group is turned off (step S205), and (6) the sixth switch and the seventh switch are turned off (step S206), and the controls from (1) to (6) above are repeated in order.

[0286] The control method is a control method for the power conversion device 1, and the control method controls switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, As shown in FIG. 13A, (1) the sixth switch and the seventh switch are turned off and the first switch is turned on (step S301), (2) the fourth switch, the fifth switch and the eighth switch are turned on (step S302), (3) the first switch is turned off (step S303), (4) the fourth switch is turned off (step S304), (5) the fifth switch and the eighth switch are turned off and the second switch is turned on (step S305), and (6) the third switch, the sixth switch and the seventh switch are turned on (step S306). (7) turn off the second switch (step S307), and (8) turn off the third switch (step S308). The above controls from (1) to (8) are repeated in order, so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and the switching phase of the first switch lags behind the switching phase of the fourth switch, and the switching phase of the second switch lags behind the switching phase of the third switch. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so as to delay the phase, as shown in FIG. 13B , (9) the sixth switch and the seventh switch are turned off, and the third switch is turned on (step S311), (10) the second switch, the fifth switch, and the eighth switch are turned on (step S312), (11) the third switch is turned off (step S313), (12) the second switch is turned off (step S314), and (13) the fifth switch and the eighth switch are turned off.The fourth switch is turned on (step S315), (14) the first switch, the sixth switch, and the seventh switch are turned on (step S316), (15) the fourth switch is turned off (step S317), (16) the first switch is turned off (step S318), and the above controls from (9) to (16) are repeated in order.

[0287] The control method is a control method for the power conversion device 1, and the control method controls switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch. 14A, (1) the first switch is turned on (step S401), (2) the sixth switch and the seventh switch are turned off (step S402), (3) the third switch is turned off (step S403), (4) the fourth switch, the fifth switch, and the eighth switch are turned on (step S404), (5) the first switch is turned off (step S405), (6) the second switch is turned on (step S406), (7) the fifth switch and the eighth switch are turned off (step S407), and (8) the fourth switch is turned off (step S408). (9) turn on the third switch, the sixth switch, and the seventh switch (step S409), and (10) turn off the second switch (step S410). The above controls from (1) to (10) are repeated in order, so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and the switching phase of the first switch is delayed relative to the switching phase of the fourth switch. When the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching phase of the second switch lags behind the switching phase of the third switch, as shown in FIG. 14B , (11) the third switch is turned on (step S411), (12) the sixth switch and the seventh switch are turned off (step S412), (13) the first switch is turned off (step S413), and (14) the second switch, the fifth switch, and the eighth switch are turned on (step S414).(15) Turn off the third switch (step S415), (16) turn on the fourth switch (step S416), (17) turn off the fifth switch and the eighth switch (step S417), (18) turn off the second switch (step S418), (19) turn on the first switch, the sixth switch and the seventh switch (step S419), (20) turn off the fourth switch (step S420), and repeat the above controls from (11) to (20) in order.

[0288] The control method is a control method for the power conversion device 2, and in the control method, when the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is lower than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, as shown in FIG. 15 , (1) one of the first switch group and the second switch group and the fifth switch is turned on (step S501), (2) the fifth switch is turned off (step S502), (3) one of the switch groups is turned off (step S503), (4) the other of the first switch group and the second switch group and the sixth switch is turned on (step S504), (5) the sixth switch is turned off (step S505), and (6) the other switch group is turned off (step S506), and the controls from (1) to (6) above are repeated in order.

[0289] The control method is a control method for the power conversion device 2, and in the control method, when the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, as shown in FIG. 16 , (1) one of the first switch group and the second switch group and the fifth switch is turned on (step S601), (2) one of the switch groups is turned off (step S602), (3) the fifth switch is turned off (step S603), (4) the other of the first switch group and the second switch group and the sixth switch is turned on (step S604), (5) the other switch group is turned off (step S605), and (6) the sixth switch is turned off (step S606), and the controls from (1) to (6) above are repeated in order.

[0290] The control method is a control method for the power conversion device 2, and the control method controls switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, As shown in FIG. 17A , (1) the sixth switch is turned off and the first switch is turned on (step S701), (2) the fourth switch and the fifth switch are turned on (step S702), (3) the first switch is turned off (step S703), (4) the fourth switch is turned off (step S704), (5) the fifth switch is turned off and the second switch is turned on (step S705), (6) the third switch and the sixth switch are turned on (step S706), and (7) the second switch is turned off (step S707). (8) Turn off the third switch (step S708), and repeat the above controls from (1) to (8) in order to control the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch. In the case of controlling the switching of the switches, as shown in FIG. 17B , (9) the sixth switch is turned off and the third switch is turned on (step S711), (10) the second switch and the fifth switch are turned on (step S712), (11) the third switch is turned off (step S713), (12) the second switch is turned off (step S714), (13) the fifth switch is turned off and the fourth switch is turned on (step S715), and (14) the first switch and the sixth switch are turned on (step S716).(15) The fourth switch is turned off (step S717), (16) the first switch is turned off (step S718), and the above controls (9) to (16) are repeated in order.

[0291] The control method is a control method for the power conversion device 2, and the control method controls switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch. As shown in FIG. 18A, (1) the first switch is turned on (step S801), (2) the sixth switch is turned off (step S802), (3) the third switch is turned off (step S803), (4) the fourth switch and the fifth switch are turned on (step S804), (5) the first switch is turned off (step S805), (6) the second switch is turned on (step S806), (7) the fifth switch is turned off (step S807), (8) the fourth switch is turned off (step S808), and (9) the third switch is turned off (step S809). (10) the second switch is turned off (step S810), and the above controls from (1) to (10) are repeated in order to set the switching frequency of the first switch, the second switch, the third switch, and the fourth switch higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and to set the switching phase of the first switch to lag behind the switching phase of the fourth switch, and the switching phase of the second switch to lag behind the switching phase of the third switch. In the case where the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so as to delay, as shown in FIG. 18B , (11) the third switch is turned on (step S811), (12) the sixth switch is turned off (step S812), (13) the first switch is turned off (step S813), (14) the second switch and the fifth switch are turned on (step S814), (15) the third switch is turned off (step S815), and (16) the fourth switch is turned on (step S816).(17) Turn off the fifth switch (step S817), (18) turn off the second switch (step S818), (19) turn on the first switch and the sixth switch (step S819), (20) turn off the fourth switch (step S820), and repeat the above controls from (11) to (20) in order.

[0292] For example, the present disclosure can be realized as a program for causing a computer (processor) to execute steps included in the control method. Furthermore, the present disclosure can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0293] For example, when the present disclosure is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU, memory, input / output circuits, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuits, etc., performing calculations, and outputting the calculation results to memory or input / output circuits, etc.

[0294] In the above-described embodiments, each component included in the power conversion device may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0295] Some or all of the functions of the power conversion device according to the above-described embodiments are typically realized as an LSI, which is an integrated circuit. These may be individually integrated into a single chip, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells within the LSI, may also be used.

[0296] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, that technology may naturally be used to integrate the components included in the power conversion device.

[0297] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope of the present disclosure.

[0298] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0299] (Technology 1) A first switch provided on a first path connecting a first input terminal and a second input terminal; A second switch provided on the first path and connected in series with the first switch; A third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; A fourth switch provided on the second path and connected in series with the third switch; An isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; A resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; A fifth switch provided on a third path connecting a first output terminal and a second output terminal; A sixth switch provided on the third path and connected in series with the fifth switch; A seventh switch provided on a fourth path different from the third path connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; and a control circuit that controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch.

[0300] Here, a secondary winding of the isolation transformer is connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is lower than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, the control circuit: (1) turns on one of the switch groups of the first switch group and the second switch group, and the fifth switch and the eighth switch; (2) turns off the fifth switch and the eighth switch; (3) turns off the one of the switch groups; (4) turns on the other of the switch groups of the first switch group and the second switch group, and the sixth switch and the seventh switch; (5) turns off the sixth switch and the seventh switch; and (6) turns off the other of the switch groups, and repeats the controls from (1) to (6) in order.

[0301] According to this, when the switching frequency of each switch on the primary side is set lower than the resonant frequency to set the output voltage to the target voltage, by sequentially repeating the above controls (1) to (6) for each switch on the primary side and the secondary side, each switch on the secondary side can be turned off at a timing when the current flowing on the secondary side is small. In this way, high-efficiency operation is possible under an operating condition in which the switching frequency of each switch on the primary side is set lower than the resonant frequency, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0302] (Technology 2) The power conversion device according to Technology 1, wherein the control circuit turns on the fifth switch and the eighth switch after turning on one of the switch groups in (1), and turns on the sixth switch and the seventh switch after turning on the other switch group in (4).

[0303] In this way, in (1) above, the turn-on of one of the switch groups does not have to be synchronized with the turn-on of the fifth switch and the eighth switch, and in (4) above, the turn-on of the other of the switch groups does not have to be synchronized with the turn-on of the sixth switch and the seventh switch.

[0304] (Technology 3) The power conversion device according to Technology 1 or 2, wherein the control circuit turns off one of the fifth switch and the eighth switch in (2), and then turns off the other of the fifth switch and the eighth switch; and turns off one of the sixth switch and the seventh switch in (5).

[0305] According to this, in (2) above, one of the fifth switch and the eighth switch is turned off earlier than the other switch, and in (5) above, one of the sixth switch and the seventh switch is turned off earlier than the other switch, thereby preventing negative current from flowing through the secondary side path and enabling even more efficient operation.

[0306] (Technology 4) The power conversion device according to Technology 3, wherein the control circuit simultaneously turns off the other of the fifth switch and the eighth switch in (2) and turns off the one group of switches in (3), and simultaneously turns off the other of the sixth switch and the seventh switch in (5) and turns off the other group of switches in (6).

[0307] As long as one of the fifth switch and the eighth switch is turned off, it does not matter if the other of the fifth switch and the eighth switch is turned on for a relatively long time. Also, as long as one of the sixth switch and the seventh switch is turned off, it does not matter if the other of the sixth switch and the seventh switch is turned on for a relatively long time. Therefore, the turning off of the other of the fifth switch and the eighth switch in (2) above and the turning off of one of the switch groups in (3) above may be performed simultaneously, and the turning off of the other of the sixth switch and the seventh switch in (5) above and the turning off of the other of the switch groups in (6) above may be performed simultaneously.

[0308] (Technology 5) The power conversion device according to any one of technologies 1 to 4, wherein the control circuit simultaneously turns on the fifth switch and the eighth switch in (1), and simultaneously turns on the sixth switch and the seventh switch in (4).

[0309] This makes it possible to balance the currents flowing through the fifth switch and the eighth switch, and also to balance the currents flowing through the sixth switch and the seventh switch, thereby suppressing the variation in loss between the switches. By suppressing the variation in loss between the switches, it is possible to optimize, for example, thermal design or device selection, and suppress costs.

[0310] (Technology 6) A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; and a control circuit that controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch.

[0311] Here, a secondary winding of the isolation transformer is connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, the control circuit: (1) turns on one of the first switch group and the second switch group, and the fifth switch and the eighth switch; (2) turns off one of the switch groups; (3) turns off the fifth switch and the eighth switch; (4) turns on the other of the first switch group and the second switch group, and the sixth switch and the seventh switch; (5) turns off the other switch group; and (6) turns off the sixth switch and the seventh switch, and repeats the controls from (1) to (6) in order.

[0312] According to this, when the switching frequency of each switch on the primary side is made higher than the resonant frequency to set the output voltage to the target voltage, by sequentially repeating the above-described controls (1) to (6) for each switch on the primary side and the secondary side, each switch on the secondary side can be turned off at a timing when the current flowing on the secondary side is small. In this way, high-efficiency operation is possible under an operating condition in which the switching frequency of each switch on the primary side is made higher than the resonant frequency, which is one operating condition for accommodating a wide input / output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input / output voltage ratio.

[0313] (Technology 7) The power conversion device according to Technology 6, wherein the control circuit turns on the fifth switch and the eighth switch after turning on one of the switch groups in (1), and turns on the sixth switch and the seventh switch after turning on the other switch group in (4).

[0314] In this way, in (1) above, the turn-on of one of the switch groups does not have to be synchronized with the turn-on of the fifth switch and the eighth switch, and in (4) above, the turn-on of the other of the switch groups does not have to be synchronized with the turn-on of the sixth switch and the seventh switch.

[0315] (Technology 8) The power conversion device according to Technology 6 or 7, wherein the control circuit turns off the other of the fifth switch and the eighth switch after turning off one of the fifth switch and the eighth switch in (3), and turns off the other of the sixth switch and the seventh switch after turning off one of the sixth switch and the seventh switch in (6).

[0316] According to this, in (3) above, one of the fifth switch and the eighth switch is turned off earlier than the other switch, and in (6) above, one of the sixth switch and the seventh switch is turned off earlier than the other switch, thereby preventing negative current from flowing through the secondary side path and enabling even more efficient operation.

[0317] (Technology 9) The power conversion device according to any one of Technologies 6 to 8, wherein the control circuit simultaneously turns on the fifth switch and the eighth switch in (1), and simultaneously turns on the sixth switch and the seventh switch in (4).

[0318] This makes it possible to balance the currents flowing through the fifth switch and the eighth switch, and also to balance the currents flowing through the sixth switch and the seventh switch, thereby suppressing the variation in loss between the switches. By suppressing the variation in loss between the switches, it is possible to optimize, for example, thermal design or device selection, and suppress costs.

[0319] (Technology 10) A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; and a control circuit that controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch.

[0320] Here, a secondary winding of the isolation transformer is connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, the control circuit (1) turns off the sixth switch and the seventh switch, and turns on the first switch, (2) turns on the fourth switch, the fifth switch, and the eighth switch, (3) turns off the first switch, (4) turns off the fourth switch, (5) turns off the fifth switch and the eighth switch, and turns on the second switch, (6) turns on the third switch, the sixth switch, and the seventh switch, (7) turns off the second switch, and (8) turns off the third switch, The controls (1) to (8) are repeated in order, and when controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch, the following steps are performed: (9) turning off the sixth switch and the seventh switch and turning on the third switch; (10) turning on the second switch, the fifth switch, and the eighth switch;(11) Turn off the third switch; (12) Turn off the second switch; (13) Turn off the fifth switch and the eighth switch, and turn on the fourth switch; (14) Turn on the first switch, the sixth switch, and the seventh switch; (15) Turn off the fourth switch; (16) Turn off the first switch; and repeat the controls from (9) to (16) in order.

[0321] According to this, when the switching frequency of each switch on the primary side is made higher than the resonant frequency and the switching phase of the third switch and the fourth switch is delayed relative to the switching phase of the first switch and the second switch in order to set the output voltage to a target voltage, by sequentially repeating the controls (1) to (8) above for each switch on the primary side and the secondary side, it is possible to turn off each switch on the secondary side at a timing when the current flowing on the secondary side is small. Also, when the switching frequency of each switch on the primary side is made higher than the resonant frequency and the switching phase of the first switch and the second switch is delayed relative to the switching phase of the third switch and the fourth switch in order to set the output voltage to a target voltage, by sequentially repeating the controls (9) to (16) above for each switch on the primary side and the secondary side, it is possible to turn off each switch on the secondary side at a timing when the current flowing on the secondary side is small. In this way, high-efficiency operation is possible under the operating condition of setting the switching frequency of each switch on the primary side higher than the resonant frequency and shifting the switching phase of a specific switch on the primary side, which is one operating condition for accommodating a wide input / output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input / output voltage ratio.

[0322] (Technology 11) The power conversion device according to technology 10, wherein the control circuit turns on the fifth switch and the eighth switch after turning on the fourth switch in (2); turns on the sixth switch and the seventh switch after turning on the third switch in (6); turns on the fifth switch and the eighth switch after turning on the second switch in (10); and turns on the sixth switch and the seventh switch after turning on the first switch in (14).

[0323] In this way, in (2) above, the turn-on of the fourth switch does not have to be synchronized with the turn-on of the fifth switch and the eighth switch; in (6) above, the turn-on of the third switch does not have to be synchronized with the turn-on of the sixth switch and the seventh switch; in (10) above, the turn-on of the second switch does not have to be synchronized with the turn-on of the fifth switch and the eighth switch; and in (14) above, the turn-on of the first switch does not have to be synchronized with the turn-on of the sixth switch and the seventh switch.

[0324] (Technology 12) The control circuit in (1) turns on the first switch after turning off the sixth switch and the seventh switch, or turns off the sixth switch and the seventh switch after turning on the first switch; in (5), turns on the second switch after turning off the fifth switch and the eighth switch, or turns off the fifth switch and the eighth switch after turning on the second switch; in (9), turns on the third switch after turning off the sixth switch and the seventh switch, or turns off the sixth switch and the seventh switch after turning on the third switch; and in (13), turns on the fourth switch after turning off the fifth switch and the eighth switch, or turns off the fifth switch and the eighth switch after turning on the fourth switch.

[0325] In this way, in (1) above, the turning off of the sixth switch and the seventh switch does not have to be synchronized with the turning on of the first switch, and in (5) above, the turning off of the fifth switch and the eighth switch does not have to be synchronized with the turning on of the second switch, and in (9) above, the turning off of the sixth switch and the seventh switch does not have to be synchronized with the turning on of the third switch, and in (13) above, the turning off of the fifth switch and the eighth switch does not have to be synchronized with the turning on of the fourth switch.

[0326] (Technology 13) The power conversion device according to any one of Technologies 10 to 12, wherein the control circuit turns off one of the sixth switch and the seventh switch in (1) and (9), and then turns off the other of the sixth switch and the seventh switch; and turns off one of the fifth switch and the eighth switch in (5) and (13).

[0327] According to this, in (1) and (9) above, one of the sixth switch and the seventh switch is turned off earlier than the other switch, and in (5) and (13) above, one of the fifth switch and the eighth switch is turned off earlier than the other switch, thereby preventing negative current from flowing through the secondary side path and enabling even more efficient operation.

[0328] (Technology 14) The control circuit, in (1), turns off the seventh switch after turning off the sixth switch, and turns on the first switch after turning off the seventh switch, or turns on the first switch after turning off the sixth switch, and turns on the first switch after turning on the seventh switch, or turns off the sixth switch after turning on the first switch, and turns off the sixth switch after turning off the seventh switch, and turns off the seventh switch after turning off the sixth switch; and in (5), turns off the eighth switch after turning off the fifth switch, and turns on the second switch after turning off the eighth switch, or turns on the second switch after turning off the fifth switch, and turns off the eighth switch after turning on the second switch, or turns off the fifth switch after turning on the second switch, and turns off the eighth switch after turning off the fifth switch, The power conversion device according to technology 10 or 11, wherein in (9), the sixth switch is turned off and then the seventh switch is turned off, and the third switch is turned on and then the seventh switch is turned off, or the sixth switch is turned off and then the third switch is turned on and then the third switch is turned on and then the seventh switch is turned off, or the sixth switch is turned on and then the third switch is turned off and then the seventh switch is turned off, or the sixth switch is turned off and then the seventh switch is turned off, and in (13), the fifth switch is turned off and then the eighth switch is turned on, or the fourth switch is turned on and then the fifth switch is turned off and then the fourth switch is turned on, or the fourth switch is turned off and then the eighth switch is turned on, or the fourth switch is turned on and then the fifth switch is turned off and then the eighth switch is turned off.

[0329] In this way, in (1) above, the turn-off of the sixth switch, the turn-off of the seventh switch, and the turn-on of the first switch do not have to be synchronized; in (5) above, the turn-off of the fifth switch, the turn-off of the eighth switch, and the turn-on of the second switch do not have to be synchronized; in (9) above, the turn-off of the sixth switch, the turn-off of the seventh switch, and the turn-on of the third switch do not have to be synchronized; and in (13) above, the turn-off of the fifth switch, the turn-off of the eighth switch, and the turn-on of the fourth switch do not have to be synchronized.

[0330] (Technology 15) A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; and a control circuit that controls switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch.

[0331] Here, a secondary winding of the isolation transformer is connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, the control circuit (1) turns on the first switch, (2) turns off the sixth switch and the seventh switch, (3) turns off the third switch, (4) turns on the fourth switch, the fifth switch, and the eighth switch, (5) turns off the first switch, (6) turns on the second switch, (7) turns off the fifth switch and the eighth switch, (8) turns off the fourth switch, (9) turns on the third switch, the sixth switch, and the seventh switch, and (10) turns off the second switch, The above-mentioned controls (1) to (10) are repeated in order.

[0332] Furthermore, when controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch, the control includes: (11) turning on the third switch; (12) turning off the sixth switch and the seventh switch; (13) turning off the first switch; (14) turning on the second switch, the fifth switch, and the eighth switch; (15) turning off the third switch; (16) turning on the fourth switch; (17) turning off the fifth switch and the eighth switch; (18) turning off the second switch; (19) turning on the first switch, the sixth switch, and the seventh switch; (20) The fourth switch is turned off, and the controls from (11) to (20) are repeated in order.

[0333] According to this, when the switching frequency of each switch on the primary side is made higher than the resonant frequency and the switching phase of the third switch and the fourth switch is delayed relative to the switching phase of the first switch and the second switch in order to set the output voltage to a target voltage, by sequentially repeating the controls (1) to (10) above for each switch on the primary side and the secondary side, it is possible to turn off each switch on the secondary side at a timing when the current flowing on the secondary side is small. Also, when the switching frequency of each switch on the primary side is made higher than the resonant frequency and the switching phase of the first switch and the second switch is delayed relative to the switching phase of the third switch and the fourth switch in order to set the output voltage to a target voltage, by sequentially repeating the controls (11) to (20) above for each switch on the primary side and the secondary side, it is possible to turn off each switch on the secondary side at a timing when the current flowing on the secondary side is small. In this way, high-efficiency operation is possible under the operating condition of setting the switching frequency of each switch on the primary side higher than the resonant frequency and shifting the switching phase of a specific switch on the primary side, which is one operating condition for accommodating a wide input / output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input / output voltage ratio.

[0334] (Technology 16) The power conversion device according to Technology 15, wherein the control circuit turns on the fifth switch and the eighth switch after turning on the fourth switch in (4), turns on the sixth switch and the seventh switch after turning on the third switch in (9), turns on the fifth switch and the eighth switch after turning on the second switch in (14), and turns on the sixth switch and the seventh switch after turning on the first switch in (19).

[0335] In this way, in (4) above, the turn-on of the fourth switch does not have to be synchronized with the turn-on of the fifth switch and the eighth switch; in (9) above, the turn-on of the third switch does not have to be synchronized with the turn-on of the sixth switch and the seventh switch; in (14) above, the turn-on of the second switch does not have to be synchronized with the turn-on of the fifth switch and the eighth switch; and in (19) above, the turn-on of the first switch does not have to be synchronized with the turn-on of the sixth switch and the seventh switch.

[0336] (Technology 17) The power conversion device according to Technology 15 or 16, wherein the control circuit turns off one of the sixth switch and the seventh switch in (2) and (12), and then turns off the other of the sixth switch and the seventh switch; and turns off one of the fifth switch and the eighth switch in (7) and (17).

[0337] According to this, in (2) and (12) above, one of the sixth switch and the seventh switch is turned off earlier than the other switch, and in (7) and (17) above, one of the fifth switch and the eighth switch is turned off earlier than the other switch, thereby preventing negative current from flowing through the secondary side path and enabling even more efficient operation.

[0338] a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; a sixth switch; and a control circuit controlling switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch.

[0339] Here, the isolation transformer has a first winding and a second winding connected in series as a secondary winding, one end of the first winding is connected to one end of the fifth switch, the other end of the first winding and one end of the second winding are connected to a first output terminal, the other end of the second winding is connected to one end of the sixth switch, and the other ends of the fifth switch and the sixth switch are connected to a second output terminal. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is lower than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, the control circuit: (1) turns on one of the first switch group and the second switch group and the fifth switch; (2) turns off the fifth switch; (3) turns off the one of the switch groups; (4) turns on the other of the first switch group and the second switch group and the sixth switch; (5) turns off the sixth switch; and (6) turns off the other of the switch groups, and repeats the controls from (1) to (6) in order.

[0340] According to this, when the switching frequency of each switch on the primary side is set lower than the resonant frequency to set the output voltage to the target voltage, by sequentially repeating the above controls (1) to (6) for each switch on the primary side and the secondary side, each switch on the secondary side can be turned off at a timing when the current flowing on the secondary side is small. In this way, high-efficiency operation is possible under an operating condition in which the switching frequency of each switch on the primary side is set lower than the resonant frequency, which is one operating condition for accommodating a wide input-output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input-output voltage ratio.

[0341] (Technology 19) The power conversion device according to Technology 18, wherein the control circuit turns on the fifth switch after turning on one of the switch groups in (1), and turns on the sixth switch after turning on the other switch group in (4).

[0342] In this way, in (1) above, the turn-on of one of the switch groups and the fifth switch does not have to be synchronized, and in (4) above, the turn-on of the other of the switch groups and the sixth switch does not have to be synchronized.

[0343] a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch, a sixth switch, and a control circuit controlling switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch.

[0344] Here, the isolation transformer has a first winding and a second winding connected in series as a secondary winding, one end of the first winding is connected to one end of the fifth switch, the other end of the first winding and one end of the second winding are connected to a first output terminal, the other end of the second winding is connected to one end of the sixth switch, and the other ends of the fifth switch and the sixth switch are connected to a second output terminal. The first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group. When the control circuit controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, the control circuit: (1) turns on one of the first switch group and the second switch group and the fifth switch; (2) turns off the one of the switch groups; (3) turns off the fifth switch; (4) turns on the other of the first switch group and the second switch group and the sixth switch; (5) turns off the other of the switch group; (6) turns off the sixth switch, and sequentially repeats the controls from (1) to (6).

[0345] According to this, when the switching frequency of each switch on the primary side is made higher than the resonant frequency to set the output voltage to the target voltage, by sequentially repeating the above-described controls (1) to (6) for each switch on the primary side and the secondary side, each switch on the secondary side can be turned off at a timing when the current flowing on the secondary side is small. In this way, high-efficiency operation is possible under an operating condition in which the switching frequency of each switch on the primary side is made higher than the resonant frequency, which is one operating condition for accommodating a wide input / output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input / output voltage ratio.

[0346] (Technology 21) The power conversion device according to Technology 20, wherein the control circuit turns on the fifth switch after turning on one of the switch groups in (1), and turns on the sixth switch after turning on the other switch group in (4).

[0347] In this way, in (1) above, the turn-on of one of the switch groups and the fifth switch does not have to be synchronized, and in (4) above, the turn-on of the other of the switch groups and the sixth switch does not have to be synchronized.

[0348] a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; a sixth switch; and a control circuit controlling switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch.

[0349] Here, the isolation transformer has a first winding and a second winding connected in series as a secondary winding, one end of the first winding is connected to one end of the fifth switch, the other end of the first winding and one end of the second winding are connected to a first output terminal, the other end of the second winding is connected to one end of the sixth switch, and the other end of the fifth switch and the other end of the sixth switch are connected to a second output terminal. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, so that the switching phase of the fourth switch lags behind the switching phase of the first switch, and so that the switching phase of the third switch lags behind the switching phase of the second switch, the control circuit (1) turns off the sixth switch and turns on the first switch, (2) turns on the fourth switch and the fifth switch, (3) turns off the first switch, (4) turns off the fourth switch, (5) turns off the fifth switch and turns on the second switch, (6) turns on the third switch and the sixth switch, (7) turns off the second switch, and (8) turns off the third switch, and repeats the controls (1) to (8) in order.Furthermore, when controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch, the control includes: (9) turning off the sixth switch and turning on the third switch; (10) turning on the second switch and the fifth switch; (11) turning off the third switch; (12) turning off the second switch; (13) turning off the fifth switch and turning on the fourth switch; (14) turning on the first switch and the sixth switch; (15) turning off the fourth switch; (16) turning off the first switch; and repeating the controls from (9) to (16) in order.

[0350] According to this, when the switching frequency of each switch on the primary side is made higher than the resonant frequency and the switching phase of the third switch and the fourth switch is delayed relative to the switching phase of the first switch and the second switch in order to set the output voltage to a target voltage, by sequentially repeating the controls (1) to (8) above for each switch on the primary side and the secondary side, it is possible to turn off each switch on the secondary side at a timing when the current flowing on the secondary side is small. Also, when the switching frequency of each switch on the primary side is made higher than the resonant frequency and the switching phase of the first switch and the second switch is delayed relative to the switching phase of the third switch and the fourth switch in order to set the output voltage to a target voltage, by sequentially repeating the controls (9) to (16) above for each switch on the primary side and the secondary side, it is possible to turn off each switch on the secondary side at a timing when the current flowing on the secondary side is small. In this way, high-efficiency operation is possible under the operating condition of setting the switching frequency of each switch on the primary side higher than the resonant frequency and shifting the switching phase of a specific switch on the primary side, which is one operating condition for accommodating a wide input / output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input / output voltage ratio.

[0351] (Technology 23) The power conversion device according to Technology 22, wherein the control circuit turns on the fifth switch after turning on the fourth switch in (2), turns on the sixth switch after turning on the third switch in (6), turns on the fifth switch after turning on the second switch in (10), and turns on the sixth switch after turning on the first switch in (14).

[0352] In this way, in (2) above, the turn-on of the fourth switch and the fifth switch does not have to be synchronized, and in (6) above, the turn-on of the third switch and the sixth switch does not have to be synchronized, and in (10) above, the turn-on of the second switch and the fifth switch does not have to be synchronized, and in (14) above, the turn-on of the first switch and the sixth switch does not have to be synchronized.

[0353] (Technology 24) The power conversion device according to Technology 22 or 23, wherein the control circuit: in (1), turns on the first switch after turning off the sixth switch, or turns off the sixth switch after turning on the first switch; in (5), turns on the second switch after turning off the fifth switch, or turns off the fifth switch after turning on the second switch; in (9), turns on the third switch after turning off the sixth switch, or turns off the sixth switch after turning on the third switch; in (13), turns on the fourth switch after turning off the fifth switch, or turns off the fifth switch after turning on the fourth switch.

[0354] In this way, in (1) above, the turning off of the sixth switch does not have to be synchronized with the turning on of the first switch, in (5) above, the turning off of the fifth switch does not have to be synchronized with the turning on of the second switch, in (9) above, the turning off of the sixth switch does not have to be synchronized with the turning on of the third switch, and in (13) above, the turning off of the fifth switch does not have to be synchronized with the turning on of the fourth switch.

[0355] a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; a sixth switch; and a control circuit controlling switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch.

[0356] Here, the isolation transformer has a first winding and a second winding connected in series as a secondary winding, one end of the first winding is connected to one end of the fifth switch, the other end of the first winding and one end of the second winding are connected to a first output terminal, the other end of the second winding is connected to one end of the sixth switch, and the other end of the fifth switch and the other end of the sixth switch are connected to a second output terminal. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, the control circuit (1) turns on the first switch, (2) turns off the sixth switch, (3) turns off the third switch, (4) turns on the fourth switch and the fifth switch, (5) turns off the first switch, (6) turns on the second switch, (7) turns off the fifth switch, (8) turns off the fourth switch, (9) turns on the third switch and the sixth switch, and (10) turns off the second switch, and sequentially repeats the controls (1) to (10).Furthermore, when controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch, the control includes: (11) turning on the third switch; (12) turning off the sixth switch; (13) turning off the first switch; (14) turning on the second switch and the fifth switch; (15) turning off the third switch; (16) turning on the fourth switch; (17) turning off the fifth switch; (18) turning off the second switch; (19) turning on the first switch and the sixth switch; (20) turning off the fourth switch; The controls from (11) to (20) are repeated in order.

[0357] According to this, when the switching frequency of each switch on the primary side is made higher than the resonant frequency and the switching phase of the third switch and the fourth switch is delayed relative to the switching phase of the first switch and the second switch in order to set the output voltage to a target voltage, by sequentially repeating the controls (1) to (10) above for each switch on the primary side and the secondary side, it is possible to turn off each switch on the secondary side at a timing when the current flowing on the secondary side is small. Also, when the switching frequency of each switch on the primary side is made higher than the resonant frequency and the switching phase of the first switch and the second switch is delayed relative to the switching phase of the third switch and the fourth switch in order to set the output voltage to a target voltage, by sequentially repeating the controls (11) to (20) above for each switch on the primary side and the secondary side, it is possible to turn off each switch on the secondary side at a timing when the current flowing on the secondary side is small. In this way, high-efficiency operation is possible under the operating condition of setting the switching frequency of each switch on the primary side higher than the resonant frequency and shifting the switching phase of a specific switch on the primary side, which is one operating condition for accommodating a wide input / output voltage ratio. Therefore, high-efficiency operation is possible while accommodating a wide input / output voltage ratio.

[0358] (Technology 26) The power conversion device according to Technology 25, wherein the control circuit turns on the fifth switch after turning on the fourth switch in (4), turns on the sixth switch after turning on the third switch in (9), turns on the fifth switch after turning on the second switch in (14), and turns on the sixth switch after turning on the first switch in (19).

[0359] In this way, in (4) above, the turn-on of the fourth switch and the fifth switch does not have to be synchronized, and in (9) above, the turn-on of the third switch and the sixth switch does not have to be synchronized, and in (14) above, the turn-on of the second switch and the fifth switch does not have to be synchronized, and in (19) above, the turn-on of the first switch and the sixth switch does not have to be synchronized.

[0360] (Technology 27) The power conversion device according to any one of Techniques 1 to 26, wherein the control circuit further determines an on-period of the plurality of switches based on a detection result indicating whether the plurality of switches connected to the secondary winding are operating as diodes and passing current.

[0361] According to this, by determining the on period of each switch on the secondary side so as to shorten the period during which each switch on the secondary side passes current in diode operation (for example, so as to shorten the period during which the detection result indicates that current is passing in diode operation), it is possible to suppress losses caused by each switch on the secondary side performing diode operation, and even more efficient operation is possible.

[0362] (Technology 28) The power conversion device according to any one of Techniques 1 to 26, wherein the control circuit further turns off the plurality of switches in synchronization with the timing at which the current flowing through the plurality of switches connected to the secondary winding becomes 0 A.

[0363] According to this, by turning off each switch on the secondary side at the timing when the current flowing through each switch on the secondary side becomes 0 A, it is possible to prevent current from flowing through the switch on the secondary side by operating as a diode when the switch on the secondary side is off. Therefore, it is possible to suppress losses caused by current flowing through the switch on the secondary side by operating as a diode, and it is possible to achieve even more efficient operation.

[0364] (Technology 29) A power conversion device according to any one of Techniques 1 to 26, wherein the control circuit further turns off the plurality of switches in synchronization with a timing that is a predetermined time earlier than the timing at which the current flowing through the plurality of switches connected to the secondary winding becomes 0 A.

[0365] There is a delay between when a control signal is sent to each switch on the secondary side and when the switch actually turns off. Therefore, by sending a control signal to turn off each switch on the secondary side at a timing that is a predetermined time earlier than the delay, that is, by sending a control signal to turn off each switch on the secondary side at a timing that is a predetermined time earlier than the delay, it is possible to turn off each switch on the secondary side at a timing when the current flowing through each switch on the secondary side becomes 0 A.

[0366] (Technology 30) A control method for a power conversion device, the power conversion device comprising: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; and a sixth switch provided on the third path and connected in series with the fifth switch. the isolation transformer includes a seventh switch provided on a fourth path different from the third path, which connects the first output terminal and the second output terminal; and an eighth switch provided on the fourth path and connected in series with the seventh switch, wherein a secondary winding of the isolation transformer is connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch, the first switch and the fourth switch being a first switch group, and the second switch and the third switch being a second switch group.

[0367] The control method controls switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is lower than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and in this case, (1) turns on one of the first switch group and the second switch group, and the fifth switch and the eighth switch, (2) turns off the fifth switch and the eighth switch, (3) turns off the one of the switch groups, (4) turns on the other of the first switch group and the second switch group, and the sixth switch and the seventh switch, (5) turns off the sixth switch and the seventh switch, and (6) turns off the other of the switch groups, and repeats the controls from (1) to (6) in order.

[0368] This makes it possible to provide a control method that enables the power conversion device to operate with high efficiency while adapting to a wide input / output voltage ratio.

[0369] (Technology 31) A control method for a power conversion device, the power conversion device comprising: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; and a sixth switch provided on the third path and connected in series with the fifth switch. a seventh switch provided on a fourth path different from the third path, which connects the first output terminal and the second output terminal; and an eighth switch provided on the fourth path and connected in series with the seventh switch, wherein a secondary winding of the isolation transformer is connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch, the first switch and the fourth switch forming a first switch group, and the second switch and the third switch forming a second switch group.

[0370] The control method controls switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and in this case, (1) turns on one switch group of the first switch group and the second switch group, and the fifth switch and the eighth switch, (2) turns off one switch group, (3) turns off the fifth switch and the eighth switch, (4) turns on the other switch group of the first switch group and the second switch group, and the sixth switch and the seventh switch, (5) turns off the other switch group, and (6) turns off the sixth switch and the seventh switch, and the controls from (1) to (6) are repeated in order.

[0371] This makes it possible to provide a control method that enables the power conversion device to operate with high efficiency while adapting to a wide input / output voltage ratio.

[0372] (Technology 32) A control method for a power conversion device, the power conversion device comprising: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; and a sixth switch provided on the third path and connected in series with the fifth switch. a seventh switch provided on a fourth path different from the third path, which connects the first output terminal and the second output terminal; and an eighth switch provided on the fourth path and connected in series with the seventh switch, wherein a secondary winding of the isolation transformer is connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch.

[0373] The control method controls switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, so that the switching phase of the fourth switch lags behind the switching phase of the first switch, and so that the switching phase of the third switch lags behind the switching phase of the second switch, and in this case, (1) turns off the sixth switch and the seventh switch, and turns on the first switch, (2) turns on the fourth switch, the fifth switch, and the eighth switch, (3) turns off the first switch, (4) turns off the fourth switch, (5) turns off the fifth switch and the eighth switch, and turns on the second switch, (6) turns on the third switch, the sixth switch, and the seventh switch, (7) turns off the second switch, and (8) turns off the third switch, The controls (1) to (8) are repeated in order, and the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch, and in this case, (9) turns off the sixth switch and the seventh switch, and turns on the third switch, (10) turns on the second switch, the fifth switch, and the eighth switch, (11) turns off the third switch, (12) turns off the second switch, and (13) turns off the fifth switch and the eighth switch, and turns on the fourth switch,(14) turning on the first switch, the sixth switch, and the seventh switch; (15) turning off the fourth switch; (16) turning off the first switch; and repeating the controls from (9) to (16) in order.

[0374] This makes it possible to provide a control method that enables the power conversion device to operate with high efficiency while adapting to a wide input / output voltage ratio.

[0375] (Technology 33) A control method for a power conversion device, the power conversion device comprising: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path connecting the first input terminal and the second input terminal, different from the first path; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; and a sixth switch provided on the third path and connected in series with the fifth switch. a seventh switch provided on a fourth path different from the third path, which connects the first output terminal and the second output terminal; and an eighth switch provided on the fourth path and connected in series with the seventh switch, wherein a secondary winding of the isolation transformer is connected between a third node on the third path between the fifth switch and the sixth switch and a fourth node on the fourth path between the seventh switch and the eighth switch.

[0376] The control method includes controlling switching of the first switch, the second switch, the third switch, and the fourth switch so that a switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than a resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, so that a switching phase of the fourth switch lags behind a switching phase of the first switch, and so that a switching phase of the third switch lags behind a switching phase of the second switch, and in this case, (1) turning on the first switch, (2) turning off the sixth switch and the seventh switch, (3) turning off the third switch, (4) turning on the fourth switch, the fifth switch, and the eighth switch, (5) turning off the first switch, (6) turning on the second switch, (7) turning off the fifth switch and the eighth switch, (8) turning off the fourth switch, and (9) turning on the third switch, the sixth switch, and the seventh switch, (10) turning off the second switch; and repeating the controls from (1) to (10) in order, controlling the switching of the first switch, the second switch, the third switch and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch; in this case, (11) turning on the third switch; (12) turning off the sixth switch and the seventh switch; (13) turning off the first switch; (14) turning on the second switch, the fifth switch and the eighth switch; (15) turning off the third switch; (16) turning on the fourth switch;(17) turning off the fifth switch and the eighth switch; (18) turning off the second switch; (19) turning on the first switch, the sixth switch, and the seventh switch; (20) turning off the fourth switch; and repeating the controls from (11) to (20) in order.

[0377] This makes it possible to provide a control method that enables the power conversion device to operate with high efficiency while adapting to a wide input / output voltage ratio.

[0378] (Technology 34) A control method for a power conversion device, the power conversion device comprising: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; and a sixth switch. The isolation transformer has a first winding and a second winding connected in series as a secondary winding, one end of the first winding is connected to one end of the fifth switch, the other end of the first winding and one end of the second winding are connected to a first output terminal, the other end of the second winding is connected to one end of the sixth switch, and the other end of the fifth switch and the other end of the sixth switch are connected to a second output terminal, the first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group.

[0379] The control method controls switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is lower than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and in this case, (1) turns on one of the first switch group and the second switch group and the fifth switch, (2) turns off the fifth switch, (3) turns off the one of the switch groups, (4) turns on the other of the first switch group and the second switch group and the sixth switch, (5) turns off the sixth switch, and (6) turns off the other of the switch groups, and the control from (1) to (6) is repeated in order.

[0380] This makes it possible to provide a control method that enables the power conversion device to operate with high efficiency while adapting to a wide input / output voltage ratio.

[0381] (Technology 35) A control method for a power conversion device, the power conversion device comprising: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; and a sixth switch. The isolation transformer has a first winding and a second winding connected in series as a secondary winding, one end of the first winding is connected to one end of the fifth switch, the other end of the first winding and one end of the second winding are connected to a first output terminal, the other end of the second winding is connected to one end of the sixth switch, and the other end of the fifth switch and the other end of the sixth switch are connected to a second output terminal, the first switch and the fourth switch form a first switch group, and the second switch and the third switch form a second switch group.

[0382] The control method controls switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and in this case, (1) turns on one of the first switch group and the second switch group and the fifth switch, (2) turns off the one switch group, (3) turns off the fifth switch, (4) turns on the other of the first switch group and the second switch group and the sixth switch, (5) turns off the other switch group, and (6) turns off the sixth switch, and the control from (1) to (6) is repeated in order.

[0383] This makes it possible to provide a control method that enables the power conversion device to operate with high efficiency while adapting to a wide input / output voltage ratio.

[0384] (Technology 36) A control method for a power conversion device, the power conversion device comprising: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; and a sixth switch. The isolation transformer has a first winding and a second winding connected in series as a secondary winding, one end of the first winding is connected to one end of the fifth switch, the other end of the first winding and one end of the second winding are connected to a first output terminal, the other end of the second winding is connected to one end of the sixth switch, and the other end of the fifth switch and the other end of the sixth switch are connected to a second output terminal.

[0385] In the control method, switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that a switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than a resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the fourth switch lags behind the switching phase of the first switch and so that the switching phase of the third switch lags behind the switching phase of the second switch, and in this case, (1) turns off the sixth switch and turns on the first switch, (2) turns on the fourth switch and the fifth switch, (3) turns off the first switch, (4) turns off the fourth switch, (5) turns off the fifth switch and turns on the second switch, (6) turns on the third switch and the sixth switch, (7) turns off the second switch, and (8) turns off the third switch, and the controls from (1) to (8) are repeated in order, controlling switching of the first switch, the second switch, the third switch, and the fourth switch so that a switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than a resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, so that the switching phase of the first switch lags behind the switching phase of the fourth switch, and so that the switching phase of the second switch lags behind the switching phase of the third switch; in this case, (9) turning off the sixth switch and turning on the third switch, (10) turning on the second switch and the fifth switch, (11) turning off the third switch, (12) turning off the second switch, (13) turning off the fifth switch and turning on the fourth switch, (14) turning on the first switch and the sixth switch, and (15) turning off the fourth switch,(16) A control method in which the first switch is turned off and the controls from (9) to (16) are repeated in order.

[0386] This makes it possible to provide a control method that enables the power conversion device to operate with high efficiency while adapting to a wide input / output voltage ratio.

[0387] (Technology 37) A control method for a power conversion device, the power conversion device comprising: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node on the first path between the first switch and the second switch and a second node on the second path between the third switch and the fourth switch; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; and a sixth switch. The isolation transformer has a first winding and a second winding connected in series as a secondary winding, one end of the first winding is connected to one end of the fifth switch, the other end of the first winding and one end of the second winding are connected to a first output terminal, the other end of the second winding is connected to one end of the sixth switch, and the other end of the fifth switch and the other end of the sixth switch are connected to a second output terminal.

[0388] The control method includes controlling switching of the first switch, the second switch, the third switch, and the fourth switch so that a switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than a resonant frequency of resonance generated by the resonant capacitor and the resonant inductor, so that a switching phase of the fourth switch lags behind a switching phase of the first switch, and so that a switching phase of the third switch lags behind a switching phase of the second switch, and in this case, (1) turning on the first switch, (2) turning off the sixth switch, (3) turning off the third switch, (4) turning on the fourth switch and the fifth switch, (5) turning off the first switch, (6) turning on the second switch, (7) turning off the fifth switch, (8) turning off the fourth switch, (9) turning on the third switch and the sixth switch, and (10) turning off the second switch. The controls (1) to (10) are repeated in order, and the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonant frequency of the resonance generated by the resonant capacitor and the resonant inductor, and so that the switching phase of the first switch lags behind the switching phase of the fourth switch and so that the switching phase of the second switch lags behind the switching phase of the third switch, and in this case, (11) turns on the third switch, (12) turns off the sixth switch, (13) turns off the first switch, (14) turns on the second switch and the fifth switch, (15) turns off the third switch, (16) turns on the fourth switch, (17) turns off the fifth switch, and (18) turns off the second switch,(19) A control method, which turns on the first switch and the sixth switch, (20) turns off the fourth switch, and sequentially repeats the controls from (11) to (20).

[0389] This makes it possible to provide a control method that enables the power conversion device to operate with high efficiency while adapting to a wide input / output voltage ratio.

[0390] The present disclosure can be applied to LLC converters and the like that are compatible with a wide range of input and output voltages.

[0391] 1, 2 Power conversion device 10, 20 Control circuit AH, AL, BH, BL, CH, CL, DH, DL, EH, EL Switch Cr Capacitor L1 First winding L2 Second winding Lm, Lr Inductor N1, N2, N3, N4 Node P1, P2, P3, P4 Path T1, T2 Transformer t1, t2, t3, t4 Terminal

Claims

1. A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an insulating transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path and connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; and a control circuit for controlling the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch. The secondary winding of the insulating transformer is connected between a third node between the fifth switch and the sixth switch on the third path and a fourth node between the seventh switch and the eighth switch on the fourth path. The first switch and the fourth switch are regarded as a first switch group, and the second switch and the third switch are regarded as a second switch group. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are lower than the resonance frequency of the resonance generated by the resonant capacitor and the resonant inductor,(1) Turn on one of the first switch group and the second switch group, the fifth switch, and the eighth switch; (2) Turn off the fifth switch and the eighth switch; (3) Turn off the one switch group; (4) Turn on the other switch group of the first switch group and the second switch group, the sixth switch, and the seventh switch; (5) Turn off the sixth switch and the seventh switch; (6) Turn off the other switch group; Repeatedly perform the controls from (1) to (6) in order. Power conversion device.

2. In the above (1), after turning on the one switch group, the control circuit turns on the fifth switch and the eighth switch. In the above (4), after turning on the other switch group, the control circuit turns on the sixth switch and the seventh switch. The power conversion device according to claim 1.

3. In the above (2), after turning off one of the fifth switch and the eighth switch, the control circuit turns off the other of the fifth switch and the eighth switch. In the above (5), after turning off one of the sixth switch and the seventh switch, the control circuit turns off the other of the sixth switch and the seventh switch. The power conversion device according to claim 1.

4. In the above (2), the control circuit simultaneously turns off the other of the fifth switch and the eighth switch and turns off the one switch group in the above (3). In the above (5), the control circuit simultaneously turns off the other of the sixth switch and the seventh switch and turns off the other switch group in the above (6). The power conversion device according to claim 3.

5. In the above (1), the control circuit simultaneously turns on the fifth switch and the eighth switch. In the above (4), the control circuit simultaneously turns on the sixth switch and the seventh switch. The power conversion device according to claim 1.

6. A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an insulating transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path and connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; and a control circuit for controlling the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch. The secondary winding of the insulating transformer is connected between a third node between the fifth switch and the sixth switch on the third path and a fourth node between the seventh switch and the eighth switch on the fourth path. Regarding the first switch and the fourth switch as a first switch group and the second switch and the third switch as a second switch group, when controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency of the resonance generated by the resonant capacitor and the resonant inductor,(1) Turn on one of the first switch group and the second switch group, as well as the fifth switch and the eighth switch. (2) Turn off the one switch group. (3) Turn off the fifth switch and the eighth switch. (4) Turn on the other switch group of the first switch group and the second switch group, as well as the sixth switch and the seventh switch. (5) Turn off the other switch group. (6) Turn off the sixth switch and the seventh switch. Repeatedly perform the control from (1) to (6) in order. Power conversion device.

7. In the above (1), after turning on the one switch group, the control circuit turns on the fifth switch and the eighth switch. In the above (4), after turning on the other switch group, the control circuit turns on the sixth switch and the seventh switch. The power conversion device according to claim 6.

8. The control circuit turns off one of the fifth switch and the eighth switch in (3) and then turns off the other of the fifth switch and the eighth switch, and turns off one of the sixth switch and the seventh switch in (6) and then turns off the other of the sixth switch and the seventh switch, in the power conversion device according to claim 6.

9. The control circuit turns on the fifth switch and the eighth switch simultaneously in (1) and turns on the sixth switch and the seventh switch simultaneously in (4), in the power conversion device according to claim 6.

10. A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an insulating transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path and connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; and a control circuit for controlling the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch, wherein a secondary winding of the insulating transformer is connected between a third node between the fifth switch and the sixth switch on the third path and a fourth node between the seventh switch and the eighth switch on the fourth path, and the control circuit controls the switching of the first switch, the second switch, the third switch, and the fourth switch such that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and such that the phase of the switching of the fourth switch lags behind the phase of the switching of the first switch, and the phase of the switching of the third switch lags behind the phase of the switching of the second switch.(1) Turn off the sixth switch and the seventh switch, and turn on the first switch. (2) Turn on the fourth switch, the fifth switch, and the eighth switch. (3) Turn off the first switch. (4) Turn off the fourth switch. (5) Turn off the fifth switch and the eighth switch, and turn on the second switch. (6) Turn on the third switch, the sixth switch, and the seventh switch. (7) Turn off the second switch. (8) Turn off the third switch. Repeat the control from (1) to (8) in order. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and the phase of the switching of the first switch lags behind the phase of the switching of the fourth switch, and the phase of the switching of the second switch lags behind the phase of the switching of the third switch: (9) Turn off the sixth switch and the seventh switch, and turn on the third switch. (10) Turn on the second switch, the fifth switch, and the eighth switch. (11) Turn off the third switch. (12) Turn off the second switch. (13) Turn off the fifth switch and the eighth switch, and turn on the fourth switch. (14) Turn on the first switch, the sixth switch, and the seventh switch. (15) Turn off the fourth switch. (16) Turn off the first switch. Repeat the control from (9) to (16) in order. Power conversion device.

11. The control circuit turns on the fourth switch and then turns on the fifth switch and the eighth switch in (2), turns on the third switch and then turns on the sixth switch and the seventh switch in (6), turns on the second switch and then turns on the fifth switch and the eighth switch in (10), and turns on the first switch and then turns on the sixth switch and the seventh switch in (14), in the power conversion device according to claim 10.

12. In the above (1), after turning off the sixth switch and the seventh switch, the control circuit turns on the first switch, or after turning on the first switch, turns off the sixth switch and the seventh switch; in the above (5), after turning off the fifth switch and the eighth switch, the control circuit turns on the second switch, or after turning on the second switch, turns off the fifth switch and the eighth switch; in the above (9), after turning off the sixth switch and the seventh switch, the control circuit turns on the third switch, or after turning on the third switch, turns off the sixth switch and the seventh switch; in the above (13), after turning off the fifth switch and the eighth switch, the control circuit turns on the fourth switch, or after turning on the fourth switch, turns off the fifth switch and the eighth switch. The power conversion device according to claim 10.

13. In the above (1) and (9), after turning off one of the sixth switch and the seventh switch, the control circuit turns off the other of the sixth switch and the seventh switch; in the above (5) and (13), after turning off one of the fifth switch and the eighth switch, the control circuit turns off the other of the fifth switch and the eighth switch. The power conversion device according to claim 10.

14. In the above (1), after turning off the sixth switch, the seventh switch is turned off, and after turning off the seventh switch, the first switch is turned on, or after turning off the sixth switch, the first switch is turned on, and after turning on the first switch, the seventh switch is turned off, or after turning on the first switch, the sixth switch is turned off, and after turning off the sixth switch, the seventh switch is turned off; in the above (5), after turning off the fifth switch, the eighth switch is turned off, and after turning off the eighth switch, the second switch is turned on, or after turning off the fifth switch, the second switch is turned on, and after turning on the second switch, the eighth switch is turned off, or after turning on the second switch, the fifth switch is turned off, and after turning off the fifth switch, the eighth switch is turned off; in the above (9), after turning off the sixth switch, the seventh switch is turned off, and after turning off the seventh switch, the third switch is turned on, or after turning off the sixth switch, the third switch is turned on, and after turning on the third switch, the seventh switch is turned off, or after turning on the third switch, the sixth switch is turned off, and after turning off the sixth switch, the seventh switch is turned off; in the above (13), after turning off the fifth switch, the eighth switch is turned off, and after turning off the eighth switch, the fourth switch is turned on, or after turning off the fifth switch, the fourth switch is turned on, and after turning on the fourth switch, the eighth switch is turned off, or after turning on the fourth switch, the fifth switch is turned off, and after turning off the fifth switch, the eighth switch is turned off. The power conversion device according to claim 10.

15. A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an insulating transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path and connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; and a control circuit for controlling the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch. The secondary winding of the insulating transformer is connected between a third node between the fifth switch and the sixth switch on the third path and a fourth node between the seventh switch and the eighth switch on the fourth path. The control circuit controls the switching of the first switch, the second switch, the third switch, and the fourth switch such that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and such that the phase of the switching of the fourth switch lags behind the phase of the switching of the first switch, and the phase of the switching of the third switch lags behind the phase of the switching of the second switch. (1) Turn on the first switch,(2) Turn off the sixth switch and the seventh switch. (3) Turn off the third switch. (4) Turn on the fourth switch, the fifth switch, and the eighth switch. (5) Turn off the first switch. (6) Turn on the second switch. (7) Turn off the fifth switch and the eighth switch. (8) Turn off the fourth switch. (9) Turn on the third switch, the sixth switch, and the seventh switch. (10) Turn off the second switch. Repeat the control from (1) to (10) in order. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and the phase of the switching of the first switch lags behind the phase of the switching of the fourth switch, and the phase of the switching of the second switch lags behind the phase of the switching of the third switch: (11) Turn on the third switch. (12) Turn off the sixth switch and the seventh switch. (13) Turn off the first switch. (14) Turn on the second switch, the fifth switch, and the eighth switch. (15) Turn off the third switch. (16) Turn on the fourth switch. (17) Turn off the fifth switch and the eighth switch. (18) Turn off the second switch. (19) Turn on the first switch, the sixth switch, and the seventh switch. (20) Turn off the fourth switch. Repeat the control from (11) to (20) in order. A power conversion device.

16. In the above (4), after turning on the fourth switch, the control circuit turns on the fifth switch and the eighth switch. In the above (9), after turning on the third switch, the control circuit turns on the sixth switch and the seventh switch. In the above (14), after turning on the second switch, the control circuit turns on the fifth switch and the eighth switch. In the above (19), after turning on the first switch, the control circuit turns on the sixth switch and the seventh switch. The power conversion device according to claim 15.

17. In the above (2) and (12), after turning off one of the sixth switch and the seventh switch, the control circuit turns off the other of the sixth switch and the seventh switch. In the above (7) and (17), after turning off one of the fifth switch and the eighth switch, the control circuit turns off the other of the fifth switch and the eighth switch. The power conversion device according to claim 15.

18. A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an insulating transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; a sixth switch; and a control circuit for controlling the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch. The insulating transformer has a first winding and a second winding connected in series as secondary windings. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other ends of the fifth switch and the sixth switch are connected to a second output terminal. Regarding the first switch and the fourth switch as a first switch group and the second switch and the third switch as a second switch group, the control circuit, when controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are lower than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, (1) turns on one of the first switch group and the second switch group and the fifth switch; (2) turns off the fifth switch; (3) turns off the one switch group;(4) Turn on the other switch group among the first switch group and the second switch group and the sixth switch; (5) Turn off the sixth switch; (6) Turn off the other switch group; Repeat the control from (1) to (6) above in order, a power conversion device.

19. In the above (1), after turning on the one switch group, the control circuit turns on the fifth switch. In the above (4), after turning on the other switch group, the control circuit turns on the sixth switch. The power conversion device according to claim 18.

20. A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; a sixth switch; and a control circuit for controlling the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch. The isolation transformer has a first winding and a second winding connected in series as secondary windings. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other ends of the fifth switch and the sixth switch are connected to a second output terminal. Regarding the first switch and the fourth switch as a first switch group and the second switch and the third switch as a second switch group, when the control circuit controls the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor: (1) turn on one of the first switch group and the second switch group and the fifth switch; (2) turn off the one switch group; (3) turn off the fifth switch.(4) Turn on the other switch group of the first switch group and the second switch group and the sixth switch, (5) Turn off the other switch group, (6) Turn off the sixth switch, and repeat the controls from (1) to (6) above in order. A power conversion device.

21. In the above (1), after turning on the one switch group, the control circuit turns on the fifth switch. In the above (4), after turning on the other switch group, the control circuit turns on the sixth switch. The power conversion device according to claim 20.

22. A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an insulating transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; a sixth switch; and a control circuit for controlling the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch. The insulating transformer has a first winding and a second winding connected in series as secondary windings. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other ends of the fifth switch and the sixth switch are connected to a second output terminal. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch such that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency generated by the resonance capacitor and the resonance inductor, and the switching phase of the fourth switch lags behind the switching phase of the first switch, and the switching phase of the third switch lags behind the switching phase of the second switch, the control circuit: (1) turns off the sixth switch and turns on the first switch; (2) turns on the fourth switch and the fifth switch; (3) turns off the first switch; (4) turns off the fourth switch.(5) Turn off the fifth switch and turn on the second switch. (6) Turn on the third switch and the sixth switch. (7) Turn off the second switch. (8) Turn off the third switch. Repeat the control from (1) to (8) in order. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and the phase of the switching of the first switch lags behind the phase of the switching of the fourth switch, and the phase of the switching of the second switch lags behind the phase of the switching of the third switch: (9) Turn off the sixth switch and turn on the third switch. (10) Turn on the second switch and the fifth switch. (11) Turn off the third switch. (12) Turn off the second switch. (13) Turn off the fifth switch and turn on the fourth switch. (14) Turn on the first switch and the sixth switch. (15) Turn off the fourth switch. (16) Turn off the first switch. Repeat the control from (9) to (16) in order. Power conversion device.

23. In the above (2), after turning on the fourth switch, the control circuit turns on the fifth switch. In the above (6), after turning on the third switch, the control circuit turns on the sixth switch. In the above (10), after turning on the second switch, the control circuit turns on the fifth switch. In the above (14), after turning on the first switch, the control circuit turns on the sixth switch. The power conversion device according to claim 22.

24. In the above (1), after turning off the sixth switch, the control circuit turns on the first switch, or after turning on the first switch, turns off the sixth switch; in the above (5), after turning off the fifth switch, the control circuit turns on the second switch, or after turning on the second switch, turns off the fifth switch; in the above (9), after turning off the sixth switch, the control circuit turns on the third switch, or after turning on the third switch, turns off the sixth switch; in the above (13), after turning off the fifth switch, the control circuit turns on the fourth switch, or after turning on the fourth switch, turns off the fifth switch. The power conversion device according to claim 22.

25. A first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an insulating transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; a sixth switch; and a control circuit for controlling the switching of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, and the sixth switch. The insulating transformer has a first winding and a second winding connected in series as secondary windings. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other ends of the fifth switch and the sixth switch are connected to a second output terminal. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch such that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency generated by the resonance capacitor and the resonance inductor, and the phase of the switching of the fourth switch lags behind the phase of the switching of the first switch, and the phase of the switching of the third switch lags behind the phase of the switching of the second switch, the control circuit: (1) turns on the first switch; (2) turns off the sixth switch; (3) turns off the third switch; (4) turns on the fourth switch and the fifth switch; (5) turns off the first switch;(6) Turn on the second switch. (7) Turn off the fifth switch. (8) Turn off the fourth switch. (9) Turn on the third switch and the sixth switch. (10) Turn off the second switch. Repeat the control from (1) to (10) in order. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and the phase of the switching of the first switch lags behind the phase of the switching of the fourth switch, and the phase of the switching of the second switch lags behind the phase of the switching of the third switch: (11) Turn on the third switch. (12) Turn off the sixth switch. (13) Turn off the first switch. (14) Turn on the second switch and the fifth switch. (15) Turn off the third switch. (16) Turn on the fourth switch. (17) Turn off the fifth switch. (18) Turn off the second switch. (19) Turn on the first switch and the sixth switch. (20) Turn off the fourth switch. Repeat the control from (11) to (20) in order. A power conversion device.

26. In the above (4), after turning on the fourth switch, the control circuit turns on the fifth switch; in the above (9), after turning on the third switch, the control circuit turns on the sixth switch; in the above (14), after turning on the second switch, the control circuit turns on the fifth switch; in the above (19), after turning on the first switch, the control circuit turns on the sixth switch. The power conversion device according to claim 25.

27. The control circuit further determines the on-periods of the plurality of switches based on a detection result indicating whether a plurality of switches connected to the secondary winding are conducting current in a diode operation. The power conversion device according to any one of claims 1 to 26.

28. The control circuit further turns off the plurality of switches in synchronization with the timing at which the current flowing through the plurality of switches connected to the secondary winding becomes 0 A. The power conversion device according to any one of claims 1 to 26.

29. The control circuit further turns off the plurality of switches in synchronization with a timing that is a predetermined time earlier than the timing at which the current flowing through the plurality of switches connected to the secondary winding becomes 0 A. The power conversion device according to any one of claims 1 to 26.

30. A control method for a power conversion device, wherein the power conversion device includes: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path and connecting the first output terminal and the second output terminal; and an eighth switch provided on the fourth path and connected in series with the seventh switch, wherein a secondary winding of the isolation transformer is connected between a third node between the fifth switch and the sixth switch on the third path and a fourth node between the seventh switch and the eighth switch on the fourth path, and the first switch and the fourth switch are defined as a first switch group, and the second switch and the third switch are defined as a second switch group. In the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled such that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are lower than the resonance frequency of the resonance generated by the resonant capacitor and the resonant inductor. In this case: (1) one of the first switch group and the second switch group and the fifth switch and the eighth switch are turned on; (2) the fifth switch and the eighth switch are turned off.(3) Turn off the one switch group; (4) Turn on the other switch group among the first switch group and the second switch group, as well as the sixth switch and the seventh switch; (5) Turn off the sixth switch and the seventh switch; (6) Turn off the other switch group; Repeat the control from (1) to (6) in order. Control method.

31. A method for controlling a power conversion device, wherein the power conversion device includes: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonant capacitor and a resonant inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path and connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; wherein a secondary winding of the isolation transformer is connected between a third node between the fifth switch and the sixth switch on the third path and a fourth node between the seventh switch and the eighth switch on the fourth path; the first switch and the fourth switch are defined as a first switch group, and the second switch and the third switch are defined as a second switch group; in the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled such that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonance frequency of the resonance generated by the resonant capacitor and the resonant inductor; in this case, (1) one of the first switch group and the second switch group and the fifth switch and the eighth switch are turned on; (2) the one switch group is turned off,(3) Turn off the fifth switch and the eighth switch. (4) Turn on the other switch group among the first switch group and the second switch group, as well as the sixth switch and the seventh switch. (5) Turn off the other switch group. (6) Turn off the sixth switch and the seventh switch. Repeatedly perform the control from (1) to (6) in order. Control method.

32. A control method for a power conversion device, wherein the power conversion device includes: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path and connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch; and a secondary winding of the isolation transformer is connected between a third node between the fifth switch and the sixth switch on the third path and a fourth node between the seventh switch and the eighth switch on the fourth path. In the control method, the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are made higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and the switching phase of the fourth switch lags behind the switching phase of the first switch, and the switching phase of the third switch lags behind the switching phase of the second switch. In this case, (1) turn off the sixth switch and the seventh switch, and turn on the first switch; (2) turn on the fourth switch, the fifth switch, and the eighth switch.(3) Turn off the first switch, (4) Turn off the fourth switch, (5) Turn off the fifth switch and the eighth switch, and turn on the second switch, (6) Turn on the third switch, the sixth switch, and the seventh switch, (7) Turn off the second switch, (8) Turn off the third switch, Repeat the control from (1) to (8) in order, Control the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and so that the phase of the switching of the first switch lags behind the phase of the switching of the fourth switch, and the phase of the switching of the second switch lags behind the phase of the switching of the third switch. In that case, (9) Turn off the sixth switch and the seventh switch, and turn on the third switch, (10) Turn on the second switch, the fifth switch, and the eighth switch, (11) Turn off the third switch, (12) Turn off the second switch, (13) Turn off the fifth switch and the eighth switch, and turn on the fourth switch, (14) Turn on the first switch, the sixth switch, and the seventh switch, (15) Turn off the fourth switch, (16) Turn off the first switch, Repeat the control from (9) to (16) in order, Control method.

33. A control method for a power conversion device, wherein the power conversion device includes: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch provided on a third path connecting a first output terminal and a second output terminal; a sixth switch provided on the third path and connected in series with the fifth switch; a seventh switch provided on a fourth path different from the third path and connecting the first output terminal and the second output terminal; an eighth switch provided on the fourth path and connected in series with the seventh switch, wherein a secondary winding of the isolation transformer is connected between a third node between the fifth switch and the sixth switch on the third path and a fourth node between the seventh switch and the eighth switch on the fourth path, and in the control method, the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are made higher than the resonance frequency of resonance generated by the resonance capacitor and the resonance inductor, and the switching phase of the fourth switch lags behind the switching phase of the first switch, and the switching phase of the third switch lags behind the switching phase of the second switch, and the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled, and in that case, (1) turn on the first switch; (2) turn off the sixth switch and the seventh switch; (3) turn off the third switch,(4) Turn on the fourth switch, the fifth switch, and the eighth switch. (5) Turn off the first switch. (6) Turn on the second switch. (7) Turn off the fifth switch and the eighth switch. (8) Turn off the fourth switch. (9) Turn on the third switch, the sixth switch, and the seventh switch. (10) Turn off the second switch. Repeat the control from (1) to (10) in order. When controlling the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and the phase of the switching of the first switch lags behind the phase of the switching of the fourth switch, and the phase of the switching of the second switch lags behind the phase of the switching of the third switch: (11) Turn on the third switch. (12) Turn off the sixth switch and the seventh switch. (13) Turn off the first switch. (14) Turn on the second switch, the fifth switch, and the eighth switch. (15) Turn off the third switch. (16) Turn on the fourth switch. (17) Turn off the fifth switch and the eighth switch. (18) Turn off the second switch. (19) Turn on the first switch, the sixth switch, and the seventh switch. (20) Turn off the fourth switch. Repeat the control from (11) to (20) in order. Control method.

34. A control method for a power conversion device, wherein the power conversion device includes: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; and a sixth switch. The isolation transformer has a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other ends of the fifth switch and the sixth switch are connected to a second output terminal. Regarding the first switch and the fourth switch as a first switch group and the second switch and the third switch as a second switch group, in the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled such that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is lower than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor. In this case: (1) Turn on one of the first switch group and the second switch group and the fifth switch. (2) Turn off the fifth switch. (3) Turn off the one switch group. (4) Turn on the other of the first switch group and the second switch group and the sixth switch. (5) Turn off the sixth switch.(6) A control method of turning off the other switch group and repeating the controls from (1) to (6) in order.

35. A control method for a power conversion device, wherein the power conversion device includes: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; and a sixth switch. The isolation transformer has a first winding and a second winding connected in series as secondary windings. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other ends of the fifth switch and the sixth switch are connected to a second output terminal. Taking the first switch and the fourth switch as a first switch group and the second switch and the third switch as a second switch group, in the control method, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled such that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor. In this case: (1) turn on one of the first switch group and the second switch group and the fifth switch; (2) turn off the one switch group; (3) turn off the fifth switch; (4) turn on the other of the first switch group and the second switch group and the sixth switch; (5) turn off the other switch group.(6) Turn off the sixth switch, and repeat the control from (1) to (6) in order. A control method.

36. A control method for a power conversion device, wherein the power conversion device includes: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; and a sixth switch. The isolation transformer has a first winding and a second winding connected in series as secondary windings. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other ends of the fifth switch and the sixth switch are connected to a second output terminal. In the control method, the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are made higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and the switching phase of the fourth switch lags behind the switching phase of the first switch, and the switching phase of the third switch lags behind the switching phase of the second switch, and the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled. In this case: (1) turn off the sixth switch and turn on the first switch; (2) turn on the fourth switch and the fifth switch; (3) turn off the first switch; (4) turn off the fourth switch; (5) turn off the fifth switch and turn on the second switch.(6) Turn on the third switch and the sixth switch. (7) Turn off the second switch. (8) Turn off the third switch. Repeat the controls from (1) to (8) in order. Control the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and so that the phase of the switching of the first switch lags behind the phase of the switching of the fourth switch, and the phase of the switching of the second switch lags behind the phase of the switching of the third switch. In that case, (9) Turn off the sixth switch and turn on the third switch. (10) Turn on the second switch and the fifth switch. (11) Turn off the third switch. (12) Turn off the second switch. (13) Turn off the fifth switch and turn on the fourth switch. (14) Turn on the first switch and the sixth switch. (15) Turn off the fourth switch. (16) Turn off the first switch. Repeat the controls from (9) to (16) in order. Control method.

37. A control method for a power conversion device, wherein the power conversion device includes: a first switch provided on a first path connecting a first input terminal and a second input terminal; a second switch provided on the first path and connected in series with the first switch; a third switch provided on a second path different from the first path and connecting the first input terminal and the second input terminal; a fourth switch provided on the second path and connected in series with the third switch; an isolation transformer having a primary winding connected between a first node between the first switch and the second switch on the first path and a second node between the third switch and the fourth switch on the second path; a resonance capacitor and a resonance inductor connected between the first node and the primary winding or between the second node and the primary winding; a fifth switch; and a sixth switch. The isolation transformer has a first winding and a second winding connected in series as a secondary winding. One end of the first winding is connected to one end of the fifth switch. The other end of the first winding and one end of the second winding are connected to a first output terminal. The other end of the second winding is connected to one end of the sixth switch. The other ends of the fifth switch and the sixth switch are connected to a second output terminal. In the control method, the switching frequencies of the first switch, the second switch, the third switch, and the fourth switch are made higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and the switching phase of the fourth switch lags behind the switching phase of the first switch, and the switching phase of the third switch lags behind the switching phase of the second switch. Then, the switching of the first switch, the second switch, the third switch, and the fourth switch is controlled. In this case: (1) turn on the first switch; (2) turn off the sixth switch; (3) turn off the third switch; (4) turn on the fourth switch and the fifth switch; (5) turn off the first switch; (6) turn on the second switch; (7) turn off the fifth switch;(8) Turn off the fourth switch, (9) Turn on the third switch and the sixth switch, (10) Turn off the second switch, Repeat the control from (1) to (10) in order, Control the switching of the first switch, the second switch, the third switch, and the fourth switch so that the switching frequency of the first switch, the second switch, the third switch, and the fourth switch is higher than the resonance frequency of the resonance generated by the resonance capacitor and the resonance inductor, and the phase of the switching of the first switch lags behind the phase of the switching of the fourth switch, and the phase of the switching of the second switch lags behind the phase of the switching of the third switch. In that case, (11) Turn on the third switch, (12) Turn off the sixth switch, (13) Turn off the first switch, (14) Turn on the second switch and the fifth switch, (15) Turn off the third switch, (16) Turn on the fourth switch, (17) Turn off the fifth switch, (18) Turn off the second switch, (19) Turn on the first switch and the sixth switch, (20) Turn off the fourth switch, Repeat the control from (11) to (20) in order, Control method.

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