Power conversion device and control method

Abstract

A power conversion device (1) comprises: a resonator (30) that has a transformer (T) and a capacitor (Cr); a primary-side full-bridge circuit (10) that has a first switch (Q1), a second switch (Q2), a third switch (Q3), and a fourth switch (Q4); and a secondary-side full-bridge circuit (20) that has a fifth diode (D5), a sixth switch (Q6), a seventh diode (D7), and an eighth switch (Q8). In accordance with a drive signal during a period that is the switching cycle of the first switch (Q1), the second switch (Q2), the third switch (Q3), and the fourth switch (Q4) with the resonance cycle of the resonator (30) excluded therefrom, the sixth switch (Q6) and the eighth switch (Q8) are operated in synchronization with a control signal for the first switch (Q1), the second switch (Q2), the third switch (Q3), and the fourth switch (Q4).

Description

Power conversion device and control method

[0001] The present disclosure relates to a power conversion device capable of unidirectional or bidirectional power conversion and a control method for the power conversion device.

[0002] Toward the realization of a carbon-neutral society, there is a demand for charging circuits that can efficiently charge home storage batteries or automotive batteries. Such charging circuits require isolated DC-DC converters, and resonant converters are commonly used for their compact size and high efficiency. Among resonant converters, LLC converters have attracted particular attention because they can achieve high efficiency with a simple circuit configuration.

[0003] However, LLC converters have the problem of generating high-frequency ringing on the secondary side of the LLC converter, which increases circuit loss. Furthermore, when the drive frequency is increased, the occurrence of high-frequency ringing causes a major problem of high-frequency loss due to the influence of harmonic components of the high-frequency ringing.

[0004] In response to this, Patent Document 1 discloses a technique for suppressing high-frequency ringing. Specifically, in an LLC type DC-DC converter, resonance occurs between a resonant inductor and a parasitic capacitance present in parallel with a switch element during a dead time period, causing high-frequency ringing. This problem is solved by turning off all switch elements at a timing when the resonant current Ioff reaches a current value that cancels out the resonant current generated by the excitation current Ip.

[0005] Japanese Patent Application Laid-Open No. 2014-217196

[0006] However, the DC-DC converter disclosed in Patent Document 1 cannot suppress high-frequency ringing due to parasitic capacitance under certain conditions. For example, LLC-type DC-DC converters used in chargers and other devices actively utilize an LLC boost operation mode to accommodate a wide voltage range of storage batteries. In LLC boost operation mode, boost operation is achieved at a switching frequency lower than the resonant frequency determined by the resonant inductor and resonant capacitor. However, in this operation mode, high-frequency ringing occurs not only during dead time but also during the period excluding the resonant period from the switching cycle. Therefore, adjusting the dead time timing alone may not be sufficient to suppress high-frequency ringing. Furthermore, calculating the threshold value for adjusting the dead time timing requires considering not only the parasitic capacitance of the switching element but also various parasitic components, including their variations, such as parasitic capacitance generated when the switching element is implemented, making it difficult to control the switching element.

[0007] Therefore, the present disclosure provides a power conversion device and the like that can effectively suppress high-frequency ringing.

[0008] A power conversion device according to the present disclosure includes a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, and a secondary-side full bridge circuit connected to a secondary side of the resonator, wherein the primary-side full bridge circuit has a first element provided on a high side of a first leg, a second element provided on a low side of the first leg, a third element provided on a high side of a second leg, and a fourth element provided on a low side of the second leg, and the secondary-side full bridge circuit has a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, and a fourth element provided on a low side of the fourth leg. The resonator has a seventh element provided on the high side and an eighth element provided on the low side of the fourth leg, wherein the first element, the second element, the third element, and the fourth element are each a switching element, and at least two of the fifth element, the sixth element, the seventh element, and the eighth element are each a switching element, and the at least two elements operate in synchronization with control signals for the first element, the second element, the third element, and the fourth element by a drive signal during a period obtained by excluding a resonance period of the resonator from the switching period of the first element, the second element, the third element, and the fourth element.

[0009] A power conversion device according to the present disclosure includes a resonator having a transformer and a resonance capacitor, a primary-side half-bridge circuit connected to the primary side of the resonator, and a secondary-side full-bridge circuit connected to the secondary side of the resonator, wherein the primary-side half-bridge circuit has a first element provided on a high side and a second element provided on a low side, and the secondary-side full-bridge circuit has a fifth element provided on the high side of a third leg, a sixth element provided on the low side of the third leg, a seventh element provided on the high side of a fourth leg, and an eighth element provided on the low side of the fourth leg, wherein the first element and the second element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the at least two elements operate in synchronization with control signals for the first element and the second element by drive signals during a period obtained by excluding a resonance period of the resonator from the switching periods of the first element and the second element.

[0010] A control method according to the present disclosure is a control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, and a secondary-side full bridge circuit connected to a secondary side of the resonator, the primary-side full bridge circuit having a first element provided on a high side of a first leg, a second element provided on a low side of the first leg, a third element provided on the high side of a second leg, and a fourth element provided on the low side of the second leg, the secondary-side full bridge circuit having a fifth element provided on the high side of a third leg, a sixth element provided on the low side of the third leg, and a fourth element provided on the low side of the second leg. The control method includes a seventh element provided on the high side of four legs and an eighth element provided on the low side of the fourth leg, wherein the first element, the second element, the third element, and the fourth element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the control method calculates a period obtained by subtracting a resonance period of the resonator from the switching periods of the first element, the second element, the third element, and the fourth element, and operates the at least two elements in synchronization with control signals for the first element, the second element, the third element, and the fourth element using a drive signal during the period.

[0011] A control method according to the present disclosure is a control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side half-bridge circuit connected to a primary side of the resonator, and a secondary-side full-bridge circuit connected to a secondary side of the resonator, the primary-side half-bridge circuit having a first element provided on a high side and a second element provided on a low side, the secondary-side full-bridge circuit having a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, and a fourth element provided on a high side of a fourth leg. the first element and the second element are each switch elements, and at least two of the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the control method calculates a period obtained by subtracting a resonance period of the resonator from the switching period of the first element and the second element, and operates the at least two elements in synchronization with control signals for the first element and the second element by a drive signal during the period.

[0012] 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.

[0013] According to the power conversion device and the like according to one aspect of the present disclosure, high-frequency ringing can be effectively suppressed.

[0014] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device according to embodiment 1. FIG. 2 is a diagram for explaining the operation of a controller according to embodiment 1. FIG. 3 is a diagram for explaining an example of the operation and effects of the power conversion device according to embodiment 1. FIG. 4 is a circuit configuration diagram showing an example of a power conversion device according to embodiment 2. FIG. 5 is a diagram for explaining an example of the operation and effects of the power conversion device according to embodiment 2. FIG. 6 is a circuit configuration diagram showing an example of a power conversion device according to embodiment 3. FIG. 7 is a diagram for explaining a first example of the operation and effects of the power conversion device according to embodiment 3. FIG. 8 is a diagram for explaining a second example of the operation and effects of the power conversion device according to embodiment 3. FIG. 9 is a diagram for explaining a third example of the operation and effects of the power conversion device according to embodiment 3. FIG. 10 is a circuit configuration diagram showing an example of a power conversion device according to embodiment 4. FIG. 11 is a diagram for explaining an example of the operation and effects of the power conversion device according to embodiment 4. FIG. 12 is a circuit configuration diagram showing an example of a power conversion device according to embodiment 5. FIG. 13 is a diagram for explaining an example of the operation and effects of the power conversion device according to embodiment 5. FIG. 14 is a flowchart showing an example of a control method according to another embodiment. FIG. 15 is a flowchart showing an example of a control method according to another embodiment.

[0015] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0016] 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.

[0017] (First embodiment) Hereinafter, a power conversion device according to a first embodiment will be described.

[0018] FIG. 1 is a circuit configuration diagram showing an example of a power conversion device 1 according to the first embodiment.

[0019] The power conversion device 1 is, for example, an isolated DC-DC converter that boosts or bucks an input voltage to a predetermined voltage and outputs it. The power conversion device 1 is capable of unidirectional power conversion. For example, the power conversion device 1 is an LLC converter. An LLC converter is a circuit that utilizes LLC resonance caused by the leakage inductance, excitation inductance, and resonant capacitor of a transformer. In an LLC converter, the input / output voltage ratio (Gain) can be changed by changing the switching frequency, making it possible to output a desired power.

[0020] The power conversion device 1 has terminals t1, t2, t3, and t4. The terminal t1 is an input terminal. The terminal t2 is a ground terminal. The terminal t3 is an output terminal. The terminal t4 is a ground terminal. Note that, since the power conversion device 1 is an isolated DC-DC converter, the terminals t2 and t4 are electrically isolated.

[0021] The power conversion device 1 includes a primary side full bridge circuit 10, a secondary side full bridge circuit 20, a resonator 30, capacitors Cin and Cout, and a controller 40. The capacitors Cin and Cout do not necessarily have to be components of the power conversion device 1.

[0022] The capacitor Cin is an input capacitor connected between the terminal t1 and the terminal t2, and the capacitor Cout is an output capacitor (smoothing capacitor) connected between the terminal t3 and the terminal t4.

[0023] The primary-side full-bridge circuit 10 is connected to the primary side of the resonator 30. The primary-side full-bridge circuit 10 has a first element provided on the high side of a first leg, a second element provided on the low side of the first leg, a third element provided on the high side of a second leg, and a fourth element provided on the low side of the second leg. The first element, second element, third element, and fourth element are each a switch element.

[0024] The primary side full bridge circuit 10 has switches Q1, Q2, Q3 and Q4, where the switch Q1 is an example of a first element, the switch Q2 is an example of a second element, the switch Q3 is an example of a third element, and the switch Q4 is an example of a fourth element.

[0025] The switch Q1 is, for example, an N-channel metal oxide semiconductor field effect transistor (MOSFET). The drain of the switch Q1 is connected to the terminal t1, and the source of the switch Q1 is connected to the drain of the switch Q2.

[0026] The switch Q2 is, for example, an N-channel MOSFET. The drain of the switch Q2 is connected to the source of the switch Q1, and the source of the switch Q2 is connected to the terminal t2.

[0027] The switch Q3 is, for example, an N-channel MOSFET. The drain of the switch Q3 is connected to the terminal t1, and the source of the switch Q3 is connected to the drain of the switch Q4.

[0028] The switch Q4 is, for example, an N-channel MOSFET. The drain of the switch Q4 is connected to the source of the switch Q3, and the source of the switch Q4 is connected to the terminal t2.

[0029] The secondary-side full-bridge circuit 20 is connected to the secondary side of the resonator 30. The secondary-side full-bridge circuit 20 has a fifth element provided on the high side of the third leg, a sixth element provided on the low side of the third leg, a seventh element provided on the high side of the fourth leg, and an eighth element provided on the low side of the fourth leg. At least two of the fifth, sixth, seventh, and eighth elements are each switch elements. The secondary-side full-bridge circuit 20 also functions as a rectifier circuit capable of full-wave rectification.

[0030] As will be described in more detail later, at least two elements operate in synchronization with the control signals for the first element, second element, third element and fourth element by a drive signal during a period that is the switching period of the first element, second element, third element and fourth element minus the resonance period of the resonator 30.

[0031] In the first embodiment, the secondary-side full-bridge circuit 20 has diodes D5 and D7 and switches Q6 and Q8, where the diode D5 is an example of a fifth element, the switch Q6 is an example of a sixth element, the diode D7 is an example of a seventh element, and the switch Q8 is an example of an eighth element. That is, in the first embodiment, the at least two elements that are switch elements are the sixth element (switch Q6) and the eighth element (switch Q8).

[0032] The anode of the diode D5 is connected to the drain of the switch Q6, and the cathode is connected to the terminal t3.

[0033] The switch Q6 is, for example, an N-channel MOSFET. The drain of the switch Q6 is connected to the anode of the diode D5, and the source of the switch Q6 is connected to the terminal t4.

[0034] The anode of the diode D7 is connected to the drain of the switch Q8, and the cathode is connected to the terminal t3.

[0035] The switch Q8 is, for example, an N-channel MOSFET. The drain of the switch Q8 is connected to the anode of the diode D7, and the source of the switch Q8 is connected to the terminal t4.

[0036] The resonator 30 includes a transformer T and a capacitor Cr.

[0037] The capacitor Cr is an example of a resonant capacitor and is connected to a node between the switch Q1 and the switch Q2 in the first leg.

[0038] The transformer T is an isolated transformer having a primary winding and a secondary winding that are isolated from each other. One end of the primary winding of the transformer T is connected via a capacitor Cr to a node between the switches Q1 and Q2 in the first leg, and the other end of the primary winding of the transformer T is connected to a node between the switches Q3 and Q4 in the second leg. One end of the secondary winding of the transformer T is connected to a node between the diode D5 and the switch Q6 in the third leg, and the other end of the secondary winding of the transformer T is connected to a node between the diode D7 and the switch Q8 in the fourth leg.

[0039] The capacitor Cr may be connected to a node between the switches Q3 and Q4 in the second leg. In this case, one end of the primary winding of the transformer T is connected to a node between the switches Q1 and Q2 in the first leg, and the other end of the primary winding of the transformer T is connected to a node between the switches Q3 and Q4 in the second leg via the capacitor Cr.

[0040] The controller 40 is a circuit for controlling the switching (on and off) of switches (e.g., switches Q1, Q2, Q3, Q4, Q6, and Q8) included in the power conversion device 1. For example, the controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q6, and Q8 by controlling a gate drive circuit (not shown) connected to the gates of the switches Q1, Q2, Q3, Q4, Q6, and Q8 via a PWM generator (not shown) or the like.

[0041] The controller 40 is, 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 to be executed by the processor. For example, the controller 40 is a microcontroller.

[0042] The controller 40 calculates a period obtained by subtracting the resonance period of the resonator 30 (the period of resonance due to the capacitance of the capacitor Cr and the leakage inductance of the transformer T, etc.) from the switching period of the switches Q1, Q2, Q3, and Q4, and operates the switches Q6 and Q8 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using a drive signal during that period.

[0043] Here, the operation of the controller 40 will be described in detail with reference to FIG.

[0044] FIG. 2 is a diagram for explaining the operation of the controller 40 according to the first embodiment.

[0045] As shown in Fig. 2, the controller 40 controls the switching of the switches Q1 and Q4 in the same phase, and controls the switching of the switches Q2 and Q3 in the same phase. The controller 40 controls the switches Q1, Q2, Q3, and Q4 so that the phase difference between the switching of the switches Q1 and Q4 and the switching of the switches Q2 and Q3 is 180 degrees. As a result, the control signals for the switches Q1, Q2, Q3, and Q4 become, for example, those shown in Fig. 2. Specifically, the switches Q1 and Q4 repeatedly turn on and off with a duty ratio of 50%, the switches Q2 and Q3 repeatedly turn on and off with a duty ratio of 50%, and when the switches Q1 and Q4 are in the on state, the switches Q2 and Q3 are in the off state, and when the switches Q2 and Q3 are in the on state, the switches Q1 and Q4 are in the off state.

[0046] When the controller 40 turns on the switches Q1 and Q4 and turns off the switches Q2 and Q3, or turns on the switches Q2 and Q3 and turns off the switches Q1 and Q4, a current (primary current) flows through the primary winding of the transformer T. The primary current resonates with the resonant period of the resonator 30. Furthermore, when a current flows through the primary winding of the transformer T, a current (secondary current) flows through the secondary winding of the transformer T. The secondary current also resonates with the resonant period of the resonator 30. As a result, the primary and secondary currents become as shown in FIG. 2 .

[0047] The controller 40 calculates a period by subtracting the resonant period of the resonator 30 (e.g., the resonant half period shown in FIG. 2 ) from the switching period of the switches Q1, Q2, Q3, and Q4 (e.g., the switching half period shown in FIG. 2 , which is the period during which the switches are on at a duty ratio of 50%). This period is a period during which no current is passed to the load connected to terminals t3 and t4, and is also referred to as a non-conduction period. During the non-conduction period, charge accumulated in the parasitic capacitance of the secondary-side devices of the transformer T (e.g., diodes D5 and D7 and switches Q6 and Q8) cannot be extracted to the load, and high-frequency ringing may occur due to free resonance between the leakage inductance of the transformer T and the parasitic capacitance of the secondary-side devices. Therefore, the controller 40 operates the switches Q6 and Q8 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using a drive signal during the non-conduction period, thereby extracting the charge of the secondary-side devices to the load. The drive signals for switches Q6 and Q8 are signals that turn on switches Q6 and Q8 during the non-conducting period that exists in the latter half of the on-period of switches Q1 and Q4 and the non-conducting period that exists in the latter half of the on-period of switches Q2 and Q3. As shown in Figure 2, the control signals for switches Q1, Q2, Q3, and Q4 and the drive signals for switches Q6 and Q8 are synchronized. Note that "the control signals and drive signals are synchronized" means that there is a certain relationship between the on-timing of the control signals and the on-timing of the drive signals. In this specification, "the control signals and drive signals are synchronized" means that the drive signal is turned on a certain period after the control signal is turned on.

[0048] Next, the operation of the power conversion device 1 and the effects achieved by this operation will be described with reference to FIG.

[0049] Fig. 3 is a diagram for explaining an example of the operation and effect of the power conversion device 1 according to embodiment 1. Fig. 3 shows, from the top to the bottom, timing charts of the gate signals of the switches Q1, Q4, and Q8, the gate signals of the switches Q2, Q3, and Q6, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), and the current flowing in the secondary winding of the transformer T (transformer secondary current).

[0050] As shown in FIG. 3 , the switches Q6 and Q8 are turned on by the drive signal before the switches Q1 and Q4 change from an on state to an off state, and before the switches Q2 and Q3 change from an on state to an off state. In other words, the controller 40 turns on the switches Q6 and Q8 by the drive signal before the switches Q1 and Q4 change from an on state to an off state, and before the switches Q2 and Q3 change from an on state to an off state. The non-conducting periods are the period before the switches Q1 and Q4 change from an on state to an off state (the period existing in the latter half of the on period of the switches Q1 and Q4) and the period before the switches Q2 and Q3 change from an on state to an off state (the period existing in the latter half of the on period of the switches Q2 and Q3). By turning on the switches Q6 and Q8 during these periods, both ends of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switches Q6 and Q8, thereby suppressing high-frequency ringing. As shown in FIG. 3, it can be seen that high frequency ringing in the transformer secondary voltage is suppressed, and also high frequency ringing in the transformer secondary current is suppressed.

[0051] The upper limit of the length of the period before the switches Q1 and Q4 change from an on state to an off state and the period before the switches Q2 and Q3 change from an on state to an off state is the length of the non-conductive period. In other words, the end of the period before the switches Q1 and Q4 change from an on state to an off state is the timing when the switches Q1 and Q4 turn off, and the start of this period is a time up to the length of the non-conductive period before the switches Q1 and Q4 turn off. Also, the end of the period before the switches Q2 and Q3 change from an on state to an off state is the timing when the switches Q2 and Q3 turn off, and the start of this period is a time up to the length of the non-conductive period before the switches Q2 and Q3 turn off.

[0052] As described above, the period obtained by subtracting the resonance period of the resonator 30 from the switching period of the switches Q1, Q2, Q3, and Q4 is a non-energized period during which no current is applied to the load. If the secondary devices of the transformer T (specifically, the switches Q6 and Q8) are not controlled, the charge accumulated in the parasitic capacitance of the secondary devices of the transformer T cannot be extracted to the load. Therefore, during this period, high-frequency ringing can occur due to free resonance caused by the leakage inductance of the transformer T and the parasitic capacitance of the secondary devices. Therefore, by operating the switches Q6 and Q8 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4, both ends of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load (in other words, the potential across the secondary winding of the transformer T can be fixed to the negative potential of the load), and the charge accumulated in the parasitic capacitance of the secondary devices can be extracted to the load. Therefore, high-frequency ringing can be effectively suppressed. This provides the effects of improving efficiency by reducing high frequency loss, improving EMC performance in the MHz band, etc. Furthermore, since ringing suppression means such as a snubber circuit or active clamp circuit are not required, miniaturization and cost reduction are possible.

[0053] Second Embodiment Next, a power conversion device according to a second embodiment will be described.

[0054] FIG. 4 is a circuit configuration diagram showing an example of a power conversion device 2 according to the second embodiment.

[0055] The power conversion device 2 differs from the power conversion device 1 in the first embodiment in the components of the secondary-side full-bridge circuit 20 and the control content of the controller 40. Since the other points are basically the same as those of the power conversion device 1 in the first embodiment, a description thereof will be omitted, and the following description will focus on the points of difference.

[0056] In the second embodiment, the secondary-side full-bridge circuit 20 has switches Q5 and Q7 and diodes D6 and D8, where the switch Q5 is an example of a fifth element, the diode D6 is an example of a sixth element, the switch Q7 is an example of a seventh element, and the diode D8 is an example of an eighth element. That is, in the second embodiment, the at least two elements that are switch elements are the fifth element (switch Q5) and the seventh element (switch Q7).

[0057] The switch Q5 is, for example, an N-channel MOSFET. The drain of the switch Q5 is connected to the terminal t3, and the source of the switch Q5 is connected to the cathode of the diode D6.

[0058] The anode of the diode D6 is connected to the terminal t4, and the cathode is connected to the source of the switch Q5.

[0059] The switch Q7 is, for example, an N-channel MOSFET. The drain of the switch Q7 is connected to the terminal t3, and the source of the switch Q7 is connected to the cathode of the diode D8.

[0060] The anode of the diode D8 is connected to the terminal t4, and the cathode is connected to the source of the switch Q7.

[0061] One end of the secondary winding of the transformer T is connected to a node between the switch Q5 and the diode D6 in the third leg, and the other end of the secondary winding of the transformer T is connected to a node between the switch Q7 and the diode D8 in the fourth leg.

[0062] For example, the controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q5, and Q7 by controlling a gate drive circuit (not shown) connected to the gates of the switches Q1, Q2, Q3, Q4, Q5, and Q7 via a PWM generator (not shown), for example.

[0063] The controller 40 calculates a period obtained by subtracting the resonance period of the resonator 30 from the switching period of the switches Q1, Q2, Q3, and Q4, and operates the switches Q5 and Q7 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using a drive signal during that period.

[0064] The controller 40 calculates a period by subtracting the resonant period (e.g., the resonant half period) of the resonator 30 from the switching period (e.g., the switching half period during which the switches Q1, Q2, Q3, and Q4 are on at a duty ratio of 50%). This period is a period during which no current is passed to the load connected to the terminals t3 and t4 and is also referred to as the non-conduction period. During the non-conduction period, charge accumulated in the parasitic capacitance of the secondary-side devices of the transformer T (e.g., diodes D6 and D8 and switches Q5 and Q7) cannot be extracted to the load, and high-frequency ringing may occur due to free resonance between the leakage inductance of the transformer T and the parasitic capacitance of the secondary-side devices. Therefore, the controller 40 operates the switches Q5 and Q7 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using a drive signal during the non-conduction period, thereby extracting charge accumulated in the parasitic capacitance of the secondary-side devices to the load. The drive signals for the switches Q5 and Q7 are signals that turn on the switches Q5 and Q7 during the non-conducting period that exists in the latter half of the on-period of the switches Q1 and Q4 and during the non-conducting period that exists in the latter half of the on-period of the switches Q2 and Q3.

[0065] Next, the operation of the power conversion device 2 and the effects achieved by this operation will be described with reference to FIG.

[0066] Fig. 5 is a diagram for explaining an example of the operation and effect of the power conversion device 2 according to embodiment 2. Fig. 5 shows, from the top, timing charts of the gate signals of the switches Q1, Q4, and Q7, the gate signals of the switches Q2, Q3, and Q5, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), and the current flowing in the secondary winding of the transformer T (transformer secondary current).

[0067] As shown in FIG. 5 , the switches Q5 and Q7 are turned on by the drive signal before the switches Q1 and Q4 change from an on state to an off state, and before the switches Q2 and Q3 change from an on state to an off state. In other words, the controller 40 turns on the switches Q5 and Q7 by the drive signal before the switches Q1 and Q4 change from an on state to an off state, and before the switches Q2 and Q3 change from an on state to an off state. By turning on the switches Q5 and Q7 during these periods, both ends of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switches Q5 and Q7, thereby suppressing high-frequency ringing. As shown in FIG. 5 , it can be seen that high-frequency ringing in the transformer secondary voltage and in the transformer secondary current are suppressed.

[0068] As described above, during the non-energized period, by operating switches Q5 and Q7 in synchronization with the control signals for switches Q1, Q2, Q3, and Q4, both ends of the secondary winding of transformer T can be connected to terminal t3 on the positive side of the load (in other words, the potential across both ends of the secondary winding of transformer T can be fixed to the potential on the positive side of the load), and the charge accumulated in the parasitic capacitance of the secondary-side device can be extracted to the load side. Therefore, high-frequency ringing can be effectively suppressed.

[0069] Third Embodiment Next, a power conversion device according to a third embodiment will be described.

[0070] FIG. 6 is a circuit configuration diagram showing an example of a power conversion device 3 according to the third embodiment.

[0071] The power conversion device 3 differs from the power conversion device 1 in embodiment 1 in the components of the secondary-side full bridge circuit 20 and the control details of the controller 40. As other points are basically the same as the power conversion device 1 in embodiment 1, a description thereof will be omitted, and the following description will focus on the differences. Note that while the power conversion device 1 in embodiment 1 is capable of unidirectional power conversion, the power conversion device 3 is capable of bidirectional power conversion as well as unidirectional power conversion.

[0072] In the third embodiment, the secondary-side full-bridge circuit 20 has switches Q5, Q6, Q7, and Q8, where the switch Q5 is an example of a fifth element, the switch Q6 is an example of a sixth element, the switch Q7 is an example of a seventh element, and the switch Q8 is an example of an eighth element. That is, in the third embodiment, the at least two elements that are switch elements are the fifth element (switch Q5), the sixth element (switch Q6), the seventh element (switch Q7), and the eighth element (switch Q8).

[0073] The switch Q5 is, for example, an N-channel MOSFET. The drain of the switch Q5 is connected to the terminal t3, and the source of the switch Q5 is connected to the drain of the switch Q6.

[0074] The switch Q6 is, for example, an N-channel MOSFET. The drain of the switch Q6 is connected to the source of the switch Q5, and the source of the switch Q6 is connected to the terminal t4.

[0075] The switch Q7 is, for example, an N-channel MOSFET. The drain of the switch Q7 is connected to the terminal t3, and the source of the switch Q7 is connected to the drain of the switch Q8.

[0076] The switch Q8 is, for example, an N-channel MOSFET. The drain of the switch Q8 is connected to the source of the switch Q7, and the source of the switch Q8 is connected to the terminal t4.

[0077] One end of the secondary winding of the transformer T is connected to a node between the switches Q5 and Q6 in the third leg, and the other end of the secondary winding of the transformer T is connected to a node between the switches Q7 and Q8 in the fourth leg.

[0078] For example, the controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 by controlling a gate drive circuit (not shown) connected to the gates of the switches Q1, Q2, Q3, Q4, Q5, Q6, Q7, and Q8 via a PWM generator (not shown), or the like.

[0079] The controller 40 calculates a period obtained by subtracting the resonance period of the resonator 30 from the switching period of the switches Q1, Q2, Q3, and Q4, and operates the switches Q5, Q6, Q7, and Q8 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using drive signals during that period.

[0080] The controller 40 calculates a period by subtracting the resonant period (e.g., the resonant half period) of the resonator 30 from the switching period (e.g., the switching half period during which the switches Q1, Q2, Q3, and Q4 are on at a duty ratio of 50%). This period is a period during which no current is passed to the load connected to the terminals t3 and t4 and is also referred to as the non-energized period. During the non-energized period, charge accumulated in the parasitic capacitance of the secondary-side devices of the transformer T (e.g., the switches Q5, Q6, Q7, and Q8) cannot be extracted to the load, and high-frequency ringing may occur due to free resonance between the leakage inductance of the transformer T and the parasitic capacitance of the secondary-side devices. Therefore, the controller 40 operates the switches Q5, Q6, Q7, and Q8 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using a drive signal during the non-energized period, thereby extracting charge accumulated in the parasitic capacitance of the secondary-side devices to the load.

[0081] In the third embodiment, first to fourth examples of a method for controlling the switches Q5, Q6, Q7, and Q8 by the controller 40 will be described.

[0082] Fig. 7 is a diagram for explaining a first example of the operation and effect of the power conversion device 3 according to embodiment 3. Fig. 7 shows, from the top to the bottom, timing charts of the gate signals of switches Q1, Q4, Q5, and Q8, the gate signals of switches Q2, Q3, Q6, and Q7, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), and the current flowing in the secondary winding of the transformer T (transformer secondary current). The same applies to Figs. 8 to 10, which will be described later.

[0083] In the first example, the drive signals for the switches Q6 and Q8 are signals that turn on the switches Q6 and Q8 during the non-current-carrying period that exists in the latter half of the on-period of the switches Q1 and Q4, and the drive signals for the switches Q5 and Q7 are signals that turn on the switches Q5 and Q7 during the non-current-carrying period that exists in the latter half of the on-period of the switches Q2 and Q3.

[0084] 7 , the switches Q6 and Q8 are turned on by the drive signal before the switches Q1 and Q4 are turned off from their on state. In other words, the controller 40 turns on the switches Q6 and Q8 by the drive signal before the switches Q1 and Q4 are turned off from their on state. By turning on the switches Q6 and Q8 during this period, both ends of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switches Q6 and Q8, thereby suppressing high-frequency ringing.

[0085] 7, the switches Q5 and Q7 are turned on before the switches Q2 and Q3 are turned off from their on state. In other words, the controller 40 uses the drive signal to turn on the switches Q5 and Q7 before the switches Q2 and Q3 are turned off from their on state. By turning on the switches Q5 and Q7 during this period, both ends of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switches Q5 and Q7, thereby suppressing high-frequency ringing.

[0086] As shown in FIG. 7, it can be seen that high frequency ringing in the transformer secondary voltage is suppressed, and also high frequency ringing in the transformer secondary current is suppressed.

[0087] FIG. 8 is a diagram for explaining a second example of the operation and effect of the power conversion device 3 according to the third embodiment.

[0088] In the second example, the drive signals for the switches Q5 and Q7 are signals that turn on the switches Q5 and Q7 during the non-current-carrying period that exists in the latter half of the on-period of the switches Q1 and Q4, and the drive signals for the switches Q6 and Q8 are signals that turn on the switches Q6 and Q8 during the non-current-carrying period that exists in the latter half of the on-period of the switches Q2 and Q3.

[0089] 8 , the switches Q5 and Q7 are turned on by the drive signal before the switches Q1 and Q4 are turned off from their on state. In other words, the controller 40 turns on the switches Q5 and Q7 by the drive signal before the switches Q1 and Q4 are turned off from their on state. By turning on the switches Q5 and Q7 during this period, both ends of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switches Q5 and Q7, and high-frequency ringing can be suppressed.

[0090] 8, the switches Q6 and Q8 are turned on before the switches Q2 and Q3 are turned off from their on state. In other words, the controller 40 uses the drive signal to turn on the switches Q6 and Q8 before the switches Q2 and Q3 are turned off from their on state. By turning on the switches Q6 and Q8 during this period, both ends of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switches Q6 and Q8, thereby suppressing high-frequency ringing.

[0091] As shown in FIG. 8, it can be seen that high frequency ringing in the transformer secondary voltage is suppressed, and also high frequency ringing in the transformer secondary current is suppressed.

[0092] FIG. 9 is a diagram for explaining a third example of the operation and effect of the power conversion device 3 according to the third embodiment.

[0093] In the third example, the drive signals for the switches Q6 and Q7 are signals that turn on the switches Q6 and Q7 during the non-current-carrying period that exists in the latter half of the on-period of the switches Q1 and Q4, and the drive signals for the switches Q5 and Q8 are signals that turn on the switches Q5 and Q8 during the non-current-carrying period that exists in the latter half of the on-period of the switches Q2 and Q3.

[0094] 9 , the switches Q6 and Q7 are turned on by the drive signal before the switches Q1 and Q4 are turned off from their on state. In other words, the controller 40 turns on the switches Q6 and Q7 by the drive signal before the switches Q1 and Q4 are turned off from their on state. By turning on the switches Q6 and Q7 during this period, one end of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switch Q6, and the other end of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switch Q7, thereby suppressing high-frequency ringing.

[0095] 9 , the switches Q5 and Q8 are turned on before the switches Q2 and Q3 are turned off from their on state. In other words, the controller 40 uses the drive signal to turn on the switches Q5 and Q8 before the switches Q2 and Q3 are turned off from their on state. By turning on the switches Q5 and Q8 during this period, one end of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switch Q5, and the other end of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switch Q8, thereby suppressing high-frequency ringing.

[0096] As shown in FIG. 9, it can be seen that high frequency ringing in the transformer secondary voltage is suppressed, and also high frequency ringing in the transformer secondary current is suppressed.

[0097] FIG. 10 is a diagram for explaining a fourth example of the operation and effect of the power conversion device 3 according to the third embodiment.

[0098] In the fourth example, the drive signals for the switches Q5 and Q8 are signals that turn on the switches Q5 and Q8 during the non-current-carrying period that exists in the latter half of the on-period of the switches Q1 and Q4, and the drive signals for the switches Q6 and Q7 are signals that turn on the switches Q6 and Q7 during the non-current-carrying period that exists in the latter half of the on-period of the switches Q2 and Q3.

[0099] 10 , the switches Q5 and Q8 are turned on by the drive signal before the switches Q1 and Q4 are turned off from their on state. In other words, the controller 40 turns on the switches Q5 and Q8 by the drive signal before the switches Q1 and Q4 are turned off from their on state. By turning on the switches Q5 and Q8 during this period, one end of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switch Q5, and the other end of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switch Q8, thereby suppressing high-frequency ringing.

[0100] 10 , the switches Q6 and Q7 are turned on before the switches Q2 and Q3 are turned off from their on state. In other words, the controller 40 uses the drive signal to turn on the switches Q6 and Q7 before the switches Q2 and Q3 are turned off from their on state. By turning on the switches Q6 and Q7 during this period, one end of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switch Q6, and the other end of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switch Q7, thereby suppressing high-frequency ringing.

[0101] As shown in FIG. 10, it can be seen that high frequency ringing in the transformer secondary voltage is suppressed, and also high frequency ringing in the transformer secondary current is suppressed.

[0102] As described above, during the non-energized period, by operating switches Q5, Q6, Q7, and Q8 in synchronization with the control signals for switches Q1, Q2, Q3, and Q4, both ends of the secondary winding of transformer T can be connected to the positive terminal t3 or the negative terminal t4 of the load (in other words, the potential across the secondary winding of transformer T can be fixed to the positive or negative potential of the load), and the charge accumulated in the parasitic capacitance of the secondary-side device can be extracted to the load side. Therefore, high-frequency ringing can be effectively suppressed.

[0103] The power conversion device 3 is capable of bidirectional power conversion, and the terminal t3 can be used as an input terminal and the terminal t1 as an output terminal. In this case, the control performed on the primary-side full-bridge circuit 10 in the above description is performed on the secondary-side full-bridge circuit 20, and the control performed on the secondary-side full-bridge circuit 20 in the above description is performed on the primary-side full-bridge circuit 10. In this case, the capacitor Cout serves as an input capacitor, and the capacitor Cin serves as an output capacitor.

[0104] (Fourth embodiment) Next, a power conversion device according to a fourth embodiment will be described.

[0105] FIG. 11 is a circuit configuration diagram showing an example of a power conversion device 4 according to the fourth embodiment.

[0106] The power conversion device 4 differs from the power conversion device 1 in embodiment 1 in the components of the secondary-side full bridge circuit 20 and the control content of the controller 40. Since the other points are basically the same as those of the power conversion device 1 in embodiment 1, a description thereof will be omitted and the following description will focus on the points of difference.

[0107] In the fourth embodiment, the secondary-side full bridge circuit 20 has switches Q6 and Q7 and diodes D5 and D8, where the diode D5 is an example of a fifth element, the switch Q6 is an example of a sixth element, the switch Q7 is an example of a seventh element, and the diode D8 is an example of an eighth element. That is, in the fourth embodiment, the at least two elements that are switch elements are the sixth element (switch Q6) and the seventh element (switch Q7).

[0108] The anode of the diode D5 is connected to the drain of the switch Q6, and the cathode is connected to the terminal t3.

[0109] The switch Q6 is, for example, an N-channel MOSFET. The drain of the switch Q6 is connected to the anode of the diode D5, and the source of the switch Q6 is connected to the terminal t4.

[0110] The switch Q7 is, for example, an N-channel MOSFET. The drain of the switch Q7 is connected to the terminal t3, and the source of the switch Q7 is connected to the cathode of the diode D8.

[0111] The anode of the diode D8 is connected to the terminal t4, and the cathode is connected to the source of the switch Q7.

[0112] One end of the secondary winding of the transformer T is connected to a node between the diode D5 and the switch Q6 in the third leg, and the other end of the secondary winding of the transformer T is connected to a node between the switch Q7 and the diode D8 in the fourth leg.

[0113] For example, the controller 40 controls the switching of the switches Q1, Q2, Q3, Q4, Q6, and Q7 by controlling a gate drive circuit (not shown) connected to the gates of the switches Q1, Q2, Q3, Q4, Q6, and Q7 via a PWM generator (not shown), for example.

[0114] The controller 40 calculates a period obtained by subtracting the resonance period of the resonator 30 from the switching period of the switches Q1, Q2, Q3, and Q4, and operates the switches Q6 and Q7 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using a drive signal during that period.

[0115] For example, the controller 40 calculates a period by subtracting the resonant period (e.g., the resonant half period) of the resonator 30 from the switching period (e.g., the switching half period during which the switches Q1, Q2, Q3, and Q4 are on at a duty ratio of 50%). This period is a period during which no current is passed to the load connected to the terminals t3 and t4, and is also referred to as a non-energized period. During the non-energized period, charge accumulated in the parasitic capacitance of the secondary-side devices of the transformer T (e.g., diodes D5 and D8 and switches Q6 and Q7) cannot be extracted to the load, and high-frequency ringing may occur due to free resonance between the leakage inductance of the transformer T and the parasitic capacitance of the secondary-side devices. Therefore, the controller 40 operates the switches Q6 and Q7 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using a drive signal during the non-energized period, thereby extracting charge accumulated in the parasitic capacitance of the secondary-side devices to the load. The drive signals for the switches Q6 and Q7 are signals that turn on the switches Q6 and Q7 during the non-conducting period that exists in the latter half of the on-period of the switches Q1 and Q4 and during the non-conducting period that exists in the latter half of the on-period of the switches Q2 and Q3.

[0116] Next, the operation of the power conversion device 4 and the effects achieved by this operation will be described with reference to FIG.

[0117] Fig. 12 is a diagram for explaining an example of the operation and effect of the power conversion device 4 according to embodiment 4. Fig. 12 shows, from the top, timing charts of the gate signals of the switches Q1 and Q4, the gate signals of the switches Q2, Q3, Q6, and Q7, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), and the current flowing in the secondary winding of the transformer T (transformer secondary current).

[0118] As shown in FIG. 12 , the switches Q6 and Q7 are turned on by the drive signal before the switches Q1 and Q4 are turned off from their on states, and before the switches Q2 and Q3 are turned off from their on states. In other words, the controller 40 turns on the switches Q6 and Q7 by the drive signal before the switches Q1 and Q4 are turned off from their on states, and before the switches Q2 and Q3 are turned off from their on states. By turning on the switch Q6 during these periods, one end of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switch Q6, thereby suppressing high-frequency ringing to some extent. Furthermore, by turning on the switch Q7 during these periods, the other end of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switch Q7, thereby suppressing high-frequency ringing to some extent. As shown in FIG. 12 , it can be seen that high-frequency ringing in the transformer secondary voltage and high-frequency ringing in the transformer secondary current are suppressed to some extent.

[0119] The secondary-side full-bridge circuit 20 may have switches Q5 and Q8 instead of the diodes D5 and D8, and may have diodes D6 and D7 instead of the switches Q6 and Q7. In this case, the controller 40 calculates a period obtained by subtracting the resonance period of the resonator 30 from the switching period of the switches Q1, Q2, Q3, and Q4, and operates the switches Q5 and Q8 in synchronization with the control signals for the switches Q1, Q2, Q3, and Q4 using a drive signal during that period.

[0120] In this case, the switches Q5 and Q8 are turned on by the drive signal before the switches Q1 and Q4 change from an on state to an off state, and before the switches Q2 and Q3 change from an on state to an off state. In other words, the controller 40 turns on the switches Q5 and Q8 by the drive signal before the switches Q1 and Q4 change from an on state to an off state, and before the switches Q2 and Q3 change from an on state to an off state. By turning on the switch Q5 during these periods, one end of the secondary winding of the transformer T can be connected to the positive terminal t3 of the load via the switch Q5, thereby suppressing high-frequency ringing to some extent. Furthermore, by turning on the switch Q8 during these periods, the other end of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switch Q8, thereby suppressing high-frequency ringing to some extent.

[0121] As described above, during the non-energized period, by operating switches Q6 and Q7 or switches Q5 or Q8 in synchronization with the control signals for switches Q1, Q2, Q3, and Q4, both ends of the secondary winding of transformer T can be connected to the positive terminal t3 or negative terminal t4 of the load (in other words, the potential across the secondary winding of transformer T can be fixed to the positive or negative potential of the load), and the charge of the secondary-side device can be extracted to the load side. Therefore, high-frequency ringing can be suppressed to some extent.

[0122] Fifth Embodiment Next, a power conversion device according to a fifth embodiment will be described.

[0123] FIG. 13 is a circuit configuration diagram showing an example of a power conversion device 5 according to the fifth embodiment.

[0124] The power conversion device 5 differs from the power conversion device 1 in the first embodiment in that it includes a primary-side half-bridge circuit 50 instead of the primary-side full-bridge circuit 10 and in the control content of the controller 40. Since the other points are basically the same as those of the power conversion device 1 in the first embodiment, a description thereof will be omitted and the following description will focus on the points of difference.

[0125] The primary half-bridge circuit 50 is connected to the primary side of the resonator 30. The primary half-bridge circuit 50 has a first element provided on the high side and a second element provided on the low side. The first element and the second element are each a switching element.

[0126] The primary half-bridge circuit 50 includes switches Q1 and Q2, where the switch Q1 is an example of a first element and the switch Q2 is an example of a second element. The switches Q1 and Q2 are the same as those in the first embodiment, and therefore a description thereof will be omitted.

[0127] As will be described in more detail later, at least two elements that are switch elements included in the secondary side full bridge circuit 20 operate in synchronization with the control signals for the first and second elements by a drive signal during a period that is the switching period of the first and second elements minus the resonance period of the resonator 30.

[0128] In the fifth embodiment, similarly to the first embodiment, the secondary-side full bridge circuit 20 has diodes D5 and D7 and switches Q6 and Q8, where diode D5 is an example of a fifth element, switch Q6 is an example of a sixth element, diode D7 is an example of a seventh element, and switch Q8 is an example of an eighth element. That is, in the fifth embodiment, at least two elements that are switch elements are the sixth element (switch Q6) and the eighth element (switch Q8).

[0129] The capacitor Cr is an example of a resonant capacitor and is connected to a node between the switch Q1 and the switch Q2.

[0130] The transformer T is an isolated transformer having a primary winding and a secondary winding that are insulated from each other. One end of the primary winding of the transformer T is connected to a node between the switches Q1 and Q2 via a capacitor Cr, and the other end of the primary winding of the transformer T is connected to the source of the switch Q2.

[0131] The capacitor Cr may be connected to the other end of the primary winding of the transformer T. In this case, one end of the primary winding of the transformer T is connected to the node between the switch Q1 and the switch Q2, and the other end of the primary winding of the transformer T is connected to the source of the switch Q2 via the capacitor Cr.

[0132] The controller 40 is a circuit for controlling the switching (on and off) of switches (e.g., switches Q1, Q2, Q6, and Q8) included in the power conversion device 1. For example, the controller 40 controls the switching of the switches Q1, Q2, Q6, and Q8 by controlling a gate drive circuit (not shown) connected to the gates of the switches Q1, Q2, Q6, and Q8 via a PWM generator (not shown) or the like.

[0133] The controller 40 calculates a period obtained by subtracting the resonance period of the resonator 30 from the switching period of the switches Q1 and Q2, and operates the switches Q6 and Q8 in synchronization with the control signals for the switches Q1 and Q2 using a drive signal during that period.

[0134] The controller 40 calculates a period by subtracting the resonant period (e.g., the resonant half period) of the resonator 30 from the switching period of the switches Q1 and Q2 (e.g., the switching half period during which the switches Q1 and Q2 are on at a duty ratio of 50%). This period is a period during which no current is passed to the load connected to terminals t3 and t4, and is also referred to as the non-conduction period. During the non-conduction period, charge accumulated in the parasitic capacitance of the secondary-side devices of the transformer T (e.g., diodes D5 and D7 and switches Q6 and Q8) cannot be extracted to the load, and high-frequency ringing may occur due to free resonance between the leakage inductance of the transformer T and the parasitic capacitance of the secondary-side devices. Therefore, the controller 40 operates the switches Q6 and Q8 in synchronization with the control signals for the switches Q1 and Q2 using a drive signal during the non-conduction period, thereby extracting charge accumulated in the parasitic capacitance of the secondary-side devices to the load. The drive signals for the switches Q6 and Q8 are signals that turn on the switches Q6 and Q8 during the non-conducting period that exists in the latter half of the on-period of the switch Q1 and during the non-conducting period that exists in the latter half of the on-period of the switch Q2.

[0135] Next, the operation of the power conversion device 5 and the effects achieved by this operation will be described with reference to FIG.

[0136] Fig. 14 is a diagram for explaining an example of the operation and effect of the power conversion device 5 according to embodiment 5. Fig. 14 shows, from the top, timing charts of the gate signals of the switches Q1 and Q8, the gate signals of the switches Q2 and Q6, the voltage generated in the secondary winding of the transformer T (transformer secondary voltage), the current flowing in the primary winding of the transformer T (transformer primary current), and the current flowing in the secondary winding of the transformer T (transformer secondary current).

[0137] As shown in FIG. 14 , the switches Q6 and Q8 are turned on by the drive signal before the switch Q1 changes from an on state to an off state, and before the switch Q2 changes from an on state to an off state. In other words, the controller 40 turns on the switches Q6 and Q8 by the drive signal before the switch Q1 changes from an on state to an off state, and before the switch Q2 changes from an on state to an off state. The non-conducting periods are the periods before the switch Q1 changes from an on state to an off state and the periods before the switch Q2 changes from an on state to an off state. By turning on the switches Q6 and Q8 during these periods, both ends of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load via the switches Q6 and Q8, thereby suppressing high-frequency ringing. As shown in FIG. 14 , it can be seen that high-frequency ringing in the transformer secondary voltage and in the transformer secondary current are suppressed.

[0138] The upper limit of the length of the period before switch Q1 changes from an on state to an off state and the period before switch Q2 changes from an on state to an off state is the length of the non-conductive period. In other words, the end of the period before switch Q1 changes from an on state to an off state is the timing when switch Q1 turns off, and the start of this period is a time up to the length of the non-conductive period before switch Q1 turns off. Also, the end of the period before switch Q2 changes from an on state to an off state is the timing when switch Q2 turns off, and the start of this period is a time up to the length of the non-conductive period before switch Q2 turns off.

[0139] As described above, the period obtained by subtracting the resonance period of the resonator 30 from the switching period of the switches Q1 and Q2 is a non-energized period during which no current is applied to the load. Therefore, if the devices on the secondary side of the transformer T (specifically, the switches Q6 and Q8) are not controlled, the charge accumulated in the parasitic capacitance of the devices on the secondary side of the transformer T cannot be extracted to the load. Therefore, during this period, high-frequency ringing can occur due to free resonance caused by the leakage inductance of the transformer T and the parasitic capacitance of the devices on the secondary side. Therefore, by operating the switches Q6 and Q8 in synchronization with the control signals for the switches Q1 and Q2, both ends of the secondary winding of the transformer T can be connected to the negative terminal t4 of the load (in other words, the potential across the secondary winding of the transformer T can be fixed to the negative potential of the load), allowing the charge of the devices on the secondary side to be extracted to the load. Therefore, high-frequency ringing can be effectively suppressed.

[0140] In the fifth embodiment, the primary-side full-bridge circuit 10 in the first embodiment is replaced with a primary-side half-bridge circuit 50, but the primary-side full-bridge circuit 10 in the second to fourth embodiments may also be replaced with a primary-side half-bridge circuit 50. In this case, although a detailed description will be omitted, high-frequency ringing can be suppressed in the same way as in the second to fourth embodiments.

[0141] (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.

[0142] For example, the diodes included in the secondary-side full bridge circuit 20 in the above embodiment may be replaced with switches (for example, N-channel MOSFETs) that function as diodes.

[0143] For example, in the above embodiment, an example was described in which the power conversion device is an LLC converter, but this is not limited to this. For example, the power conversion device may be a resonant converter including a resonator configured in series and parallel of LC, such as an LCC converter or an CLLC converter.

[0144] For example, in the above embodiment, an example of an LLC converter including a transformer magnetizing inductance, a leakage inductance, and a resonant capacitor has been described, but instead of the leakage inductance, a separate inductor equivalent to the leakage inductance may be provided.

[0145] For example, the present disclosure can be realized not only as a power conversion device, but also as a control method for controlling a power conversion device (specifically, a control method including steps (processing) performed by components that constitute the power conversion device (specifically, controller 40)).

[0146] 15 and 16 are flowcharts showing an example of a control method according to another embodiment.

[0147] For example, the control method is a control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to the primary side of the resonator, and a secondary-side full bridge circuit connected to the secondary side of the resonator, the primary-side full bridge circuit having a first element provided on the high side of a first leg, a second element provided on the low side of the first leg, a third element provided on the high side of the second leg, and a fourth element provided on the low side of the second leg, and the secondary-side full bridge circuit having a fifth element provided on the high side of the third leg, a sixth element provided on the low side of the third leg, and a fourth element provided on the high side of the fourth leg. The control method includes a seventh element provided on the high side of the fourth leg and an eighth element provided on the low side of the fourth leg, wherein the first element, the second element, the third element, and the fourth element are each a switching element, and at least two of the fifth element, the sixth element, the seventh element, and the eighth element are each a switching element, and the control method includes, as shown in FIG. 15 , calculating a period obtained by subtracting the resonance period of the resonator from the switching periods of the first element, the second element, the third element, and the fourth element (step S11), and operating at least two elements in synchronization with control signals for the first element, the second element, the third element, and the fourth element by drive signals during the period (step S12).

[0148] For example, the control method is a control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side half-bridge circuit connected to the primary side of the resonator, and a secondary-side full-bridge circuit connected to the secondary side of the resonator, the primary-side half-bridge circuit having a first element provided on the high side and a second element provided on the low side, and the secondary-side full-bridge circuit having a fifth element provided on the high side of a third leg, a sixth element provided on the low side of the third leg, and a seventh element provided on the high side of a fourth leg. and an eighth element provided on the low side of the fourth leg, wherein the first element and the second element are each a switch element, and at least two of the fifth element, sixth element, seventh element and eighth element are each a switch element, and the control method includes, as shown in FIG. 16 , calculating a period obtained by subtracting the resonance period of the resonator from the switching period of the first element and the second element (step S21), and operating the at least two elements in synchronization with the control signals for the first element and the second element by drive signals during the period (step S22).

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0156] (Technology 1) A power supply includes a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to the primary side of the resonator, and a secondary-side full bridge circuit connected to the secondary side of the resonator, wherein the primary-side full bridge circuit has a first element provided on the high side of a first leg, a second element provided on the low side of the first leg, a third element provided on the high side of a second leg, and a fourth element provided on the low side of the second leg, and the secondary-side full bridge circuit has a fifth element provided on the high side of a third leg, a sixth element provided on the low side of the third leg, and a fourth element provided on the high side of the fourth leg. a seventh element provided on the low side of the fourth leg, and an eighth element provided on the low side of the fourth leg, wherein the first element, the second element, the third element, and the fourth element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the at least two elements operate in synchronization with control signals for the first element, the second element, the third element, and the fourth element by drive signals in a period obtained by excluding a resonance period of the resonator from switching periods of the first element, the second element, the third element, and the fourth element.

[0157] According to this, the period obtained by subtracting the resonance period of the resonator from the switching period of the first, second, third, and fourth elements is a non-energized period during which no current is applied to the load. If the devices (specifically, at least two elements) on the secondary side of the transformer are not controlled, the charge accumulated in the parasitic capacitance of the devices on the secondary side of the transformer cannot be extracted to the load. Therefore, during this period, high-frequency ringing may occur due to free resonance caused by the leakage inductance of the transformer and the parasitic capacitance of the devices on the secondary side. Therefore, by operating at least two elements in synchronization with the control signals for the first, second, third, and fourth elements, during this period, both ends of the transformer's secondary winding can be connected to the positive or negative terminal of the load (in other words, the potential across the transformer's secondary winding can be fixed to the positive or negative potential of the load), allowing the charge accumulated in the parasitic capacitance of the devices on the secondary side to be extracted to the load. Therefore, high-frequency ringing can be effectively suppressed. This provides the effects of improving efficiency by reducing high frequency loss, improving EMC performance in the MHz band, etc. Furthermore, since ringing suppression means such as a snubber circuit or active clamp circuit are not required, miniaturization and cost reduction are possible.

[0158] (Technology 2) The power conversion device according to Technology 1, wherein the at least two elements are the sixth element and the eighth element.

[0159] This allows both ends of the secondary winding of the transformer to be connected to the negative terminal of the load via the sixth element and the eighth element, thereby suppressing high frequency ringing.

[0160] (Technology 3) The sixth element and the eighth element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and are turned on by the drive signal before the second element and the third element are turned off from an on state. This is a power conversion device described in Technology 2.

[0161] The period obtained by subtracting the resonance period of the resonator from the switching periods of the first, second, third, and fourth elements is the period before the first and fourth elements change from an on state to an off state, and the period before the second and third elements change from an on state to an off state. Therefore, by turning on the sixth and eighth elements during these periods, both ends of the secondary winding of the transformer can be connected to the negative terminal of the load via the sixth and eighth elements, and high-frequency ringing can be suppressed.

[0162] (Technology 4) The power conversion device according to Technology 1, wherein the at least two elements are the fifth element and the seventh element.

[0163] This allows both ends of the secondary winding of the transformer to be connected to the positive terminal of the load via the fifth element and the seventh element, thereby suppressing high frequency ringing.

[0164] (Technology 5) A power conversion device according to Technology 4, wherein the fifth element and the seventh element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and are turned on by the drive signal before the second element and the third element are turned off from an on state.

[0165] The period obtained by subtracting the resonance period of the resonator from the switching periods of the first, second, third, and fourth elements is the period before the first and fourth elements change from an on state to an off state, and the period before the second and third elements change from an on state to an off state. Therefore, by turning on the fifth and seventh elements during these periods, both ends of the secondary winding of the transformer can be connected to the positive terminal of the load via the fifth and seventh elements, and high-frequency ringing can be suppressed.

[0166] (Technology 6) The power conversion device according to Technology 1, wherein the at least two elements are the fifth element, the sixth element, the seventh element, and the eighth element.

[0167] This allows both ends of the secondary winding of the transformer to be connected to the positive terminal or negative terminal of the load via the fifth, sixth, seventh, and eighth elements, thereby suppressing high-frequency ringing.

[0168] (Technology 7) A power conversion device according to Technology 6, wherein the sixth element and the eighth element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and the fifth element and the seventh element are turned on by the drive signal before the second element and the third element are turned off from an on state.

[0169] The period obtained by subtracting the resonance period of the resonator from the switching periods of the first, second, third, and fourth elements is the period before the first and fourth elements change from an on state to an off state and the period before the second and third elements change from an on state to an off state. Therefore, by turning on the sixth and eighth elements during the period before the first and fourth elements change from an on state to an off state, both ends of the secondary winding of the transformer can be connected to the negative terminal of the load via the sixth and eighth elements, thereby suppressing high-frequency ringing. Furthermore, by turning on the fifth and seventh elements during the period before the second and third elements change from an on state to an off state, both ends of the secondary winding of the transformer can be connected to the positive terminal of the load via the fifth and seventh elements, thereby suppressing high-frequency ringing.

[0170] (Technology 8) A power conversion device according to Technology 6, wherein the fifth element and the seventh element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and the sixth element and the eighth element are turned on by the drive signal before the second element and the third element are turned off from an on state.

[0171] The period obtained by subtracting the resonance period of the resonator from the switching periods of the first, second, third, and fourth elements is the period before the first and fourth elements change from an on state to an off state and the period before the second and third elements change from an on state to an off state. Therefore, by turning on the fifth and seventh elements during the period before the first and fourth elements change from an on state to an off state, both ends of the secondary winding of the transformer can be connected to the positive terminal of the load via the fifth and seventh elements, thereby suppressing high-frequency ringing. Furthermore, by turning on the sixth and eighth elements during the period before the second and third elements change from an on state to an off state, both ends of the secondary winding of the transformer can be connected to the negative terminal of the load via the sixth and eighth elements, thereby suppressing high-frequency ringing.

[0172] (Technology 9) A power conversion device according to Technology 6, wherein the sixth element and the seventh element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and the fifth element and the eighth element are turned on by the drive signal before the second element and the third element are turned off from an on state.

[0173] The period obtained by subtracting the resonance period of the resonator from the switching periods of the first, second, third, and fourth elements is the period before the first and fourth elements change from an on state to an off state and the period before the second and third elements change from an on state to an off state. Therefore, by turning on the sixth and seventh elements during the period before the first and fourth elements change from an on state to an off state, one end of the transformer's secondary winding can be connected to the negative terminal of the load via the sixth element, and the other end of the transformer's secondary winding can be connected to the positive terminal of the load via the seventh element, thereby suppressing high-frequency ringing. Furthermore, by turning on the fifth and eighth elements during the period before the second and third elements change from an on state to an off state, one end of the transformer's secondary winding can be connected to the positive terminal of the load via the fifth element, and the other end of the transformer's secondary winding can be connected to the negative terminal of the load via the eighth element, thereby suppressing high-frequency ringing.

[0174] (Technology 10) A power conversion device according to Technology 6, wherein the fifth element and the eighth element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and the sixth element and the seventh element are turned on by the drive signal before the second element and the third element are turned off from an on state.

[0175] The period obtained by subtracting the resonance period of the resonator from the switching periods of the first, second, third, and fourth elements is the period before the first and fourth elements change from an on state to an off state and the period before the second and third elements change from an on state to an off state. Therefore, by turning on the fifth and eighth elements during the period before the first and fourth elements change from an on state to an off state, one end of the transformer's secondary winding can be connected to the positive terminal of the load via the fifth element, and the other end of the transformer's secondary winding can be connected to the negative terminal of the load via the eighth element, thereby suppressing high-frequency ringing. Furthermore, by turning on the sixth and seventh elements during the period before the second and third elements change from an on state to an off state, one end of the transformer's secondary winding can be connected to the negative terminal of the load via the sixth element, and the other end of the transformer's secondary winding can be connected to the positive terminal of the load via the seventh element, thereby suppressing high-frequency ringing.

[0176] (Technology 11) A power supply comprising: a resonator having a transformer and a resonance capacitor; a primary-side half-bridge circuit connected to the primary side of the resonator; and a secondary-side full-bridge circuit connected to the secondary side of the resonator, wherein the primary-side half-bridge circuit has a first element provided on a high side and a second element provided on a low side; and the secondary-side full-bridge circuit has a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, and a seventh element provided on a high side of a fourth leg. an eighth element provided on a low side of the fourth leg, wherein the first element and the second element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the at least two elements operate in synchronization with control signals for the first element and the second element by drive signals during a period obtained by excluding a resonance period of the resonator from the switching periods of the first element and the second element.

[0177] According to this, the period obtained by subtracting the resonance period of the resonator from the switching period of the first and second elements is a non-energized period during which no current is applied to the load. If the devices (specifically, at least two elements) on the secondary side of the transformer are not controlled, the charge accumulated in the parasitic capacitance of the devices on the secondary side of the transformer cannot be extracted to the load. Therefore, during this period, high-frequency ringing may occur due to free resonance caused by the leakage inductance of the transformer and the parasitic capacitance of the devices on the secondary side. Therefore, by operating at least two elements in synchronization with the control signals for the first and second elements, both ends of the transformer's secondary winding can be connected to the positive or negative terminal of the load (in other words, the potential across the transformer's secondary winding can be fixed to the positive or negative potential of the load), allowing the charge accumulated in the parasitic capacitance of the devices on the secondary side to be extracted to the load. Therefore, high-frequency ringing can be effectively suppressed.

[0178] (Technology 12) A control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side full bridge circuit connected to a primary side of the resonator, and a secondary-side full bridge circuit connected to a secondary side of the resonator, the primary-side full bridge circuit having a first element provided on a high side of a first leg, a second element provided on a low side of the first leg, a third element provided on a high side of a second leg, and a fourth element provided on a low side of the second leg, the secondary-side full bridge circuit having a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, and a fourth element provided on a high side of the fourth leg. a seventh element provided on the low side of the fourth leg, and an eighth element provided on the low side of the fourth leg, wherein the first element, the second element, the third element, and the fourth element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the control method calculates a period obtained by subtracting a resonance period of the resonator from the switching periods of the first element, the second element, the third element, and the fourth element, and operates the at least two elements in synchronization with control signals for the first element, the second element, the third element, and the fourth element by a drive signal during the period.

[0179] This provides a control method that can effectively suppress high-frequency ringing.

[0180] (Technology 13) A control method for controlling a power conversion device, the power conversion device including a resonator having a transformer and a resonance capacitor, a primary-side half-bridge circuit connected to a primary side of the resonator, and a secondary-side full-bridge circuit connected to a secondary side of the resonator, the primary-side half-bridge circuit having a first element provided on a high side and a second element provided on a low side, the secondary-side full-bridge circuit having a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, and a fourth element provided on a high side of a fourth leg. a seventh element provided on the low side of the fourth leg, and an eighth element provided on the low side of the fourth leg, wherein the first element and the second element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, the control method comprising: calculating a period obtained by subtracting a resonance period of the resonator from a switching period of the first element and the second element; and operating the at least two elements in synchronization with control signals for the first element and the second element by a drive signal during the period.

[0181] This provides a control method that can effectively suppress high-frequency ringing.

[0182] The present disclosure can be applied to an isolated DC-DC converter or the like.

[0183] 1, 2, 3, 4, 5 Power conversion device 10 Primary side full bridge circuit 20 Secondary side full bridge circuit 30 Resonator 40 Controller 50 Primary side half bridge circuit Cin, Cout, Cr Capacitors D5, D6, D7, D8 Diodes Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 Switch T Transformer t1, t2, t3, t4 Terminals

Claims

1. A power supply comprising: a resonator having a transformer and a resonance capacitor; a primary-side full bridge circuit connected to the primary side of the resonator; and a secondary-side full bridge circuit connected to the secondary side of the resonator, wherein the primary-side full bridge circuit has a first element provided on a high side of a first leg, a second element provided on a low side of the first leg, a third element provided on the high side of a second leg, and a fourth element provided on the low side of the second leg, wherein the secondary-side full bridge circuit has a fifth element provided on the high side of a third leg, a sixth element provided on the low side of the third leg, a seventh element provided on the high side of a fourth leg, and an eighth element provided on the low side of the fourth leg, wherein the first element, the second element, the third element, and the fourth element are each a switch element, and at least two of the fifth element, the sixth element, the seventh element, and the eighth element are each a switch element, the at least two elements operate in synchronization with control signals for the first element, the second element, the third element, and the fourth element by a drive signal during a period excluding a resonance period of the resonator from a switching period of the first element, the second element, the third element, and the fourth element.

2. The power conversion device according to claim 1, wherein the at least two elements are the sixth element and the eighth element.

3. The power conversion device as described in claim 2, wherein the sixth element and the eighth element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and turned on before the second element and the third element are turned off from an on state.

4. The power conversion device according to claim 1, wherein the at least two elements are the fifth element and the seventh element.

5. The power conversion device as described in claim 4, wherein the fifth element and the seventh element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and turned on before the second element and the third element are turned off from an on state.

6. The power conversion device according to claim 1, wherein the at least two elements are the fifth element, the sixth element, the seventh element and the eighth element.

7. The power conversion device as described in claim 6, wherein the sixth element and the eighth element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and the fifth element and the seventh element are turned on by the drive signal before the second element and the third element are turned off from an on state.

8. The power conversion device as described in claim 6, wherein the fifth element and the seventh element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and the sixth element and the eighth element are turned on by the drive signal before the second element and the third element are turned off from an on state.

9. The power conversion device of claim 6, wherein the sixth element and the seventh element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and the fifth element and the eighth element are turned on by the drive signal before the second element and the third element are turned off from an on state.

10. The power conversion device of claim 6, wherein the fifth element and the eighth element are turned on by the drive signal before the first element and the fourth element are turned off from an on state, and the sixth element and the seventh element are turned on by the drive signal before the second element and the third element are turned off from an on state.

11. A resonator having a transformer and a resonance capacitor; a primary half-bridge circuit connected to the primary side of the resonator; and a secondary full-bridge circuit connected to the secondary side of the resonator, wherein the primary half-bridge circuit has a first element provided on a high side and a second element provided on a low side, and the secondary full-bridge circuit has a fifth element provided on a high side of a third leg, a sixth element provided on a low side of the third leg, a seventh element provided on a high side of a fourth leg, and an eighth element provided on a low side of the fourth leg, wherein the first element and the second element are each switch elements, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element are each switch elements, and the at least two elements operate in synchronization with a control signal for the first element and the second element by a drive signal during a period obtained by excluding a resonance period of the resonator from a switching period of the first element and the second element. Power conversion equipment.

12. A control method for controlling a power conversion device, the power conversion device comprising: a resonator having a transformer and a resonance capacitor; a primary-side full bridge circuit connected to the primary side of the resonator; and a secondary-side full bridge circuit connected to the secondary side of the resonator, the primary-side full bridge circuit having a first element provided on a high side of a first leg, a second element provided on a low side of the first leg, a third element provided on the high side of a second leg, and a fourth element provided on the low side of the second leg, the secondary-side full bridge circuit having a fifth element provided on the high side of a third leg, a sixth element provided on the low side of the third leg, a seventh element provided on the high side of a fourth leg, and an eighth element provided on the low side of the fourth leg, the first element, the second element, the third element, and the fourth element being each a switch element, At least two of the fifth element, the sixth element, the seventh element, and the eighth element are each a switching element, and the control method includes calculating a period obtained by subtracting a resonance period of the resonator from the switching periods of the first element, the second element, the third element, and the fourth element, and operating the at least two elements in synchronization with control signals for the first element, the second element, the third element, and the fourth element by a drive signal during the period.

13. A control method for controlling a power conversion device, the power conversion device comprising: a resonator having a transformer and a resonance capacitor; a primary side half-bridge circuit connected to the primary side of the resonator; and a secondary side full-bridge circuit connected to the secondary side of the resonator, the primary side half-bridge circuit having a first element provided on a high side and a second element provided on a low side, the secondary side full-bridge circuit having a fifth element provided on the high side of a third leg, a sixth element provided on the low side of the third leg, a seventh element provided on the high side of a fourth leg, and an eighth element provided on the low side of the fourth leg, the first element and the second element being each a switching element, and at least two elements among the fifth element, the sixth element, the seventh element, and the eighth element being each a switching element, the control method comprising: calculating a period obtained by subtracting a resonance period of the resonator from a switching period of the first element and the second element; a drive signal during the period causing the at least two elements to operate in synchronization with control signals for the first element and the second element.

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