Power Conversion Equipment

Abstract

To provide a power conversion device capable of reducing a turn-off power loss.SOLUTION: A power conversion device comprises: a transformer that has a primary winding and a secondary winding; a first bridge circuit in which the primary winding is provided at a bridge portion that connects a connection point between a first arm and a second arm with a connection point between a third arm and a fourth arm; and a second bridge circuit in which the secondary winding is provided at a bridge portion that connects a connection point between a fifth arm and a sixth arm with a connection point between a seventh arm and an eighth arm. The fourth arm is turned off after the first arm is turned off and before a current flowing in the primary winding crosses zero. The third arm is turned off after the second arm is turned off and before the current flowing in the primary winding crosses zero.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device. [Background technology]

[0002] Conventionally, a dual active bridge (DAB) converter is known as a power conversion device capable of supplying power in both directions. A conventional DAB converter generates a square wave voltage in the primary and secondary windings of a transformer by simultaneously switching switch pairs arranged diagonally in each bridge circuit, and adjusts the transmission power between both circuits by controlling the phase difference between the bridge circuits (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-130997 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when diagonally arranged switch pairs are turned off simultaneously, the turn-off occurs when the currents flowing through both switch pairs reach their peaks, which may increase turn-off losses.

[0005] The present disclosure provides a power conversion device capable of reducing turn-off loss. [Means for solving the problem]

[0006] In one aspect of the present disclosure, a transformer having a primary winding and a secondary winding; a first bridge circuit including a first leg in which a first arm on a high side and a second arm on a low side are connected in series, and a second leg in which a third arm on a high side and a fourth arm on a low side are connected in series, the primary winding being provided in a bridge portion connecting a connection point between the first arm and the second arm and a connection point between the third arm and the fourth arm; a second bridge circuit including a third leg in which a fifth arm on a high side and a sixth arm on a low side are connected in series, and a fourth leg in which a seventh arm on a high side and an eighth arm on a low side are connected in series, the secondary winding being provided in a bridge portion connecting a connection point between the fifth arm and the sixth arm and a connection point between the seventh arm and the eighth arm; a control device that controls a phase difference of switching between the first bridge circuit and the second bridge circuit so that power is transmitted between the first bridge circuit and the second bridge circuit, A power conversion device is provided in which the fourth arm is turned off before a current flowing through the primary winding crosses zero after the first arm is turned off, and the third arm is turned off before a current flowing through the primary winding crosses zero after the second arm is turned off. Effect of the Invention

[0007] According to one aspect of the present disclosure, turn-off loss can be reduced. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram showing a configuration example of a power conversion device according to an embodiment of the present invention, together with a primary side device and a secondary side device. [Diagram 2] FIG. 4 is a diagram showing a comparative example of operational waveforms of the power conversion device according to the present embodiment. [Diagram 3] 4 is a diagram showing an example of an operational waveform of the power conversion device according to the present embodiment. FIG. [Figure 4] 4 is a diagram showing a path along which a current flows during a period T1 shown in FIG. 3. [Diagram 5]4 is a diagram showing a path through which a current flows during a period T2 shown in FIG. 3. [Figure 6] 4 is a diagram showing a path along which a current flows during a period T3 shown in FIG. 3. [Figure 7] 4 is a diagram showing a path along which a current flows in a period T4 shown in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] Fig. 1 is a diagram showing an example of a configuration of a power conversion device according to this embodiment, together with a primary side device and a secondary side device. The power conversion device 100 shown in Fig. 1 may be an isolated DC / DC converter, and is capable of supplying power in both directions between a primary side device 110 connected to the primary side and a secondary side device 120 connected to the secondary side.

[0011] The primary side device 110 and the secondary side device 120 are devices connected to the power conversion device 100. Each of the primary side device 110 and the secondary side device 120 may have a function of outputting power and a function of receiving power. For example, one of the primary side device 110 and the secondary side device 120 (the primary side device 110 as an example) may be a power storage device. In this case, the primary side power storage device may receive power transmitted from the other of the primary side device 110 and the secondary side device 120 (the secondary side device 120 as an example) via the power conversion device 100 to be charged, and may supply the charged power to the secondary side device 120 as necessary. Also, for example, one of the primary side device 110 and the secondary side device 120 (the secondary side device 120 as an example) may be a driving device such as a motor. In this case, the secondary side driving device may be driven using power supplied from the other of the primary side device 110 and the secondary side device 120 (as an example, the primary side device 110), and during regenerative operation, may supply the regenerated power to the primary side device 110. Furthermore, each of the primary side device 110 and the secondary side device 120 may be a system combining, for example, a solar power generation device and a power storage device.

[0012] The power conversion device 100 includes, for example, a transformer Tr, a primary circuit 130, a secondary circuit 140, and a control device 150.

[0013] The transformer Tr is a transformer having a primary winding and a secondary winding, which are magnetically coupled. The winding ratio of the primary winding and the secondary winding of the transformer Tr may be determined according to the ratio of the rated voltages of the primary side device 110 and the secondary side device 120. For convenience of explanation, the present specification will exemplify a case where the winding ratio of the transformer Tr is 1:1.

[0014] The primary circuit 130 is connected to the positive terminal and the negative terminal of the primary device 110, and exchanges power with the primary device 110. The primary circuit 130 is also connected to the primary side of a transformer Tr, and exchanges power with the primary winding of the transformer Tr.

[0015] The primary circuit 130 has a primary side DC bus pair P1, N1, with a positive terminal of the primary side device 110 connected to a positive side DC bus P1 and a negative terminal of the primary side device 110 connected to a negative side DC bus N1. The primary circuit 130 may be an inverter capable of switching the polarity of the voltage applied to the primary winding of the transformer Tr by the primary side DC bus pair P1, N1.

[0016] The primary circuit 130 is an example of a first bridge circuit, and more specifically, a full bridge circuit.

[0017] The primary circuit 130 has, for example, a U1-phase leg 11 in which a high-side arm Q1 and a low-side arm Q2 are connected in series, and a V1-phase leg 12 in which a high-side arm Q3 and a low-side arm Q4 are connected in series. The arm Q1 is an example of a first arm, the arm Q2 is an example of a second arm, the arm Q3 is an example of a third arm, and the arm Q4 is an example of a fourth arm. The U1-phase leg 11 is an example of a first leg, and the V1-phase leg 12 is an example of a second leg.

[0018] The primary circuit 130 is a full-bridge circuit in which a primary winding of a transformer Tr is provided in a bridge portion connecting an intermediate connection point a1 between the arms Q1 and Q2 and an intermediate connection point b1 between the arms Q3 and Q4. The primary circuit 130 may have a reactor 21 connected in series to the primary winding of the transformer Tr in the bridge portion.

[0019] The primary circuit 130 has a capacitor C1, arms Q1 to Q4, and a reactor 21 in the example shown in FIG.

[0020] The capacitor C1 is connected between the primary DC bus pair P1, N1, and smoothes the voltage and current transmitted between the primary circuit 130 and the primary device 110.

[0021] The arms Q1 to Q4 are primary-side switching elements, specific examples of which include semiconductor switching elements such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors).

[0022] The arms Q1 and Q2 are connected in series between the DC bus pair P1, N1. The arms Q1 and Q2 each have a first main terminal, a second main terminal, and a control terminal. For example, the first main terminal corresponds to a drain or collector, the second main terminal corresponds to a source or emitter, and the control terminal corresponds to a gate. The arms Q1 and Q2 may include a diode connected inversely between the main terminals. When the arms Q1 and Q2 are MOSFETs, the diode may be a parasitic diode.

[0023] The arms Q3 and Q4 are connected in series between the pair of DC buses P1 and N1. Like the arms Q1 and Q2, the arms Q3 and Q4 each have a first main terminal, a second main terminal, and a control terminal, and may include a diode connected inversely between the main terminals.

[0024] The reactor 21 is an inductor connected in series with the primary winding of the transformer Tr between the intermediate connection point a1 and the intermediate connection point b1.

[0025] With this configuration, when the arms Q1 and Q4 are turned on and the arms Q2 and Q3 are turned off, the primary circuit 130 electrically connects the intermediate connection point a1 to the DC bus P1 and electrically connects the intermediate connection point b1 to the DC bus N1, and sets the voltage V1 between the intermediate connection point a1 and the intermediate connection point b1 to a positive voltage "E1". E1 is the voltage value between the DC bus pair P1, N1. Also, when the arms Q1 and Q4 are turned off and the arms Q2 and Q3 are turned on, the primary circuit 130 electrically connects the intermediate connection point a1 to the DC bus N1 and electrically connects the intermediate connection point b1 to the DC bus P1, and sets the voltage V1 to a negative voltage "-E1". In this way, the primary circuit 130 switches the polarity of the voltage applied to the primary winding of the transformer Tr by the primary side DC bus pair P1, N1.

[0026] Furthermore, when the arms Q1 and Q3 are turned on and the arms Q2 and Q4 are turned off, the primary circuit 130 electrically connects both the intermediate connection point a1 and the intermediate connection point b1 to the DC bus P1, making the voltage V1 substantially zero. Alternatively, when the arms Q1 and Q3 are turned off and the arms Q2 and Q4 are turned on, the primary circuit 130 electrically connects both the intermediate connection point a1 and the intermediate connection point b1 to the DC bus N1, making the voltage V1 substantially zero.

[0027] The secondary circuit 140 is connected to the positive terminal and the negative terminal of the secondary device 120, and exchanges power with the secondary device 120. The secondary circuit 140 is also connected to the secondary side of the transformer Tr, and exchanges power with the secondary winding of the transformer Tr.

[0028] The secondary circuit 140 is connected to the secondary side of the transformer Tr and the secondary side device 120, and has substantially the same configuration as the primary circuit 130, except that the withstand voltage and the like may differ from those of the primary circuit 130 depending on the transformation ratio of the transformer Tr. For this reason, a description of the secondary circuit 140 will be omitted, except for the differences from the primary circuit 130.

[0029] The secondary circuit 140 has a secondary side DC bus pair P2, N2. The DC bus pair P2, N2 corresponds to the DC bus pair P1, N1 in the primary circuit 130. The secondary circuit 140 may be an inverter capable of switching the polarity of the voltage applied to the secondary winding of the transformer Tr by the secondary side DC bus pair P2, N2.

[0030] The secondary circuit 140 is an example of a second bridge circuit, and more specifically, a full bridge circuit.

[0031] The secondary circuit 140 has, for example, a U2-phase leg 13 in which a high-side arm Q5 and a low-side arm Q6 are connected in series, and a V2-phase leg 14 in which a high-side arm Q7 and a low-side arm Q8 are connected in series. The arm Q5 is an example of a fifth arm, the arm Q6 is an example of a sixth arm, the arm Q7 is an example of a seventh arm, and the arm Q8 is an example of an eighth arm. The U2-phase leg 13 is an example of a third leg, and the V2-phase leg 14 is an example of a fourth leg.

[0032] 1, the secondary circuit 140 has a capacitor C2, arms Q5 to Q8, and a reactor 22. The capacitor C2 corresponds to the capacitor C1 in the primary circuit 130, the arms Q5 to Q8 correspond to the arms Q1 to Q4 in the primary circuit 130, and the reactor 22 corresponds to the reactor 21 in the primary circuit 130.

[0033] With this configuration, when the arms Q5 and Q8 are turned on and the arms Q6 and Q7 are turned off, the secondary circuit 140 electrically connects the intermediate connection point a2 to the DC bus P2 and electrically connects the intermediate connection point b2 to the DC bus N2, and sets the voltage V2 between the intermediate connection point a2 and the intermediate connection point b2 to a positive voltage "E2". E2 is the voltage value between the DC bus pair P2, N2. Furthermore, when the arms Q5 and Q8 are turned off and the arms Q6 and Q7 are turned on, the secondary circuit 140 electrically connects the intermediate connection point a2 to the DC bus N2 and electrically connects the intermediate connection point b2 to the DC bus P2, and sets the voltage V2 to a negative voltage "-E2". In this way, the secondary circuit 140 switches the polarity of the voltage applied to the secondary winding of the transformer Tr by the secondary side DC bus pair P2, N2.

[0034] Furthermore, when the arms Q5 and Q7 are turned on and the arms Q6 and Q8 are turned off, the secondary circuit 140 electrically connects both the intermediate connection point a2 and the intermediate connection point b2 to the DC bus P2 to make the voltage V2 substantially zero. Alternatively, when the arms Q5 and Q7 are turned off and the arms Q6 and Q8 are turned on, the secondary circuit 140 electrically connects both the intermediate connection point a2 and the intermediate connection point b2 to the DC bus N2 to make the voltage V2 substantially zero.

[0035] The control device 150 controls the phase difference of switching between the primary circuit 130 and the secondary circuit 140 so that power is transmitted between the primary circuit 130 and the secondary circuit 140. The control device 150 adjusts the power transmitted between the primary circuit 130 and the secondary circuit 140 by controlling the phase difference between the voltage V1 and the voltage V2. The control device 150 outputs a control signal for controlling the on or off of the control terminals c1 to c4 of the arms Q1 to Q4 of the primary circuit 130, and a control signal for controlling the on or off of the control terminals c5 to c8 of the arms Q5 to Q8 of the secondary circuit 140. For example, a direction command value, an E1 command value, an E1 detection value, an E2 command value, and an E2 detection value are input to the control device 150, and the control device 150 controls the phase difference of switching between the primary circuit 130 and the secondary circuit 140 based on these input values.

[0036] The direction command value is a command value that indicates whether to transmit power from the primary side to the secondary side or from the secondary side to the primary side. The E1 detection value is an example of an index value indicating the magnitude of the output from the primary circuit 130 to the primary-side device 110 when power is transmitted from the secondary side to the primary side. In the present embodiment, it is a value obtained by measuring the voltage E1 supplied to the primary-side device 110. The E1 command value is an example of a target value of the output from the primary circuit 130 to the primary-side device 110. In the present embodiment, it is a value that indicates the target value of the voltage E1 to be supplied to the primary-side device 110. The E2 detection value and the E2 command value are the same as the E1 detection value and the E1 command value, except that they are an index value and a target value indicating the magnitude of the output from the secondary circuit 140 to the secondary-side device 120 when power is transmitted from the primary side to the secondary side.

[0037] In the present embodiment, the control device 150 inputs, as the index value and the target value, a value indicating the voltage value of the output destination. Alternatively, the control device 150 may input, as the index value and the target value, a value indicating the current value of the output destination, or a value indicating the power value supplied to the output destination, etc., and control the arms Q1 to Q8 based on such values.

[0038] The functions of the control device 150 are realized by a processor such as a CPU (Central Processing Unit) operating according to a program stored in a memory. The functions of the control device 150 may be realized by an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0039] FIG. 2 is a diagram showing a comparative example of the operation waveforms of the power conversion device according to the present embodiment. FIG. 2 shows, in order from the top, the waveform of the voltage V1 between the intermediate connection point a1 and the midpoint connection point b1 in the primary circuit 130, the waveform of the voltage V2 between the intermediate connection point a2 and the intermediate connection point b2 in the secondary circuit 140, the waveform of the current I1 flowing through the primary winding of the transformer Tr and the reactor 21 (when E1 < E2), and the waveform of the current I1 (when E1 > E2). The horizontal axis represents time.

[0040] The control device 150 controls the primary circuit 130 and the secondary circuit 140 to be switched with a phase difference. This allows the power conversion device 100 to function as a DAB converter. Fig. 2 illustrates a case where power is supplied from the primary side to the secondary side.

[0041] 2, the control device 150 switches the voltage V1 between a positive voltage and a negative voltage by switching the primary circuit 130 at a certain frequency. The control device 150 can set the voltage V1 to a positive voltage "E1" by supplying a control signal to the primary circuit 130 that turns on the arms Q1 and Q4 and turns off the arms Q2 and Q3. The control device 150 can set the voltage V1 to a negative voltage "-E1" by supplying a control signal to the primary circuit 130 that turns off the arms Q1 and Q4 and turns on the arms Q2 and Q3.

[0042] Moreover, the control device 150 switches the voltage V2 between a positive voltage and a negative voltage by switching the secondary circuit 140 at the same frequency as the primary circuit 130. The control device 150 can set the voltage V2 to a positive voltage "E2" by supplying a control signal to the secondary circuit 140 that turns on the arms Q5 and Q8 and turns off the arms Q6 and Q7. The control device 150 can set the voltage V2 to a negative voltage "-E2" by supplying a control signal to the secondary circuit 140 that turns off the arms Q5 and Q8 and turns on the arms Q6 and Q7.

[0043] The control device 150 provides a phase difference between the switching of the voltage V1 and the switching of the voltage V2, as shown as "primary / secondary phase difference" in FIG. 2. Here, the transformer Tr ideally passes the primary side current I1 and the secondary side current I2 at a ratio according to the reciprocal of the winding ratio. When the winding ratio is 1:1, ideally the current I1=the current I2. Therefore, when considering the current flowing in the power conversion device 100, the transformer Tr may be ignored.

[0044] In FIG. 2, during the period when the polarities of voltage V1 and voltage V2 do not match, (E1 + E2) is applied to the sum (L1 + L2) of inductance L1 and inductance L2, and current I1 (= I2) increases. Inductance L1 is approximately equal to the sum of the leakage inductance of the primary winding of transformer Tr and the inductance of reactor 21, and inductance L2 is approximately equal to the sum of the leakage inductance of the secondary winding of transformer Tr and the inductance of reactor 22. On the other hand, during the period when the polarities of voltage V1 and voltage V2 match, due to the difference in the magnitude relationship between E1 and E2, current I1 (= I2) decreases or increases.

[0045] In FIG. 2, first, when voltage V1 = E1 and voltage V2 = -E2, for inductances L1 and L2 connected in series, primary-side device 110 and secondary-side device 120 are connected in series in the forward direction. As a result, voltage (E1 + E2) is applied to inductance (L1 + L2), so current I1 (= I2) rises at a slope of (E1 + E2) / (L1 + L2), and current I1 becomes positive.

[0046] Next, after the primary / secondary phase difference, when voltage V1 = E1 and voltage V2 = E2, the positive terminals of primary-side device 110 and secondary-side device 120 are connected via inductances L1 and L2. As a result, voltage (E1 - E2) is applied to inductance (L1 + L2), so current I1 (= I2) changes at a slope of (E1 - E2) / (L1 + L2).

[0047] Here, when E1 < E2, current I1 decreases. When voltage E1 > E2, current I1 further increases. When voltage E1 = E2, current I1 does not change. However, in an actual circuit, since there are some losses, current I1 tends to decrease compared to the ideal case.

[0048] A positive current I1 (=current I2) flows when the positive terminal of the primary device 110 and the positive terminal of the secondary device 120 are connected via inductances L1 and L2. As a result, the positive current I2 is supplied to the positive terminal of the secondary device 120, and power is supplied to the secondary device 120, such as for charging.

[0049] Next, when voltage V1=-E1 and voltage V2=E2, the primary side device 110 and secondary side device 120 are connected in series in the forward direction with respect to inductances L1 and L2, which is the opposite direction to the case where voltage V1=E1 and voltage V2=-E2. In this case, the current I1 changes in the opposite direction, which is the same as the case where voltage V1=E1 and voltage V2=-E2.

[0050] Next, when the voltage V1=-E1 and the voltage V2=-E2, power supply such as charging is performed to the secondary device 120, similarly to the case where the voltage V1=E1 and the voltage V2=E2.

[0051] When supplying power from the secondary side to the primary side, the control device 150 may delay the switching of the voltage V1 relative to the switching of the voltage V2. In this way, by controlling the switching of the primary circuit 130 and the secondary circuit 140 with a phase difference, power can be exchanged between the primary side device 110 and the secondary side device 120. When the winding ratio is not 1:1, the voltage changes according to the winding ratio, and the current changes according to the inverse of the winding ratio, as described above.

[0052] However, as shown in Fig. 2, when the diagonally arranged arms Q1 and Q4 are turned off simultaneously, the turn-off occurs when the current I1 flowing through both arms Q1 and Q4 reaches a peak, which may increase the turn-off loss. For the same reason, when the diagonally arranged arms Q2 and Q3 are turned off simultaneously, when the diagonally arranged arms Q5 and Q8 are turned off simultaneously, or when the diagonally arranged arms Q6 and Q7 are turned off simultaneously, the turn-off loss may increase.

[0053] 3 is a diagram showing an example of operating waveforms of the power conversion device according to this embodiment capable of reducing turn-off loss, and is a timing chart showing an example of switching operation of each arm Q1 to Q8. In the on-off waveforms of each arm Q1 to Q8, a high level indicates an on state, and a low level indicates an off state. V1 indicates a voltage between the intermediate connection point a1 and the midpoint connection point b1 in the primary circuit 130, and V2 indicates a voltage between the intermediate connection point a2 and the intermediate connection point b2 in the secondary circuit 140. I1 indicates a current flowing through the primary winding of the transformer Tr and the reactor 21, and Ir2 indicates a rectified current flowing through the DC bus P2 in the secondary circuit 140.

[0054] Fig. 4 is a diagram showing a path through which a current flows in a period T1 shown in Fig. 3. Fig. 5 is a diagram showing a path through which a current flows in a period T2 shown in Fig. 3. Fig. 6 is a diagram showing a path through which a current flows in a period T3 shown in Fig. 3. Fig. 7 is a diagram showing a path through which a current flows in a period T4 shown in Fig. 3. Figs. 3 to 7 illustrate the case where E1 is greater than E2 and the transformation ratio of the transformer Tr is 1:1.

[0055] As shown in Fig. 3, the control device 150 turns off the arm Q4 before the current I1, which is decreasing after the arm Q1 is turned off, crosses zero. As a result, the arm Q4 is turned off when the current I1, which starts to decrease due to the turning off of the arm Q1, approaches zero, so that the combined turn-off loss of the arms Q1 and Q4 can be reduced compared to the case where the arms Q1 and Q4 are turned off simultaneously. When the arm Q1 is turned off, a transition occurs from the period T1 to the period T2, the voltage V1 transitions from the positive voltage "E1" to zero, and the voltage V2 remains at the positive voltage "E2". Therefore, the current I1 (=I2) decreases at a slope of "-E2 / (L1+L2)".

[0056] 3, the control device 150 turns off the arm Q3 before the current I1, which is rising after the arm Q2 is turned off, crosses zero. As a result, the arm Q3 is turned off when the current I1, which starts to rise due to the turn-off of the arm Q2, approaches zero, so that the combined turn-off loss of the arms Q2 and Q3 can be reduced compared to the case where the arms Q2 and Q3 are turned off simultaneously. When the arm Q2 is turned off, a transition occurs from the period T5 to the period T6, the voltage V1 transitions from the negative voltage "-E1" to zero, and the voltage V2 remains at the negative voltage "-E2". Therefore, the current I1 (=I2) rises at a slope of "E2 / (L1+L2)".

[0057] Although not shown in detail in Fig. 3, the control device 150 provides a dead time td1 during which both arms are in the off state from when a low-side arm (e.g., arm Q4) is turned off until a high-side arm (e.g., arm Q3) opposing the low-side arm is turned on. Similarly, the control device 150 provides a dead time td2 during which both arms are in the off state from when a high-side arm is turned off until a low-side arm opposing the high-side arm is turned on. By providing a dead time, it is possible to prevent a through current from flowing through a pair of opposing arms in the on state.

[0058] Furthermore, if arm Q4 is turned off "after" the current I1 crosses zero after arm Q1 is turned off, arm Q3 is turned on after dead time td1 in a state in which current I1 flows through the diode in anti-parallel to arm Q4. This may increase reverse recovery loss that occurs during the reverse recovery time of the diode in anti-parallel to arm Q4. In response to this, control device 150 turns off arm Q4 "before" the current I1 crosses zero after arm Q1 is turned off. As a result, arm Q3 is turned on after dead time td1 before current I1 flows through the diode in anti-parallel to arm Q4. This suppresses the occurrence of reverse recovery loss as described above, thereby suppressing an increase in loss in power conversion device 100.

[0059] Furthermore, if arm Q3 is turned off "after" the current I1 crosses zero after arm Q2 is turned off, arm Q4 is turned on after dead time td2 while the current I1 is flowing through the diode in anti-parallel to arm Q3. This may increase the reverse recovery loss that occurs during the reverse recovery time of the diode in anti-parallel to arm Q3. In response to this, control device 150 turns off arm Q3 "before" the current I1 crosses zero after arm Q2 is turned off. As a result, arm Q4 is turned on after dead time td2 before the current I1 flows through the diode in anti-parallel to arm Q3. This suppresses the occurrence of the above-mentioned reverse recovery loss, thereby suppressing an increase in loss in power conversion device 100.

[0060] After turning off the arm Q1, the control device 150 may determine whether or not the current I1 (e.g., the instantaneous current value of the current I1) detected by the current sensor has fallen within a predetermined range including zero. In this case, when the control device 150 determines that the current I1 detected by the current sensor has fallen within a predetermined range including zero, the control device 150 may turn off the arm Q4 before the falling current I1 crosses zero. As a result, the arm Q4 is turned off when the current I1, which starts to fall due to the turn-off of the arm Q1, approaches zero, so that the combined turn-off loss of the arms Q1 and Q4 can be reduced compared to the case where the arms Q1 and Q4 are turned off simultaneously.

[0061] After turning off the arm Q2, the control device 150 may determine whether or not the current I1 (for example, the instantaneous current value of the current I1) detected by the current sensor has risen within a predetermined range including zero. In this case, when the control device 150 determines that the current I1 detected by the current sensor has risen within a predetermined range including zero, the control device 150 may turn off the arm Q3 before the rising current I1 crosses zero. As a result, the arm Q3 is turned off when the current I1 that starts to rise due to the turn-off of the arm Q2 approaches zero, so that the combined turn-off loss of the arms Q2 and Q3 can be reduced compared to the case where the arms Q2 and Q3 are turned off simultaneously.

[0062] The control device 150 may use a timer to determine whether a predetermined time T has elapsed since the arm Q1 was turned off. In this case, when the control device 150 determines that the predetermined time T has elapsed since the arm Q1 was turned off, the control device 150 may turn off the arm Q4 before the decreasing current I1 crosses zero. As a result, the arm Q4 is turned off when the current I1, which starts to decrease due to the turning off of the arm Q1, approaches zero, so that the combined turn-off loss of the arms Q1 and Q4 can be reduced compared to the case where the arms Q1 and Q4 are turned off simultaneously.

[0063] The control device 150 may use a timer to determine whether a predetermined time T has elapsed since the arm Q2 was turned off. In this case, when the control device 150 determines that the predetermined time T has elapsed since the arm Q2 was turned off, the control device 150 may turn off the arm Q3 before the rising current I1 crosses zero. As a result, the arm Q3 is turned off when the current I1, which starts to rise due to the turning off of the arm Q2, approaches zero, so that the combined turn-off loss of the arms Q2 and Q3 can be reduced compared to the case where the arms Q2 and Q3 are turned off simultaneously.

[0064] The time tz for the current I1 to fall from the positive peak value "I1s" to zero (or the time tz for the current I1 to rise from the negative peak value "-I1s" to zero) is tz=(L1+L2)×I1s / E2 It is therefore preferable that the predetermined time T is set to a value equal to or less than the time tz. The predetermined time T may be a fixed value preset in a memory, or may be a value calculated sequentially using the detection value of the peak value I1s of the current I1 detected by the current sensor.

[0065] The control device 150 may turn off the arm Q4 before the decreasing current I1 crosses zero when at least one of the following conditions is satisfied: the current I1 detected by the current sensor has fallen within a predetermined range including zero, and a predetermined time T has elapsed since the arm Q1 was turned off. Alternatively, the control device 150 may turn off the arm Q3 before the increasing current I1 crosses zero when at least one of the following conditions is satisfied: the current I1 detected by the current sensor has risen within a predetermined range including zero, and a predetermined time T has elapsed since the arm Q2 was turned off.

[0066] The control device 150 may determine the predetermined time T according to at least one of the magnitude of the DC current (input current Id1) input to the primary circuit 130, the DC current (output current Id2) output from the secondary circuit 140, the DC voltage E1 input to the primary circuit 130, and the DC voltage E2 output from the secondary circuit 140, instead of the current I1s. This is because the time tz taken for the current I1 to drop from the positive peak value "I1s" to zero (or the time tz taken for the current I1 to rise from the negative peak value "-I1s" to zero) correlates with the magnitude of the input current Id1, the output current Id2, the DC voltage E1, or the DC voltage E2.

[0067] The magnitude of the input current Id1 or the output current Id2 can be detected by a current sensor. A current sensor that detects the substantially constant input current Id1 or the output current Id2 requires a lower response speed than a current sensor that detects the current I1 that changes at a relatively high frequency, which allows for simplification of the current detection logic and reduction in cost. The magnitude of the DC voltage E1 or the DC voltage E2 can be detected by a voltage sensor.

[0068] The control device 150 may sequentially derive the predetermined time T according to a predetermined relationship rule using at least one of the detection values ​​of the input current Id1 or the output current Id2 detected by the current sensor and the detection value of the DC voltage E1 or the DC voltage E2 detected by the voltage sensor.

[0069] As shown in Fig. 3, the control device 150 may gate off the arm Q8 simultaneously with or immediately after the turn-off of the arm Q4. Fig. 3 illustrates a case where the control device 150 gates off the arm Q8 immediately after the turn-off of the arm Q4. Simultaneously with or immediately after the turn-off of the arm Q4 means a state in which the decreasing currents I1 and I2 are zero or sufficiently close to zero. Therefore, by the control device 150 gates off the arm Q8 simultaneously with or immediately after the turn-off of the arm Q4, the gate-off timing of the arm Q8 is a state in which the decreasing current I2 is zero or sufficiently close to zero, so that the turn-off loss of the arm Q8 can be reduced.

[0070] When the control device 150 gates off the arm Q8 simultaneously with or immediately after the turn-off of the arm Q4, the current I2 flows in a reverse conduction state via a diode in anti-parallel to the arm Q8 (see FIG. 6). After that, when the current I2 crosses zero, the current I2 flows in a natural commutation state via a diode in anti-parallel to the arm Q7 because the arm Q8 is in a gate-off state (see FIG. 7). Therefore, as shown in FIG. 3, the control device 150 may gate off the arm Q8 simultaneously with or immediately after the turn-off of the arm Q4, and then gate on the arm Q7 after the decreasing current I1 or current I2 crosses zero. As a result, the current I2 passes through the arm Q7 in a gate-on state without passing through a diode in anti-parallel to the arm Q7, thereby reducing the forward loss of the diode.

[0071] Similarly, as shown in Fig. 3, the control device 150 may gate off the arm Q7 simultaneously with or immediately after the turn-off of the arm Q3. Fig. 3 illustrates a case where the control device 150 gates off the arm Q7 immediately after the turn-off of the arm Q3. Simultaneous with or immediately after the turn-off of the arm Q3 means a state in which the rising currents I1 and I2 are zero or sufficiently close to zero. Therefore, by the control device 150 gates off the arm Q7 simultaneously with or immediately after the turn-off of the arm Q3, the gate-off timing of the arm Q7 is a state in which the rising current I2 is zero or sufficiently close to zero, so that the turn-off loss of the arm Q7 can be reduced.

[0072] Similarly, when the control device 150 gates off the arm Q7 simultaneously or immediately after the turn-off of the arm Q3, the current I2 flows in a reverse conduction state via a diode in anti-parallel to the arm Q7. After that, when the current I2 crosses zero, the current I2 flows in a natural commutation state via a diode in anti-parallel to the arm Q8 because the arm Q7 is in a gate-off state. Therefore, as shown in FIG. 3, the control device 150 may gate off the arm Q7 simultaneously or immediately after the turn-off of the arm Q3, and then gate on the arm Q8 after the rising current I1 or current I2 crosses zero. As a result, the current I2 passes through the arm Q8 in a gate-on state without passing through a diode in anti-parallel to the arm Q8, thereby reducing the forward loss of the diode.

[0073] Note that "turn off" refers to cutting off the transistor by turning off the gate voltage during forward conduction, and "gate off" refers to cutting off the transistor by turning off the gate voltage during reverse conduction.

[0074] In this way, the turn-off loss of V2-phase arms Q7, Q8 is sufficiently small, and the arms in which switching loss mainly occurs are U1-phase arms Q1, Q2 and U2-phase arms Q5, Q6, so that the switching loss of the entire power conversion device 100 can be sufficiently reduced.

[0075] Although the embodiments have been described above, the technology of the present disclosure is not limited to the above-described embodiments. Various modifications and improvements, such as combinations with or substitutions for part or all of other embodiments, are possible. [Explanation of symbols]

[0076] 100 Power conversion device Legs 11, 12, 13, 14 21,22 Reactor 110 Primary side device 120 Secondary side device 130 Primary circuit 140 Secondary circuit 150 Control Device Q1~Q8 Arm

Claims

1. a transformer having a primary winding and a secondary winding; a first bridge circuit including a first leg in which a first arm on a high side and a second arm on a low side are connected in series, and a second leg in which a third arm on a high side and a fourth arm on a low side are connected in series, the primary winding being provided in a bridge portion connecting a connection point between the first arm and the second arm and a connection point between the third arm and the fourth arm; a second bridge circuit including a third leg in which a fifth arm on a high side and a sixth arm on a low side are connected in series, and a fourth leg in which a seventh arm on a high side and an eighth arm on a low side are connected in series, the secondary winding being provided in a bridge portion connecting a connection point between the fifth arm and the sixth arm and a connection point between the seventh arm and the eighth arm; a control device that controls a phase difference of switching between the first bridge circuit and the second bridge circuit so that power is transmitted between the first bridge circuit and the second bridge circuit, the fourth arm is turned off before a current flowing through the primary winding crosses zero after the first arm is turned off, and the third arm is turned off before a current flowing through the primary winding crosses zero after the second arm is turned off, the seventh arm is gated off simultaneously with or immediately after the fourth arm is turned off, and then is gated on after a current flowing through the primary winding or the secondary winding crosses zero; a seventh arm turns off simultaneously with or immediately after the third arm is turned off, and the eighth arm turns on after a current flowing through the primary winding or the secondary winding crosses zero;

2. A power conversion device as described in claim 1, wherein when the eighth arm is gated off simultaneously with or immediately after the fourth arm is turned off, the current flowing in the secondary winding flows through a diode in anti-parallel to the eighth arm, and then the seventh arm is gated on after the current flowing in the secondary winding is naturally commutated to the diode in anti-parallel to the seventh arm.

3. A power conversion device as described in claim 2, wherein when the seventh arm is gated off simultaneously with or immediately after the third arm is turned off, the current flowing in the secondary winding flows through a diode in anti-parallel to the seventh arm, and then the eighth arm is gated on after the current flowing in the secondary winding is naturally commutated to the diode in anti-parallel to the eighth arm.

4. A power conversion device described in any one of claims 1 to 3, wherein the on state of the fifth arm is maintained at least from the time the fourth arm is turned off until the time when the seventh arm and the eighth arm are both turned off.

5. A power conversion device as described in claim 4, wherein the on state of the sixth arm is maintained at least from the time the third arm is turned off until the time when the seventh arm and the eighth arm are both turned off.

6. The power conversion device according to claim 1 , wherein the fourth arm and the third arm are turned off when a current flowing through the primary winding falls within a predetermined range including zero.

7. Detecting a current flowing through the primary winding; The power conversion device according to claim 6 , wherein the fourth arm and the third arm are turned off when a detected current flowing through the primary winding falls within a predetermined range including zero.

8. 4. The power conversion device according to claim 1, wherein the fourth arm is turned off before a current flowing through the primary winding crosses zero when a predetermined time has elapsed since the first arm is turned off, and the third arm is turned off before a current flowing through the primary winding crosses zero when a predetermined time has elapsed since the second arm is turned off.

9. 9. The power conversion device according to claim 8, wherein the predetermined time is a time determined according to a magnitude of at least one of a DC current input to the first bridge circuit, a DC current output from the second bridge circuit, a DC voltage input to the first bridge circuit, and a DC voltage output from the second bridge circuit.

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