Power conversion device and control method for the same

Abstract

To achieve high efficiency through simple control.SOLUTION: A power conversion device 100 is configured to turn off both side arms of one leg among first leg to fourth leg of a bridge circuit having a high DC voltage, and to control the ON / OFF states of each arm of the remaining legs when transmitting power from a bridge circuit with a lower DC voltage to a bridge circuit with a higher DC voltage under conditions where a DC voltage E1 of a primary-side bridge circuit 130, having a first leg 11 and a second leg 12, differs from a DC voltage E2 of a secondary-side bridge circuit 140, having a third leg 13 and a fourth leg 14.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A bidirectional isolated DC / DC converter called DAB (Dual Active Bridge) is known, in which two single-phase bridge circuits are connected via a high-frequency isolation transformer (see, for example, Non-Patent Document 1). When power control that adjusts the phase difference between the bridges is used, this converter can apply ZVS (Zero-Voltage Switching), which can reduce switching loss, making it suitable for high-power applications.

[0003] Also, a power conversion device is known that reduces loss by controlling the duty ratio of the AC voltage on one or both sides in addition to controlling the phase difference between the bridges (see, for example, Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] RWAA De Doncker, DM Divan, and MH Kheraluwala, "A Three-Phase Soft-Switched High-Power-Density dc / dc Converter for High-Power Applications", IEEE Transactions on Industry Applications, Volume 27, Issue 1, Pages 63-73, January / February 1991. [Patent documents]

[0005] [Patent Document 1] Patent No. 6259009 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional methods for reducing loss have the problem that they are complicated and difficult to implement on a computer.

[0007] The present disclosure provides a power conversion device and a control method thereof that can achieve high efficiency through simple control. [Means for solving the problem]

[0008] In a first aspect of the present disclosure, a transformer having a primary winding and a secondary winding; a primary-side bridge circuit having a first leg in which a high-side first arm and a low-side second arm are connected in series, and a second leg in which a high-side third arm and a low-side fourth arm 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 secondary-side bridge circuit including a third leg in which a high-side fifth arm and a low-side sixth arm are connected in series, and a fourth leg in which a high-side seventh arm and a low-side eighth arm 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; When power is transmitted from a bridge circuit with a lower DC voltage to a bridge circuit with a higher DC voltage under the condition that the DC voltage of the primary-side bridge circuit and the DC voltage of the secondary-side bridge circuit differ, a control device is provided that sets the arms on both sides of one of the first to fourth legs of the bridge circuit with a higher DC voltage to an off state and controls the on and off states of each arm of the remaining legs.

[0009] In a second aspect of the present disclosure, a transformer having a primary winding and a secondary winding; a primary-side bridge circuit having a first leg in which a high-side first arm and a low-side second arm are connected in series, and a second leg in which a high-side third arm and a low-side fourth arm 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 control method for a power conversion device including a secondary-side bridge circuit having 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, and in which the secondary winding is 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, When power is transmitted from a bridge circuit with a lower DC voltage to a bridge circuit with a higher DC voltage under the condition that the DC voltage of the primary-side bridge circuit and the DC voltage of the secondary-side bridge circuit differ, the control method for a power conversion device is provided, in which arms on both sides of any one of the first to fourth legs of the bridge circuit with a higher DC voltage are set to an off state, and the on state and off state of each arm of the remaining legs are controlled. [Effects of the Invention]

[0010] According to the present disclosure, high efficiency can be achieved through simple control. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating an example of a configuration of a power conversion device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram showing an example of the configuration of a main part of a control device. [Figure 3] 10 is a timing chart illustrating control signals g1 to g8 when power is transmitted from the secondary side bridge circuit to the primary side bridge circuit under the condition that the DC voltage of the primary side bridge circuit is higher than the DC voltage of the secondary side bridge circuit. [Figure 4]10 is a timing chart illustrating control signals g1 to g8 when power is transmitted from the primary side bridge circuit to the secondary side bridge circuit under the condition that the DC voltage of the primary side bridge circuit is lower than the DC voltage of the secondary side bridge circuit. [Figure 5] FIG. 10 is a diagram showing an example of a simulation operation waveform when an SPS (Single Phase Shift) method is applied. [Figure 6] FIG. 10 is a diagram showing an example of a simulation operation waveform when the new method according to the present disclosure is applied. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0013] Fig. 1 is a diagram showing an example of the configuration of a power conversion device according to this embodiment. The power conversion device 100 shown in Fig. 1 is a bidirectional isolated DC / DC converter having bridge circuits on both sides of a transformer 30. The power conversion device 100 can supply power bidirectionally between a primary-side bridge circuit 130 and a secondary-side bridge circuit 140.

[0014] The power conversion device 100 includes a transformer 30, a primary bridge circuit 130, a secondary bridge circuit 140, and a control device 150.

[0015] The transformer 30 is a transformer having a primary winding 31 and a secondary winding 32, which are magnetically coupled. The turns ratio of the primary winding 31 and the secondary winding 32 is set appropriately. For the sake of convenience, the present specification will exemplify a case where the turns ratio of the primary winding 31 and the secondary winding 32 is 1:1.

[0016] The primary bridge circuit 130 is connected to primary DC terminals (positive terminal and negative terminal) and exchanges power with an external device connected to the primary DC terminals. The primary bridge circuit 130 is also connected to the primary side of the transformer 30 and exchanges power with the primary winding 31 of the transformer 30.

[0017] The primary-side bridge circuit 130 has a pair of primary-side DC buses P1 and N1, and has a positive terminal of the primary-side DC terminal connected to the positive-side DC bus P1 and a negative terminal of the primary-side DC terminal connected to the negative-side DC bus N1. The primary-side bridge circuit 130 switches the polarity of the voltage applied to the primary winding 31 of the transformer 30 by the pair of primary-side DC buses P1 and N1.

[0018] The primary bridge circuit 130 is a full bridge circuit having a plurality of legs 11 and 12 .

[0019] The primary-side bridge circuit 130 has, for example, a leg 11 in which a high-side arm Q1 and a low-side arm Q2 are connected in series, and a 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 leg 11 is an example of a first leg, and the leg 12 is an example of a second leg.

[0020] The primary-side bridge circuit 130 is a full-bridge circuit in which a primary winding 31 of a transformer 30 is provided in a bridge portion 21 that connects 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-side bridge circuit 130 may include a reactor in the bridge portion 21 that is connected in series to the primary winding 31 of the transformer 30. The intermediate connection point a1 is an example of a first connection point. The intermediate connection point b1 is an example of a second connection point. The bridge portion 21 is an example of a first bridge portion.

[0021] The primary bridge circuit 130 includes a capacitor C1 and arms Q1 to Q4.

[0022] The capacitor C1 is connected between the pair of DC buses P1 and N1 on the primary side, and smoothes the voltage between the pair of DC buses P1 and N1 (the voltage of the capacitor C1).

[0023] The arms Q1 to Q4 are primary-side switching elements, and specific examples thereof include semiconductor switching elements such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors).

[0024] Leg 11 includes a configuration in which arms Q1 and Q2 are connected in series between the pair of DC buses P1 and N1, and leg 12 includes a configuration in which arms Q3 and Q4 are connected in series between the pair of DC buses P1 and N1. Each of arms Q1 to Q4 has a first main terminal, a second main terminal, and a control terminal. For example, the first main terminal corresponds to the drain or collector, the second main terminal corresponds to the source or emitter, and the control terminal corresponds to the gate. Arms Q1 to Q4 may include a diode connected in reverse between the main terminals. If arms Q1 to Q4 are MOSFETs, this diode may be a parasitic diode. FIG. 1 illustrates freewheeling diodes D1, D2, D3, and D4.

[0025] With this configuration, when the arms Q1 and Q4 are turned on and the arms Q2 and Q3 are turned off, the primary-side bridge circuit 130 electrically connects the intermediate node a1 to the DC bus P1 and electrically connects the intermediate node b1 to the DC bus N1, causing the voltage V1 between the intermediate node a1 and the intermediate node b1 to be a positive voltage "E1." E1 is the voltage value between the DC bus pair P1 and N1. Furthermore, when the arms Q1 and Q4 are turned off and the arms Q2 and Q3 are turned on, the primary-side bridge circuit 130 electrically connects the intermediate node a1 to the DC bus N1 and electrically connects the intermediate node b1 to the DC bus P1, causing the voltage V1 to be a negative voltage "-E1." In this way, the primary-side bridge circuit 130 switches the polarity of the voltage applied to the primary winding 31 of the transformer 30 by the primary-side DC bus pair P1 and N1.

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

[0027] The secondary bridge circuit 140 is connected to secondary DC terminals (positive terminal and negative terminal) and exchanges power with an external device connected to the secondary DC terminals. The secondary bridge circuit 140 is also connected to the secondary side of the transformer 30 and exchanges power with the secondary winding 32 of the transformer 30.

[0028] The secondary bridge circuit 140 has a pair of secondary DC buses P2 and N2, and has a positive terminal of the secondary DC terminal connected to the positive DC bus P2 and a negative terminal of the secondary DC terminal connected to the negative DC bus N2. The secondary bridge circuit 140 switches the polarity of the voltage applied to the secondary winding 32 of the transformer 30 by the pair of secondary DC buses P2 and N2.

[0029] The secondary bridge circuit 140 is a full bridge circuit having a plurality of legs 13 and 14 .

[0030] The secondary-side bridge circuit 140 includes, for example, a leg 13 in which a high-side arm Q5 and a low-side arm Q6 are connected in series, and a 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 leg 13 is an example of a third leg, and the leg 14 is an example of a fourth leg.

[0031] The secondary-side bridge circuit 140 is a full-bridge circuit in which a secondary winding 32 of a transformer 30 is provided in a bridge portion 23 that connects an intermediate connection point a2 between the arms Q5 and Q6 and an intermediate connection point b2 between the arms Q7 and Q8. The secondary-side bridge circuit 140 may include a reactor in the bridge portion 23 that is connected in series with the secondary winding 32 of the transformer 30. The intermediate connection point a2 is an example of a third connection point. The intermediate connection point b2 is an example of a fourth connection point. The bridge portion 23 is an example of a second bridge portion.

[0032] The secondary bridge circuit 140 includes a capacitor C2 and arms Q5 to Q8.

[0033] The capacitor C2 is connected between the pair of DC buses P2 and N2 on the secondary side, and smoothes the voltage between the pair of DC buses P2 and N2 (the voltage of the capacitor C2).

[0034] The arms Q5 to Q8 are secondary-side switching elements, and specific examples thereof include semiconductor switching elements such as MOSFETs and IGBTs, similar to the arms Q1 to Q4.

[0035] Leg 13 includes a configuration in which arms Q5 and Q6 are connected in series between the pair of DC buses P2 and N2, and leg 14 includes a configuration in which arms Q7 and Q8 are connected in series between the pair of DC buses P2 and N2. Similar to arms Q1 to Q4, arms Q5 to Q8 each have a first main terminal, a second main terminal, a control terminal, and a diode. Fig. 1 illustrates freewheeling diodes D5, D6, D7, and D8.

[0036] With this configuration, when the arms Q5 and Q8 are turned on and the arms Q6 and Q7 are turned off, the secondary-side bridge circuit 140 electrically connects the intermediate node a2 to the DC bus P2 and electrically connects the intermediate node b2 to the DC bus N2, causing the voltage V2 between the intermediate node a2 and the intermediate node b2 to be a positive voltage "E2." E2 is the voltage value between the DC bus pair P2 and N2. Furthermore, when the arms Q5 and Q8 are turned off and the arms Q6 and Q7 are turned on, the secondary-side bridge circuit 140 electrically connects the intermediate node a2 to the DC bus N2 and electrically connects the intermediate node b2 to the DC bus P2, causing the voltage V2 to be a negative voltage "-E2." In this way, the secondary-side bridge circuit 140 switches the polarity of the voltage applied to the secondary winding 32 of the transformer 30 by the secondary-side DC bus pair P2 and N2.

[0037] Furthermore, when the arms Q5 and Q7 are turned on and the arms Q6 and Q8 are turned off, the secondary-side bridge circuit 140 electrically connects both the intermediate node a2 and the intermediate node b2 to the DC bus P2, thereby making 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-side bridge circuit 140 electrically connects both the intermediate node a2 and the intermediate node b2 to the DC bus N2, thereby making the voltage V2 substantially zero.

[0038] The control device 150 is a controller that controls the primary-side bridge circuit 130 and the secondary-side bridge circuit 140. The control device 150 controls the switching phase difference (hereinafter also referred to as phase difference δ) between the primary-side bridge circuit 130 and the secondary-side bridge circuit 140 so that power is transmitted between the primary-side bridge circuit 130 and the secondary-side bridge circuit 140. The control device 150 adjusts the power transmitted between the primary-side bridge circuit 130 and the secondary-side bridge circuit 140 by controlling the phase difference δ between the voltage V1 and the voltage V2. The control device 150 outputs control signals g1 to g4 for controlling the on / off of control terminals of the arms Q1 to Q4 of the primary-side bridge circuit 130, and control signals g5 to g8 for controlling the on / off of control terminals of the arms Q5 to Q8 of the secondary-side bridge circuit 140. The control signals g1 to g8 are signals for controlling the on / off of corresponding arms among the arms Q1 to Q8.

[0039] The power conversion device 100 includes a primary-side GDU 160 and a secondary-side GDU 170. The primary-side GDU 160 is a primary-side drive circuit that controls the on / off switching of arms Q1 to Q4 of the primary-side bridge circuit 130 in accordance with control signals g1 to g4. The secondary-side GDU 170 is a secondary-side drive circuit that controls the on / off switching of arms Q5 to Q8 of the secondary-side bridge circuit 140 in accordance with control signals g5 to g8.

[0040] The control device 150 acquires the DC voltage detection values ​​of the primary-side bridge circuit 130 and the secondary-side bridge circuit 140, and the DC current detection value of one of the bridge circuits (for example, the secondary-side bridge circuit 140). Based on these detection values ​​and a current or power command value, the control device 150 generates control signals g1 to g8 for controlling the power transmitted between the bridges, and controls the arms Q1 to Q8. For example, the control device 150 acquires a voltage detection value E1, a voltage detection value E2, and a current detection value I2, and based on these detection values ​​and a current command value I2*, generates control signals g1 to g8 for controlling the power transmitted between the bridges, and controls the arms Q1 to Q8.

[0041] The voltage detection value E1 is the detection value of the DC voltage of the primary-side bridge circuit 130, more specifically, the detection value of the voltage E1 between the pair of DC buses P1 and N1. The voltage detection value E2 is the detection value of the DC voltage of the secondary-side bridge circuit 140, more specifically, the detection value of the voltage E2 between the pair of DC buses P2 and N2. The current detection value I2 is the detection value of the secondary-side DC current I2 flowing in the secondary-side bridge circuit 140, more specifically, the detection value of the secondary-side DC current I2 flowing in the DC bus P2. The current command value I2* is the command value of the secondary-side DC current I2 flowing in the secondary-side bridge circuit 140, more specifically, the command value of the secondary-side DC current I2 flowing in the DC bus P2. The command value is also referred to as a target value.

[0042] Fig. 2 is a block diagram showing an example of the configuration of the main parts of a control device. In the example shown in Fig. 2, the control device 150 determines a switching phase difference δ between the primary side bridge circuit 130 and the secondary side bridge circuit 140 so that the secondary side DC current I2 flowing through the secondary side bridge circuit 140 follows the current command value I2*. The control device 150 has a current control unit 51, a signal generation unit 56, and a leg control unit 52. The signal generation unit 56 has a gate signal generation unit 53 and logical product circuits 56a, 56b, 56e, and 56f.

[0043] The current control unit 51 calculates a switching phase difference δ between the primary side bridge circuit 130 and the secondary side bridge circuit 140 based on the current detection value I2 of the secondary side DC current and the current command value I2* of the secondary side DC current. The current control unit 51 determines the phase difference δ between the AC voltage V1 of the primary side bridge circuit 130 and the AC voltage V2 of the secondary side bridge circuit 140, for example, so that the current detection value I2 follows the current command value I2*.

[0044] The current control unit 51 includes, for example, a subtractor 54 and a PI regulator 55. The subtractor 54 calculates the difference (current difference ΔI) between the current command value I2* and the current detection value I2. The PI regulator 55 calculates a phase difference δ by PI control or PID control (P: proportional control, I: integral control, D: differential control) such that the current difference ΔI calculated by the subtractor 54 converges to zero.

[0045] The gate signal generating unit 53 generates gate signals g10 to g80 based on the phase difference δ output from the current control unit 51. A well-known method may be used to generate the gate signals g10 to g80 based on the phase difference δ. The gate signals g10 to g80 are control signals for controlling the on / off of the corresponding arms among the arms Q1 to Q8.

[0046] The AND circuit 56a outputs a control signal g1, which is the logical product of the gate signal g10 and the pulse-off command POFF1. The AND circuit 56b outputs a control signal g2, which is the logical product of the gate signal g20 and the pulse-off command POFF1. The AND circuit 56e outputs a control signal g5, which is the logical product of the gate signal g50 and the pulse-off command POFF2. The AND circuit 56f outputs a control signal g6, which is the logical product of the gate signal g60 and the pulse-off command POFF2. The control signals g3, g4, g7, and g8 are the same as the corresponding gate signals g30, g40, g70, and g80.

[0047] The leg control unit 52 determines a pulse-off command POFF1 for the primary leg and a pulse-off command POFF2 for the secondary leg, as shown in the table in Fig. 2, based on the detected voltage value E1 of the primary-side DC voltage, the detected voltage value E2 of the secondary-side DC voltage, and the current command value I2* of the secondary-side DC current. The pulse-off command POFF1 is a command to turn off the arms on both sides of one of the primary legs 11 and 12. The pulse-off command POFF2 is a command to turn off the arms on both sides of one of the secondary legs 13 and 14.

[0048] In this example, the pulse-off command POFF1 is a command to turn off the high-side arm Q1 and the low-side arm Q2 of the primary-side leg 11. When the pulse-off command POFF1 is 0, it represents a command to turn off the arms Q1 and Q2. When the pulse-off command POFF1 is 1, it represents a command to turn on the arms Q1 and Q2. The pulse-off command POFF2 is a command to turn off the high-side arm Q5 and the low-side arm Q6 of the secondary-side leg 13. When the pulse-off command POFF2 is 0, it represents a command to turn off the arms Q5 and Q6. When the pulse-off command POFF2 is 1, it represents a command to turn on the arms Q5 and Q6.

[0049] 2, when I2* is a positive value, it represents a command to transmit power from the primary-side bridge circuit 130 to the secondary-side bridge circuit 140. When I2* is a negative value, it represents a command to transmit power from the secondary-side bridge circuit 140 to the primary-side bridge circuit 130. When I2* is zero, it represents a command to stop power transmission between the primary-side bridge circuit 130 and the secondary-side bridge circuit 140.

[0050] When power is transmitted from the low-voltage side bridge circuit to the high-voltage side bridge circuit under conditions where E1 and E2 are different, one leg of the high-voltage side bridge circuit is controlled to the off state by the pulse-off commands POFF1 and POFF2 generated by the leg control unit 52 according to the table in FIG. 2.

[0051] 3 is a timing chart illustrating control signals g1 to g8 when power is transmitted from the secondary-side bridge circuit to the primary-side bridge circuit under the condition that the DC voltage of the primary-side bridge circuit is higher than the DC voltage of the secondary-side bridge circuit. ωt on the horizontal axis represents the phase. In the control signals g1 to g8, a high level indicates an ON state, and a low level indicates an OFF state.

[0052] In the case of FIG. 3, the pulse-off command POFF1 is set to 0 according to the conditions in the table in FIG. 2, so that the control signals g1 and g2 for the arms Q1 and Q2 of the primary leg 11 are fixed to a low level (0) by the logical product circuits 56a and 56b (FIG. 2). In this case, the arms Q1 and Q2 are fixed to an off state regardless of the logic levels of the gate signals g10 and g20 (FIG. 2). On the other hand, the pulse-off command POFF2 is set to 1 according to the conditions in the table in FIG. 2, so that the control signals g5 and g6 for the arms Q5 and Q6 of the secondary leg 13 are not fixed to a low level (0) by the logical product circuits 56e and 56f. In this case, the arms Q5 and Q6 are switched at a predetermined duty cycle having a pulse width π according to the off or on logic levels of the gate signals g50 and g60 (FIG. 2). Arms Q3 and Q4 of primary leg 12 and arms Q7 and Q8 of secondary leg 14 switch at a predetermined duty cycle having a pulse width π according to the off or on logic level of gate signals g30, g40, g70, and g80 (FIG. 2).

[0053] 3, the control device 150 fixes the arms Q1 and Q2 in the OFF state, and alternates between a state in which the arm Q3 is OFF and the arm Q4 is ON and a state in which the arm Q3 is ON and the arm Q4 is OFF, and alternates between a state in which the arms Q5 and Q8 are ON and the arms Q6 and Q7 are OFF and a state in which the arms Q5 and Q8 are OFF and the arms Q6 and Q7 are ON. There is a phase difference δ between the control signal g4 and the control signal g5, and the control signal g4 lags behind the control signal g5 by the phase difference δ.

[0054] 4 is a timing chart illustrating control signals g1 to g8 when power is transmitted from the primary-side bridge circuit to the secondary-side bridge circuit under the condition that the DC voltage of the primary-side bridge circuit is lower than the DC voltage of the secondary-side bridge circuit. ωt on the horizontal axis represents the phase. In the control signals g1 to g8, a high level indicates an ON state, and a low level indicates an OFF state.

[0055] In the case of FIG. 4, the pulse-off command POFF2 is set to 0 according to the conditions in the table in FIG. 2, so that the control signals g5 and g6 of the arms Q5 and Q6 of the secondary leg 13 are fixed to a low level (0) by the AND circuits 56e and 56f (FIG. 2). In this case, the arms Q5 and Q6 are fixed to an OFF state regardless of the logic levels of the gate signals g50 and g60 (FIG. 2). On the other hand, the pulse-off command POFF1 is set to 1 according to the conditions in the table in FIG. 2, so that the control signals g1 and g2 of the arms Q1 and Q2 of the primary leg 11 are not fixed to a low level (0) by the AND circuits 56a and 56b. In this case, the arms Q1 and Q2 are switched at a predetermined duty cycle having a pulse width π according to the OFF or ON logic levels of the gate signals g10 and g20 (FIG. 2). Arms Q3 and Q4 of primary leg 12 and arms Q7 and Q8 of secondary leg 14 switch at a predetermined duty cycle having a pulse width π according to the off or on logic level of gate signals g30, g40, g70, and g80 (FIG. 2).

[0056] 4, the control device 150 fixes the arms Q5 and Q6 in the OFF state, and alternates between a state in which the arm Q7 is OFF and the arm Q8 is ON and a state in which the arm Q7 is ON and the arm Q8 is OFF, and alternates between a state in which the arms Q1 and Q4 are ON and the arms Q2 and Q3 are OFF and a state in which the arms Q1 and Q4 are OFF and the arms Q2 and Q3 are ON. There is a phase difference δ between the control signal g4 and the control signal g8, and the control signal g4 leads the control signal g8 by the phase difference δ.

[0057] Fig. 5 is a diagram showing an example of a simulated operating waveform when the SPS method is applied. Fig. 6 is a diagram showing an example of a simulated operating waveform when the new method according to the present disclosure is applied. The simulation conditions in Figs. 5 and 6 are as follows: E1 <E2 Power transmission direction: from primary side to secondary side is.

[0058] 5 shows control signals g1 to g8 for arms Q1 to Q8, AC voltages V1 and V2 of the primary-side bridge circuit 130 and the secondary-side bridge circuit 140, and AC current Iac1 (current flowing through the primary winding 31) of the primary-side bridge circuit 130 when the SPS method is applied. For convenience, the symbols used are the same as those in FIG. 1.

[0059] In FIG. 5, the AC current Iac1 includes a current component ir that transfers power in the reverse direction from the secondary side to the primary side. To transfer commanded power from the primary side to the secondary side, the power conversion device 100 additionally flows a current component if equivalent to the current component ir in the forward direction from the primary side to the secondary side. These current components ir and if are called circulating currents or reactive currents. When power is transferred under conditions where the DC voltage E1 on the primary side and the DC voltage E2 on the secondary side are not equal, particularly under light loads, as shown in FIG. 5, the proportion of the circulating current in the AC current Iac1 increases. The circulating current (current components ir and if) that does not contribute to power transfer increases the conduction loss of semiconductor devices such as arms Q1 to Q8 and the copper loss of the transformer 30, reducing the power conversion efficiency of the power conversion device 100.

[0060] FIG. 6 shows the control signals g1 to g8 for arms Q1 to Q8, the AC voltages V1 and V2 of the primary side bridge circuit 130 and the secondary side bridge circuit 140, and the AC current Iac1 of the primary side bridge circuit 130 (the current flowing through the primary winding 31) when the new method is applied.

[0061] In Fig. 6, a command is given to transmit power from the low-voltage primary side to the high-voltage secondary side under the condition that E1 < E2. Therefore, the control signals g5 and g6 of the arms Q5 and Q6 of leg 13 of the high-voltage side bridge circuit become 0 by the leg control unit 52, and thus the arms Q5 and Q6 are in the off state respectively. Since arm Q5 functions as a diode by the freewheeling diode D5 and arm Q6 functions as a diode by the freewheeling diode D6, leg 13 operates as a diode. Due to the diode operation of leg 13, the circulating current (current component ir) that does not contribute to power transmission is reduced, and an increase in the conduction loss of semiconductor devices such as arms Q1 to Q8 and the copper loss of transformer 30 is suppressed. As a result, compared with the case where the SPS method of Fig. 5 is applied, the circulating current component of the alternating current Iac1 is reduced, and thus the power conversion efficiency of the power conversion device 100 is increased.

[0062] Thus, when the power conversion device or its control method according to the present embodiment transmits power from the bridge circuit with a lower DC voltage to the bridge circuit with a higher DC voltage under the condition that the DC voltage E1 on the primary side and the DC voltage E2 on the secondary side are different, among legs 11, 12, 13, and 14, the arms on both sides of any one leg of the bridge circuit with a higher DC voltage are turned off, and the on-state and off-state of each arm of the remaining legs are controlled. By such a simple control, the circulating current component is reduced, and thus high efficiency of the power conversion device 100 can be achieved.

[0063] In the present disclosure, the control circuit, control device, controller or control unit is an electronic circuit such as a CPU (Central Processing Unit), FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit). The control circuit, control device, controller or control unit may also be a computer having a memory and a processor. The control circuit, control device, controller or control unit executes various control operations described in this specification by executing a program such as instruction codes stored in the memory or by being circuit-designed for special purposes.

[0064] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0065] For example, the pulse-off command POFF1 may be a command to turn off the arms Q3 and Q4 of the leg 12 on the primary side, and the pulse-off command POFF2 may be a command to turn off the arms Q7 and Q8 of the leg 14 on the secondary side. [Explanation of symbols]

[0066] 100 Power conversion device Legs 11, 12, 13, and 14 21,23 Bridge part 30 Transformer 31 Primary Winding 32 Secondary Winding 51 Current control section 52 Leg control section 53 Gate signal generator 54 Subtractor 55 PI regulator 56 Signal generation unit 56a, 56b, 56e, 56f logical product circuits 130 Primary side bridge circuit 140 Secondary bridge circuit 150 control device 160 Primary GDU 170 Secondary GDU 180 DC / DC Converter C1, C2 capacitors D1~D8 Freewheeling diodes Q1~Q8 Arms

Claims

1. a transformer having a primary winding and a secondary winding; a primary-side bridge circuit having a first leg in which a high-side first arm and a low-side second arm are connected in series, and a second leg in which a high-side third arm and a low-side fourth arm 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 secondary-side 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; and a control device that, when power is transferred from a bridge circuit with a lower DC voltage to a bridge circuit with a higher DC voltage under a condition where the DC voltage of the primary side bridge circuit and the DC voltage of the secondary side bridge circuit are different, sets arms on both sides of any one of the first to fourth legs of the bridge circuit with a higher DC voltage to an off state and controls the on state and off state of each arm of each of the remaining legs.

2. 2. The power conversion device according to claim 1, wherein, when transferring power from the secondary side bridge circuit to the primary side bridge circuit under a condition in which a DC voltage of the primary side bridge circuit is higher than a DC voltage of the secondary side bridge circuit, the control device keeps the first arm and the second arm in an off state, and repeats a state in which the third arm is off and the fourth arm is on and a state in which the third arm is on and the fourth arm is off, and repeats a state in which the fifth arm and the eighth arm are on and the sixth arm and the seventh arm are off, and a state in which the fifth arm and the eighth arm are off and the sixth arm and the seventh arm are on.

3. 3. The power conversion device according to claim 2, wherein, when transferring power from the primary side bridge circuit to the secondary side bridge circuit under a condition where the DC voltage of the primary side bridge circuit is lower than the DC voltage of the secondary side bridge circuit, the control device keeps the fifth arm and the sixth arm in an off state, and repeats a state where the seventh arm is off and the eighth arm is on and a state where the seventh arm is on and the eighth arm is off, and repeats a state where the first arm and the fourth arm are on and the second arm and the third arm are off and a state where the first arm and the fourth arm are off and the second arm and the third arm are on.

4. a transformer having a primary winding and a secondary winding; a primary-side bridge circuit having a first leg in which a high-side first arm and a low-side second arm are connected in series, and a second leg in which a high-side third arm and a low-side fourth arm 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 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, and the secondary winding is 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 method for a power conversion device, wherein, when power is transmitted from a bridge circuit having a lower DC voltage to a bridge circuit having a higher DC voltage under a condition where the DC voltage of the primary side bridge circuit and the DC voltage of the secondary side bridge circuit are different, arms on both sides of any one of the first to fourth legs of the bridge circuit having a higher DC voltage are set to an off state, and the on state and off state of each arm of each of the remaining legs are controlled.

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