Power conversion device and control method thereof

Abstract

To provide a power conversion device capable of suppressing a voltage to the ground, and a control method thereof.SOLUTION: A power conversion device includes a transformer (30) having a primary winding (31) and a secondary winding (32), a primary bridge circuit (130) configured to switch a first voltage (v1) to be applied to the primary winding, a secondary bridge circuit (140) configured to switch a second voltage (v2) to be applied to the secondary winding, and a control device configured to select a second switching pattern (SP1) in which a ground-referenced voltage (VPG) between a ground and a DC bus of the secondary bridge circuit is lower than in the first switching pattern (SP2) during a period in which the first voltage or the second voltage is zero.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] BACKGROUND ART A bidirectional isolated DC / DC converter in which two bridge circuits are connected via a transformer is known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 121665 Summary of the Invention [Problem to be solved by the invention]

[0004] The voltage to ground between the ground and the DC bus of the bridge circuit fluctuates with the switching operation of the bridge circuit. High-frequency leakage currents caused by the fluctuations in the voltage to ground can adversely affect other devices connected to the power conversion device.

[0005] The present disclosure provides a power conversion device capable of suppressing voltage to ground and a control method thereof. [Means for solving the problem]

[0006] In a first aspect of the present disclosure, a transformer having a primary winding and a secondary winding; a primary-side bridge circuit that switches a first voltage applied to the primary winding; a secondary-side bridge circuit that switches a second voltage applied to the secondary winding; and a control device that selects a second switching pattern in which the voltage to ground between the ground and the DC bus of the secondary side bridge circuit is lower than that of the first switching pattern during a period in which the first voltage or the second voltage is zero.

[0007] In a second aspect of the present disclosure, a transformer having a primary winding and a secondary winding; a primary-side bridge circuit that switches a first voltage applied to the primary winding; a secondary-side bridge circuit that switches a second voltage applied to the secondary winding, There is provided a control method for a power conversion device, which selects a second switching pattern in which the voltage to ground between the ground and the DC bus of the secondary side bridge circuit is lower than that of a first switching pattern, and switches the primary side bridge circuit and the secondary side bridge circuit using the second switching pattern during a period in which the first voltage or the second voltage is zero. [Effects of the Invention]

[0008] According to the present disclosure, the voltage to ground can be suppressed. [Brief explanation of the drawings]

[0009] [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 diagram for explaining a voltage to ground. [Figure 3] 10 is a diagram showing an example of a period in which the first voltage or the second voltage is set to zero voltage. FIG. [Figure 4] FIG. 10 is a diagram showing an example of list data of a plurality of switching pattern candidates in which the first voltage or the second voltage is set to zero voltage. [Figure 5] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 1 of operation mode A and a calculation formula for voltage to ground. FIG. [Figure 6]10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 2 of operation mode A and a calculation formula for voltage to ground. FIG. [Figure 7] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 3 of operation mode B and a calculation formula for voltage to ground. FIG. [Figure 8] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 4 of operation mode B and a calculation formula for voltage to ground. FIG. [Figure 9] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 5 of operation mode C and a calculation formula for voltage to ground. FIG. [Figure 10] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 6 of operation mode C and a calculation formula for voltage to ground. FIG. [Figure 11] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 7 of operation mode D and a calculation formula for voltage to ground. FIG. [Figure 12] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 8 of operation mode D and a calculation formula for voltage to ground. FIG. [Figure 13] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 9 of operation mode E and a calculation formula for voltage to ground. FIG. [Figure 14] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in a switching pattern 10 of an operation mode E and a calculation formula for a voltage to ground. FIG. [Figure 15] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 11 of operation mode F and a calculation formula for voltage to ground. FIG. [Figure 16] 10 is a diagram showing a common mode equivalent circuit of a power conversion device in switching pattern 12 of operation mode F and a calculation formula for voltage to ground. FIG. [Figure 17] FIG. 2 is a diagram illustrating an example of the configuration of a control device. [Figure 18] 10 is a timing chart for explaining a method for suppressing a voltage to ground. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] 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.

[0012] The power conversion device 100 includes a transformer 30, a primary bridge circuit 130, a secondary bridge circuit 140, and a control device 150.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] The primary bridge circuit 130 is a full bridge circuit having a plurality of legs 11 and 12 .

[0017] 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.

[0018] 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.

[0019] The primary bridge circuit 130 includes a capacitor C1 and arms Q1 to Q4.

[0020] The capacitor C1 is connected between the DC bus pair P1 and N1 on the primary side, and the voltage V between the DC bus pair P1 and N1 in (Voltage of capacitor C1) is smoothed.

[0021] 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).

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Voltage V1 is an example of a first voltage. "Making voltage V1 substantially zero" means making the first voltage zero. "Making the first voltage zero" does not necessarily mean making the first voltage strictly zero. The zero voltage includes an error voltage due to a voltage drop in each arm, etc., and may be a very small positive voltage slightly larger than zero or a very small negative voltage slightly smaller than zero.

[0026] 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.

[0027] 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.

[0028] The secondary bridge circuit 140 is a full bridge circuit having a plurality of legs 13 and 14 .

[0029] 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.

[0030] 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.

[0031] The secondary bridge circuit 140 includes a capacitor C2 and arms Q5 to Q8.

[0032] The capacitor C2 is connected between the DC bus pair P2 and N2 on the secondary side, and the voltage V between the DC bus pair P2 and N2 out (Voltage of capacitor C2) is smoothed.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Voltage V2 is an example of the second voltage. "Making voltage V2 substantially zero" means making the second voltage zero. "Making the second voltage zero" does not necessarily mean making the second voltage strictly zero. The zero voltage includes an error voltage due to a voltage drop in each arm, etc., and may be a very small positive voltage slightly larger than zero or a very small negative voltage slightly smaller than 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 a detection value of the DC voltage of the primary side bridge circuit 130, and more specifically, the voltage V between the DC bus pair P1 and N1. in The voltage detection value E2 is a detection value of the DC voltage of the secondary bridge circuit 140, and more specifically, the voltage V between the DC bus pair P2 and N2. out The current detection value I2 is a detection value of the secondary side DC current I2 flowing through the secondary side bridge circuit 140, more specifically, a detection value of the secondary side DC current I2 flowing through the DC bus P2. The current command value I2* is a command value of the secondary side DC current I2 flowing through the secondary side bridge circuit 140, more specifically, a command value of the secondary side DC current I2 flowing through the DC bus P2. The command value is also called a target value.

[0042] The control device 150 has a current control unit that calculates 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 current control unit calculates, for example, the difference between the current command value I2* and the current detection value I2 (current difference ΔI), and calculates the phase difference δ by PI control or PID control such that the calculated current difference ΔI converges to zero (P: proportional control, I: integral control, D: differential control).

[0043] The control device 150 has a duty ratio calculation unit that calculates a duty ratio D1 of the voltage V1 of the primary-side bridge circuit 130 and a duty ratio D2 of the voltage V2 of the secondary-side bridge circuit 140 based on the voltage detection values ​​E1 and E2. For example, when the voltage detection values ​​E1 and E2 differ, the duty ratio calculation unit adjusts the duty ratios D1 and D2 so as to satisfy D1 / D2=E1 / E2.

[0044] When the detected voltage values ​​E1 and E2 are equal, the duty ratio calculation unit fixes the duty ratio D1 of voltage V1 and the duty ratio D2 of voltage V2 to 1 (pulse width W1 of voltage V1 = pulse width W2 of voltage V2 = π).When the detected voltage value E1 is lower than the detected voltage value E2, the duty ratio calculation unit fixes the duty ratio D1 of voltage V1 to 1 (pulse width W1 = π) and adjusts the duty ratio D2 of voltage V2 to satisfy D2 = E2 / E1 (pulse width W2 = E2 / E1 × π).When the detected voltage value E1 is higher than the detected voltage value E2, the duty ratio calculation unit fixes the duty ratio D2 of voltage V2 to 1 (pulse width W2 = π) and adjusts the duty ratio D1 of voltage V1 to satisfy D1 = E1 / E2 (pulse width W1 = E1 / E2 × π).

[0045] The pulse width W1 of the voltage V1 is determined by the duty ratio D1, and the pulse width W2 of the voltage V2 is determined by the duty ratio D2.

[0046] The control device 150 generates control signals g1 to g8 based on the phase difference δ output from the current control unit and the duty ratios D1, D2 (pulse widths W1, W2) output from the duty ratio calculation unit. A known method may be used to generate the control signals g1 to g8 based on the phase difference δ and the duty ratios D1, D2 (pulse widths W1, W2).

[0047] Next, the voltage to ground will be described.

[0048] 2 is a diagram for explaining the voltage to ground. As the arms Q1 to Q8 are switched, the potentials of the intermediate nodes a1, b1, a2, and b2 change, and the voltage to ground V PG ,V NG The voltage V to ground shown in Figure 2 fluctuates. PG represents the potential difference between the ground G and the DC bus P2, and is the voltage V NG indicates the potential difference between the ground G and the DC bus N2.

[0049] The ground G is a conductive part that is grounded to the earth. Examples of the ground G include a housing that covers the power conversion device, a heat sink 40 that dissipates heat from the arms Q5 to Q8, etc. However, the examples of the ground G are not limited to these.

[0050] Voltage to ground V PG ,V NG The magnitude of each of C depends on the capacitance of the stray capacitance due to the transformer 30 and arms Q1 to Q8. P2 represents the stray capacitance between the ground G and the DC bus P2. U2 represents the stray capacitance between the ground G and the intermediate connection point a2. N2 represents the stray capacitance between the ground G and the DC bus N2. V2 represents the stray capacitance between ground G and intermediate node b2. Tr1 ,C Tr2 represents the stray capacitance of the transformer 30.

[0051] Voltage to ground V PG ,V NG The high-frequency leakage current (common mode current) generated by the fluctuations in the voltage flows through the stray capacitance to the ground G. The common mode current may have adverse effects, such as deterioration, on other devices connected to the power conversion device (for example, batteries connected to the DC bus pair P2, N2).

[0052] The control device 150 controls the voltage V to ground during a period when the voltage V1 or the voltage V2 is zero (zero voltage period). PG Select a switching pattern that makes the voltage V to ground lower than other switching patterns. PG Hereinafter, for convenience, the other switching pattern will be referred to as the first switching pattern SP1, and the voltage to ground V PG The switching pattern in which is lower than the other switching patterns is referred to as a second switching pattern SP2.

[0053] The control device 150 switches the primary-side bridge circuit 130 and the secondary-side bridge circuit 140 in the second switching pattern SP2 during the zero voltage period. By selecting the second switching pattern SP2, the voltage V PG is suppressed. PG is suppressed, the voltage to ground V PG Since high frequency leakage current caused by fluctuations in the power supply voltage is also suppressed, adverse effects such as deterioration on other devices connected to the power conversion device can be reduced.

[0054] By selecting the second switching pattern SP2, the voltage to ground V PG Therefore, for example, the voltage V to ground can be reduced by reducing the design of each stray capacitance due to the structure of the transformer 30 or the structure of the semiconductor switching elements used in the arms Q1 to Q8, or by inserting an EMI filter. PG This makes it easier to reduce costs and size compared to methods that suppress this.

[0055] 3 is a diagram showing an example of a period (zero voltage period) in which the first voltage (voltage V1) or the second voltage (voltage V2) is zero voltage. in is the DC voltage V of the secondary bridge circuit 140 OUT 3, a zero voltage period occurs in which the voltage V1 is zero and the voltage V2 is a positive voltage "E2" or a negative voltage "-E2." The control device 150 selects a switching pattern candidate from among a plurality of switching pattern candidates in which the voltage V1 or the voltage V2 is zero, and adjusts the duty ratio D2 of the voltage V2 to 1 (pulse width W2=π) and the duty ratio D1 of the voltage V1 to satisfy D1=E1 / E2 (pulse width W1=E1 / E2×π). PG The second switching pattern SP2 is selected so that the voltage V to ground during the zero voltage period is lower than that of the first switching pattern SP1. PG is suppressed.

[0056] FIG. 4 is a diagram showing an example of list data of a plurality of switching pattern candidates in which the first voltage (voltage V1) or the second voltage (voltage V2) is set to zero voltage.

[0057] In operation mode A, voltage V1 is connected to a positive voltage "V in The switching pattern 1 includes two switching patterns 1 and 2 in which a1 is electrically connected to the DC bus P1 and b1 is electrically connected to the DC bus N1, and the voltage V1 is set to a positive voltage "V in =E1", and both a2 and b2 are electrically connected to the DC bus N2, and the voltage V2 is set to zero. In switching pattern 2, a1 is electrically connected to the DC bus P1, and b1 is electrically connected to the DC bus N1, and the voltage V1 is set to a positive voltage "V in =E1", and both a2 and b2 are electrically connected to the DC bus P2, making the voltage V2 zero.

[0058] In operation mode B, voltage V1 is set to a negative voltage "-V in The switching pattern 3 includes two switching patterns 3 and 4 in which a1 is electrically connected to the DC bus N1 and b1 is electrically connected to the DC bus P1, and the voltage V1 is set to a negative voltage "-V in =-E1", and both a2 and b2 are electrically connected to the DC bus N2, making the voltage V2 zero. Switching pattern 4 electrically connects a1 to the DC bus N1 and b1 to the DC bus P1, making the voltage V1 a negative voltage "-V in =-E1", and both a2 and b2 are electrically connected to the DC bus P2, making the voltage V2 zero.

[0059] In operation mode C, voltage V1 is set to zero voltage and voltage V2 is set to a positive voltage "V out The switching pattern 5 includes two switching patterns 5 and 6 in which a1 and b1 are both connected to the DC bus N1, the voltage V1 is zero, and a2 is electrically connected to the DC bus P2 and b2 is electrically connected to the DC bus N2, and the voltage V2 is a positive voltage "V out=E2". In switching pattern 6, both a1 and b1 are connected to the DC bus P1, the voltage V1 is set to zero voltage, and a2 is electrically connected to the DC bus P2 and b2 is electrically connected to the DC bus N2, and the voltage V2 is set to a positive voltage "V out =E2".

[0060] In operation mode D, voltage V1 is set to zero voltage and voltage V2 is set to a negative voltage "-V out The switching pattern 7 includes two switching patterns 7 and 8 in which both a1 and b1 are connected to the DC bus N1, the voltage V1 is set to zero voltage, and a2 is electrically connected to the DC bus N2 and b2 is electrically connected to the DC bus P2, and the voltage V2 is set to a negative voltage "-V out In switching pattern 8, both a1 and b1 are connected to the DC bus P1, the voltage V1 is set to zero, and a2 is electrically connected to the DC bus N2 and b2 is electrically connected to the DC bus P2, and the voltage V2 is set to a negative voltage "-V out =-E2".

[0061] Operating mode E includes two switching patterns 9 and 10 in which both voltages V1 and V2 are zero. Switching pattern 9 connects both a1 and b1 to DC bus N1, causing voltage V1 to be zero, and connects both a2 and b2 to DC bus N2, causing voltage V2 to be zero. Switching pattern 10 connects both a1 and b1 to DC bus N1, causing voltage V1 to be zero, and connects both a2 and b2 to DC bus P2, causing voltage V2 to be zero.

[0062] Operation mode F includes two switching patterns 11 and 12 in which both voltages V1 and V2 are zero. Switching pattern 11 connects both a1 and b1 to DC bus P1, causing voltage V1 to be zero, and connects both a2 and b2 to DC bus N2, causing voltage V2 to be zero. Switching pattern 12 connects both a1 and b1 to DC bus P1, causing voltage V1 to be zero, and connects both a2 and b2 to DC bus P2, causing voltage V2 to be zero.

[0063] Figure 4 shows the voltage V to ground in each switching pattern where the first voltage (V1) or the second voltage (V2) is set to zero. PG The magnitude of the voltage to ground V PG The magnitude of varies depending on the switching pattern.

[0064] Figures 5 to 16 show the common mode equivalent circuits of the power conversion device in each switching pattern of each operating mode, and the voltage to ground V derived from the equivalent circuits. PG 5 to 16, the common mode equivalent circuit changes depending on each switching pattern, so the voltage to ground V PG The magnitude of varies depending on the switching pattern.

[0065] 4, the control device 150 selects, as the second switching pattern P2, one of switching patterns 2, 4, 10, and 12, which electrically connect both ends of the secondary winding 32 to the positive bus P2 during a period in which the voltage V2 is set to zero. When one of the switching patterns 2, 4, 10, and 12 is selected, the stray capacitance between the ground G (heat sink 40) and the DC bus P2 becomes larger than the stray capacitance between the ground G (heat sink 40) and the DC bus N2 (see FIGS. 6, 8, 14, and 16). As a result, the voltage V to ground PG can be reduced.

[0066] 4, the control device 150 sets the voltage V1 to zero voltage and the voltage V2 to a positive voltage "V out "or negative voltage" -V out During the period when " " is set to ", one of the switching patterns 5 and 7 is selected to electrically connect both ends of the primary winding 31 to the negative bus N1. When one of the switching patterns 5 and 7 is selected, the stray capacitance between the ground G (heat sink 40) and the DC bus P2 is equal to the stray capacitance C Tr1 ,C Tr2 through the voltage V in(See Figures 9 and 11.) This reduces the voltage to ground V PG can be reduced.

[0067] 17 is a diagram showing an example configuration of a control device. The control device 150 may select the second switching pattern SP2 based on, for example, a phase difference command related to the phase difference δ between the voltages V1 and V2 and a pulse width command related to the pulse width W1 of the voltage V1 or the pulse width W2 of the voltage V2. By using the phase difference command and the pulse width command, the control device 150 can identify a zero voltage period during which the voltage V1 or the voltage V2 is zero, and can therefore appropriately select the second switching pattern SP2 for the identified zero voltage period.

[0068] The control device 150 includes, for example, a command unit 51, a specification unit 52, and a selection unit 53.

[0069] The command unit 51 includes the current control unit and the duty ratio calculation unit, and generates a phase difference command related to the phase difference δ calculated by the current control unit and a pulse width command related to the duty ratios D1 and D2 (pulse widths W1 and W2) calculated by the duty ratio calculation unit.

[0070] The determination unit 52 determines the value of the voltage V1 (first voltage value v1) that the primary side bridge circuit 130 applies to the primary winding 31 and the value of the voltage V2 (second voltage value v2) that the secondary side bridge circuit 140 applies to the secondary winding 32 based on the phase difference command and the pulse width command.

[0071] One or both of the phase difference command and the pulse width command may be fixed values.

[0072] The selector 53 generates control signals g1 to g8 based on the first voltage value v1 and the second voltage value v2. For example, in a period in which the first voltage value v1 is a positive voltage "E1" and the second voltage value v2 is a positive voltage "E2," the selector 53 generates control signals g1 to g8 that create a switching pattern in which the voltage V1 is the positive voltage "E1" and the voltage V2 is the positive voltage "E2." The same applies to other periods. Therefore, the selector 53 can appropriately select the second switching pattern SP2 in the zero-voltage period based on the first voltage value v1 and the second voltage value v2, and generates control signals g1 to g8 that create the second switching pattern SP2.

[0073] The selector 53 may select the second switching pattern SP2 corresponding to the first voltage value v1 and the second voltage value v2 based on a plurality of switching pattern candidates in which the voltage V1 or the voltage V2 is zero voltage and the correspondence relationship between the voltage V1 and the voltage V2 (FIG. 4). For example, based on the list of FIG. 4, the selector 53 selects the switching pattern 2 as the second switching pattern SP2 in a period in which the first voltage value v1 is a positive voltage "E1" and the second voltage value v2 is zero voltage.

[0074] The control device 150 detects the voltage V PG The selection unit 53 may detect a plurality of switching pattern candidates in which the voltage V1 or the voltage V2 is zero voltage and a voltage V PG Based on the correspondence relationship (Figure 4), the voltage to ground V PG For example, the specifying unit 52 specifies a zero voltage period in which the voltage V1 or the voltage V2 is zero based on the phase difference command and the pulse width command. The specifying unit 52 then selects a second switching pattern SP2 corresponding to the detected value. PG , the V in the list in Figure 4 PG The selection unit 53 stores the voltage V PG The detected value of the voltage V to ground is calculated based on the list shown in Figure 4 stored for each switching pattern. PGis lower than the other switching patterns, is selected as the second switching pattern SP.

[0075] Figure 18 shows the voltage to ground V PG 1 is a timing chart for explaining a method for suppressing the voltage V. The first period T1 and the second period T2 are periods in which the voltage V1 and the voltage V2 are set to zero. PGA indicates the case where switching pattern 11 is selected in the first period T1 and switching pattern 10 is selected in the second period T2. PGB indicates a case where switching pattern 9 is selected in the first period T1 and switching pattern 12 is selected in the second period T2.

[0076] The switching pattern 11 is selected from among a plurality of switching pattern candidates to select the voltage V PG The switching pattern 10 is the switching pattern in which the voltage to ground V is the maximum among the multiple switching pattern candidates. PG The control device 150 controls the voltage V to ground during the first period T1. PG is selected, and the voltage V to ground is PG is higher than that of switching pattern 10.

[0077] This reduces the voltage to ground V PG The fluctuation range of the voltage V decreases from A1 to A2. PG Since high frequency leakage current caused by fluctuations in the power supply voltage is also suppressed, adverse effects such as deterioration on other devices connected to the power conversion device can be reduced.

[0078] In this disclosure, the control device is an electronic circuit such as a central processing unit (CPU), a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC). The control device may be a computer having a memory and a processor. The control device performs the various control operations described in this specification by executing a program such as instruction code stored in the memory, or by being a circuit designed for a specific application.

[0079] 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.

[0080] The following additional notes are provided regarding the above embodiment. (Appendix 1) a transformer having a primary winding and a secondary winding; a primary-side bridge circuit that switches a first voltage applied to the primary winding; a secondary-side bridge circuit that switches a second voltage applied to the secondary winding; a control device that selects, from a plurality of switching patterns in which the first voltage or the second voltage is zero, a switching pattern in which a voltage to ground between ground and a DC bus of the secondary side bridge circuit is lower than that of other switching patterns. [Explanation of symbols]

[0081] 100 Power conversion device Legs 11, 12, 13, and 14 21,23 Bridge part 30 Transformer 31 Primary Winding 32 Secondary Winding 130 Primary side bridge circuit 140 Secondary bridge circuit 150 control device 160 Primary GDU 170 Secondary GDU C1, C2 capacitors D1~D8 Freewheeling diodes Q1~Q8 Arm

Claims

1. a transformer having a primary winding and a secondary winding; a primary-side bridge circuit that switches a first voltage applied to the primary winding; a secondary-side bridge circuit that switches a second voltage applied to the secondary winding; a control device that selects a second switching pattern in which a voltage to ground between ground and a DC bus of the secondary side bridge circuit is lower than that of a first switching pattern during a period in which the first voltage or the second voltage is zero.

2. The power conversion device according to claim 1 , wherein the second switching pattern is a pattern in which both ends of the secondary winding are electrically connected to a positive bus of the secondary side bridge circuit during a period in which the second voltage is zero.

3. 2. The power conversion device according to claim 1, wherein the second switching pattern is a pattern in which both ends of the primary winding are electrically connected to a negative bus of the primary bridge circuit during a period in which the first voltage is zero and the second voltage is a voltage across a pair of DC buses of the secondary bridge circuit.

4. The second switching pattern is a first pattern electrically connecting both ends of the primary winding to a positive bus bar of the primary-side bridge circuit and electrically connecting both ends of the secondary winding to a positive bus bar of the secondary-side bridge circuit during a first period in which the first voltage and the second voltage are zero; a second pattern that electrically connects both ends of the primary winding to a negative bus bar of the primary-side bridge circuit and electrically connects both ends of the secondary winding to a negative bus bar of the secondary-side bridge circuit during a second period in which the first voltage and the second voltage are zero voltage.

5. Among a plurality of switching patterns in which the first voltage or the second voltage is zero, a switching pattern in which the voltage to ground is maximized is defined as a maximum switching pattern, and a switching pattern in which the voltage to ground is minimized is defined as a minimum switching pattern, 2. The power conversion device according to claim 1, wherein the second switching pattern includes: a first pattern in which the voltage to ground is lower than that of the maximum switching pattern in a first period in which the first voltage or the second voltage is zero; and a second pattern in which the voltage to ground is higher than that of the minimum switching pattern in a second period in which the first voltage or the second voltage is zero.

6. The power conversion device according to claim 5 , wherein the first period and the second period are periods in which the first voltage and the second voltage are both zero voltage.

7. 7. The power conversion device according to claim 1, wherein the control device selects the second switching pattern based on a phase difference command related to a phase difference between the first voltage and the second voltage and a pulse width command related to a pulse width of the first voltage or the second voltage.

8. 8. The power conversion device according to claim 7, wherein the control device specifies a first voltage value that the primary side bridge circuit applies to the primary winding and a second voltage value that the secondary side bridge circuit applies to the secondary winding, based on the phase difference command and the pulse width command, and selects the second switching pattern based on the first voltage value and the second voltage value.

9. 9. The power conversion device according to claim 8, wherein the control device selects the second switching pattern corresponding to the first voltage value and the second voltage value based on a correspondence relationship between a plurality of switching patterns in which the first voltage or the second voltage is zero voltage and the first voltage and the second voltage.

10. The power conversion device according to claim 1 , wherein the control device detects the voltage to ground and selects the second switching pattern such that the detected value of the voltage to ground is lower than that of the first switching pattern.

11. 11. The power conversion device according to claim 10, wherein the control device selects the second switching pattern corresponding to the detected value based on a correspondence relationship between a plurality of switching patterns in which the first voltage or the second voltage is zero voltage and the voltage to ground.

12. a transformer having a primary winding and a secondary winding; a primary-side bridge circuit that switches a first voltage applied to the primary winding; a secondary-side bridge circuit that switches a second voltage applied to the secondary winding, a second switching pattern in which a voltage to ground between a ground and a DC bus of the secondary side bridge circuit is lower than that of a first switching pattern, and the primary side bridge circuit and the secondary side bridge circuit are switched using the second switching pattern during a period in which the first voltage or the second voltage is zero.

Images