Power conversion system

Abstract

To limit the amplitude of an AC current flowing in an insulating transformer to an overcurrent level or less.SOLUTION: A control device configured to generate a drive pulse for operating a first bridge circuit and a second bridge circuit, and a drive circuit configured to drive the first bridge circuit and the second bridge circuit based on the drive pulse, wherein the control device selects, as the drive pulse, a first command drive pulse that causes the primary side AC current and the secondary side AC current to flow when the primary side AC current flowing through the primary side of the isolation transformer and the secondary side AC current flowing through the secondary side of the isolation transformer are less than an overcurrent level, and selects, as the drive pulse, a second command drive pulse that does not increase the primary side AC current and the secondary side AC current when the primary side AC current or the secondary side AC current reaches an overcurrent level.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] A bidirectional isolated DC / DC converter (DAB converter) known as a DAB (Dual Active Bridge) is known as one type of DC / DC converter. This DAB converter has a configuration in which two single-phase bridge circuits are connected via a high-frequency isolation transformer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7060179 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional DAB converters, if the voltage of the DC bus connected to the bridge circuit suddenly changes and operation continues to maintain the power transmitted between the bridge circuits, the amplitude of the AC current flowing through the isolation transformer increases, which can cause an overcurrent.

[0005] An object of the present disclosure is to limit the amplitude of an AC current flowing through an isolation transformer to an overcurrent level or less. [Means for solving the problem]

[0006] The present disclosure provides: An isolation transformer, a first bridge circuit connected to a primary side of the isolation transformer and having a plurality of switching elements; a second bridge circuit connected to a secondary side of the isolation transformer and having a plurality of switching elements; a control device that generates a drive pulse for operating the first bridge circuit and the second bridge circuit; a drive circuit that drives the first bridge circuit and the second bridge circuit based on the drive pulse; The control device Provided is a power conversion system in which, when a primary-side AC current flowing on the primary side of the isolation transformer and a secondary-side AC current flowing on the secondary side of the isolation transformer are below an overcurrent level, a first command drive pulse that causes the primary-side AC current and the secondary-side AC current to flow is selected as the drive pulse, and when the primary-side AC current or the secondary-side AC current reaches an overcurrent level, a second command drive pulse that does not increase the primary-side AC current and the secondary-side AC current is selected as the drive pulse. [Effects of the Invention]

[0007] According to the present disclosure, the amplitude of the AC current flowing through the isolation transformer can be limited to an overcurrent level or less. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a circuit diagram showing a configuration example of a power conversion system according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of a hardware configuration of a control device. [Figure 3] 3A and 3B are diagrams illustrating an example of an operational waveform of a DC / DC converter and a processing process of a control device. [Figure 4] 1 is a diagram illustrating an example of an operation in which a DC / DC converter generates an overcurrent due to a disturbance in a DC voltage. [Figure 5] 2 is a circuit diagram showing a detailed configuration example of the power conversion system according to the first embodiment. FIG. [Figure 6] FIG. 2 is a diagram illustrating a first configuration example of a selection unit. [Figure 7] 10A and 10B are diagrams showing first examples of four patterns of second command driving pulses that do not increase the amplitude of the AC current. [Figure 8]10A and 10B are diagrams illustrating output conditions of a reset signal for ending a period in which the amplitude of an AC current is not increased. [Figure 9] FIG. 8 is a diagram illustrating an example of operation when pattern 1 in FIG. 7 is used. [Figure 10] 8 is a diagram showing a path of an AC current flowing through an isolation transformer during a current amplitude limiting period when pattern 1 in FIG. 7 is used. FIG. [Figure 11] 10A and 10B are diagrams showing a second example of four patterns of second command driving pulses g1b to g8b that do not increase the amplitude of the AC current. [Figure 12] 12 is a diagram illustrating an example of operation when pattern 1 in FIG. 11 is used. [Figure 13] 12 is a diagram showing a path of an AC current flowing through an isolation transformer during a current amplitude limiting period when pattern 1 in FIG. 11 is used. FIG. [Figure 14] FIG. 10 is a diagram showing a third example of four patterns of second command driving pulses g1b to g8b that do not increase the amplitude of the AC current. [Figure 15] FIG. 15 is a diagram illustrating an example of operation when pattern 1 in FIG. 14 is used. [Figure 16] 15 is a diagram showing a path of an AC current flowing through an isolation transformer during a current amplitude limiting period when pattern 1 in FIG. 14 is used. FIG. [Figure 17] FIG. 10 is a diagram illustrating a second configuration example of the selection unit. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] First Embodiment Fig. 1 is a diagram showing an example of the configuration of a power conversion system according to a first embodiment. The power conversion system 100 shown in Fig. 1 includes a bidirectional isolated DC / DC converter (isolated DC / DC converter 110) in which bridge circuits are provided on both sides of an isolation transformer 102. The power conversion system 100 supplies power bidirectionally between a first bridge circuit 111 and a second bridge circuit 112.

[0011] The power conversion system 100 includes an isolation transformer 102, a first bridge circuit 111, a second bridge circuit 112, and a control device 106.

[0012] The isolation transformer 102 has a primary winding 31 and a secondary winding 32, and is a transformer in which the primary winding 31 and the secondary winding 32 are magnetically coupled. The turns ratio of the primary winding 31 and the secondary winding 32 is set as appropriate. The isolation transformer 102 has a magnetic core 33 around which the primary winding 31 and the secondary winding 32 are wound.

[0013] In this specification, unless otherwise specified, the turns ratio of the primary winding 31 and the secondary winding 32 may be considered to be 1:1. However, when the turns ratio of the primary winding 31 and the secondary winding 32 is other than 1:1, the voltage value on the secondary side or the primary side may be converted to the voltage value on the primary side or the secondary side, and the current value on the secondary side or the primary side may be converted to the current value on the primary side or the secondary side. For example, in the following description, the secondary-side DC voltage E2 and the secondary-side AC voltage V2 mean the voltage values converted to the primary side. That is, when the number of turns of the primary winding 31 of the isolation transformer 102 is n1 and the number of turns of the secondary winding 32 is n2, the voltage value obtained by multiplying the actual secondary-side DC voltage by the coefficient n1 / n2 (the voltage value converted to the primary side) is the secondary-side DC voltage E2. The same applies to the secondary-side AC voltage V2. Also, in the following description, the low-voltage side and the high-voltage side mean the side where low voltage is generated and the side where high voltage is generated among the primary side and the secondary side of the isolation DC / DC converter 110. For example, if there is a relationship of E1 < E2 between the primary-side DC voltage E1 and the secondary-side DC voltage E2 converted to the primary-side value, the primary side is the low-voltage side and the secondary side is the high-voltage side, and if there is a relationship of E1 > E2, the primary side is the high-voltage side and the secondary side is the low-voltage side.

[0014] The first bridge circuit 111 is a primary-side bridge circuit connected to the primary side of the isolation transformer 102, and exchanges power with the primary winding 31 of the isolation transformer 102. The first bridge circuit 111 has a positive terminal 41p and a negative terminal 41n as primary-side DC terminals electrically connected to an external device (not shown). The first bridge circuit 111 exchanges power with the external device connected to the primary-side DC terminals.

[0015] The first bridge circuit 111 has a positive bus 43p and a negative bus 43n as a primary-side DC bus pair. The positive bus 43p is connected to the positive terminal 41p. The negative bus 43n is connected to the negative terminal 41n. The first bridge circuit 111 switches the polarity of the voltage V1 applied to the primary winding 31 of the isolation transformer 102 by the primary-side DC bus pair 43p, 43n.

[0016] The first bridge circuit 111 is a full bridge circuit having a plurality of legs 11 and 12 connected in parallel.

[0017] The first bridge circuit 111 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. The high-side arm and the low-side arm may be collectively referred to as upper and lower arms.

[0018] The first bridge circuit 111 is a full-bridge circuit in which a primary winding 31 of an isolation transformer 102 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 first bridge circuit 111 may include a reactor 104a in the bridge portion 21 that is connected in series to the primary winding 31 of the isolation transformer 102. 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 first bridge circuit 111 includes a capacitor C1 and arms Q1 to Q4.

[0020] The capacitor C1 is connected between the pair of DC buses 43p and 43n on the primary side, and smoothes the voltage between the pair of DC buses 43p and 43n (the voltage of the capacitor C1).

[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 43p and 43n, and leg 12 includes a configuration in which arms Q3 and Q4 are connected in series between the pair of DC buses 43p and 43n. 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. Each of 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] When the arms Q1 and Q4 are turned on and the arms Q2 and Q3 are turned off, the first bridge circuit 111 electrically connects the intermediate node a1 to the positive bus 43p and electrically connects the intermediate node b1 to the negative bus 43n. As a result, the first bridge circuit 111 sets the voltage V1 to a positive voltage "E1." The voltage V1 is a primary-side AC voltage between the intermediate node a1 and the intermediate node b1. E1 is a voltage value (primary-side DC voltage) between the pair of DC buses 43p and 43n. When the arms Q1 and Q4 are turned off and the arms Q2 and Q3 are turned on, the first bridge circuit 111 electrically connects the intermediate node a1 to the negative bus 43n and electrically connects the intermediate node b1 to the positive bus 43p. As a result, the first bridge circuit 111 sets the voltage V1 to a negative voltage "-E1." By operating in this manner, the first bridge circuit 111 switches the polarity of the voltage V1 applied to the primary winding 31 of the isolation transformer 102 by the primary-side DC bus pair 43p, 43n.

[0024] When the arms Q1 and Q3 are turned on and the arms Q2 and Q4 are turned off, the first bridge circuit 111 electrically connects both the intermediate connection point a1 and the intermediate connection point b1 to the positive bus 43p, thereby making the voltage V1 substantially zero. When the arms Q1 and Q3 are turned off and the arms Q2 and Q4 are turned on, the first bridge circuit 111 electrically connects both the intermediate connection point a1 and the intermediate connection point b1 to the negative bus 43n, thereby making the voltage V1 substantially zero.

[0025] The second bridge circuit 112 is a secondary-side bridge circuit connected to the secondary side of the isolation transformer 102, and exchanges power with the secondary winding 32 of the isolation transformer 102. The second bridge circuit 112 has a positive terminal 42p and a negative terminal 42n as secondary-side DC terminals electrically connected to an external device (not shown). The second bridge circuit 112 exchanges power with the external device connected to the secondary-side DC terminals.

[0026] The second bridge circuit 112 has a positive bus 44p and a negative bus 44n as a secondary-side DC bus pair. The positive bus 44p is connected to the positive terminal 42p. The negative bus 44n is connected to the negative terminal 42n. The second bridge circuit 112 switches the polarity of the voltage V2 applied to the secondary winding 32 of the isolation transformer 102 by the secondary-side DC bus pair 44p, 44n.

[0027] The second bridge circuit 112 is a full bridge circuit having a plurality of legs 13 and 14 connected in parallel.

[0028] The second bridge circuit 112 has, 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. The high-side arm and the low-side arm may be collectively referred to as upper and lower arms.

[0029] The second bridge circuit 112 is a full-bridge circuit in which the secondary winding 32 of the isolation transformer 102 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 second bridge circuit 112 may include a reactor 104b in the bridge portion 23 that is connected in series to the secondary winding 32 of the isolation transformer 102. 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.

[0030] The second bridge circuit 112 includes a capacitor C2 and arms Q5 to Q8.

[0031] The capacitor C2 is connected between the pair of DC buses 44p and 44n on the secondary side, and smoothes the voltage between the pair of DC buses 44p and 44n (the voltage of the capacitor C2).

[0032] 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.

[0033] Leg 13 includes a configuration in which arms Q5 and Q6 are connected in series between the pair of DC buses 44p and 44n, and leg 14 includes a configuration in which arms Q7 and Q8 are connected in series between the pair of DC buses 44p and 44n. 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.

[0034] When the arms Q5 and Q8 are turned on and the arms Q6 and Q7 are turned off, the second bridge circuit 112 electrically connects the intermediate node a2 to the positive bus 44p and electrically connects the intermediate node b2 to the negative bus 44n. As a result, the second bridge circuit 112 sets the voltage V2 to a positive voltage "E2." The voltage V2 is a secondary AC voltage between the intermediate node a2 and the intermediate node b2. E2 is a voltage value (secondary DC voltage) between the pair of DC buses 44p and 44n. When the arms Q5 and Q8 are turned off and the arms Q6 and Q7 are turned on, the second bridge circuit 112 electrically connects the intermediate node a2 to the negative bus 44n and electrically connects the intermediate node b2 to the positive bus 44p. As a result, the second bridge circuit 112 sets the voltage V2 to a negative voltage "-E2." By operating in this manner, the second bridge circuit 112 switches the polarity of the voltage V2 applied to the secondary winding 32 of the isolation transformer 102 by the secondary-side DC bus pair 44p, 44n.

[0035] When the arms Q5 and Q7 are turned on and the arms Q6 and Q8 are turned off, the second bridge circuit 112 electrically connects both the intermediate node a2 and the intermediate node b2 to the positive bus 44p, thereby making the voltage V2 substantially zero. When the arms Q5 and Q7 are turned off and the arms Q6 and Q8 are turned on, the second bridge circuit 112 electrically connects both the intermediate node a2 and the intermediate node b2 to the negative bus 43n, thereby making the voltage V2 substantially zero.

[0036] An external device (not shown) connected to the positive terminal 41p and the negative terminal 41n is, for example, a charging / discharging device capable of charging / discharging a battery, etc. An external device (not shown) connected to the positive terminal 42p and the negative terminal 42n is, for example, a DC system capable of charging / discharging energy of a charging / discharging device connected to the primary side.

[0037] The control device 106 controls the first bridge circuit 111 and the second bridge circuit 112. The control device 106 generates drive pulses g1 to g4 for driving the arms Q1 to Q4 of the first bridge circuit 111, respectively, and drive pulses g5 to g8 for driving the arms Q5 to Q8 of the second bridge circuit 112, respectively. The drive pulses g1 to g8 are drive signals for controlling the on / off of corresponding arms among the arms Q1 to Q8. The drive pulses g1 to g4 are commands output from the control device 106 as first drive pulses that the control device 106 supplies to the first bridge circuit 111. The drive pulses g5 to g8 are commands output from the control device 106 as second drive pulses that the control device 106 supplies to the second bridge circuit 112.

[0038] The power conversion system 100 includes a drive circuit 105a and a drive circuit 105b. The drive circuit 105a is a primary side drive circuit (first drive circuit) that drives a first bridge circuit 111 based on drive pulses g1 to g4 provided by a control device 106. The drive circuit 105a controls the on / off switching of arms Q1 to Q4 of the first bridge circuit 111 in accordance with the drive pulses g1 to g4. The drive circuit 105b is a secondary side drive circuit (second drive circuit) that drives a second bridge circuit 112 based on drive pulses g5 to g8 provided by the control device 106. The drive circuit 105b controls the on / off switching of arms Q5 to Q8 of the second bridge circuit 112 in accordance with the drive pulses g5 to g8.

[0039] The power conversion system 100 includes a DC voltage detection unit 107a and a DC voltage detection unit 107b. The DC voltage detection unit 107a is a circuit that detects a primary side DC voltage E1 applied to the DC bus pair 43p, 43n of the first bridge circuit 111. The DC voltage detection unit 107b is a circuit that detects a secondary side DC voltage E2 applied to the DC bus pair 44p, 44n of the second bridge circuit 112.

[0040] The power conversion system 100 includes a DC current detection unit 108a and a DC current detection unit 108b. The DC current detection unit 108a is a circuit that detects a primary side DC current I1 that flows through the positive electrode bus 43p of the first bridge circuit 111. The DC current detection unit 108b is a circuit that detects a secondary side DC current I2 that flows through the positive electrode bus 44p of the second bridge circuit 112.

[0041] The control device 106 controls the phases of the edges of drive pulses g1 to g8 for driving the arms Q1 to Q8 based on the primary side DC voltage E1 detected by the DC voltage detection unit 107a and the secondary side DC voltage E2 detected by the DC voltage detection unit 107b. The control device 106 controls the phases of the edges of the drive pulses g1 to g8, thereby controlling the power transmission of the isolated DC / DC converter 110 (power transmission between the first bridge circuit 111 and the second bridge circuit 112).

[0042] A part or all of the control device 106 is an electronic circuit such as a central processing unit (CPU), a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC). A part or all of the control device 106 may be a computer having a memory and a processor. A part or all of the control device 106 executes various control operations described in this specification by executing a program such as instruction code stored in a memory, or by being a circuit designed for a specific application.

[0043] 2 is a diagram showing an example of the hardware configuration of a control device. The control device 500 corresponds to a part or all of the control device 106. The control device 500 includes a memory 501, a processor 502, an interface 503, an A / D converter 504, a counter 505, a comparator 506, and a data bus 507.

[0044] The processor 502 sequentially processes the programs stored in the memory 501. This realizes the various control operations described in this specification. The processor 502 is, for example, a CPU.

[0045] The interface 503 has an input / output function (I / O) for connecting to the outside, and transmits and receives signals to and from the outside. In the control device 500 that realizes a DC / DC converter, the interface 503 plays a role in providing drive pulses g1 to g8 to drive circuits (drive circuits 105a and 105b) outside the control device 500.

[0046] The A / D converter 504 converts a continuous voltage signal (analog signal) input from outside the control device 500 into a digital signal. The A / D converter 504 takes in the detected values ​​of the voltage detection unit and the current detection unit into the control device 500.

[0047] The control device 500 controls the switching of the arms Q1 to Q8 by performing pulse width modulation and phase modulation using a counter 505 and a comparator 506. A data bus 507 is a signal line for exchanging data between the components in the control device 500.

[0048] Fig. 3 is a diagram showing an example of the operating waveforms of the DC / DC converter 110 and the processing process of the control device 106. In Fig. 3, g* with "~" (* is an arbitrary character) represents a logically inverted signal of the drive pulse g* (the same applies to each drawing described later).

[0049] The control device 106 captures the detection values ​​output by the DC voltage detection units 107a and 107b and the DC current detection units 108a and 108b at a predetermined control period (generally the same as the switching period of the switching elements) using an A / D converter 504. The control device 106 executes calculations and commands in accordance with a predetermined procedure using these detection values, and updates gate commands for generating drive pulses g1 to g8 for the arms Q1 to Q8 based on the calculation results.

[0050] In the example of FIG. 3, the control device 106 generates drive pulses g1 to g8 for each of the arms Q1 to Q8 by phase-modulating a rectangular wave signal. The drive pulses may be generated using pulse-width modulation or a combination of phase modulation and pulse-width modulation. The first bridge circuit 111 outputs a primary-side AC voltage V1 in accordance with the drive pulses g1 to g4 for each of the arms Q1 to Q4 generated by modulation. The second bridge circuit 112 outputs a secondary-side AC voltage V2 in accordance with the drive pulses g5 to g8 for each of the arms Q5 to Q8 generated by modulation. The voltage difference between V1 and V2 is applied to the leakage inductance of the isolation transformer 102 and the external reactors 104a and 104b, and AC currents Iac1 and Iac2 flow through the isolation transformer 102 and the external reactors 104a and 104b.

[0051] Using this control method, the control device 106 controls the AC currents Iac1 and Iac2 flowing through the isolation transformer 102 and the external reactors 104a and 104b based on the detected DC voltage. This allows the power conversion system 100 to transmit power in any direction and magnitude between the primary-side DC bus pair 43p, 43n and the secondary-side DC bus pair 44p, 44n.

[0052] Incidentally, a momentary drop or interruption of DC voltage may occur in the DC bus connected to the primary side DC terminals (positive terminal 41p and negative terminal 41n) or the secondary side DC terminals (positive terminal 42p and negative terminal 42n). In this case, if the control device 106 continues operation to maintain the transmission power, the amplitude of the AC current Iac1 or Iac2 flowing through the isolation transformer 102 may increase, and the DC / DC converter 110 may be damaged by an overcurrent. Therefore, some kind of countermeasure is required.

[0053] Fig. 4 is a diagram showing an example of an operation in which DC / DC converter 110 experiences an overcurrent due to a disturbance in the DC voltage. Fig. 4 illustrates a case in which the secondary-side DC voltage E2 suddenly drops. As shown in Fig. 4, a delay of at least the control period occurs between the occurrence of a sudden change in the DC voltage and the time when control device 106 detects the sudden change in the DC voltage and updates the drive pulses of the switching elements in accordance with the detected value. During this delay time, there is a possibility that AC current Iac1 or Iac2 will exceed the overcurrent level.

[0054] The control device 106 according to the present disclosure limits the amplitude of the AC current to a predetermined overcurrent level or less by instantly controlling the drive pulse of the switching element in accordance with the result of comparing the detected value of the AC current flowing through the isolation transformer 102 with a predetermined overcurrent level. This provides the power conversion system 100 that can continue to operate even when a disturbance occurs in the voltage of the DC bus without an overcurrent flowing in the AC section (bridge portion 21 or bridge portion 23).

[0055] 5 is a circuit diagram showing a detailed configuration example of the power conversion system according to the first embodiment. The control device 106 has a generation unit 107 and a selection unit 108.

[0056] The generator 107 generates first command drive pulses g1a-g8a for driving the arms Q1-Q8 based on the primary side DC voltage E1 detected by the DC voltage detector 107a and the secondary side DC voltage E2 detected by the DC voltage detector 107b. The generator 107 generates the first command drive pulses g1a-g8a based on the detected value of the primary side DC voltage E1 and the detected value of the secondary side DC voltage E2 so that power corresponding to a command given to the control device 106 is transmitted between the bridge circuits. The first command drive pulses g1a-g8a are drive pulses that cause a primary side AC current Iac1 and a secondary side AC current Iac2 to flow.

[0057] The selection unit 108 selects whether the drive pulses g1 to g8 that operate the first bridge circuit 111 and the second bridge circuit 112 are the first command drive pulses g1a to g8a or the second command drive pulses g1b to g8b. The second command drive pulses g1b to g8b are drive pulses that do not increase the primary side AC current Iac1 and the secondary side AC current Iac2.

[0058] The selector 108 compares the primary-side AC current Iac1 flowing on the primary side of the isolation transformer 102 and the secondary-side AC current Iac2 flowing on the secondary side of the isolation transformer 102 with a predetermined overcurrent level.

[0059] When the primary side AC current Iac1 and the secondary side AC current Iac2 are less than a predetermined overcurrent level, the selection unit 108 selects the first command drive pulses g1a-g8a generated by the generation unit 107 as drive pulses g1-g8. The selection unit 108 supplies the first command drive pulses g1a-g8a selected as the drive pulses g1-g8 to the drive circuits 105a and 105b.

[0060] On the other hand, when the primary side AC current Iac1 or the secondary side AC current Iac2 reaches a predetermined overcurrent level, the selector 108 selects the predetermined second command drive pulses g1b to g8b as the drive pulses g1 to g8. The selector 108 supplies the second command drive pulses g1b to g8b selected as the drive pulses g1 to g8 to the drive circuits 105a and 105b.

[0061] The selection unit 108 may be realized by processing a program stored in the memory of the control device 106, or may be realized by a hardware circuit including a logic circuit and a comparator.

[0062] 6 is a diagram showing a first configuration example of the selection unit 108. The selection unit 108 shown in FIG.

[0063] Comparator 51 compares the detected value of primary side AC current Iac1 with a predetermined positive overcurrent level. Comparator 52 compares the detected value of primary side AC current Iac1 with a predetermined negative overcurrent level. Comparator 53 compares the detected value of secondary side AC current Iac2 with a predetermined positive overcurrent level. Comparator 54 compares the detected value of secondary side AC current Iac2 with a predetermined negative overcurrent level. Because the current flowing through isolation transformer 102 is AC, primary side AC current Iac1 and secondary side AC current Iac2 are each compared with both positive and negative overcurrent levels.

[0064] When the comparators 51 to 54 detect that the detected values ​​of the primary side AC current Iac1 and the secondary side AC current Iac2 have not reached a predetermined overcurrent level, the latches 55 to 58 hold the overcurrent detection signal OC output from the OR gate 59 inactive. In this case, the multiplexer 60 (MUX60) outputs the first command drive pulses g1a to g8a generated by the generator 107 as drive pulses g1 to g8.

[0065] When one of the comparators 51-54 detects that the detected value of the primary-side AC current Iac1 or the secondary-side AC current Iac2 has reached a predetermined overcurrent level, the latches 55-58 hold the overcurrent detection signal OC output from the OR gate 59 active. In this case, the MUX 60 outputs second command drive pulses g1b-g8b that do not increase the amplitude of the AC currents Iac1 and Iac2 as drive pulses g1-g8. When the AC current Iac1 or Iac2 has reached the predetermined overcurrent level, the MUX 60 switches the drive pulses g1-g8 supplied to the drive circuits 105a and 105b from the first command drive pulses g1a-g8a to the second command drive pulses g1b-g8b. This state is maintained until the latches 55-58 receive a reset signal R1 or R2 from the reset units 61 and 62.

[0066] 7 is a diagram showing a first example of four patterns of second command driving pulses g1b to g8b that do not increase the amplitude of the AC current. The selection unit 108 selects second command driving pulses g1b to g8b of one of patterns 1 to 4 prepared in advance and shown in FIG.

[0067] Whichever pattern is selected, the pair of AC output points a1, b1 of the first bridge circuit 111 is short-circuited by any of the arms Q1 to Q4, and the pair of AC output points a2, b2 of the second bridge circuit 112 is short-circuited by any of the arms Q5 to Q8. By short-circuiting the pair of AC output points a1, b1 and the pair of AC output points a2, b2, the amplitudes of the AC currents Iac1 and Iac2 are suppressed.

[0068] 8 is a diagram illustrating output conditions for a reset signal for ending a period during which the amplitude of the AC current is not increased (current amplitude limit period). When drive pulse g1a is a signal for turning off arm Q1 and drive pulse g7a is a signal for turning off arm Q7, reset units 61 and 62 output a reset signal R1 for ending a period during which the amplitude of the AC currents Iac1 and Iac2 is not increased in the positive direction. When drive pulse g3a is a signal for turning off arm Q3 and drive pulse g5a is a signal for turning off arm Q5, reset units 61 and 62 output a reset signal R2 for ending a period during which the amplitude of the AC currents Iac1 and Iac2 is not increased in the negative direction.

[0069] 8 is satisfied, the first command drive pulses g1a to g8a provided by the generating unit 107 are commands to decrease the magnitudes of the AC currents Iac1 and Iac2 flowing through the insulating transformer 102. The reset signals R1 and R2 may be provided by the generating unit 107 based on the conditions shown in FIG.

[0070] Fig. 9 is a diagram showing an example of operational waveforms when the second command drive pulses g1b to g8b of pattern 1 in Fig. 7 are selected as drive pulses that do not increase the amplitudes of the AC currents Iac1 and Iac2. Fig. 9 illustrates a case where the secondary side DC voltage E2 drops suddenly.

[0071] When the AC current Iac1 reaches a positive overcurrent level, the overcurrent detection signal OC becomes active, and the drive pulses g1-g8 are switched from the first command drive pulses g1a-g8a to the second command drive pulses g1b-g8b by the MUX60 of the selector 108. When the drive pulses are switched to the second command drive pulses g1b-g8b, the AC currents Iac1 and Iac2 circulate through the first bridge circuit 111 and the second bridge circuit 112, as shown in FIG. 10. While the AC currents Iac1 and Iac2 are circulating, they do not increase but are maintained constant or slightly decreasing. This limits the amplitude of the AC current flowing through the isolation transformer to below the overcurrent level.

[0072] When a reset signal R1 is given to the latches 55-58 of the selection unit 108, the overcurrent detection signal OC becomes inactive. As a result, the drive pulses g1-g8 given to the drive circuits 105a, 105b are switched from the second command drive pulses g1b-g8b to the first command drive pulses g1a-g8a by the MUX 60 of the selection unit 108. As a result, the power conversion system 100 can return to normal operation in which the arms Q1-Q8 are switched in accordance with the first command drive pulses g1a-g8a generated by the generation unit 107.

[0073] Note that the operational waveform example in Fig. 9 and the current path in Fig. 10 show the case where pattern 1 in Fig. 7 is selected, but regardless of which of patterns 2, 3, or 4 in Fig. 7 is selected, the amplitude of the AC current flowing through the isolation transformer can be limited to below the overcurrent level. Also, Fig. 9 illustrates the case where the secondary-side DC voltage E2 drops suddenly, but regardless of whether the secondary-side DC voltage E2 rises suddenly or the primary-side DC voltage E1 rises or falls suddenly, the amplitude of the AC current can be limited to below the overcurrent level by selecting any of the patterns in Fig. 7. These points also apply to the operational waveform example and other pattern examples described below.

[0074] 11 is a diagram showing a second example of four patterns of second command driving pulses g1b to g8b that do not increase the amplitude of the AC current. The selection unit 108 selects second command driving pulses g1b to g8b of one of patterns 1 to 4 prepared in advance and shown in FIG.

[0075] Whichever pattern is selected, one of the multiple legs 11 and 12 of the first bridge circuit 111 is turned off, and one of the multiple legs 13 and 14 of the second bridge circuit 112 is turned off. For example, in the case of pattern 1, the arms Q1 and Q2 of the leg 11 are turned off, and the arms Q5 and Q6 of the leg 13 are turned off. By turning off one leg of the first bridge circuit 111 and one leg of the second bridge circuit 112, the amplitudes of the AC currents Iac1 and Iac2 are suppressed.

[0076] Of the multiple legs 11 and 12, the upper and lower arms of a leg (e.g., leg 12 in the case of pattern 1) other than the one leg that is turned off are switched in accordance with first command drive pulses (e.g., g3a and g4a in the case of leg 12) generated by the generator 107. Similarly, of the multiple legs 13 and 14, the upper and lower arms of a leg (e.g., leg 14 in the case of pattern 1) other than the one leg that is turned off are switched in accordance with first command drive pulses (e.g., g7a and g8a in the case of leg 14) generated by the generator 107.

[0077] Fig. 12 is a diagram showing an example of operational waveforms when second command drive pulses g1b to g8b of pattern 1 in Fig. 11 are selected as drive pulses that do not increase the amplitudes of AC currents Iac1 and Iac2. Fig. 12 illustrates a case where the secondary side DC voltage E2 drops suddenly.

[0078] When the AC current Iac1 reaches a positive overcurrent level while the primary-side AC voltage V1 is positive, the overcurrent detection signal OC becomes active, and the drive pulses g1-g8 are switched from the first command drive pulses g1a-g8a to the second command drive pulses g1b-g8b by the MUX60 of the selector 108. In this case, as shown in FIG. 13, the AC current Iac1 flowing through the primary winding 31 circulates via the arm Q4 and the freewheeling diode D2, and the AC current Iac2 flowing through the secondary winding 32 flows to the secondary-side DC bus via the freewheeling diode D5 and the arm Q8. At this time, the second bridge circuit 112 operates as a rectifier, and energy flows from the AC side connected to the isolation transformer 102 to the DC side. Therefore, the magnitudes of the AC currents Iac1 and Iac2 flowing through the isolation transformer 102 decrease.

[0079] 11 is selected, the AC currents Iac1 and Iac2 decrease while the overcurrent detection signal OC is active, and therefore the reset signals R1 and R2 may be output at any timing. In the example of FIG. 12, the overcurrent detection signal OC is reset (becomes inactive) when the gate command generated by the generation unit 107 is updated.

[0080] 14 is a diagram showing a third example of four patterns of second command driving pulses g1b to g8b that do not increase the amplitude of the AC current. The selection unit 108 selects second command driving pulses g1b to g8b of one of patterns 1 to 4 prepared in advance and shown in FIG.

[0081] When pattern 1 or pattern 2 is selected, a pair of AC output points a1, b1 of the first bridge circuit 111 is short-circuited by one of arms Q1 to Q4, and arms Q5 to Q8 of the second bridge circuit 112 are all open. With all arms Q5 to Q8 open, the second bridge circuit 112 operates as a rectifier. When pattern 1 or pattern 2 is selected, the first bridge circuit 111 is a bridge circuit that transmits power to the isolation transformer 102, and the second bridge circuit 112 is a bridge circuit that receives power from the isolation transformer 102. When pattern 1 or pattern 2 is selected, the amplitudes of the AC currents Iac1 and Iac2 are suppressed.

[0082] When pattern 3 or pattern 4 is selected, a pair of AC output points a2, b2 of the second bridge circuit 112 is short-circuited by one of arms Q5 to Q8, and arms Q1 to Q4 of the first bridge circuit 111 are all open. With all arms Q1 to Q4 open, the first bridge circuit 111 operates as a rectifier. When pattern 3 or pattern 4 is selected, the first bridge circuit 111 is a bridge circuit that receives power from the isolation transformer 102, and the second bridge circuit 112 is a bridge circuit that transmits power to the isolation transformer 102. When pattern 3 or pattern 4 is selected, the amplitudes of the AC currents Iac1 and Iac2 are suppressed.

[0083] Fig. 15 is a diagram showing an example of operational waveforms when second command drive pulses g1b to g8b of pattern 1 in Fig. 14 are selected as drive pulses that do not increase the amplitudes of AC currents Iac1 and Iac2. Fig. 15 illustrates a case where the secondary side DC voltage E2 drops suddenly.

[0084] When the AC current Iac1 reaches a positive overcurrent level while the primary-side AC voltage V1 is positive, the overcurrent detection signal OC becomes active, and the drive pulses g1 to g8 are switched from the first command drive pulses g1a to g8a to the second command drive pulses g1b to g8b by the MUX60 of the selector 108. In this case, as shown in FIG. 16, the AC current Iac1 flowing through the primary winding 31 circulates through arms Q1 and Q3, and the AC current Iac2 flowing through the secondary winding 32 flows to the secondary-side DC bus through freewheeling diodes D5 and D8. Note that in Pattern 2, the path of the AC current circulating through the first bridge circuit 111 is different from that in Pattern 1, but the current flows in the same manner as in Pattern 1. In Pattern 3, the operations of the first bridge circuit 111 and the second bridge circuit 112 are reversed from those in Pattern 1. In the case of pattern 4, the operations of the first bridge circuit 111 and the second bridge circuit 112 are reversed from those in the case of pattern 2.

[0085] 14 is selected, the AC currents Iac1 and Iac2 decrease while the overcurrent detection signal OC is active, and therefore the reset signals R1 and R2 may be output at any timing. In the example of FIG. 15, the overcurrent detection signal OC is reset (becomes inactive) when the gate command generated by the generation unit 107 is updated.

[0086] FIG. 17 is a diagram showing a second configuration example of the selection unit. The second command driving pulses g1b to g8b of pattern 1 in FIG. 11 can be generated by a selection unit 108 configured as shown in FIG. 17. The selection unit 108 shown in FIG. 17 differs from the selection unit 108 shown in FIG. 6 in that the MUX 60 is replaced with logic gates (a logical NOT gate 63 and logical AND gates 64, 65, 66, and 67). When the selection unit 108 is realized with the configuration shown in FIG. 17, the number of logic gates is reduced compared to when the selection unit 108 is realized with the configuration shown in FIG. 6, and therefore the circuit scale can be reduced. The above-mentioned method of reducing the number of logic gates is a method commonly used as so-called logic compression. This method allows for many variations in the configuration of the selection unit.

[0087] The selection unit 108 shown in FIG. 17 includes comparators 51, 52, 53, and 54, latches 55, 56, 57, and 58, an OR gate 59, a NOT gate 63, AND gates 64 to 67, and reset units 61 and 62.

[0088] The logic of the overcurrent detection signal OC output from OR gate 59 is inverted by NOT gate 63. The overcurrent detection signal OC (signal OC') after logic inversion is input to each of AND gates 64 to 67. AND gate 64 outputs the logical product of drive pulse g1a and signal OC' as drive pulse g1. AND gate 65 outputs the logical product of drive pulse g2a and signal OC' as drive pulse g2. AND gate 66 outputs the logical product of drive pulse g5a and signal OC' as drive pulse g5. AND gate 67 outputs the logical product of drive pulse g6a and signal OC' as drive pulse g6.

[0089] The present invention is not limited to the above-described embodiments. The above-described embodiments can be embodied 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 in the scope and spirit of the invention, and are also included in the inventions described in the claims and their equivalents. [Explanation of symbols]

[0090] 100 Power Conversion System 102 Isolation transformer 106 Control device 107 Generation part 108 Selection Section 110 Isolated DC / DC Converter 111 First bridge circuit 112 Second bridge circuit

Claims

1. An isolation transformer, a first bridge circuit connected to a primary side of the isolation transformer and having a plurality of switching elements; a second bridge circuit connected to a secondary side of the isolation transformer and having a plurality of switching elements; a control device that generates a drive pulse for operating the first bridge circuit and the second bridge circuit; a drive circuit that drives the first bridge circuit and the second bridge circuit based on the drive pulse; The control device a first command drive pulse that causes the primary side AC current and the secondary side AC current to flow is selected as the drive pulse when a primary side AC current flowing in the primary side of the isolation transformer and a secondary side AC current flowing in the secondary side of the isolation transformer are less than an overcurrent level, and a second command drive pulse that does not increase the primary side AC current and the secondary side AC current is selected as the drive pulse when the primary side AC current or the secondary side AC current reaches an overcurrent level.

2. 2. The power conversion system according to claim 1, wherein the second command drive pulse is a drive pulse that short-circuits a pair of AC output points of the first bridge circuit by the switching elements of the first bridge circuit, and short-circuits a pair of AC output points of the second bridge circuit by the switching elements of the second bridge circuit.

3. 2. The power conversion system according to claim 1, wherein the second command drive pulse is a drive pulse that turns off one leg of the plurality of legs of the first bridge circuit and turns off one leg of the plurality of legs of the second bridge circuit.

4. 2. The power conversion system according to claim 1, wherein the second command drive pulse is a drive pulse that shorts a pair of AC output points of one of the first bridge circuit and the second bridge circuit that transmits power to the isolation transformer by the switching elements of the bridge circuit, and that opens all of the switching elements of the bridge circuit that receives power from the isolation transformer.

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