Bidirectional converter module, bidirectional traction converter system and control method thereof

Abstract

The application provides a bidirectional current conversion module, a bidirectional traction current conversion system and a control method thereof. The bidirectional current conversion module is applied to a bidirectional traction current conversion system with multiple bidirectional current conversion modules in parallel, and comprises positive and negative DC buses and a power grid. The bidirectional current conversion module comprises: an inverter bridge circuit having a DC end and an AC end, the DC end being used for connection with the positive and negative DC buses, and the AC end being used for connection with the AC power grid; a decoupling circuit connected with the midpoint of the inverter bridge circuit to decouple the midpoints of the multiple bidirectional current conversion modules; first and second fuses respectively arranged between the DC end of the inverter bridge circuit and the positive and negative DC buses. When half-bus short circuit occurs in the inverter bridge circuit of the first bidirectional current conversion module, the first and / or second fuses are fused to decouple the DC end of the first bidirectional current conversion module from other bidirectional current conversion modules, wherein the first bidirectional current conversion module is any one of the multiple bidirectional current conversion modules.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of rail transit technology, and in particular to a bidirectional conversion module, a bidirectional traction conversion system and a control method thereof. BACKGROUND

[0002] The rail transit traction power supply system supplies power to rail transit vehicles and other loads through a bidirectional traction conversion device.

[0003] The bidirectional traction conversion device usually includes multiple bidirectional conversion modules. When the multiple modules are operated in parallel, due to differences in the output voltage amplitude, phase and frequency between the modules, circulating current is generated between the parallel branches. This increases the loss of the modules and reduces the efficiency of the system. Meanwhile, excessive circulating current can cause overcurrent of the switching tube, trigger the overcurrent protection device, affect the normal operation of the system, and even cause damage to the modules.

[0004] Secondly, during operation of the bidirectional traction conversion device, the positive half bus or the negative half bus of the DC side may be short-circuited due to reasons such as insulation aging, overvoltage breakdown, line fault, load imbalance or load mutation. The midpoint potential of a single module is pulled to the potential of the DC bus, which can cause the switching device in the module to be broken or increase the stress of other modules, resulting in failure of the entire system. SUMMARY

[0005] The present application mainly provides a bidirectional conversion module, a bidirectional traction conversion system and a control method thereof. The technical solution of the present application is implemented as follows:

[0006] In a first aspect, a bidirectional conversion module is provided, which is applied to a bidirectional traction conversion system in which multiple bidirectional conversion modules are connected in parallel. The bidirectional traction conversion system includes a positive DC bus, a negative DC bus and a power grid. The bidirectional conversion module includes an inverter bridge circuit having a DC end and an AC end. The DC end is used to connect with the positive DC bus and the negative DC bus, and the AC end is used to connect with the AC power grid. A decoupling circuit is connected to the midpoint of the inverter bridge circuit to decouple the midpoints of the multiple bidirectional conversion modules. A first fuse is arranged between the DC end of the inverter bridge circuit and the positive DC bus, and a second fuse is arranged between the DC end of the inverter bridge circuit and the negative DC bus. When a half bus short circuit occurs in the inverter bridge circuit of a first bidirectional conversion module among the multiple bidirectional conversion modules, the first fuse and / or the second fuse is fused to decouple the DC end of the first bidirectional conversion module from the DC end of other bidirectional conversion modules. The first bidirectional conversion module is any one of the multiple bidirectional conversion modules.

[0007] According to the technical solution provided in the embodiments of the present application, the midpoint of each bidirectional current conversion module is decoupled from each other, so that the chain reaction caused by the change of the midpoint potential of some bidirectional current conversion modules on the midpoint potential of other modules is avoided. The first and second fuses are arranged between the bidirectional current conversion module and the DC bus, so that when half bus short circuit occurs in some bidirectional current conversion modules, the fuses can intervene in time to decouple the short-circuit module from other modules, so that the other modules can still work normally. When applied to a rail transit vehicle, the overall shutdown caused by the failure of a single module can be avoided.

[0008] In some embodiments, the bidirectional current conversion module further comprises a plurality of third fuses, which are arranged between the AC end of the inverter bridge circuit and the multi-phase of the power grid, respectively; when half bus short circuit occurs in the inverter bridge circuit of the first bidirectional current conversion module, one or more of the plurality of third fuses are fused to decouple the AC end of the first bidirectional current conversion module from other bidirectional current conversion modules.

[0009] According to the above technical means, when half bus short circuit occurs, the short-circuit current flowing into the transformer through the AC end of the first converter is greater than the minimum melting current of F3, so that the third fuse F3 connected to the AC end of the first converter is fused quickly, the connection between the short-circuit point in the first bidirectional current conversion module and the AC bus is cut off, and the AC end of the first bidirectional current conversion module is decoupled from other bidirectional current conversion modules. In this way, the influence of the short-circuit current on other switch tubes in the first bidirectional current conversion module and other bidirectional current conversion modules can be avoided, and the other modules can still work normally.

[0010] In some embodiments, the decoupling circuit comprises a first balancing switch tube, a second balancing switch tube and a balancing inductor. The first balancing switch tube and the second balancing switch tube are connected in series and then connected in parallel at the DC end of the inverter bridge circuit. The first end of the balancing inductor is connected to the middle node of the first balancing switch tube and the second balancing switch tube, and the second end of the balancing inductor is connected to the midpoint of the inverter bridge circuit. The decoupling circuit is used to decouple the midpoints of the plurality of bidirectional current conversion modules by adjusting the on-off of the first balancing switch tube and the second balancing switch tube.

[0011] According to the above technical means, the midpoint of each module can be independently controlled through the decoupling circuit, the midpoints of the modules are decoupled, and thus the influence of the change of the midpoint potential of a single module on other modules can be avoided, and the circulation between different modules can be avoided. On the other hand, the decoupling circuit and the plurality of fuses work together, so that the DC end, the AC end and the midpoint of the plurality of bidirectional current conversion modules in the current conversion circuit are decoupled, the plurality of bidirectional current conversion modules can work together, and when one or more modules fail, the service can be quickly withdrawn to ensure the safe operation of the entire system.

[0012] In some embodiments, the inverter bridge circuit further comprises: a positive bus capacitor and a negative bus capacitor, which are respectively arranged between the positive DC bus and the negative DC bus and the midpoint of the inverter bridge circuit; one end of the first fuse is connected to the positive DC bus, and the other end is connected to one end of the positive bus capacitor away from the midpoint of the inverter bridge circuit; one end of the second fuse is connected to the negative DC bus, and the other end is connected to one end of the negative bus capacitor away from the midpoint of the inverter bridge circuit.

[0013] In the second aspect, a bidirectional traction current conversion system is provided, comprising a plurality of bidirectional current conversion modules connected in parallel, a controller, a positive DC bus, a negative DC bus and a power grid; the bidirectional current conversion module comprises: an inverter bridge circuit having a DC end and an AC end, the DC end being connected to the positive DC bus and the negative DC bus, and the AC end being connected to the power grid; a decoupling circuit connected to the midpoint of the inverter bridge circuit to decouple the midpoints of the plurality of bidirectional current conversion modules; a first fuse arranged between the DC end of the inverter bridge circuit and the positive DC bus; a second fuse arranged between the DC end of the inverter bridge circuit and the negative DC bus; when a half bus short circuit occurs in the inverter bridge circuit of a first bidirectional current conversion module in the plurality of bidirectional current conversion modules, the first fuse and / or the second fuse are fused to decouple the DC end of the first bidirectional current conversion module from other bidirectional current conversion modules; wherein the first bidirectional current conversion module is any one of the plurality of bidirectional current conversion modules; the controller is connected to the plurality of bidirectional current conversion modules and is used to control the inverter bridge circuit in the plurality of bidirectional current conversion modules to perform bidirectional current conversion between the DC end and the AC end, so as to supply power to a DC load through the positive DC bus and the negative DC bus, or to convert the power generated by the DC load to the power grid.

[0014] In some embodiments, the bidirectional current conversion module further comprises a plurality of third fuses respectively arranged between the AC end of the inverter bridge circuit and the plurality of phases of the power grid; when a half bus short circuit occurs in the inverter bridge circuit of the first bidirectional current conversion module, one or more of the plurality of third fuses are blown to decouple the AC end of the first bidirectional current conversion module from the AC end of other bidirectional current conversion modules.

[0015] In some embodiments, the decoupling circuit comprises a first balancing switch tube, a second balancing switch tube, and a balancing inductor; the first balancing switch tube and the second balancing switch tube are connected in series and then connected in parallel at the DC end of the inverter bridge circuit; a first end of the balancing inductor is connected to an intermediate node of the first balancing switch tube and the second balancing switch tube, and a second end of the balancing inductor is connected to the midpoint of the inverter bridge circuit; the controller is configured to adjust the on-off of the first balancing switch tube and the second balancing switch tube, thereby decoupling the midpoints of the plurality of bidirectional current conversion modules.

[0016] In some embodiments, the inverter bridge circuit further comprises a positive bus capacitor and a negative bus capacitor respectively arranged between the positive DC bus and the negative DC bus and the midpoint of the inverter bridge circuit; one end of the first fuse is connected to the positive DC bus, and the other end is connected to one end of the positive bus capacitor away from the midpoint of the inverter bridge circuit; one end of the second fuse is connected to the negative DC bus, and the other end is connected to one end of the negative bus capacitor away from the midpoint of the inverter bridge circuit.

[0017] In a third aspect, a control method of a bidirectional traction current conversion system is provided, the bidirectional traction current conversion system comprising: a plurality of bidirectional current conversion modules connected in parallel, a positive DC bus, a negative DC bus, and a power grid; each bidirectional current conversion module comprising: an inverter bridge circuit having a DC end and an AC end, the DC end being configured to be connected to the positive DC bus and the negative DC bus, and the AC end being configured to be connected to the power grid; a decoupling circuit connected to the midpoint of the inverter bridge circuit to decouple the midpoints of the plurality of bidirectional current conversion modules; a first fuse arranged between the DC end of the inverter bridge circuit and the positive DC bus; and a second fuse arranged between the DC end of the inverter bridge circuit and the negative DC bus; when a half bus short circuit occurs in the inverter bridge circuit of a first bidirectional current conversion module among the plurality of bidirectional current conversion modules, the first fuse and / or the second fuse is blown to decouple the DC end of the first bidirectional current conversion module from the DC end of other bidirectional current conversion modules, wherein the first bidirectional current conversion module is any one of the plurality of bidirectional current conversion modules; the method comprising: controlling the inverter bridge circuit in the plurality of bidirectional current conversion modules to perform bidirectional current conversion between the DC end and the AC end, so as to supply power to a DC load through the positive DC bus and the negative DC bus, or to invert the power generated by the DC load to the power grid.

[0018] In some embodiments, the decoupling circuit comprises a first balanced switch tube, a second balanced switch tube, and a balanced inductor, the first balanced switch tube and the second balanced switch tube are connected in series and then connected in parallel at the DC end of the inverter bridge circuit, a first end of the balanced inductor is connected to the middle node of the first balanced switch tube and the second balanced switch tube, and a second end of the balanced inductor is connected to the midpoint of the inverter bridge circuit; the method further comprises: determining a DC bus voltage difference value, the DC bus voltage difference value being the difference between a first voltage between the positive DC bus and the midpoint of the inverter bridge circuit and a second voltage between the negative DC bus and the midpoint of the inverter bridge circuit; determining a first pulse width modulation signal and a second pulse width modulation signal based on a proportional and integral control algorithm according to the DC bus voltage difference value; and controlling the on-off of the first balanced switch tube and the second balanced switch tube according to the first pulse width modulation signal and the second pulse width modulation signal, so as to adjust the DC bus voltage difference value to a target range. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A schematic diagram of a rail transit traction system to which the technical scheme provided by the embodiments of the present application is applied;

[0020] Figure 2 A schematic diagram of a bidirectional traction conversion device in a rail transit vehicle in Figure 1

[0021] Figure 3 A circuit topology diagram of an ANPC type three-level conversion circuit;

[0022] Figure 4 A schematic diagram of a bidirectional traction conversion circuit;

[0023] Figure 5 A schematic circuit diagram of a bidirectional traction conversion system of a bidirectional conversion module provided by the embodiments of the present application;

[0024] Figure 6 A schematic circuit diagram of a bidirectional traction conversion system provided by the embodiments of the present application;

[0025] Figure 7 A schematic circuit diagram of a bidirectional traction conversion system provided by another embodiment of the present application;

[0026] Figure 8 A schematic circuit diagram of a bidirectional traction conversion system provided by another embodiment of the present application;

[0027] Figure 9 A schematic structural diagram of a bidirectional traction conversion system provided by the embodiments of the present application;

[0028] ​Figure 10 A schematic flow chart of a control method of the bidirectional traction conversion system is also provided for the embodiments of the present application. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application.

[0030] It should be noted that the “connection” in the embodiments of the present application refers to electrical connection, and the connection between two electrical elements can be direct or indirect connection between the two electrical elements. For example, A is connected with B, which can be direct connection between A and B, or indirect connection between A and B through one or more other electrical elements. For example, A is connected with B, which can also be that A is directly connected with C, C is directly connected with B, and A is connected with B through C.

[0031] In addition, the reference to “one embodiment” or “some embodiments” and the like in the present specification means that a particular feature, structure or characteristic described in connection with the embodiment is included in one or more embodiments of the present application. Therefore, the statements “in one embodiment”, “in some embodiments”, “in other some embodiments”, “in yet some embodiments” and the like appearing in different places in the present specification are not necessarily all referring to the same embodiment, but mean “one or more but not all embodiments”, unless otherwise specifically emphasized. The terms “include”, “contain”, “have” and their variants mean “including but not limited to”, unless otherwise specifically emphasized.

[0032] The ordinal numbers “first”, “second” and the like mentioned in the embodiments of the present application are used to distinguish a plurality of objects, and are not used to limit the order, time sequence, priority or importance of the plurality of objects.

[0033] Currently, the power supply system of rail transit mostly uses a unidirectional rectifying device to convert electrical energy from three-phase alternating current into direct current to provide direct current power for rail transit vehicles. In order to realize the bidirectional flow of energy between the direct current side and the alternating current side of the power supply system of rail transit and provide stable direct current overhead line voltage, a regenerative bidirectional traction power supply device is also introduced into the power supply system of rail transit. The alternating current side of the regenerative bidirectional traction power supply device is connected to an alternating current power grid, and the direct current side is connected to a direct current traction network. When the rail transit vehicle is in a traction state, the power supply device works in a rectifying state to convert alternating current from the alternating current power grid into direct current to supply power to the direct current traction network. When the rail transit vehicle is in a braking state, the power supply device works in an inverting state to convert direct current from the direct current traction network into alternating current to feed back to the alternating current power grid.

[0034] Figure 1is a schematic diagram of a rail transit traction system to which the technical solution provided by the embodiments of the present application is applied.

[0035] As shown in Figure 1 , the rail transit traction system 100 includes an alternating current power grid 110, a bidirectional traction converter 120, and a traction motor 130.

[0036] Figure 1 The rail 140 and the vehicle 150 in the rail transit system are also shown in the figure, wherein the rail 140 is provided with a direct current contact network 160 above, the bidirectional traction converter 120 is arranged between the alternating current power grid 110 and the direct current contact network 160, and is used to rectify the alternating current provided by the alternating current power grid 110 to provide direct current suitable for the traction motor 130, and the vehicle 150 can obtain the direct current through the pantograph 151 thereon. In addition, when the vehicle 150 is in a braking state, the traction motor 130 can generate direct current under the action of electromagnetic induction and transmit it to the direct current contact network 160; at this time, the bidirectional traction converter 120 can invert the direct current to feed back the direct current generated by the traction motor 130 to the alternating current power grid 110.

[0037] Figure 2 is Figure 1 a schematic diagram of the bidirectional traction converter 120 in the figure, as shown in Figure 2 , the bidirectional traction converter 120 includes at least one bidirectional converter module 121, the alternating current end of the bidirectional converter module 121 is connected with the alternating current bus, and the direct current end is connected with the direct current load.

[0038] When the bidirectional traction converter 120 includes at least two bidirectional converter modules 121, the bidirectional converter modules are connected in parallel. Each bidirectional converter module can work simultaneously, or part of the bidirectional converter modules work simultaneously, and the remaining bidirectional converter modules are used as backup, and when the working bidirectional converter module fails, the backup bidirectional converter module replaces the failed bidirectional converter module. Exemplarily, if the bidirectional traction converter includes two bidirectional converter modules, the two bidirectional converter modules can work simultaneously, or one of the bidirectional converter modules works and the other bidirectional converter module is used as backup, and when the working bidirectional converter module fails, the backup bidirectional converter module replaces the failed bidirectional converter module to work.

[0039] The bidirectional converter module can be any one of a three-level converter, an interleaved converter, a cascaded H-bridge converter, and the like. The active neutral-point-clamped (ANPC) three-level converter is a topology developed on the basis of a conventional neutral-point-clamped (NPC) three-level converter, and achieves more flexible neutral-point potential control and lower switching loss by introducing active switching devices.

[0040] Figure 3 A circuit topology of an ANPC three-level converter is shown, and a detailed description is provided below in combination with Figure 3 .

[0041] The ANPC three-level converter is suitable for working in an inverter mode and / or a rectifier mode, and includes a control circuit and a main circuit. The main circuit includes an upper bridge arm composed of a first switching tube T1, a second switching tube T2, and a fifth switching tube T5, and a lower bridge arm composed of a third switching tube T3, a fourth switching tube T4, and a sixth switching tube T6. The first switching tube T1 and the fourth switching tube T4 are respectively connected to a positive terminal BUS+ and a negative terminal BUS- of a DC network, a connection point of the fifth switching tube T5 and the sixth switching tube T6 is connected to a neutral terminal of the DC network, and a connection point of the second switching tube T2 and the third switching tube T3 is connected to an AC network.

[0042] As a possible implementation, the first switching tube T1 and the fifth switching tube T5 are packaged in the same switching tube packaging module, the fourth switching tube T4 and the sixth switching tube T6 are packaged in the same switching tube packaging module, and the second switching tube T2 and the third switching tube T3 are packaged in the same switching tube packaging module.

[0043] The control circuit is used to control the on-off of each switching tube in the main circuit, including: when the AC network is an input end, controlling the conduction and turn-off of the switching device to realize rectification of the AC voltage; and when the DC network is an input end, controlling the conduction and turn-off of the switching device to convert the DC voltage into a three-phase AC voltage to form a required AC waveform.

[0044] In the ANPC three-level converter shown in Figure 3 , each switching tube is a controllable switching tube with an anti-parallel diode, and the diodes corresponding to the switching tubes are denoted by D1, D2, D3, D4, D5, and D6.

[0045] In actual applications, pulse width modulation (PWM) technology is usually used to control the conduction time and turn-off time of the switching tubes, and the duty cycle of the PWM signal is adjusted to control the size of the output DC voltage.

[0046] In the case that the aforementioned alternating current power grid is a three-phase alternating current power grid, as shown in Figure 4 each bidirectional current conversion module includes three ANPC type three-level converters in parallel, the direct current ends of the three ANPC type three-level converters are connected with the direct current bus, and the alternating current ends are respectively connected with different phases of the three-phase alternating current power grid, and by controlling the phase of the conduction and the opening of the multiple switch tubes in the three ANPC type three-level converters, the conversion between the direct current and the three-phase alternating current can be realized.

[0047] The problems existing in the actual application of the bidirectional traction current conversion device are described in detail below.

[0048] Firstly, when the multiple ANPC three-level converters operate in parallel, due to the parameter differences between the ANPC modules, the conduction voltage drop differences of the switch tubes, and the load imbalance and other factors, the output voltage amplitude, phase and frequency of each converter will be different, and then the circulating current will be generated between the parallel branches. The circulating current refers to the current flowing between the parallel converters without flowing through the load. The circulating current will increase the loss of the converter and reduce the efficiency of the system. At the same time, the circulating current may be too large to trigger the overcurrent protection device, which will affect the normal operation of the system, and even may damage the converter.

[0049] Secondly, when the parallel system adopts a three-level circuit, in order to ensure the power quality and the efficiency, the midpoint potentials of each three-level circuit need to be controlled to be consistent. For example, in the case that the midpoint potentials of the first module and the second module are inconsistent, i.e. there is a potential difference between the midpoints of different modules, the existence of the potential difference will generate a current flowing from the midpoint of the first module to the midpoint of the second module through the alternating current side, which is the aforementioned circulating current. In the related art, in order to suppress the circulating current between different modules, the midpoints of different modules can be directly connected to make the midpoint potentials of different modules consistent, so as to achieve the purpose of suppressing the circulating current.

[0050] Finally, during the operation of the bidirectional traction current conversion device, the positive half bus or the negative half bus of the direct current side may be short-circuited due to insulation aging, overvoltage breakdown, line fault, load imbalance or load mutation and other reasons.

[0051] In the case that the aforementioned alternating current power grid is a three-phase alternating current power grid, as shown in Figure 4The circuit shown is an example, and each bidirectional current conversion module further includes a first capacitor and a second capacitor, which are respectively arranged between the direct current positive bus and the direct current negative bus and the midpoint. Taking the first bidirectional current conversion module in the figure as an example, when the first capacitor C1 is short-circuited, the half bus of the first module is short-circuited at this time, and the midpoint potential of the first module is pulled up to be consistent with the potential of the positive direct current bus at this time. At this time, the potential difference between the negative direct current bus and the midpoint is also pulled up. If the potential difference between the negative direct current bus and the midpoint is greater than the withstand voltage limit of the second capacitor or the third switch tube T3, the fourth switch tube T4 and the sixth switch tube T6 in the lower bridge arm, the above-mentioned devices will be broken down, resulting in the failure of the entire module. Further, if a module is short-circuited, since the direct current end and the alternating current end of each module are connected together, the midpoint of all modules will be pulled up to be consistent with the positive direct current bus, which will cause the stress of other modules to increase synchronously.

[0052] In view of the above problems, the embodiment of the present application provides a modular bidirectional current conversion module, a bidirectional traction current conversion system and a control method thereof.

[0053] Figure 5 is a schematic circuit diagram of a bidirectional traction current conversion system 500 applying the current conversion module provided by the embodiment of the present application, and the bidirectional traction current conversion system 500 includes a plurality of current conversion modules 510, a positive direct current bus BUS+, a negative direct current bus BUS- and a power grid 520.

[0054] The plurality of current conversion modules 510 in the bidirectional traction current conversion system 500 are connected in parallel with each other, and each current conversion module 510 includes an inverter bridge circuit 511, a decoupling circuit 512, a first fuse F1 and a second fuse F2.

[0055] The inverter bridge circuit 511 is a core component of the current conversion module 510, and can work in an inverter mode or a rectifier mode. For example, when applied to the foregoing rail transit vehicle, in the vehicle braking state, the inverter bridge circuit can work in the inverter mode, so as to convert the direct current generated by the motor braking into alternating current and feedback to the power grid 520; in the normal running state of the vehicle, the inverter bridge circuit is in the rectifier mode, for converting the alternating current provided by the power grid 520 into direct current, so as to drive the motor and other direct current loads.

[0056] In the embodiment of the present application, the inverter bridge circuit 511 has a direct current end and an alternating current end, wherein the direct current end is used for connecting with the positive direct current bus BUS+ and the negative direct current bus BUS-, and the alternating current end is used for connecting with the power grid 520.

[0057] The form of the inverter bridge circuit is not specifically limited in the embodiment of the present application, and the inverter bridge circuit may, for example, be a full-bridge inverter circuit, a three-phase inverter circuit, a multi-level inverter circuit and the like.

[0058] For example,Figure 6 As shown, each inverter bridge circuit in the bidirectional traction converter system includes three ANPC type three-level converters connected in parallel. The DC positive and DC negative terminals of the three ANPC type three-level converters are connected to BUS+ and BUS- respectively, and the DC terminals are connected to the three phases of the three-phase AC power grid. The midpoints of the three ANPC type three-level converters are connected to each other.

[0059] See Figure 5 and Figure 6 The decoupling circuit is connected to the midpoint of the inverter bridge circuit to decouple the midpoints of multiple bidirectional converter modules. This decoupling circuit ensures that there is no direct electrical connection between the midpoints of multiple bidirectional converter modules, preventing mutual interference in case of faults. For example, when a module experiences a short circuit or a sudden change in midpoint potential, the decoupling circuit can prevent it from affecting the midpoint potentials of other modules, avoiding a series of chain reactions.

[0060] The first fuse F1 is installed between the DC terminal of the inverter bridge circuit and the positive DC bus, and the second fuse F2 is installed between the DC terminal of the inverter bridge circuit and the negative DC bus.

[0061] The first fuse F1 and the second fuse F2 can melt when the current exceeds their own limit, thereby cutting off the connection between the module and the DC bus.

[0062] When a half-bus short circuit occurs in the inverter bridge circuit of the first bidirectional converter module among multiple bidirectional converter modules, the first fuse F1 and / or the second fuse F2 blows, thereby decoupling the DC terminals of the first bidirectional converter module from those of other bidirectional converter modules. The aforementioned first bidirectional converter module can be any one of the multiple bidirectional converter modules.

[0063] In some embodiments of this application, such as Figure 6 As shown, the bidirectional converter module also includes a positive bus capacitor C3 and a negative bus capacitor C4, which are respectively located between the positive DC bus and the negative DC bus and the midpoint of the inverter bridge circuit; the first end of the aforementioned first fuse F1 is connected to the positive DC bus, and the other end is connected to the end of the positive bus capacitor away from the midpoint; one end of the aforementioned second fuse F2 is connected to the negative DC bus, and the other end is connected to the end of the negative bus capacitor away from the midpoint.

[0064] The following is combined with Figure 6 To further explain the above process, let's take the first bidirectional converter module as an example. Figure 6Taking the first bidirectional converter module shown as an example, when a short circuit occurs on the positive half bus of the first bidirectional converter module, the positive DC bus is directly connected to the midpoint, forming a low-impedance path. The potential of the midpoint jumps to the same level as the potential of the positive DC bus. At the moment of the short circuit, the current of the positive DC bus rises rapidly, possibly reaching 10-20 times the normal current value. When this current exceeds the minimum melting current of F1 and F2, the fuses of the first fuse F1 and / or the second fuse F2 heat up and melt, cutting off the connection between the DC terminal of the first bidirectional converter module and the DC bus, thereby decoupling the first bidirectional converter module from other modules and preventing the failure of the module from affecting the normal operation of other modules.

[0065] According to the technical solution provided in the embodiments of this application, by setting a decoupling circuit for each bidirectional converter module, the midpoints of multiple bidirectional converter modules in the bidirectional traction converter system are decoupled from each other, avoiding the chain reaction caused by the influence of midpoint potential changes of some bidirectional converter modules on the midpoint potentials of other modules; by setting a first fuse and a second fuse between the bidirectional converter module and the DC bus, when a half-bus short circuit occurs in some bidirectional converter modules, the fuse can intervene in time to decouple the short-circuited module from other modules, ensuring that other modules can still work normally. When applied to rail transit vehicles, it can avoid the overall shutdown caused by the failure of a single module.

[0066] In some embodiments, such as Figure 7 As shown, the bidirectional converter module also includes multiple third fuses F3, which are disposed between the AC terminals of the inverter bridge circuit and multiple phases of the AC power grid.

[0067] Still with Figure 6 Taking the circuit shown as an example, the A-phase, B-phase, and C-phase inputs of the three-phase AC power grid are converted into a-phase output, b-phase output, and c-phase output by a transformer, which are respectively connected to the AC terminals of the three ANPC type three-level converters in the inverter bridge module.

[0068] In some implementations, a filter circuit is also provided between the three-phase AC power grid and the inverter bridge circuit, including three filter inductors L and three filter capacitors C. The three filter inductors are respectively set between the three phases of the three-phase AC power grid and the AC terminals of the three ANPC type three-level converters. One end of the three filter capacitors is connected, and the other end is respectively connected to the end of the three filter inductors that is closer to the three-phase AC power grid.

[0069] exist Figure 6 In the circuit shown, each bidirectional converter module is equipped with three third fuses F3, which are located between the three filter inductors and the three-phase AC power grid.

[0070] When a half bus short circuit occurs in the inverter bridge circuit of the first bidirectional current conversion module, one or more of the plurality of third fuses F3 are fused to decouple the AC terminal of the first bidirectional current conversion module from the AC terminals of other bidirectional current conversion modules.

[0071] Still taking the first bidirectional current conversion module as an example, the first bidirectional current conversion module is taken as the first bidirectional current conversion module in the bidirectional traction current conversion system. Figure 6 Taking the first bidirectional current conversion module as an example, the three ANPC type three-level converters in parallel in the first bidirectional current conversion module are denoted as a first converter, a second converter and a third converter respectively.

[0072] For example, in the case of a short circuit of the first switch tube and the second switch tube of the first converter, the AC terminal of the first converter is conductive with the DC bus to form a low impedance path, at this time, the current of the positive DC bus flows to the transformer through the short circuit point and the AC terminal of the first converter; in the transformer, since the three-phase transformer coils are connected with each other, the current of the positive DC bus flows to the AC terminals of the second converter and the third converter through the AC terminal.

[0073] At the same time, since the inverter bridge circuits of the plurality of bidirectional current conversion modules in the bidirectional traction current conversion system are connected with the AC transformer in the AC power grid, the short circuit current in the first bidirectional current conversion module will flow into other bidirectional current conversion modules through the AC bus.

[0074] In the case of a short circuit of the first switch tube and the second switch tube of the first converter, the short circuit current will sharply increase due to the small impedance of the current path, which will cause other switch tubes in the first bidirectional current conversion module and each switch tube in other bidirectional current conversion modules to bear a large current, which will cause the other switch tubes to be impacted.

[0075] In the technical solution of the present application, since the third fuse exists, when the above-mentioned short circuit occurs, the short circuit current flowing into the transformer through the AC terminal of the first converter is greater than the minimum melting current of the F3, so that the third fuse F3 connected with the AC terminal of the first converter is quickly fused, cutting off the connection between the short circuit point in the first bidirectional current conversion module and the AC bus, thereby decoupling the AC terminals of the first bidirectional current conversion module from the AC terminals of other bidirectional current conversion modules, so that the influence of the short circuit current on other switch tubes in the first bidirectional current conversion module and other bidirectional current conversion modules can be avoided, and normal work of other modules can be ensured.

[0076] In some embodiments, as Figure 8As shown, the decoupling circuit 512 includes a first balance switch tube Q1, a second balance switch tube Q2 and a balance inductor Lb. The first balance switch tube Q1 and the second balance switch tube Q2 are connected in series and then in parallel to the DC end of the inverter bridge circuit 511, the first end of the balance inductor Lb is connected to the middle node of the first balance switch tube Q1 and the second balance switch tube Q2, and the second end of the balance inductor Lb is connected to the midpoint of the inverter bridge circuit 511.

[0077] The decoupling circuit 512 is used to decouple the midpoint of the plurality of bidirectional current conversion modules by adjusting the on-off of the first balance switch tube Q1 and the second balance switch tube Q2.

[0078] For each bidirectional current conversion module, the voltage of the positive bus capacitor C3 and the negative bus capacitor C4 is controlled by the switching of the first balance switch tube Q1 and the second balance switch tube Q2. When the voltage of the positive bus capacitor C3 is greater than the voltage of the negative bus capacitor C4, the first balance switch tube Q1 is turned on to charge the balance inductor Lb. When the first balance switch tube Q1 is turned off, the balance inductor Lb charges the negative bus capacitor C4 due to the freewheeling of the balance inductor Lb, thereby increasing the voltage of the negative bus capacitor C4. Conversely, when the voltage of the negative bus capacitor C4 is greater than the voltage of the positive bus capacitor C3, the second balance switch tube Q2 is turned on to charge the balance inductor Lb. When the second balance switch tube Q2 is turned off, the balance inductor Lb charges the positive bus capacitor C3. This process is repeated to ensure that the midpoint potential of each bidirectional current conversion module is balanced and stable. By independently adjusting the midpoint potential of each bidirectional current conversion module, the midpoint decoupling between the plurality of modules is achieved.

[0079] In the technical scheme of the embodiments of the present application, the decoupling circuit can independently control the midpoint of each module, achieve the midpoint decoupling between the plurality of modules, and thereby avoid the influence of the change of the midpoint potential of a single module on other modules and avoid the formation of circulating current between different modules. On the other hand, the decoupling circuit and the plurality of fuses described above jointly act to decouple the DC end, the AC end and the midpoint of the plurality of bidirectional current conversion modules in the bidirectional traction current conversion system, so that the plurality of bidirectional current conversion modules can work together and quickly exit the work when one or more modules fail, thereby ensuring the safe operation of the entire system.

[0080] Figure 9 is a schematic structural diagram of the bidirectional traction current conversion system 900 provided by the embodiments of the present application. As shown, Figure 9 The bidirectional traction current conversion system 900 includes a plurality of bidirectional current conversion modules 910 connected in parallel, a controller 920, a power grid 930, a positive DC bus BUS+, and a negative DC bus BUS-. The positive DC bus and the negative DC bus are used to be connected with a DC load.

[0081] The bidirectional converter module 910 includes an inverter bridge circuit 911, a decoupling circuit 912, a first fuse 913 and a second fuse 914.

[0082] The inverter bridge circuit 911 includes a DC end and an AC end, the DC end is connected with the positive DC bus and the negative DC bus, and the AC end is connected with the power grid 930.

[0083] In some embodiments, the inverter bridge circuit 911 includes an ANPC type three-level conversion circuit as shown in the foregoing. Figure 3

[0084] The decoupling circuit 912 is connected with the midpoint of the inverter bridge circuit 911 to decouple the midpoints of the plurality of bidirectional converter modules 910.

[0085] The first fuse 913 is arranged between the DC end of the inverter bridge circuit 911 and the positive DC bus, and the second fuse 914 is arranged between the DC end of the inverter bridge circuit 911 and the negative DC bus.

[0086] When the inverter bridge circuit of a first bidirectional converter module in the plurality of bidirectional converter modules has a half bus short circuit, the first fuse and / or the second fuse corresponding to the first bidirectional converter module are fused to decouple the DC end of the first bidirectional converter module from other bidirectional converter modules, wherein the first bidirectional converter module is any one of the plurality of bidirectional converter modules.

[0087] The controller 920 is connected with the plurality of bidirectional converter modules 910 to control the inverter bridge circuit 911 in the plurality of bidirectional converter modules 910 to perform bidirectional conversion between the DC end and the AC end, so as to supply power to the DC load through the positive DC bus and the negative DC bus, or to convert the power generated by the DC load to the power grid.

[0088] As a possible implementation manner, the number of the controller 920 can be multiple, and the multiple controllers 920 are connected with the plurality of bidirectional converter modules 910 correspondingly. Each controller 920 is used to control the turn-on and turn-off of each switch tube in the corresponding connected bidirectional converter module 910, and to execute the module-level protection logic, etc.

[0089] In addition to the multiple controllers 920, the bidirectional traction converter system 900 further includes a system-level controller which can be connected with the multiple controllers 920 to execute the system-level scheduling and the system-level protection logic.

[0090] Alternatively, as another possible implementation manner, the number of the controller 920 can be one, and the one controller 920 is connected with the plurality of bidirectional converter modules 910 to control the switch tubes in the bidirectional converter modules 910.

[0091] ​In some embodiments, the bidirectional current conversion module further comprises a plurality of third fuses respectively arranged between the AC end of the inverter bridge circuit and the plurality of phases of the power grid.

[0092] When a half bus short circuit occurs in the inverter bridge circuit of the first bidirectional current conversion module, one or more of the plurality of third fuses are blown to decouple the AC end of the first bidirectional current conversion module from the AC end of the other bidirectional current conversion modules.

[0093] In some embodiments, the decoupling circuit comprises a first balancing switch tube, a second balancing switch tube and a balancing inductor. The first balancing switch tube and the second balancing switch tube are connected in series and then in parallel to the DC end of the inverter bridge circuit. The first end of the balancing inductor is connected to the middle node of the first balancing switch tube and the second balancing switch tube, and the second end of the balancing inductor is connected to the midpoint of the inverter bridge circuit.

[0094] The controller is configured to adjust the on-off of the first balancing switch tube and the second balancing switch tube, so as to decouple the midpoints of the plurality of bidirectional current conversion modules.

[0095] In some embodiments, the inverter bridge circuit further comprises a positive bus capacitor and a negative bus capacitor respectively arranged between the positive DC bus and the negative DC bus and the midpoint of the inverter bridge circuit.

[0096] One end of the first fuse is connected to the positive DC bus, and the other end is connected to one end of the positive bus capacitor away from the midpoint.

[0097] One end of the second fuse is connected to the negative DC bus, and the other end is connected to one end of the negative bus capacitor away from the midpoint.

[0098] The above describes the device embodiments of the present application in detail. Figures 1-9 The method embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the method embodiments correspond to the aforementioned device embodiments, and therefore, the parts not described in detail can be referred to the aforementioned device embodiments.

[0099] Figure 10 is a schematic flowchart of a control method of a bidirectional traction current conversion system provided by the embodiments of the present application. The bidirectional traction current conversion system may, for example, be Figure 9The bidirectional traction converter system 900 shown in the figure. The bidirectional traction converter system comprises: a plurality of bidirectional converter modules connected in parallel, a positive DC bus, a negative DC bus and a power grid; wherein the bidirectional converter module comprises: an inverter bridge circuit having a DC end and an AC end, the DC end being used to connect with the positive DC bus and the negative DC bus, and the AC end being used to connect with the power grid; a decoupling circuit connected with the midpoint of the inverter bridge circuit to decouple the midpoints of the plurality of bidirectional converter modules; a first fuse arranged between the DC end of the inverter bridge circuit and the positive DC bus; a second fuse arranged between the DC end of the inverter bridge circuit and the negative DC bus; when the inverter bridge circuit of a first bidirectional converter module in the plurality of bidirectional converter modules occurs a half-bus short circuit, the first fuse and / or the second fuse are fused to decouple the DC end of the first bidirectional converter module from other bidirectional converter modules, wherein the first bidirectional converter module is any one of the plurality of bidirectional converter modules.

[0100] Figure 10 The method in the figure comprises: step S1010, controlling the inverter bridge circuit in the plurality of bidirectional converter modules to perform bidirectional conversion between the DC end and the AC end, to supply power to a DC load through the positive DC bus and the negative DC bus, or to invert the electric energy generated by the DC load to the power grid.

[0101] In some embodiments, the decoupling circuit comprises a first balancing switch tube, a second balancing switch tube and a balancing inductor, the first balancing switch tube and the second balancing switch tube are connected in series and then connected in parallel at the DC end of the inverter bridge circuit, a first end of the balancing inductor is connected with an intermediate node of the first balancing switch tube and the second balancing switch tube, and a second end of the balancing inductor is connected with the midpoint of the inverter bridge circuit.

[0102] The foregoing control method further comprises: determining a DC bus voltage difference value, the DC bus voltage difference value being a difference between a first voltage between the positive DC bus and the midpoint and a second voltage between the negative DC bus and the midpoint; determining the first pulse width modulation signal and the second pulse width modulation signal based on a proportional and integral control algorithm according to the DC bus voltage difference value; and controlling the on-off of the first balancing switch tube and the second balancing switch tube according to the first pulse width modulation signal and the second pulse width modulation signal, to adjust the DC bus voltage difference value to a target range.

[0103] The embodiments of the present application also provide a computer readable storage medium, which stores a computer program, and the computer program is executed to implement the foregoing method steps.

[0104] In several embodiments provided in the present application, it should be understood that the disclosed system, device and method can be implemented by other manners. For example, the above-described device embodiments are merely illustrative, for example, the division of the units is merely a logical function division, and in actual implementation, another division manner can be adopted, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units shown or discussed can be indirect coupling or communication connection through some interfaces, devices or units, and can be electrical, mechanical or other forms.

[0105] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e., can be located in one place or can be distributed to a plurality of network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.

[0106] In addition, the functional units in each embodiment of the present application can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit.

[0107] In the above embodiments, all or part can be realized by software, hardware, firmware or any combination thereof. When realized by software, all or part can be realized in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network or other programmable device. The computer instructions can be stored in a computer readable storage medium or transferred from one computer readable storage medium to another, for example, the computer instructions can be transferred from one website, computer, server or data center to another website, computer, server or data center through wired (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.) manner. The computer readable storage medium can be any available medium readable by a computer or a data storage device such as a server, data center, etc. integrated with one or more available media. The available media can be magnetic media (such as floppy disk, hard disk, magnetic tape), optical media (such as digital video disc (DVD)) or semiconductor media (such as solid state disk (SSD)) etc.

[0108] The above description is only specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A bidirectional current conversion module, characterized in that, The application relates to a bidirectional traction converter system applied to multiple parallel bidirectional converter modules, wherein the bidirectional traction converter system comprises a positive DC bus, a negative DC bus and a power grid. The bidirectional converter module comprises: an inverter bridge circuit having a DC end and an AC end, wherein the DC end is used for being connected with the positive DC bus and the negative DC bus, the positive DC bus and the negative DC bus are used for being connected with a DC load, and the AC end is used for being connected with the power grid; a decoupling circuit connected with a midpoint of the inverter bridge circuit, so that the midpoints of the multiple bidirectional converter modules are decoupled without being directly connected; a first fuse arranged between the DC end of the inverter bridge circuit and the positive DC bus; a second fuse arranged between the DC end of the inverter bridge circuit and the negative DC bus; when a half-bus short circuit occurs in the inverter bridge circuit of a first bidirectional converter module in the multiple bidirectional converter modules, the first fuse and / or the second fuse are fused, so that the DC end of the first bidirectional converter module is decoupled from other bidirectional converter modules, wherein the first bidirectional converter module is any one of the multiple bidirectional converter modules.

2. The bidirectional converter module according to claim 1, wherein the bidirectional converter module further comprises multiple third fuses respectively arranged between the AC end of the inverter bridge circuit and multiple phases of the power grid; when the half-bus short circuit occurs in the inverter bridge circuit of the first bidirectional converter module, one or more of the multiple third fuses are fused, so that the AC end of the first bidirectional converter module is decoupled from other bidirectional converter modules.

3. The bidirectional converter module according to claim 2, wherein the decoupling circuit comprises a first balance switch tube, a second balance switch tube and a balance inductor, the first balance switch tube and the second balance switch tube are connected in series and then connected in parallel at the DC end of the inverter bridge circuit, a first end of the balance inductor is connected with an intermediate node of the first balance switch tube and the second balance switch tube, and a second end of the balance inductor is connected with the midpoint of the inverter bridge circuit; the decoupling circuit is used for adjusting the on-off of the first balance switch tube and the second balance switch tube, so that the midpoints of the multiple bidirectional converter modules are decoupled.

4. A bidirectional current module according to any one of claims 1-3, characterized in that, the inverter bridge circuit further comprises: a positive bus capacitor and a negative bus capacitor arranged between the positive DC bus and the negative DC bus and the midpoint of the inverter bridge circuit; one end of the first fuse is connected with the positive DC bus, and the other end is connected with one end of the positive bus capacitor away from the midpoint of the inverter bridge circuit; one end of the second fuse is connected with the negative DC bus, and the other end is connected with one end of the negative bus capacitor away from the midpoint of the inverter bridge circuit.

5. A bi-directional traction converter system, characterized by, The application relates to a bidirectional traction converter system applied to multiple parallel bidirectional converter modules, wherein the bidirectional traction converter system comprises a positive DC bus, a negative DC bus and a power grid. The bidirectional converter module comprises: an inverter bridge circuit having a DC end and an AC end, wherein the DC end is used for being connected with the positive DC bus and the negative DC bus, the positive DC bus and the negative DC bus are used for being connected with a DC load, and the AC end is used for being connected with the power grid; a decoupling circuit connected to the midpoint of the inverter bridge circuit to decouple the midpoints of the plurality of bidirectional current conversion modules without direct connection; a first fuse arranged between the DC end of the inverter bridge circuit and the positive DC bus; a second fuse arranged between the DC end of the inverter bridge circuit and the negative DC bus; when a half bus short circuit occurs in the inverter bridge circuit of a first bidirectional current conversion module in the plurality of bidirectional current conversion modules, the first fuse and / or the second fuse is fused to decouple the DC end of the first bidirectional current conversion module from other bidirectional current conversion modules; wherein the first bidirectional current conversion module is any one of the plurality of bidirectional current conversion modules; the controller is connected to the plurality of bidirectional current conversion modules to control the inverter bridge circuit in the plurality of bidirectional current conversion modules to perform bidirectional current conversion between the DC end and the AC end, so as to supply power to a DC load through the positive DC bus and the negative DC bus, or to invert the power generated by the DC load to the power grid.

6. The bidirectional traction current conversion system according to claim 5, wherein the bidirectional current conversion module further comprises a plurality of third fuses arranged between the AC end of the inverter bridge circuit and the multi-phase of the power grid; when a half bus short circuit occurs in the inverter bridge circuit of the first bidirectional current conversion module, one or more of the plurality of third fuses is fused to decouple the AC end of the first bidirectional current conversion module from other bidirectional current conversion modules.

7. The bidirectional traction current conversion system according to claim 6, wherein the decoupling circuit comprises a first balancing switch tube, a second balancing switch tube, and a balancing inductor, the first balancing switch tube and the second balancing switch tube are connected in series and then connected in parallel at the DC end of the inverter bridge circuit, a first end of the balancing inductor is connected to the middle node of the first balancing switch tube and the second balancing switch tube, and a second end of the balancing inductor is connected to the midpoint of the inverter bridge circuit; the controller is configured to adjust the on-off of the first balancing switch tube and the second balancing switch tube, so as to decouple the midpoints of the plurality of bidirectional current conversion modules.

8. A bidirectional traction converter system according to any one of claims 5-7, characterized in that, the inverter bridge circuit further comprises: a positive bus capacitor and a negative bus capacitor arranged between the positive DC bus and the negative DC bus and the midpoint of the inverter bridge circuit; one end of the first fuse is connected to the positive DC bus, and the other end is connected to one end of the positive bus capacitor away from the midpoint of the inverter bridge circuit; one end of the second fuse is connected to the negative DC bus, and the other end is connected to one end of the negative bus capacitor away from the midpoint of the inverter bridge circuit.

9. A control method of a bidirectional traction converter system, characterized by, The bidirectional traction current conversion system comprises: a plurality of bidirectional current conversion modules connected in parallel, a positive DC bus, a negative DC bus, and a power grid; the bidirectional current conversion module comprises: an inverter bridge circuit having a DC end and an AC end, the DC end being configured to be connected to the positive DC bus and the negative DC bus, the positive DC bus and the negative DC bus being configured to be connected to a DC load, and the AC end being configured to be connected to a power grid; A decoupling circuit is connected to the midpoint of the inverter bridge circuit to decouple the midpoints of the plurality of bidirectional current conversion modules without direct connection; A first fuse is arranged between the DC end of the inverter bridge circuit and the positive DC bus; A second fuse is arranged between the DC end of the inverter bridge circuit and the negative DC bus; When a half-bus short circuit occurs in the inverter bridge circuit of a first bidirectional current conversion module in the plurality of bidirectional current conversion modules, the first fuse and / or the second fuse are fused to decouple the DC end of the first bidirectional current conversion module from other bidirectional current conversion modules, wherein the first bidirectional current conversion module is any one of the plurality of bidirectional current conversion modules; The method comprises: controlling the inverter bridge circuit in the plurality of bidirectional current conversion modules to perform bidirectional current conversion between the DC end and the AC end to supply power to a DC load through the positive DC bus and the negative DC bus, or to invert the power generated by the DC load to the power grid.

10. The method of claim 9, wherein The decoupling circuit comprises a first balancing switch tube, a second balancing switch tube, and a balancing inductor, the first balancing switch tube and the second balancing switch tube are connected in series and then connected in parallel at the DC end of the inverter bridge circuit, a first end of the balancing inductor is connected to the midpoint of the first balancing switch tube and the second balancing switch tube, and a second end of the balancing inductor is connected to the midpoint of the inverter bridge circuit; The method comprises: determining a DC bus voltage difference value, the DC bus voltage difference value being the difference between a first voltage between the positive DC bus and the midpoint of the inverter bridge circuit and a second voltage between the negative DC bus and the midpoint of the inverter bridge circuit; determining a first pulse width modulation signal and a second pulse width modulation signal based on a proportional and integral control algorithm according to the DC bus voltage difference value; controlling the on-off of the first balancing switch tube and the second balancing switch tube according to the first pulse width modulation signal and the second pulse width modulation signal to adjust the DC bus voltage difference value to a target range.

Images