Bidirectional rail transit traction system and short circuit control method thereof

Abstract

The application provides a bidirectional rail transit traction system and a short circuit control method thereof. The bidirectional rail transit traction system comprises at least one converter module, a DC bus, an AC bus, a power grid, a short circuit module and a controller. The DC bus comprises a positive DC bus and a negative DC bus. The converter module comprises a DC end and an AC end. The DC end is connected with the DC bus, and the AC end is connected with the power grid through the AC bus. The DC side of the short circuit module is connected with the DC bus, and the AC side is connected with the AC bus. The controller is connected with the converter module, and is used for controlling the converter module to perform wave-by-wave current limiting when detecting that the current change in the DC bus reaches a first current threshold. The short circuit module is used for bypassing the short circuit current to flow through the short circuit module in the case of external load short circuit. The impedance of the first path defined by the coupling of the AC bus and the DC bus through the short circuit module is smaller than the impedance of the second path defined by the coupling of the AC bus and the DC bus through the converter module.

Description

Technical Field

[0001] This application relates to the field of rail transit technology, and in particular to a two-way rail transit traction system and its short-circuit control method. Background Technology

[0002] The rail transit traction power supply system supplies power to rail transit vehicles and other loads through a bidirectional rail transit traction system. During operation, the bidirectional rail transit traction system may encounter situations where the DC bus current abnormally increases. Causes of abnormal DC bus current include, but are not limited to, sudden load changes, overload, grid voltage fluctuations, and external load short circuits. For example, in the event of an external load short circuit, the current in the DC bus will increase sharply. This may lead to an increase in the temperature of the power devices in the converter module, causing irreversible damage to the power devices.

[0003] In related technologies, when the aforementioned current surge occurs, the connection between the converter module and the external load and power grid is quickly disconnected to avoid damage to the components in the converter module. However, immediately disconnecting the converter module from the external load and power grid in the event of a fault, while effectively protecting the bidirectional rail transit traction system itself, is not conducive to fault troubleshooting and may even lead to load damage or create potential faults for the next startup. If the bidirectional rail transit traction system could have the ability to continue operating for a period of time during a short circuit, allowing the short-circuited external load to be safely disconnected or sufficient time to troubleshoot, the aforementioned risks could be overcome. However, in the bidirectional rail transit traction system described above, the capacity of the IGBT module in the converter module alone is clearly insufficient to meet the requirements of short-circuit protection. Summary of the Invention

[0004] This application mainly provides a two-way rail transit traction system and its short-circuit control method. The technical solution of this application is implemented as follows:

[0005] In a first aspect, a bidirectional rail transit traction system is provided, comprising at least one converter module, a DC bus, an AC bus, a power grid, a short-circuit module, and a controller; the DC bus includes a positive DC bus and a negative DC bus; the converter module includes 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 through the AC bus; the DC side of the short-circuit module is connected to the positive DC bus and the negative DC bus, and the AC side of the short-circuit module is connected to the AC bus; the controller is connected to the converter module and is used to control the converter module to perform wave-by-wave current limiting when a change in current in the DC bus is detected to reach a first current threshold; the short-circuit module is used to: allow the short-circuit current to bypass through the short-circuit module in the event of a short circuit in the external load of the bidirectional rail transit traction system; wherein, the AC bus is coupled to the DC bus through the short-circuit module to form a first path, and the AC bus is coupled to the DC bus through the converter module to form a second path, and the impedance of the first path is less than the impedance of the second path.

[0006] Based on the aforementioned technical means, by setting a low-impedance first path and a high-impedance second path, when an external short circuit occurs, the short-circuit current preferentially flows through the short-circuit module, thereby avoiding large current flowing through the IGBT devices in the converter module, reducing the impact on power devices, and thus improving the short-circuit withstand capability and operational safety of the overall system. At the same time, when the controller detects an abnormal change in current, it immediately performs wave-by-wave current limiting, which helps to quickly limit the current rise, improve the system response speed, and provide sufficient detection time for short-circuit detection, avoiding misjudgment or incorrect switching of short-circuit protection that could affect the normal operation of the equipment.

[0007] In some embodiments, the bidirectional rail transit traction system further includes: a DC-side switching device disposed on the DC bus for controlling the switching of the converter module with the external load; a controller connected to the DC-side switching device, the controller being further configured to: control the DC-side switching device to disconnect when the duration of the short-circuit current is greater than or equal to a first preset time, so as to disconnect the converter module from the external load.

[0008] Based on the above technical means, after the short-circuit current lasts for more than a preset time, the controller controls the DC-side switching device to disconnect, isolating the converter module from the system, preventing further damage to the equipment caused by prolonged short circuit, and improving the safety and stability of the system.

[0009] In some embodiments, the short-circuit module includes a rectifier bridge circuit, the DC terminal of which is connected to the positive DC bus and the negative DC bus respectively, and the AC terminal of which is connected to the AC bus.

[0010] Based on the above technical means, using a rectifier bridge circuit as a short-circuit module can provide a stable low-impedance path under short-circuit conditions, ensuring that the short-circuit current can be effectively diverted and reducing the impact on the converter module.

[0011] In some embodiments, the rectifier bridge circuit is a phase-controlled rectifier circuit, which is connected to the controller; the converter module includes multiple IGBT modules, and the controller is further configured to: when the current in the DC bus changes to a first current threshold, control the switching on and off of the multiple IGBT modules in the converter module to perform wave-by-wave current limiting; when the voltage at the DC terminal of the converter module drops to the uncontrolled rectified voltage of the anti-parallel diode of the IGBT module, control the multiple IGBT modules in the converter module to disconnect, so as to perform uncontrolled rectification through the anti-parallel diode; when the current in the DC bus is detected to be a short-circuit current caused by a short circuit of the external load of the bidirectional rail transit traction system, control the phase-controlled rectifier circuit to conduct, so that the short-circuit current flows through the phase-controlled rectifier circuit by bypass.

[0012] Based on the aforementioned technical means, by setting a phase-controlled rectifier circuit as the core component of the short-circuit module, and combining it with the wave-by-wave current limiting control of the IGBT module and the uncontrolled rectification mechanism of the anti-parallel diode, the current can be quickly guided to a safe path when a short-circuit current is detected, thereby preventing damage to the main converter module. This effectively improves the system's short-circuit withstand capability.

[0013] In some embodiments, the rectifier bridge circuit is an uncontrolled rectifier circuit; the converter module includes multiple IGBT modules, and the controller is further configured to: when the current in the DC bus changes to a first current threshold, control the switching on and off of the multiple IGBT modules in the converter module to perform wave-by-wave current limiting; and when the voltage at the DC terminal of the converter module drops to the uncontrolled rectifier voltage, control the multiple IGBT modules in the converter module to disconnect, so that the short-circuit current flows through the uncontrolled rectifier circuit via a bypass.

[0014] Based on the above technical means, the structure of the short-circuit module is simplified by adopting an uncontrolled rectifier circuit, which reduces the system cost while ensuring that the short-circuit current can be effectively shunted.

[0015] In some embodiments, the converter module further includes: a common-mode inductor disposed between the DC terminal of the converter module and the DC bus, for suppressing circulating current between different converter modules when the bidirectional rail transit traction system is operating, and for consuming the short-circuit current as an impedance in the second path when the short-circuit current exists in the DC bus; and a filter inductor disposed between the AC terminal of the converter module and the AC bus, for performing AC filtering when the bidirectional rail transit traction system is operating, and for consuming the short-circuit current as an impedance in the second path.

[0016] Based on the aforementioned technical means, by setting a common-mode inductor at the DC end of the converter module and a filter inductor at the AC end, they act as key impedance components in the second path during a short circuit, working together to improve the system's short-circuit withstand capability and operational stability. Furthermore, the common-mode inductor and the filter inductor respectively undertake the tasks of noise suppression and electromagnetic compatibility improvement during normal system operation, thereby enhancing the overall performance of the system during short-circuit protection without increasing complexity.

[0017] In some embodiments, the ratio of the impedance of the second path to the impedance of the first path is greater than 20.

[0018] Secondly, a short-circuit control method for a bidirectional rail transit traction system is provided. The bidirectional rail transit traction system includes at least one converter module, a DC bus, an AC bus, a power grid, and a short-circuit module. The DC bus includes a positive DC bus and a negative DC bus. The converter module includes a DC terminal and an AC terminal; the DC terminal is connected to the positive DC bus and the negative DC bus, and the AC terminal is connected to the power grid through the AC bus. The DC side of the short-circuit module is connected to the positive DC bus and the negative DC bus, and the AC side of the short-circuit module is connected to the AC bus. The method includes: when the current in the DC bus changes to a first current threshold, controlling the converter module to perform wave-by-wave current limiting; in the event of a short circuit in the external load of the bidirectional rail transit traction system, using the short-circuit module to shunt the short-circuit current, allowing the short-circuit current to bypass through the short-circuit module; wherein, the AC bus coupled to the DC bus through the short-circuit module is defined as a first path, and the AC bus coupled to the DC bus through the converter module is defined as a second path, and the impedance of the first path is less than the impedance of the second path.

[0019] In some embodiments, the bidirectional rail transit traction system further includes: a DC-side switching device disposed on the DC bus for controlling the switching of the converter module with the external load; the method further includes: when the duration of the short-circuit current is greater than or equal to a first preset time, controlling the DC-side switching device to open, so as to disconnect the converter module from the external load.

[0020] In some embodiments, the converter module includes multiple IGBT modules, the short-circuit module includes a rectifier bridge circuit, the DC terminal of the rectifier bridge circuit is connected to the positive DC bus and the negative DC bus respectively, and the AC terminal of the rectifier bridge circuit is connected to the AC bus; the rectifier bridge circuit is a phase-controlled rectifier circuit, and the method further includes: when the current in the DC bus changes to a first current threshold, controlling the switching on and off of the multiple IGBT modules in the converter module to perform wave-by-wave current limiting; when the voltage at the DC terminal of the converter module drops to the uncontrolled rectified voltage of the anti-parallel diode of the IGBT module, controlling the multiple IGBT modules in the converter module to disconnect, so as to pass through the anti-parallel... The method further includes: using diodes for uncontrolled rectification; when the current in the DC bus is detected to be a short-circuit current caused by a short circuit of the external load of the bidirectional rail transit traction system, controlling the phase-controlled rectifier circuit to conduct, allowing the short-circuit current to bypass through the phase-controlled rectifier circuit; or, the rectifier bridge circuit is an uncontrolled rectifier circuit, and the method further includes: when the current in the DC bus changes to a first current threshold, controlling the switching on and off of multiple IGBT modules in the converter module to perform wave-by-wave current limiting; when the voltage at the DC terminal of the converter module drops to the uncontrolled rectifier voltage, controlling the multiple IGBT modules in the converter module to disconnect, allowing the short-circuit current to bypass through the uncontrolled rectifier circuit. Attached Figure Description

[0021] Figure 1 A schematic diagram of a rail transit traction system for applying the technical solutions provided in the embodiments of this application;

[0022] Figure 2 for Figure 1 A schematic diagram of a bidirectional traction converter in a rail transit vehicle.

[0023] Figure 3 The circuit topology diagram of the ANPC type three-level converter circuit;

[0024] Figure 4 This is a schematic diagram of a bidirectional traction converter circuit;

[0025] Figure 5 Schematic principle of the bidirectional rail transit traction system provided in the embodiments of this application Figure 1 ;

[0026] Figure 6 Schematic circuit diagram of a two-way rail transit traction system provided in the embodiments of this application. Figure 1 ;

[0027] Figure 7 Schematic principle of the bidirectional rail transit traction system provided in the embodiments of this application Figure 2 ;

[0028] Figure 8 Schematic circuit diagram of a two-way rail transit traction system provided in the embodiments of this application. Figure 2 ;

[0029] Figure 9 Schematic principle of the bidirectional rail transit traction system provided in the embodiments of this application Figure 3 ;

[0030] Figure 10 Schematic principle of the bidirectional rail transit traction system provided in the embodiments of this application Figure 4 ;

[0031] Figure 11 Short-circuit control timing diagram of a two-way rail transit traction system provided in the embodiments of this application;

[0032] Figure 12 Schematic principle of the bidirectional rail transit traction system provided in the embodiments of this application Figure 5 ;

[0033] Figure 13 Schematic principle of the bidirectional rail transit traction system provided in the embodiments of this application Figure 6 ;

[0034] Figure 14 Schematic circuit diagram of a two-way rail transit traction system provided in the embodiments of this application. Figure 3 ;

[0035] Figure 15 A schematic flowchart illustrating the short-circuit control method for a bidirectional rail transit traction system provided in this application embodiment. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0037] It should be noted that in the embodiments of this application, "connection" refers to electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components. For example, the connection between A and B can also be a direct connection between A and C, a direct connection between C and B, with A and B connected through C.

[0038] Furthermore, references to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in still other embodiments" appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0039] In this application, the ordinal numbers such as "first" and "second" are used to distinguish multiple objects, but are not used to limit the order, sequence, priority or importance of multiple objects.

[0040] Currently, most rail transit power supply systems use unidirectional rectifiers to convert three-phase AC power into DC power to provide DC power to rail transit vehicles. To achieve bidirectional energy flow between the DC and AC sides of the rail transit power supply system and provide a stable DC contact voltage, a rechargeable bidirectional traction power supply device has been introduced into this system. The AC side of the rechargeable bidirectional traction power supply device is connected to the AC power grid, and the DC side is connected to the DC traction network. When the rail transit vehicle is in traction mode, the power supply device operates in rectification mode, converting the AC power from the AC power grid into DC power to supply the DC traction network. When the rail transit vehicle is in braking mode, the power supply device operates in inverter mode, converting the DC power from the DC traction network back into AC power and feeding it back to the AC power grid.

[0041] Figure 1 This is a schematic diagram of a rail transit traction system applying the technical solutions provided in the embodiments of this application.

[0042] like Figure 1 As shown, the rail transit traction system 100 includes an AC power grid 110, a bidirectional traction converter 120, and a traction motor 130.

[0043] Figure 1The diagram also shows a track 140 and a vehicle 150 in a rail transit system. A DC contact network 160 is installed above the track 140. A bidirectional traction converter 120 is positioned between the AC power grid 110 and the DC contact network 160 to rectify the AC power supplied by the AC power grid 110, providing DC power suitable for the traction motor 130 to the DC contact network 160. The vehicle 150 can obtain DC power through its pantograph 151. Furthermore, when the vehicle 150 is braking, the traction motor 130 generates DC power through electromagnetic induction and transmits it to the DC contact network 160. At this time, the bidirectional traction converter 120 inverts this DC power, feeding it back to the AC power grid 110.

[0044] Figure 2 yes Figure 1 A schematic diagram of the bidirectional traction converter 120 is shown below. Figure 2 As shown, the bidirectional traction converter 120 includes at least one bidirectional converter module 121. The AC terminal of the bidirectional converter module 121 is connected to the AC bus, and the DC terminal is connected to the DC load.

[0045] 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 operate simultaneously, or some bidirectional converter modules can operate simultaneously while the remaining bidirectional converter modules serve as backups. When a working bidirectional converter module fails, the backup bidirectional converter module takes over. For example, if the bidirectional traction converter includes two bidirectional converter modules, the two bidirectional converter modules can operate simultaneously, or one bidirectional converter module can operate while the other serves as a backup. When the working bidirectional converter module fails, the backup bidirectional converter module takes over.

[0046] The aforementioned bidirectional converter module can be any of several types, including three-level converters, interleaved parallel converters, and cascaded H-bridge converters. Among them, the active neutral-point-clamped (ANPC) three-level converter is a topology developed based on the traditional neutral-point-clamped (NPC) three-level converter. It achieves more flexible neutral-point potential control and lower switching losses by introducing active switching devices.

[0047] Figure 3 The diagram shown is the circuit topology of an ANPC-type three-level converter circuit. The following section will discuss this in conjunction with... Figure 3 Please provide a detailed explanation.

[0048] The ANPC type three-level converter is suitable for operation in inverter mode and / or rectification mode, and includes a control circuit and a main circuit. The main circuit includes an upper bridge arm composed of a first switch T1, a second switch T2 and a fifth switch T5 connected together, and a lower bridge arm composed of a third switch T3, a fourth switch T4 and a sixth switch T6. The first switch T1 and the fourth switch T4 are respectively connected to the positive terminal BUS+ and the negative terminal BUS- of the DC network. The connection point of the fifth switch T5 and the sixth switch T6 is connected to the neutral terminal of the DC network. The connection point of the second switch T2 and the third switch T3 is connected to the AC network.

[0049] As one possible implementation, the first switch T1 and the fifth switch T5 are packaged in the same switch package module, the fourth switch T4 and the sixth switch T6 are packaged in the same switch package module, and the second switch T2 and the third switch T3 are packaged in the same switch package module.

[0050] The control circuit is used to control the on / off state of each switching transistor in the main circuit, including: when the AC network is the input terminal, controlling the switching devices to turn on and off to rectify the AC voltage; and when the DC network is the input terminal, controlling the switching devices to turn on and off to convert the DC voltage into a three-phase AC voltage to form the required AC waveform.

[0051] exist Figure 3 In the ANPC type three-level converter shown, each switching transistor is a controllable switching transistor with an anti-parallel diode, and the diodes corresponding to each switching transistor are represented by D1, D2, D3, D4, D5 and D6.

[0052] In practical applications, pulse width modulation (PWM) technology is usually used to control the on-time and off-time of the switching transistor, and the magnitude of the output DC voltage is controlled by adjusting the duty cycle of the PWM signal.

[0053] In the case where the aforementioned AC power grid is a three-phase AC power grid, such as Figure 4 As shown, each bidirectional converter module includes three ANPC-type three-level converters connected in parallel. The DC terminals of the three ANPC-type three-level converters are all connected to the DC bus, and the AC terminals are respectively connected to different phases of the three-phase AC power grid. By controlling the on and off phases of multiple switching transistors in the three ANPC-type three-level converters, the conversion between DC power and three-phase AC power can be realized.

[0054] exist Figure 4As shown, each bidirectional converter module also includes a first capacitor C1 and a second capacitor C2, which are respectively located between the positive DC bus and the negative DC bus and the midpoint. When the converter module is working normally, the two capacitors jointly store energy, buffer the energy exchange between the DC side and the AC side, and suppress the fluctuation of the DC bus voltage. At the same time, the first capacitor C1 and the second capacitor C2 are used to smooth the DC bus voltage, reduce high-frequency ripple, and provide a stable operating voltage for the switching devices.

[0055] During the operation of the aforementioned bidirectional rail transit traction system, there may be situations where the DC bus current abnormally increases. Causes of abnormal DC bus current include, but are not limited to, sudden load changes, overload, grid voltage fluctuations, and external load short circuits. For example, in the event of an external load short circuit, the first capacitor C1 and the second capacitor C2 will act as power sources, supplying energy to the short circuit point, causing a sharp increase in the DC bus current. Excessive bus current may lead to an increase in the temperature of the power devices in the converter module, resulting in irreversible damage to the power devices.

[0056] In related technologies, when the aforementioned sudden current change occurs, the usual solution is to quickly disconnect the converter module from the external load and the power grid to avoid damage to the components in the converter module. However, this method has some problems: immediately disconnecting the converter module from the external load and the power grid in the event of a fault will hinder fault troubleshooting; in addition, immediately disconnecting the bidirectional rail transit traction system from the external load and the power grid after the system detects a short circuit may prevent the load from being powered down normally, leading to load damage. Moreover, although the short-circuit current disappears after the source is cut off, the short-circuit fault may not have disappeared, and the next startup may lead to a new round of faults.

[0057] If a bidirectional rail transit traction system could operate continuously for a period of time during a short circuit, allowing the external load to be successfully disconnected or sufficient time to clear the fault, the aforementioned risks could be overcome. However, in the bidirectional rail transit traction systems described above, the capacity of the IGBT modules within the converter module is clearly insufficient to meet short-circuit protection requirements. Therefore, it is urgent to improve existing bidirectional rail transit traction systems to enable them to withstand larger short-circuit circuits for a certain period, thereby achieving short-circuit protection for the entire system.

[0058] In view of the above problems, this application provides a two-way rail transit traction system and its control method. The technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0059] Figure 5 This is a schematic diagram of a bidirectional rail transit traction system 500 provided in an embodiment of this application. Figure 5The bidirectional rail transit traction system 500 includes at least one converter module 510, DC bus 520, AC bus 530, power grid 540, short-circuit module 550, and controller 560.

[0060] DC bus 520 includes a positive DC bus BUS+ and a negative DC bus BUS-, which are used to connect the DC side circuit between converter module 510 and external load.

[0061] The converter module 510 includes a DC terminal and an AC terminal. The DC terminal is connected to the positive DC bus BUS+ and the negative DC bus BUS-, and the AC terminal is connected to the power grid 540 through the AC bus 530.

[0062] It should be noted that the number of the above-mentioned at least one converter module 510 can be one or more. When there are multiple converter modules 510, the DC terminal of each converter module 510 is connected to the DC bus 520, and the AC terminal is connected to the AC bus 530. That is to say, multiple converter modules 510 are connected in parallel between the DC bus 520 and the AC bus 530.

[0063] In this embodiment, the converter module 510 may include an inverter bridge circuit capable of operating in either inverter or rectification mode. For example, when applied to the aforementioned rail transit vehicle, during vehicle braking, the inverter bridge circuit can operate in inverter mode, converting the DC power generated by motor braking into AC power and feeding it back to the power grid 540; during normal vehicle operation, the inverter bridge circuit operates in rectification mode, converting the AC power provided by the power grid 540 into DC power to drive DC loads such as motors.

[0064] It should be noted that the embodiments of this application do not specifically limit the form of the inverter bridge circuit. The inverter bridge circuit can be, for example, a full-bridge inverter circuit, a three-phase inverter circuit, or a multi-level inverter circuit.

[0065] For example, such as Figure 6 As shown, the converter module in the two-way rail transit traction 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.

[0066] The DC side of short-circuit module 550 is connected to the positive DC bus BUS+ and the negative DC bus BUS-, and the AC side is connected to AC bus 530. This module is used to provide a low-impedance path to bypass current in the main converter module when an external load is short-circuited.

[0067] The short-circuit module 550 is typically composed of a rectifier bridge, including phase-controlled rectifier circuits, uncontrolled rectifier circuits, or fully controlled rectifier circuits. The short-circuit module 550 can carry large currents for a short time, thereby protecting the IGBT modules in the main circuit from damage by short-circuit current. The specific operation of the short-circuit module 550 will be explained in more detail later.

[0068] The controller 560 is connected to the converter module 510 and is used to control the converter module 510 to perform wave-by-wave current limiting when the current change value in the DC bus 520 exceeds the first current threshold.

[0069] The controller 560 monitors the current changes in the DC bus 520 in real time. Once the current exceeds a preset first current threshold (e.g., 4kA), it triggers a wave-by-wave current limiting mechanism. Wave-by-wave current limiting means that the controller 560 dynamically adjusts the on / off time of the IGBT in each cycle according to the current fluctuation, thereby gradually reducing the duty cycle and preventing the instantaneous excessive current from damaging the converter module 510.

[0070] In actual implementation, the controller 560 can select an appropriate current limiting strategy according to different current change modes. For example, when the current continues to rise, the duty cycle of the IGBT can be reduced quickly to limit the current growth rate; while after the current is relatively stable, the current duty cycle can be maintained or the duty cycle can be adjusted slightly.

[0071] The short-circuit module 550 is used to allow short-circuit current to bypass the external load of the bidirectional rail transit traction system 500 in the event of a short circuit. Specifically, the AC bus 530 is coupled to the DC bus 520 through the short-circuit module 550, forming a first path; the AC bus 530 is coupled to the DC bus 520 through the converter module 510, forming a second path. The impedance of the first path is less than the impedance of the second path.

[0072] When a short circuit occurs in the external load of the bidirectional rail transit traction system 500, the short circuit module 550 will be activated. Since the impedance of the first path is less than that of the second path, the current will preferentially flow through the first path, thereby effectively avoiding the converter module 510 and preventing the short circuit current from directly impacting the IGBT module.

[0073] In actual implementation, the activation of the short-circuit module 550 requires a certain delay for confirmation to avoid malfunction. For example, after detecting an abnormal increase in current, the controller 560 will first activate wave-by-wave current limiting measures, and then further determine whether it is a real short-circuit event. If a short circuit is confirmed, the short-circuit module 550 will be activated immediately to divert the current and protect the main circuit.

[0074] In the embodiments of this application, there are many ways to make the impedance of the first path less than that of the second path. For example, it can be achieved by selecting a suitable rectifier bridge structure or using low-impedance devices. For example, the short-circuit module 550 can use a thyristor rectifier bridge with an impedance of about 0.126 ohms, while the converter module 510, due to the inclusion of IGBTs, common-mode inductors, and other components, has a total impedance of more than 2.83 ohms. The difference between the two is more than 20 times, thereby ensuring that the current preferentially flows through the short-circuit module 550.

[0075] Based on the aforementioned technical means, by setting a low-impedance first path and a high-impedance second path, when an external short circuit occurs, the short-circuit current preferentially flows through the short-circuit module, thereby avoiding large current flowing through the IGBT devices in the converter module, reducing the impact on power devices, and thus improving the short-circuit withstand capability and operational safety of the overall system. At the same time, when the controller detects an abnormal change in current, it immediately performs wave-by-wave current limiting, which helps to quickly limit the current rise, improve the system response speed, and provide sufficient detection time for short-circuit detection, avoiding misjudgment or incorrect switching of short-circuit protection that could affect the normal operation of the equipment.

[0076] In some embodiments, see Figure 7 and Figure 8 The bidirectional rail transit traction system also includes a DC-side switching device 570, mounted on the DC bus 520, used to control the connection and disconnection between the converter module 510 and external loads. This DC-side switching device 570 can remain closed during normal operation, allowing current to flow; it is controlled to open upon detecting an abnormal condition (such as a short circuit) to cut off the current path, thereby protecting the converter module 510 and the bidirectional rail transit traction system 500. Common DC-side switching devices 570 include contactors, relays, or solid-state switches.

[0077] The controller 560 is connected to the DC-side switching device 570. The controller 560 is also used to: control the DC-side switching device 570 to disconnect when the duration of the short-circuit current is greater than or equal to a first preset time, so as to disconnect the converter module 510 from the external load.

[0078] The aforementioned first preset time is a time threshold set based on system design requirements and external load characteristics. This first preset time is greater than the rated short-circuit protection time of the converter module 510. For example, the first preset time can be 120 milliseconds.

[0079] The purpose of setting the aforementioned first preset time is to ensure that the circuit breaker or fuse in the external load experiencing a short-circuit fault has sufficient reaction time to disconnect after the system's internal short-circuit protection mechanism is activated, thus preventing premature disconnection and subsequent failure of downstream equipment to respond correctly. Performing the disconnection operation only after the short circuit has lasted for a certain period of time can achieve coordinated and safe protection for both the system and the load.

[0080] Based on the aforementioned technical means, by introducing DC-side switching devices and coordinating them with the controller, the connection between the converter module and the external load is automatically disconnected when the short-circuit current duration meets a preset condition. This effectively isolates the fault point, preventing damage to the converter module from the short-circuit current, thereby improving the system's stability and safety.

[0081] In some embodiments, such as Figure 8 and Figure 9 As shown, the system may also include an AC-side switching device 580, which is mounted on the AC bus 530 and used to control the connection between the converter module 510 and the power grid 540. The AC-side switching device 580 remains closed during normal operation, allowing AC current to flow; in case of an abnormality, it is controlled to open, disconnecting the converter module 510 from the power grid 540. The AC-side switching device 580 can be a contactor, relay, or solid-state switch, etc.

[0082] The controller 560 is also connected to the AC-side switching device 580 so that when the duration of the aforementioned short-circuit current is greater than or equal to a first preset time, it controls both the AC-side switching device 580 and the DC-side switching device 570 to disconnect, thereby completely isolating both the DC and AC sides of the converter module 510 from the outside, ensuring the safety of the bidirectional rail transit traction system.

[0083] In some embodiments, the short-circuit module 550 includes a rectifier bridge circuit, the DC terminal of which is connected to the positive DC bus BUS+ and the negative DC bus BUS- respectively, and the AC terminal is connected to the AC bus 530.

[0084] A rectifier bridge circuit is a power electronic topology composed of multiple semiconductor devices, whose function is to convert input AC voltage into DC output. In the technical solution of this application embodiment, the rectifier bridge circuit, as the core component of the short-circuit module 550, achieves rapid response and effective shunting of short-circuit current through its low impedance characteristics. This circuit is typically composed of devices such as silicon controlled rectifiers (SCRs) or diodes, and the controllable or uncontrollable rectification method is selected according to specific application requirements.

[0085] The DC terminal of the rectifier bridge circuit is connected to the positive and negative DC buses, ensuring that the current can quickly flow into the short-circuit module without passing through the main converter module during a short circuit, thereby protecting the main circuit from large current surges. The AC terminal is connected to the AC bus, enabling the short-circuit module to quickly start operation after detecting a short-circuit signal and form a stable short-circuit loop.

[0086] The introduction of the short-circuit module 550 enhances the system's short-circuit withstand capability. In the event of a short-circuit fault, the short-circuit module 550 quickly conducts, guiding most of the short-circuit current through its low-impedance path to flow through itself, rather than through the main converter module. This prevents power devices such as IGBTs from being damaged by excessive current. This design not only improves the system's safety and reliability but also extends the equipment's lifespan.

[0087] Furthermore, the choice of rectifier bridge circuit directly affects the response speed and current withstand capability of the short-circuit module. For example, using thyristors enables controllable on / off switching, facilitating precise control in conjunction with a control system; while using diodes enables uncontrolled rectification, suitable for scenarios where high control precision is not required. In practical applications, the appropriate rectifier bridge type can be flexibly selected based on system requirements.

[0088] Based on the above technical means, using a rectifier bridge circuit as a short-circuit module can provide a stable low-impedance path under short-circuit conditions, ensuring that the short-circuit current can be effectively diverted and reducing the impact on the converter module.

[0089] In some embodiments, such as Figure 10 As shown, the rectifier bridge circuit can be a phase-controlled rectifier circuit 551, which is connected to the controller 560.

[0090] A phase-controlled rectifier circuit is a rectification method that regulates output voltage and current by controlling the conduction angle of thyristors (SCRs). It enables dynamic control of the rectification process and is particularly suitable for short-circuit protection scenarios in high-power systems. The circuit consists of multiple thyristors connected to a controller, which can adjust the thyristor firing angles in real time to adapt to different load conditions.

[0091] The converter module 510 includes multiple IGBT modules, and the controller 560 is further configured to: control the switching on and off of the multiple IGBT modules in the converter module 510 when the current in the DC bus 520 changes to a first current threshold to perform wave-by-wave current limiting; and, when the voltage at the DC terminal of the converter module 510 drops to the uncontrolled rectified voltage of the anti-parallel diode of the IGBT module, control the multiple IGBT modules in the converter module 510 to disconnect so as to perform uncontrolled rectification through the anti-parallel diode; and when the current in the DC bus 520 is detected to be a short-circuit current caused by a short circuit of an external load of the bidirectional rail transit traction system, control the phase-controlled rectifier circuit to conduct so that the short-circuit current flows through the phase-controlled rectifier circuit 551 in a bypass manner.

[0092] When the DC terminal voltage of the converter module 510 drops below the uncontrolled rectified voltage of the IGBT anti-parallel diode, the controller 560 will actively shut down the IGBT module. At this time, the anti-parallel diode will automatically turn on, entering the uncontrolled rectification mode. On the other hand, when the current in the DC bus 520 is detected to be caused by an external load short circuit, the controller 560 will control the phase-controlled rectifier circuit 551 to turn on, allowing the short-circuit current to bypass the main converter module. This ensures that the main system is not affected by short circuits, improving the system's stability and safety.

[0093] Figure 11 The timing diagram of the above short-circuit control process is shown, as follows: Figure 11 As shown, before time t0, the DC bus current and DC side voltage are stable at 4kA and 1750V, respectively. At time t0, the DC bus current begins to increase, and the controller controls the converter module to perform wave-by-wave current limiting. By time t2, the DC side voltage drops to the uncontrolled rectified voltage of the diode, and the DC bus current increases to 18kA. From time t0, the system performs short-circuit detection, and at time t3, a short circuit is detected in the external load. At time t4, the controller controls the phase-controlled rectifier circuit to operate, so as to discharge the short-circuit protection through the phase-controlled rectifier circuit. At time t4, the DC side voltage drops to 350V, and the DC bus current rises to 25.4kA. During the operation of the phase-controlled rectifier circuit, the DC bus current remains at 25.4kA, while the DC side voltage gradually decreases. After time t4, the fuse of the external load is switched on and off to disconnect the external load.

[0094] In some embodiments, the converter module 510 can also be replaced with other circuits having an uncontrolled rectification mode, such as a full-bridge inverter circuit or a T-type three-level circuit, which will not be elaborated here. The duration of the uncontrolled control can be adjusted according to actual needs. Under one control, it can directly enter the conduction stage of the rectifier bridge circuit (short-circuit module 550) from the wave-by-wave current limiting stage, that is, the running time of the uncontrolled rectification mode of the anti-parallel diode is 0. Correspondingly, the wave-by-wave current limiting is not limited to exiting when the voltage at the DC terminal of the converter module 510 drops to the uncontrolled rectified voltage of the anti-parallel diode of the IGBT module. It can exit after running for a certain period of time or after the current limiting condition is not met. The specific control strategy can be adjusted according to the actual situation.

[0095] In this embodiment, by setting a phase-controlled rectifier circuit as the core component of the short-circuit module, and combining it with the wave-by-wave current limiting control of the IGBT module and the uncontrolled rectification mechanism of the anti-parallel diode, the current can be quickly guided to a safe path when a short-circuit current is detected, thereby preventing damage to the main converter module. This effectively improves the system's short-circuit withstand capability.

[0096] The phase-controlled rectifier circuit may include two thyristors, the connection point of which is the midpoint of the phase-controlled rectifier circuit, and the ends of the two thyristors that are far apart from each other are connected to the positive DC bus BUS+ and the negative DC bus BUS-, respectively.

[0097] In some embodiments, see Figure 12 The rectifier bridge circuit can also be an uncontrolled rectifier circuit 552; the converter module 510 includes multiple IGBT modules, and the controller 560 is further configured to: when the current in the DC bus 520 changes to a first current threshold, control the switching on and off of the multiple IGBT modules in the converter module 510 to perform wave-by-wave current limiting; and, when the voltage at the DC terminal of the converter module 510 drops to the uncontrolled rectifier voltage, control the multiple IGBT modules in the converter module 510 to disconnect, so that the short-circuit current flows through the phase-controlled rectifier circuit by bypass.

[0098] An uncontrolled rectifier circuit is a rectifier structure composed of diodes. It is not connected to a controller and therefore lacks controllability; its conduction is determined solely by the polarity of the input voltage. This circuit acts as a bypass during short-circuit protection. When the main power circuit (such as an IGBT module) is interrupted due to a short circuit, the uncontrolled rectifier circuit allows the short-circuit current to flow through its path, thereby preventing damage to internal system components.

[0099] The uncontrolled rectifier voltage refers to the minimum DC voltage required for the uncontrolled rectifier circuit to conduct normally. When the DC bus voltage drops below this voltage, it means that the converter module can no longer provide enough energy to support the system operation. At this time, the controller will actively shut down the IGBT module, forcing the short-circuit current to form a closed loop through the uncontrolled rectifier circuit.

[0100] Based on the above technical means, the structure of the short-circuit module is simplified by adopting an uncontrolled rectifier circuit, which reduces the system cost while ensuring that the short-circuit current can be effectively shunted.

[0101] In some embodiments, such as Figure 13 As shown, the converter module 510 also includes a common-mode inductor 511, which is disposed between the DC terminal of the converter module 510 and the DC bus 520. It is used to suppress the circulating current between different converter modules 510 when the bidirectional rail transit traction system is working, and to consume the short-circuit current as an impedance in the second path when there is a short-circuit current in the DC bus 520.

[0102] Common-mode inductors typically consist of two sets of coils with the same number of turns but in opposite directions, used to suppress common-mode noise. In the technical solution of this application, a common-mode inductor 511 is configured between the DC terminal of the converter module 510 and the DC bus 520 to suppress circulating current among multiple converter modules 510, and as an impedance element in the short-circuit protection path to absorb short-circuit current.

[0103] When multiple converter modules 510 are operating in parallel, circulating currents may occur due to differences in parameters or control timing between modules. These circulating currents not only increase losses but may also lead to module imbalance or even damage. The common-mode inductor 511 effectively suppresses these circulating currents by generating a large inductive reactance to the common-mode current, thereby improving the stability and efficiency of the system.

[0104] In the event of a DC-side short-circuit fault, especially under conditions of a large current surge on the DC side, the common-mode inductor 511 can also act as part of the impedance in the second path, serving to shunt and limit the short-circuit current. Due to its high inductive reactance, it can guide part of the short-circuit current to other paths, reducing the direct impact on main power devices (such as IGBTs), extending their lifespan, and improving the overall short-circuit withstand capability of the system. This allows for effective short-circuit protection without relying on additional current-limiting circuits, thereby improving the safety and reliability of system operation and ensuring stable operation of equipment under high-voltage, high-current environments.

[0105] Continue reading Figure 13 The converter module 510 also includes a filter inductor 512, which is disposed between the AC terminal of the converter module 510 and the AC bus 530. It is used for AC filtering when the bidirectional rail transit traction system 500 is working, and as an impedance to consume short-circuit current in the second path.

[0106] A filter inductor is a passive component used to suppress high-frequency noise and smooth current fluctuations. In this application, the filter inductor 512 is disposed between the AC terminal of the converter module 510 and the AC bus 530.

[0107] Under normal operating conditions, the filter inductor 512 can effectively suppress high-frequency interference signals from the mains 540 or other loads, improve the quality of output voltage and current, reduce electromagnetic interference, and enhance the electromagnetic compatibility performance of the system.

[0108] In the event of a short-circuit fault, the filter inductor 512 can also act as an impedance element in the second path, limiting the rate of increase of the short-circuit current through its own inductive reactance, thereby providing more response time for the control system. Simultaneously, it can also alleviate the current pressure on the main power devices to some extent, reducing device stress and enhancing the system's short-circuit withstand capability.

[0109] Based on the aforementioned technical means, by setting a common-mode inductor at the DC end of the converter module and a filter inductor at the AC end, they act as key impedance components in the second path during a short circuit, working together to improve the system's short-circuit withstand capability and operational stability. Furthermore, the common-mode inductor and the filter inductor respectively undertake the tasks of noise suppression and electromagnetic compatibility improvement during normal system operation, thereby enhancing the overall performance of the system during short-circuit protection without increasing complexity.

[0110] In some embodiments, the ratio of the impedance of the second path to the impedance of the first path is greater than 20.

[0111] Setting the impedance of the first path to be much smaller than that of the second path ensures that in the event of a short circuit, current preferentially flows through the lower-impedance first path, preventing the converter module from bearing a large short-circuit current. For example, as a possible implementation, the impedance of the first path can be set to 0.126Ω, and the impedance of the second path to 2.83Ω, with a ratio of approximately 22.4, which meets the requirement of being greater than 20.

[0112] In some embodiments, the first preset time is greater than 120ms.

[0113] As described above, the first preset time is the time window from the detection of a short circuit event to the system executing the disconnection operation. During this time, the system needs to maintain stable operation to ensure that the circuit breaker or fuse of the external load can complete the disconnection action within the predetermined time.

[0114] The 120ms in this embodiment is determined based on the requirements of the external system for short-circuit response time.

[0115] In some embodiments, the converter module includes multiple ANPC type three-level converters, the DC terminals of which are respectively connected to the positive DC bus BUS+ and the negative DC bus BUS-, and the AC terminals of which are respectively connected to multiple phase lines of the power grid via AC buses.

[0116] Figure 14 This is an exemplary circuit diagram of a bidirectional rail transit traction system provided in an embodiment of this application. Figure 14 As shown, the bidirectional rail transit traction system includes multiple converter modules. Each converter module includes three ANPC-type three-level converters. The DC terminals of the three converters are connected to the positive DC bus BUS+ and the negative DC bus BUS-, respectively. Their midpoints are interconnected to form the midpoint of the converter module. The first capacitor C3 and the second capacitor C4 are connected between the positive DC bus BUS+ and the midpoint, and between the negative DC bus BUS- and the midpoint, respectively.

[0117] The common-mode inductor L1 is positioned between the three converters and the mixed circuit consisting of the first capacitor C3 and the second capacitor C4 and the DC bus.

[0118] exist Figure 14 In the illustrated bidirectional rail transit traction system, the power grid has three phase lines, each connected to the AC terminal of the converter via three AC buses. Three filter inductors L2 are installed on the AC buses, and one end of each of the three filter capacitors C is connected, with the other end connected to the end of each of the three filter inductors L2 closest to the power grid. The bidirectional rail transit traction system also includes a contactor KM1 and multiple circuit breakers K2. The contactor is installed on the DC bus, and the multiple circuit breakers K2 are installed on multiple AC buses, used to control the connection and disconnection between the converter module and external loads and the power grid.

[0119] Figure 14 In the bidirectional rail transit traction system shown, the converter module also includes a first fuse F1 and multiple second fuses F2. The first end of the first fuse is connected to the midpoint of the converter module, and the second ends of the first fuses in the multiple converter modules are interconnected to connect the midpoints of the multiple converter modules, thereby achieving midpoint potential balance. When a half-busbar short circuit occurs in one of the converter modules, the first and second fuses of the faulty converter module will disconnect to avoid affecting other converter modules or the power grid.

[0120] The above text combined Figures 1-14 The device embodiments of this application have been described in detail above. The method embodiments of this application will now be described in detail with reference to the accompanying drawings. It should be understood that the method embodiments correspond to the foregoing device embodiments; therefore, any parts not described in detail can be referred to the foregoing device embodiments.

[0121] Figure 15 This is a schematic flowchart of a short-circuit control method for a bidirectional rail transit traction system provided in this application embodiment. The bidirectional rail transit traction system can be any of the bidirectional rail transit traction systems described in the preceding embodiments. The system includes at least one converter module, a DC bus, an AC bus, a power grid, and a short-circuit module. The DC bus includes a positive DC bus and a negative DC bus. The converter module includes a DC terminal and an AC terminal; the DC terminal is connected to the positive DC bus and the negative DC bus, and the AC terminal is connected to the power grid via the AC bus. The DC side of the short-circuit module is connected to the positive DC bus and the negative DC bus, and the AC side of the short-circuit module is connected to the AC bus.

[0122] Figure 15 The method includes steps S1510-S1520. In step S1510, when the current in the DC bus changes to the first current threshold, the converter module is controlled to perform wave-by-wave current limiting.

[0123] In step S1520, in the event of a short circuit in the external load of the bidirectional rail transit traction system, the short-circuit module is used to divert the short-circuit current, allowing the short-circuit current to flow through the bypass of the short-circuit module.

[0124] The AC bus is coupled to the DC bus through the short-circuit module, which is defined as the first path. The AC bus is coupled to the DC bus through the converter module, which is defined as the second path. The impedance of the first path is less than the impedance of the second path.

[0125] In some embodiments, the bidirectional rail transit traction system further includes: a DC-side switching device disposed on the DC bus, used to control the connection and disconnection between the converter module and the external load.

[0126] The above-mentioned short-circuit control method further includes: when the duration of the short-circuit current is greater than or equal to a first preset time, controlling the DC-side switching device to disconnect, so as to disconnect the converter module from the external load.

[0127] In some embodiments, the converter module includes multiple IGBT modules, the short-circuit module includes a rectifier bridge circuit, the DC terminal of the rectifier bridge circuit is connected to the positive DC bus and the negative DC bus respectively, and the AC terminal of the rectifier bridge circuit is connected to the AC bus.

[0128] The rectifier bridge circuit is a phase-controlled rectifier circuit, and the aforementioned short-circuit control method further includes:

[0129] When the current in the DC bus changes to a first current threshold, the switching on and off of multiple IGBT modules in the converter module is controlled to perform wave-by-wave current limiting; when the voltage at the DC terminal of the converter module drops to the uncontrolled rectified voltage of the anti-parallel diode of the IGBT module, the multiple IGBT modules in the converter module are switched off to perform uncontrolled rectification through the anti-parallel diode; when the current in the DC bus is detected to be a short-circuit current caused by a short circuit of the external load of the bidirectional rail transit traction system, the phase-controlled rectifier circuit is controlled to be turned on, so that the short-circuit current flows through the phase-controlled rectifier circuit.

[0130] Alternatively, the rectifier bridge circuit is an uncontrolled rectifier circuit, and the aforementioned short-circuit control method further includes:

[0131] When the current in the DC bus changes to a first current threshold, the switching on and off of multiple IGBT modules in the converter module is controlled to perform wave-by-wave current limiting; when the voltage at the DC terminal of the converter module drops to the uncontrolled rectifier voltage, the multiple IGBT modules in the converter module are controlled to disconnect, allowing the short-circuit current to bypass through the uncontrolled rectifier circuit.

[0132] This application also provides a computer-readable storage medium storing a computer program that, when executed, implements the aforementioned method steps.

[0133] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0134] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0135] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0136] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially 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 this 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 transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can read or a data storage device such as a server or data center that integrates one or more available media. The available media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., digital video discs (DVDs)), or semiconductor media (e.g., solid-state disks (SSDs)).

[0137] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A two-way rail transit traction system, characterized in that, It includes at least one converter module, DC bus, AC bus, power grid, short-circuit module and controller; The DC bus includes a positive DC bus and a negative DC bus; The converter module includes a DC terminal and an AC terminal. The DC terminal is connected to the positive DC bus and the negative DC bus, and the AC terminal is connected to the power grid through the AC bus. The DC side of the short-circuit module is connected to the positive DC bus and the negative DC bus, and the AC side of the short-circuit module is connected to the AC bus. The controller is connected to the converter module and is used to control the converter module to perform wave-by-wave current limiting when it detects that the current in the DC bus changes to a first current threshold. The short-circuit module is used to: allow the short-circuit current to bypass through the short-circuit module in the event of a short circuit in the external load of the bidirectional rail transit traction system. The AC bus is coupled to the DC bus through the short-circuit module to form a first path, and the AC bus is coupled to the DC bus through the converter module to form a second path. The impedance of the first path is less than the impedance of the second path.

2. The bidirectional rail transit traction system according to claim 1, characterized in that, The bidirectional rail transit traction system also includes: A DC-side switching device is installed on the DC bus to control the connection and disconnection between the converter module and the external load. The controller is connected to the DC-side switching device, and the controller is also used for: If the duration of the short-circuit current is greater than or equal to a first preset time, the DC-side switching device is controlled to open, thereby disconnecting the converter module from the external load.

3. The bidirectional rail transit traction system according to claim 2, characterized in that, The short-circuit module includes a rectifier bridge circuit, the DC terminal of which is connected to the positive DC bus and the negative DC bus respectively, and the AC terminal of which is connected to the AC bus.

4. The bidirectional rail transit traction system according to claim 3, characterized in that, The rectifier bridge circuit is a phase-controlled rectifier circuit, and the phase-controlled rectifier circuit is connected to the controller; The converter module includes multiple IGBT modules, and the controller is further used for: When the current in the DC bus changes to a first current threshold, the switching on and off of multiple IGBT modules in the converter module is controlled to perform wave-by-wave current limiting. When the voltage at the DC terminal of the converter module drops to the uncontrolled rectified voltage of the anti-parallel diode of the IGBT module, the multiple IGBT modules in the converter module are controlled to disconnect so that uncontrolled rectification can be performed through the anti-parallel diode. If the current in the DC bus is detected to be a short-circuit current caused by a short circuit of the external load of the bidirectional rail transit traction system, the phase-controlled rectifier circuit is turned on to allow the short-circuit current to bypass the phase-controlled rectifier circuit.

5. The bidirectional rail transit traction system according to claim 3, characterized in that, The rectifier bridge circuit is an uncontrolled rectifier circuit. The converter module includes multiple IGBT modules, and the controller is further used for: When the current in the DC bus changes to a first current threshold, the switching on and off of multiple IGBT modules in the converter module is controlled to perform wave-by-wave current limiting. When the voltage at the DC terminal of the converter module drops to the uncontrolled rectifier voltage, multiple IGBT modules in the converter module are disconnected, allowing the short-circuit current to bypass through the uncontrolled rectifier circuit.

6. The bidirectional rail transit traction system according to any one of claims 1-5, characterized in that, The converter module also includes: A common-mode inductor is disposed between the DC terminal of the converter module and the DC bus, used to suppress circulating current between different converter modules when the bidirectional rail transit traction system is working, and to consume the short-circuit current as an impedance on the second path when the short-circuit current exists in the DC bus. A filter inductor is disposed between the AC terminal of the converter module and the AC bus, for AC filtering when the bidirectional rail transit traction system is working, and for consuming the short-circuit current as an impedance on the second path.

7. The bidirectional rail transit traction system according to any one of claims 1-5, characterized in that, The ratio of the impedance of the second path to the impedance of the first path is greater than 20.

8. A short-circuit control method for a two-way rail transit traction system, characterized in that, The bidirectional rail transit traction system includes at least one converter module, DC bus, AC bus, power grid, and short-circuit module; The DC bus includes a positive DC bus and a negative DC bus; The converter module includes a DC terminal and an AC terminal. The DC terminal is connected to the positive DC bus and the negative DC bus, and the AC terminal is connected to the power grid through the AC bus. The DC side of the short-circuit module is connected to the positive DC bus and the negative DC bus, and the AC side of the short-circuit module is connected to the AC bus. The method includes: When the current in the DC bus changes to a first current threshold, the converter module is controlled to perform wave-by-wave current limiting. In the event of a short circuit in the external load of the bidirectional rail transit traction system, the short-circuit module is used to divert the short-circuit current, allowing the short-circuit current to bypass through the short-circuit module. The AC bus is coupled to the DC bus through the short-circuit module to form a first path, and the AC bus is coupled to the DC bus through the converter module to form a second path. The impedance of the first path is less than the impedance of the second path.

9. The short-circuit control method according to claim 8, characterized in that, The bidirectional rail transit traction system also includes: A DC-side switching device is installed on the DC bus to control the connection and disconnection between the converter module and the external load. The method further includes: If the duration of the short-circuit current is greater than or equal to a first preset time, the DC-side switching device is controlled to open, thereby disconnecting the converter module from the external load.

10. The short-circuit control method according to claim 9, characterized in that, The converter module includes multiple IGBT modules, and the short-circuit module includes a rectifier bridge circuit. The DC terminal of the rectifier bridge circuit is connected to the positive DC bus and the negative DC bus, respectively, and the AC terminal of the rectifier bridge circuit is connected to the AC bus. The rectifier bridge circuit is a phase-controlled rectifier circuit, and the method further includes: When the current in the DC bus changes to a first current threshold, the switching on and off of multiple IGBT modules in the converter module is controlled to perform wave-by-wave current limiting. When the voltage at the DC terminal of the converter module drops to the uncontrolled rectified voltage of the anti-parallel diode of the IGBT module, the multiple IGBT modules in the converter module are controlled to disconnect so that uncontrolled rectification can be performed through the anti-parallel diode. When it is detected that the current in the DC bus is a short-circuit current caused by a short circuit of the external load of the bidirectional rail transit traction system, the phase-controlled rectifier circuit is turned on so that the short-circuit current flows through the phase-controlled rectifier circuit. or, The rectifier bridge circuit is an uncontrolled rectifier circuit, and the method further includes: When the current in the DC bus changes to a first current threshold, the switching on and off of multiple IGBT modules in the converter module is controlled to perform wave-by-wave current limiting. When the voltage at the DC terminal of the converter module drops to the uncontrolled rectifier voltage, multiple IGBT modules in the converter module are disconnected, allowing the short-circuit current to bypass through the uncontrolled rectifier circuit.

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