Bidirectional rail transit traction system and short circuit control method thereof

Abstract

The invention provides a bidirectional rail transit traction system and a short circuit control method thereof. The bidirectional rail-AC traction system comprises at least one converter module, a direct-current bus, an alternating-current bus, a power grid, a short-circuit module and a controller, the direct-current bus comprises a positive direct-current bus and a negative direct-current bus; the converter module comprises a direct-current end and an alternating-current end, the direct-current end is connected with the direct-current bus, and the alternating-current end is connected with a power grid through the alternating-current 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 current transformation module and is used for controlling the current transformation module to carry out wave-by-wave current limiting when detecting that the current in the direct current bus is changed to a first current threshold value; the short-circuit module is used for enabling short-circuit current to circulate through a bypass of the short-circuit module under the condition that an external load is short-circuited; wherein the impedance of the first path defined by coupling the AC bus with the DC bus through the short circuit module is smaller than that of the second path defined by coupling the AC bus with the DC bus through the converter module.

Description

Technical Field

[0001] The present application relates to the field of rail transit technology, and in particular to a bidirectional rail transit traction system and a short-circuit control method thereof. Background Art

[0002] The rail transit traction power supply system provides power to rail transit vehicles and other loads through a bidirectional rail transit traction system. During operation, the bidirectional rail transit traction system may experience abnormal increases in DC bus current. Causes of abnormal DC bus current include, but are not limited to, sudden load changes, overloads, grid voltage fluctuations, and external load short circuits. For example, if an external load short circuits, the DC bus current will increase dramatically. This can cause the power components in the converter module to heat up, potentially causing irreversible damage to the components.

[0003] In the related art, when the above-mentioned current mutation occurs, the connection between the converter module and the external load and the power grid will be quickly cut off, thereby avoiding damage to the components in the converter module. However, in the event of a fault, the converter module is immediately disconnected from the external load and the power grid. Although it can effectively protect the bidirectional rail transit traction system itself, it is not conducive to troubleshooting, and may also cause load damage or bury hidden faults for the next startup. If the bidirectional rail transit traction system can have the ability to continue to operate for a period of time when a short circuit occurs, so that the short-circuited external load can be safely disconnected or there is enough time to troubleshoot during this period of time, the above-mentioned hidden dangers can be overcome. However, in the bidirectional rail transit traction system in the above-mentioned related art, relying solely on the capacity of the IGBT module in the converter module is obviously not enough to meet the requirements of short-circuit protection. Summary of the Invention

[0004] This application mainly provides a bidirectional rail transit traction system and a short-circuit control method thereof. The technical solution of this application is implemented as follows: 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 comprises a positive DC bus and a negative DC bus; the converter module comprises 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 via the AC bus; the DC side of the short-circuit module being connected to the positive DC bus and the negative DC bus, and the AC side of the short-circuit module being connected to the AC bus; the controller being connected to the converter module and configured to control the converter module to perform wave-by-wave current limiting upon detecting that the current in the DC bus changes to a first current threshold; the short-circuit module being configured to bypass the short-circuit current through the short-circuit module in the event of a short circuit in an external load of the bidirectional rail transit traction system; wherein the AC bus coupled to the DC bus via the short-circuit module is defined as a first path, and the AC bus coupled to the DC bus via 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.

[0005] According to the above 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 flows preferentially through the short-circuit module, thereby avoiding large current flowing through the IGBT devices in the converter module, reducing the impact on the power devices, and thereby improving the short-circuit tolerance and operational safety of the overall system; at the same time, when the controller detects abnormal current changes, it immediately performs wave-by-wave current limiting, which helps to quickly limit the current rise and improve the system response speed, while providing sufficient detection time for short-circuit detection, avoiding misjudgment and erroneous switching of short-circuit protection affecting the normal operation of the equipment.

[0006] In some embodiments, the bidirectional rail transit traction system further includes: a DC side switching device, arranged on the DC bus, for controlling the on and off of the converter module and the external load; the controller is connected to the DC side switching device, and the controller is further used to: when the duration of the short-circuit current is greater than or equal to a first preset time, control the DC side switching device to disconnect, so that the converter module is disconnected from the external load.

[0007] According to the above technical means, after the short-circuit current lasts for more than a preset time, the controller controls the DC side switch device to disconnect, isolating the converter module from the system, preventing the long-term short circuit from causing further damage to the equipment, and improving the safety and stability of the system.

[0008] In some embodiments, the short-circuit module includes a rectifier bridge circuit, wherein the DC end of the rectifier bridge circuit is connected to the positive DC bus and the negative DC bus respectively, and the AC end of the rectifier bridge circuit is connected to the AC bus.

[0009] According to the above technical means, a rectifier bridge circuit is used as a short-circuit module, which can provide a stable low-impedance path in a short-circuit situation, ensure that the short-circuit current can be effectively diverted, and reduce the impact on the conversion module.

[0010] 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 also used to: when it is detected that the current in the DC bus changes to a first current threshold, control the on and off of the multiple IGBT modules in the converter module to perform the wave-by-wave current limiting; when the voltage at the DC end of the converter module drops to the uncontrolled rectification voltage of the anti-parallel diode of the IGBT module, control the multiple IGBT modules in the converter module to be disconnected to perform uncontrolled rectification 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 an external load of the bidirectional rail transit traction system, control the phase-controlled rectifier circuit to be turned on, so that the short-circuit current flows through the phase-controlled rectifier circuit bypass.

[0011] The aforementioned technical approach, by providing a phase-controlled rectifier circuit as the core component of the short-circuit module, combined with the IGBT module's wave-by-wave current limiting control and the uncontrolled rectification mechanism of the anti-parallel diode, can quickly direct the current 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 tolerance.

[0012] In some embodiments, the rectifier bridge circuit is an uncontrolled rectifier circuit; the converter module includes multiple IGBT modules, and the controller is also used to: when it is detected that the current in the DC bus changes to a first current threshold, control the on and off of the multiple IGBT modules in the converter module to perform the wave-by-wave current limiting; when the voltage at the DC end of the converter module drops to the uncontrolled rectifier voltage, control the multiple IGBT modules in the converter module to be disconnected, so that the short-circuit current flows through the uncontrolled rectifier circuit bypass.

[0013] According to the above technical means, the structure of the short-circuit module is simplified by adopting an uncontrolled rectifier circuit, which reduces the cost of the system while ensuring that the short-circuit current can be effectively shunted.

[0014] In some embodiments, the conversion module further includes: a common-mode inductor, which is arranged between the DC end of the conversion module and the DC bus, and is used to suppress the circulating current between different conversion modules when the bidirectional rail traction system is operating, and, when the short-circuit current exists in the DC bus, serves as an impedance on the second path to consume the short-circuit current; a filter inductor, which is arranged between the AC end of the conversion module and the AC bus, and is used to perform AC filtering when the bidirectional rail traction system is operating, and serves as an impedance on the second path to consume the short-circuit current.

[0015] The above technical approach employs common-mode inductors on the DC side of the converter module and filter inductors on the AC side. These inductors act as key impedance components in the secondary path during a short circuit, working together to enhance the system's short-circuit tolerance and operational stability. Furthermore, the common-mode inductors and filter inductors, respectively, suppress noise and improve electromagnetic compatibility during normal system operation, thereby enhancing the system's overall short-circuit protection performance without increasing complexity.

[0016] In some embodiments, a ratio of the impedance of the second path to the impedance of the first path is greater than 20.

[0017] In a second aspect, a short-circuit control method for a bidirectional rail transit traction system is provided, wherein 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 end and an AC end, the DC end is connected to the positive DC bus and the negative DC bus, and the AC end 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 detecting that 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 that an external load of the bidirectional rail transit traction system is short-circuited, using the short-circuit module to shunt the short-circuit current so that the short-circuit current bypasses the short-circuit module; wherein the AC bus is coupled to the DC bus through the short-circuit module and is defined as a first path, and the AC bus is coupled to the DC bus through the converter module and is defined as a second path, and the impedance of the first path is less than the impedance of the second path.

[0018] In some embodiments, the bidirectional rail transit traction system further includes: a DC side switching device, arranged on the DC bus, for controlling the on and off of the converter module and 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 disconnect so as to disconnect the converter module from the external load.

[0019] In some embodiments, the converter module includes multiple IGBT modules, the short-circuit module includes a rectifier bridge circuit, the DC end of the rectifier bridge circuit is respectively connected to the positive DC bus and the negative DC bus, and the AC end 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 it is detected that the current in the DC bus changes to a first current threshold, controlling the on and off of the multiple IGBT modules in the converter module to perform the wave-by-wave current limiting; when the voltage at the DC end of the converter module drops to the uncontrolled rectifier voltage of the anti-parallel diode of the IGBT module, controlling the disconnection of the multiple IGBT modules in the converter module to pass the anti-parallel diode. The diode performs uncontrolled rectification; when it is detected that the current in the DC bus is a short-circuit current caused by a short circuit of an 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 is bypassed through the phase-controlled rectifier circuit; or, the rectifier bridge circuit is an uncontrolled rectifier circuit, and the method further includes: when it is detected that the current in the DC bus changes to a first current threshold, controlling the on and off of multiple IGBT modules in the converter module to perform the wave-by-wave current limiting; when the voltage at the DC end of the converter module drops to the uncontrolled rectifier voltage, controlling the disconnection of multiple IGBT modules in the converter module to make the short-circuit current bypassed through the uncontrolled rectifier circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a rail transit traction system to which the technical solution provided in an embodiment of the present application is applied; Figure 2 for Figure 1 Schematic diagram of a bidirectional traction converter device in a rail transit vehicle; Figure 3 This is the circuit topology diagram of the ANPC type three-level converter circuit; Figure 4 is a schematic diagram of a bidirectional traction converter circuit; Figure 5 Schematic principle of the bidirectional rail transit traction system provided in the embodiment of this application Figure 1 ; Figure 6 Schematic circuit diagram of a bidirectional rail transit traction system provided in an embodiment of the present application Figure 1 ; Figure 7 Schematic principle of the bidirectional rail transit traction system provided in the embodiment of this application Figure 2 ; Figure 8 Schematic circuit diagram of a bidirectional rail transit traction system provided in an embodiment of the present application Figure 2 ; Figure 9 Schematic principle of the bidirectional rail transit traction system provided in the embodiment of this application Figure 3 ; Figure 10 Schematic principle of the bidirectional rail transit traction system provided in the embodiment of this application Figure 4 ; Figure 11 A short-circuit control timing diagram of a bidirectional rail transit traction system provided in an embodiment of the present application; Figure 12 Schematic principle of the bidirectional rail transit traction system provided in the embodiment of this application Figure 5 ; Figure 13 Schematic principle of the bidirectional rail transit traction system provided in the embodiment of this application Figure 6 ; Figure 14 Schematic circuit diagram of a bidirectional rail transit traction system provided in an embodiment of the present application Figure 3 ; Figure 15 A schematic flowchart of a short-circuit control method for a bidirectional rail transit traction system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application.

[0022] It should be noted that in the embodiments of the present 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 either 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, and C and B can be directly connected, with A and B connected through C.

[0023] In addition, references to "one embodiment" or "some embodiments" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in other embodiments" appearing in various places in 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 "including," "comprising," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0024] In the embodiments of the present application, ordinal numbers such as "first" and "second" are mentioned to distinguish multiple objects, and are not used to limit the order, timing, priority or importance of multiple objects.

[0025] Currently, rail transit power supply systems mostly use unidirectional rectifiers to convert electrical energy from three-phase AC to DC, providing DC power for 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 regenerative bidirectional traction power supply device has been introduced into the rail transit power supply system. The AC side of the regenerative bidirectional traction power supply device is connected to the AC grid, and the DC side is connected to the DC traction grid. When the rail transit vehicle is in traction mode, the power supply device operates in a rectifier mode, converting AC power from the AC grid to DC power for the DC traction grid. When the rail transit vehicle is in braking mode, the power supply device operates in an inverter mode, converting DC power from the DC traction grid to AC power and feeding it back to the AC grid.

[0026] Figure 1 It is a schematic diagram of a rail transit traction system that applies the technical solution provided in the embodiment of the present application.

[0027] 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 .

[0028] Figure 1The figure also shows a track 140 and a vehicle 150 in a rail transit system. A DC catenary 160 is installed above the track 140. A bidirectional traction converter 120 is located between the AC grid 110 and the DC catenary 160. It rectifies the AC power provided by the AC grid 110 to provide DC power suitable for the traction motor 130 to the DC catenary 160. The vehicle 150 then receives this DC power via 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 catenary 160. At this point, the bidirectional traction converter 120 inverts this DC power, feeding it back to the AC grid 110.

[0029] Figure 2 yes Figure 1 A schematic diagram of the bidirectional traction converter 120 is shown in FIG. Figure 2 As shown, the bidirectional traction converter 120 includes at least one bidirectional converter module 121 , wherein the AC end of the bidirectional converter module 121 is connected to the AC bus, and the DC end is connected to the DC load.

[0030] When the bidirectional traction converter 120 includes at least two bidirectional converter modules 121, each bidirectional converter module is connected in parallel. Each bidirectional converter module can operate simultaneously, or some of the bidirectional converter modules can operate simultaneously, with the remaining bidirectional converter modules serving as backup. When an active bidirectional converter module fails, the backup bidirectional converter module replaces the failed bidirectional converter module. For example, if the bidirectional traction converter device includes two bidirectional converter modules, the two bidirectional converter modules can operate simultaneously, or one of the bidirectional converter modules can operate while the other serves as backup. When an active bidirectional converter module fails, the backup bidirectional converter module replaces the failed bidirectional converter module.

[0031] The bidirectional converter module can be any of a variety of types, including a three-level converter, an interleaved parallel converter, and a cascaded H-bridge converter. The active neutral-point-clamped (ANPC) three-level converter is a topology developed from the traditional neutral-point-clamped (NPC) three-level converter. By introducing active switching devices, it achieves more flexible neutral-point potential control and lowers switching losses.

[0032] Figure 3 The circuit topology diagram of ANPC type three-level converter circuit is shown below. Figure 3 Provide detailed explanation.

[0033] The ANPC three-level converter is suitable for operating 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 consisting of a first switch tube T1, a second switch tube T2, and a fifth switch tube T5 connected together, and a lower bridge arm consisting of a third switch tube T3, a fourth switch tube T4, and a sixth switch tube T6. The first switch tube T1 and the fourth switch tube 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 tube T5 and the sixth switch tube T6 is connected to the neutral terminal of the DC network, and the connection point of the second switch tube T2 and the third switch tube T3 is connected to the AC network.

[0034] As a possible implementation, the first switch tube T1 and the fifth switch tube T5 are packaged in the same switch tube packaging module, the fourth switch tube T4 and the sixth switch tube T6 are packaged in the same switch tube packaging module, and the second switch tube T2 and the third switch tube T3 are packaged in the same switch tube packaging module.

[0035] The control circuit is used to control the on and off of each switch tube in the main circuit, including: when the AC network is the input end, controlling the conduction and off of the switch device to realize the rectification of the AC voltage; and when the DC network is the input end, controlling the conduction and off of the switch device to convert the DC voltage into a three-phase AC voltage to form the required AC waveform.

[0036] exist Figure 3 In the ANPC three-level converter shown, each switch tube is a controllable switch tube with an anti-parallel diode, wherein the diodes corresponding to the switch tubes are represented by D1, D2, D3, D4, D5 and D6.

[0037] In practical applications, pulse width modulation (PWM) technology is usually used to control the on-time and off-time of the switch tube, and the output DC voltage is controlled by adjusting the duty cycle of the PWM signal.

[0038] In the case where the aforementioned AC power grid is a three-phase AC power grid, Figure 4 As shown, each bidirectional conversion module may include three ANPC-type three-level converters connected in parallel. The DC ends of the three ANPC-type three-level converters are all connected to the DC bus, and the AC ends are respectively connected to different phases of the three-phase AC power grid. By controlling the on and off phases of multiple switching tubes in the three ANPC-type three-level converters, conversion between DC power and three-phase AC power can be achieved.

[0039] exist Figure 4As shown, each bidirectional converter module further includes a first capacitor C1 and a second capacitor C2, which are respectively arranged between the positive DC bus and the negative DC bus and the midpoint. When the converter module is operating normally, the two capacitors jointly store energy, buffer the energy exchange between the DC side and the AC side, and suppress fluctuations in 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 device.

[0040] During operation, the aforementioned bidirectional rail transit traction system may also experience abnormal increases in DC bus current. Causes of abnormal DC bus current include, but are not limited to, sudden load changes, overloads, 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 to provide energy to the short circuit point, causing a sharp increase in the DC bus current. Excessive bus current may cause the power devices in the converter module to heat up, causing irreversible damage to the power devices.

[0041] In the related art, when the above-mentioned current mutation occurs, the usual solution is to quickly cut off the connection between the converter module and the external load and the power grid, thereby avoiding damage to the components in the converter module. However, this method still has some problems: immediately disconnecting the converter module from the external load and the power grid in the event of a fault will not be conducive to troubleshooting; in addition, after the system detects a short circuit, it will immediately disconnect the bidirectional rail transit traction system from the external load and the power grid. The load may not be powered off normally, causing damage to the load. Moreover, after the power source is cut off, the short-circuit current disappears, but the short-circuit fault may not disappear. The next startup may cause a new round of failures.

[0042] If a bidirectional rail transit traction system could maintain continuous operation for a period of time in the event of a short circuit, allowing the short-circuited external load to be successfully disconnected or sufficient time for troubleshooting, the aforementioned hidden dangers could be overcome. However, in the bidirectional rail transit traction systems described in the related art, relying solely on the capacity of the IGBT modules in the converter modules is clearly insufficient to meet the short-circuit protection requirements. Therefore, there is an urgent need to improve existing bidirectional rail transit traction systems so that they can withstand larger short circuits for a certain period of time, thereby achieving short-circuit protection for the entire system.

[0043] In view of the above problems, the embodiment of the present application provides a bidirectional rail transit traction system and a control method thereof. The technical solution of the present application will be described in detail below with reference to the accompanying drawings.

[0044] Figure 5 It is a schematic principle diagram of a bidirectional rail transit traction system 500 provided in an embodiment of the present application. Figure 5The bidirectional rail transit traction system 500 includes at least one converter module 510 , a DC bus 520 , an AC bus 530 , a power grid 540 , a short-circuit module 550 , and a controller 560 .

[0045] The DC bus 520 includes a positive DC bus BUS+ and a negative DC bus BUS-, and is used to connect a DC side circuit between the converter module 510 and an external load.

[0046] The converter module 510 includes a DC terminal and an AC terminal, wherein the DC terminal is connected to a positive DC bus BUS+ and a negative DC bus BUS−, and the AC terminal is connected to a power grid 540 via an AC bus 530 .

[0047] It should be noted that the number of the at least one converter module 510 can be one or more. When there are multiple converter modules 510, the DC end of each converter module 510 is connected to the DC bus 520, and the AC end 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.

[0048] In an embodiment of the present application, the converter module 510 may include an inverter bridge circuit capable of operating in either an inverter or rectifier mode. For example, when used in the aforementioned rail transit vehicle, the inverter bridge circuit may operate in the inverter mode when the vehicle is braking, thereby converting the DC power generated by the motor braking into AC power and feeding it back to the power grid 540. During normal vehicle operation, the inverter bridge circuit operates in the rectifier mode, converting the AC power provided by the power grid 540 into DC power to drive DC loads such as motors.

[0049] It should be noted that the embodiments of the present 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, a multi-level inverter circuit, etc.

[0050] For example, Figure 6 As shown, the converter module in the bidirectional rail transit traction system includes three ANPC type three-level converters connected in parallel. The DC positive terminal and DC negative terminal of the three ANPC type three-level converters are connected to BUS+ and BUS- respectively, and the DC terminal is connected to the three phases of the three-phase AC power grid respectively. The midpoints of the three ANPC type three-level converters are connected to each other.

[0051] The DC side of the 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 the AC bus 530. This module is used to provide a low-impedance path to bypass the current in the main converter module when an external load is short-circuited.

[0052] Short-circuit module 550 typically consists of a rectifier bridge, including a phase-controlled rectifier circuit, an uncontrolled rectifier circuit, or a fully controlled rectifier circuit. Short-circuit module 550 can carry high currents for a short period of time, thereby protecting the IGBT modules in the main circuit from damage caused by short-circuit currents. The specific operation of short-circuit module 550 will be described in more detail below.

[0053] The controller 560 is connected to the current conversion module 510 and is configured to control the current conversion module 510 to perform wave-by-wave current limiting when detecting that a current change value in the DC bus 520 exceeds a first current threshold.

[0054] Controller 560 monitors the current changes in DC bus 520 in real time. Once it detects that the current exceeds a preset first current threshold (for example, 4kA), it triggers the cycle-by-cycle current limiting mechanism. This mechanism dynamically adjusts the on-off time of the IGBT within each cycle based on current fluctuations, thereby gradually reducing the duty cycle and preventing damage to the converter module 510 caused by sudden surges in current.

[0055] In actual implementation, the controller 560 can select a suitable current limiting strategy according to different current change patterns. For example, when the current continues to rise, the duty cycle of the IGBT can be quickly reduced to limit the current growth rate; and after the current is relatively stable, the current duty cycle can be appropriately maintained or slightly adjusted.

[0056] The short-circuit module 550 is used to bypass the short-circuit current through the short-circuit module 550 when an external load of the bidirectional rail transit traction system 500 is short-circuited. The AC bus 530 is coupled to the DC bus 520 via the short-circuit module 550, forming a first path. The AC bus 530 is coupled to the DC bus 520 via the converter module 510, forming a second path. The impedance of the first path is lower than that of the second path.

[0057] 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 smaller than the impedance of the second path, the current will flow through the first path first, thereby effectively avoiding the converter module 510 and preventing the short-circuit current from directly impacting the IGBT module.

[0058] In actual implementation, the activation of short-circuit module 550 requires a certain delay to confirm activation to avoid malfunction. For example, upon detecting an abnormally high current, controller 560 will first initiate a wave-by-wave current limiting measure before further determining whether a true short-circuit event has occurred. If a short-circuit is confirmed, short-circuit module 550 will immediately activate to divert current and protect the main circuit.

[0059] In the embodiments of the present application, there are many ways to make the impedance of the first path lower than the impedance of the second path. For example, this can be achieved by selecting an appropriate rectifier bridge structure, using low-impedance devices, etc. For example, the short-circuit module 550 can use a thyristor rectifier bridge, whose impedance is approximately 0.126 ohms, while the converter module 510, because it includes components such as IGBTs and common-mode inductors, has a total impedance of more than 2.83 ohms. This difference is more than 20 times, thereby ensuring that current flows preferentially through the short-circuit module 550.

[0060] According to the above 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 flows preferentially through the short-circuit module, thereby avoiding large current flowing through the IGBT devices in the converter module, reducing the impact on the power devices, and thereby improving the short-circuit tolerance and operational safety of the overall system; at the same time, when the controller detects abnormal current changes, it immediately performs wave-by-wave current limiting, which helps to quickly limit the current rise and improve the system response speed, while providing sufficient detection time for short-circuit detection, avoiding misjudgment and erroneous switching of short-circuit protection affecting the normal operation of the equipment.

[0061] In some embodiments, see Figure 7 and Figure 8 The bidirectional rail transit traction system also includes a DC-side switch 570, installed on the DC bus 520, for controlling the connection between the converter module 510 and the external load. During normal operation, this DC-side switch 570 remains closed, allowing current to flow. Upon detecting an abnormality (such as a short circuit), it is controlled to open, severing the current path and protecting the converter module 510 and the bidirectional rail transit traction system 500. Common DC-side switches 570 include contactors, relays, or solid-state switches.

[0062] The controller 560 is connected to the DC side switch device 570. The controller 560 is further used to control the DC side switch device 570 to disconnect when the short circuit current duration is greater than or equal to a first preset time, so as to disconnect the converter module 510 from the external load.

[0063] The first preset time is a time threshold set based on system design requirements and external load characteristics, and the first preset time is greater than the rated short-circuit protection time of the converter module 510. For example, the first preset time may be 120 milliseconds.

[0064] The purpose of setting this first preset time is to ensure that the circuit breaker or fuse in the external load experiencing a short circuit has sufficient time to disconnect after the system's internal short-circuit protection mechanism is activated, preventing the system from disconnecting prematurely and preventing downstream equipment from responding correctly. By delaying the disconnection operation until the short circuit has persisted for a certain period of time, safe and coordinated protection for the system and the load is achieved.

[0065] The above technical approach introduces DC-side switching devices and coordinates them with the controller to automatically disconnect the converter module from the external load when the short-circuit current duration meets preset conditions. This effectively isolates the fault point, preventing short-circuit current damage to the converter module, and thus improving system stability and safety.

[0066] In some embodiments, as Figure 8 and Figure 9 As shown, the system may further include an AC-side switch device 580, which is disposed on the AC bus 530 and is used to control the connection between the converter module 510 and the power grid 540. The AC-side switch device 580 remains closed during normal operation, allowing AC current to pass through; in the event of an abnormality, it is controlled to open, severing the connection between the converter module 510 and the power grid 540. The AC-side switch device 580 may be a contactor, a relay, or a solid-state switch.

[0067] The controller 560 is also connected to the AC side switch device 580 to control the AC side switch device 580 and the DC side switch device 570 to be disconnected when the duration of the aforementioned short-circuit current is greater than or equal to the first preset time, thereby completely disconnecting the DC side and AC side of the converter module 510 from the outside, ensuring the safety of the bidirectional rail transit traction system.

[0068] In some embodiments, the short-circuit module 550 includes a rectifier bridge circuit, a DC end of which is connected to the positive DC bus BUS+ and the negative DC bus BUS−, and an AC end of which is connected to the AC bus 530 .

[0069] A bridge rectifier circuit is a power electronic topology composed of multiple semiconductor devices that converts input AC voltage into DC output. In the technical solution of the embodiments of this application, the bridge rectifier circuit serves as the core component of the short-circuit module 550. Its low impedance allows for rapid response to short-circuit currents and effective current diversion. This circuit typically consists of devices such as thyristors (SCRs) or diodes, with either controlled or uncontrolled rectification selected based on specific application requirements.

[0070] The DC side of the rectifier bridge circuit is connected to the positive and negative DC busbars, ensuring that in the event of a short circuit, current flows quickly into the short-circuit module rather than through the main converter module, thereby protecting the main circuit from high current surges. The AC side is connected to the AC busbar, enabling the short-circuit module to quickly operate after detecting a short-circuit signal and forming a stable short-circuit loop.

[0071] The introduction of the short-circuit module 550 gives the system greater short-circuit resistance. In the event of a short-circuit fault, the short-circuit module 550 quickly conducts, directing most of the short-circuit current through its low-impedance path rather than through the main converter module. This prevents damage to power devices such as IGBTs due to excessive current. This design not only improves system safety and reliability but also extends the life of the equipment.

[0072] Furthermore, the choice of rectifier bridge circuit directly impacts the short-circuit module's response speed and current handling capacity. For example, using thyristors allows for controlled on / off switching, facilitating precise control in conjunction with the control system. Diodes, on the other hand, provide uncontrolled rectification, suitable for scenarios requiring less precise control. In practical applications, the appropriate rectifier bridge type can be flexibly selected based on system requirements.

[0073] According to the above technical means, a rectifier bridge circuit is used as a short-circuit module, which can provide a stable low-impedance path in a short-circuit situation, ensure that the short-circuit current can be effectively diverted, and reduce the impact on the conversion module.

[0074] In some embodiments, as Figure 10 As shown, the rectifier bridge circuit may be a phase-controlled rectifier circuit 551 , which is connected to a controller 560 .

[0075] A phase-controlled rectifier circuit regulates output voltage and current by controlling the conduction angle of thyristors (SCRs). This circuit enables dynamic control of the rectification process and is particularly suitable for short-circuit protection in high-power systems. The circuit consists of multiple thyristors connected to a controller, which adjusts the thyristor trigger angle in real time to adapt to varying load conditions.

[0076] The converter module 510 includes multiple IGBT modules, and the controller 560 is also used to: when it is detected that the current in the DC bus 520 changes to a first current threshold, control the 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 end of the converter module 510 drops to the uncontrolled rectification voltage of the anti-parallel diode of the IGBT module, control the multiple IGBT modules in the converter module 510 to be disconnected to perform uncontrolled rectification through the anti-parallel diode; when it is detected that the current in the DC bus 520 is 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 be turned on so that the short-circuit current is bypassed through the phase-controlled rectifier circuit 551.

[0077] When the DC terminal voltage of the converter module 510 drops below the uncontrolled rectification voltage of the IGBT anti-parallel diode, the controller 560 will actively shut down the IGBT module, automatically turning on the anti-parallel diode, and the system enters uncontrolled rectification mode. On the other hand, if 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 conduct, bypassing the short-circuit current through this circuit and avoiding the main converter module. This ensures that the main system is not affected by short circuits, improving system stability and safety.

[0078] Figure 11 The timing diagram of the short circuit control process is shown in FIG. Figure 11 As shown in the figure, before time t0, the DC bus current and DC link 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 implement wave-by-wave current limiting. By time t2, the DC link voltage drops to the uncontrolled rectifier voltage of the diode, and the DC bus current increases to 18kA. Starting at time t0, the system performs short-circuit detection, and at time t3, it determines that the external load has a short circuit. At time t4, the controller controls the phase-controlled rectifier circuit to operate, discharging the short-circuit protection circuit. At time t4, the DC link voltage drops to 350V, and the DC bus current increases to 25.4kA. During the operation of the phase-controlled rectifier circuit, the DC bus current remains at 25.4kA, while the DC link voltage gradually decreases. After time t4, the external load fuse opens and closes, disconnecting the external load.

[0079] 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 described in detail here. The duration of the uncontrolled control can be adjusted according to actual needs. Under one control, it is possible to directly enter the conduction phase of the rectifier bridge circuit (short-circuit module 550) from the wave-by-wave current limiting phase, that is, the operation duration of the uncontrolled rectification mode of the anti-parallel diode is 0. Accordingly, 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 rectification voltage of the anti-parallel diode of the IGBT module. It can exit after a certain period of operation or after the current limiting conditions are no longer met. The specific control strategy is adjusted according to actual conditions.

[0080] In the embodiments of the present application, by providing a phase-controlled rectifier circuit as the core component of the short-circuit module, combined 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 directed 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 tolerance.

[0081] The phase-controlled rectifier circuit may include two thyristors, the connection point of the two thyristors is the midpoint of the phase-controlled rectifier circuit, and the ends of the two thyristors that are far away from each other are respectively connected to the positive DC bus BUS+ and the negative DC bus BUS- 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 also used to: when it is detected that the current in the DC bus 520 changes to a first current threshold, control the 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 end of the converter module 510 drops to the uncontrolled rectifier voltage, control the multiple IGBT modules in the converter module 510 to be disconnected, so that the short-circuit current flows through the phase-controlled rectifier circuit bypass.

[0082] The uncontrolled rectifier circuit is a diode-based rectifier structure that is not connected to the controller and therefore uncontrollable. 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 the IGBT module) is disconnected 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.

[0083] The uncontrolled rectifier voltage is the minimum DC voltage required for normal conduction in the uncontrolled rectifier circuit. When the DC bus voltage drops below this voltage, it means that the converter module can no longer provide sufficient energy to support 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.

[0084] According to the above technical means, the structure of the short-circuit module is simplified by adopting an uncontrolled rectifier circuit, which reduces the cost of the system while ensuring that the short-circuit current can be effectively shunted.

[0085] In some embodiments, as Figure 13 As shown, the converter module 510 further includes a common-mode inductor 511, which is arranged between the DC end of the converter module 510 and the DC bus 520, and is used to suppress the circulating current between different converter modules 510 when the bidirectional rail transit traction system is working, and, when a short-circuit current exists in the DC bus 520, serves as an impedance on the second path to consume the short-circuit current.

[0086] Common-mode inductors typically consist of two coils with the same number of turns but wound in opposite directions, and are used to suppress common-mode noise. In the technical solution of this application, common-mode inductors 511 are configured between the DC terminals of the converter modules 510 and the DC bus 520 to suppress circulating currents between the multiple converter modules 510 and to act as an impedance element in the short-circuit protection path to absorb short-circuit currents.

[0087] When multiple converter modules 510 operate in parallel, circulating currents may occur due to differences in parameters or control timing between the modules. This circulating current not only increases losses but can also cause module imbalance or even damage. Common-mode inductors 511 effectively suppress this circulating current by providing a large inductive reactance to common-mode currents, improving system stability and efficiency.

[0088] In the event of a DC-side short-circuit fault, especially when a high-current surge occurs on the DC side, the common-mode inductor 511 can also serve as a portion of the impedance in the second path, shunting and limiting the short-circuit current. Due to its high inductive reactance, it can divert some of the short-circuit current to other paths, reducing the direct impact on the main power components (such as IGBTs), extending their service life, and improving the system's overall short-circuit tolerance. This enables effective short-circuit protection without relying on additional current-limiting circuitry, thereby improving the safety and reliability of system operation and ensuring stable operation of the equipment in high-voltage, high-current environments.

[0089] Continue reading Figure 13 The converter module 510 further includes a filter inductor 512, which is disposed between the AC end of the converter module 510 and the AC bus 530, and is used for performing AC filtering when the bidirectional rail transit traction system 500 is working, and serving as an impedance on the second path to consume short-circuit current.

[0090] The filter inductor is a passive component used to suppress high-frequency noise and smooth current fluctuations. In this application, the filter inductor 512 is arranged between the AC end of the converter module 510 and the AC bus 530.

[0091] Under normal operating conditions, the filter inductor 512 can effectively suppress high-frequency interference signals from the power grid 540 or other loads, improve the quality of output voltage and current, reduce electromagnetic interference, and enhance the electromagnetic compatibility performance of the system.

[0092] In the event of a short-circuit fault, filter inductor 512 also serves as an impedance element in the second path, limiting the growth rate of the short-circuit current through its own inductive reactance, thereby providing more response time for the control system. It also, to a certain extent, shares the current pressure of the main power components, reducing component stress and enhancing the system's short-circuit tolerance.

[0093] The above technical approach employs common-mode inductors on the DC side of the converter module and filter inductors on the AC side. These inductors act as key impedance components in the secondary path during a short circuit, working together to enhance the system's short-circuit tolerance and operational stability. Furthermore, the common-mode inductors and filter inductors, respectively, suppress noise and improve electromagnetic compatibility during normal system operation, thereby enhancing the system's overall short-circuit protection performance without increasing complexity.

[0094] In some embodiments, a ratio of the impedance of the second path to the impedance of the first path is greater than 20.

[0095] Setting the impedance of the first path to be significantly smaller than that of the second path ensures that, in the event of a short circuit, current preferentially flows through the low-impedance first path, preventing the converter module from experiencing significant short-circuit currents. For example, as a possible implementation, the impedance of the first path can be set to 0.126Ω, while the impedance of the second path can be set to 2.83Ω. The ratio between the two is approximately 22.4, meeting the requirement of being greater than 20.

[0096] In some embodiments, the first preset time is greater than 120 ms.

[0097] According to the description above, the first preset time is the time window from the detection of the short circuit event to the execution of the system's disengagement operation position. 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.

[0098] The 120ms in the embodiment of the present application is determined based on the requirements of the external system for the short-circuit response time.

[0099] In some embodiments, the conversion module includes multiple ANPC type three-level converters, the DC ends of the multiple ANPC type three-level converters are respectively connected to the positive DC bus BUS+ and the negative DC bus BUS-, and the AC ends of the multiple ANPC type three-level converters are respectively connected to multiple phase lines of the power grid through the AC bus.

[0100] Figure 14 This is an exemplary circuit diagram of a bidirectional rail transit traction system provided in an embodiment of the present application. Figure 14 As shown, the bidirectional rail transit traction system includes multiple converter modules. Each converter module includes three ANPC 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. The midpoints of the three converters 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.

[0101] The common-mode inductor L1 is provided between the DC bus and a hybrid circuit formed by the three converters, the first capacitor C3 and the second capacitor C4.

[0102] exist Figure 14In the bidirectional rail transit traction system shown, the grid has three phase lines, each connected to the AC terminal of the converter via three AC busbars. Three filter inductors L2 are installed on the AC busbars, and one end of three filter capacitors C is connected to the end of the three wave inductors L2 closest to the grid. The bidirectional rail transit traction system also includes a contactor KM1 installed on the DC busbar and multiple circuit breakers K2 installed on multiple AC busbars, respectively used to control the connection and disconnection between the converter module and the external load and the grid.

[0103] 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 connected to each other, so that the midpoints of the multiple converter modules are connected to each other, thereby achieving midpoint potential balance; when a half-bus short circuit occurs in one of the converter modules, the first fuse and the second fuse of the faulty converter module will be disconnected to avoid affecting other converter modules or the power grid.

[0104] Combined with the above Figures 1-14 , describes the device embodiment of the present application in detail, and the method embodiment of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the method embodiment corresponds to the aforementioned device embodiment, so for parts not described in detail, reference can be made to the aforementioned device embodiment.

[0105] Figure 15 This is a schematic flow chart of a short-circuit control method for a bidirectional rail transit traction system provided in an embodiment of the present application. The bidirectional rail transit traction system may be the bidirectional rail transit traction system described in any of the embodiments above. The system includes at least one converter module, a DC bus, an AC bus, a power grid, and a short-circuit module; wherein 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 being connected to the positive DC bus and the negative DC bus, and the AC terminal being connected to the power grid via the AC bus; the DC side of the short-circuit module being connected to the positive DC bus and the negative DC bus, and the AC side of the short-circuit module being connected to the AC bus.

[0106] Figure 15 The method includes steps S1510-S1520. In step S1510, when it is detected that the current in the DC bus changes to a first current threshold, the converter module is controlled to perform wave-by-wave current limiting.

[0107] In step S1520, when an external load of the bidirectional rail transit traction system is short-circuited, the short-circuit current is shunted by using a short-circuit module, so that the short-circuit current flows through the short-circuit module in a bypass manner.

[0108] The AC bus coupled with the DC bus through the short-circuit module is defined as a first path, and the AC bus coupled with the DC bus through the converter module is defined as a second path. The impedance of the first path is smaller than the impedance of the second path.

[0109] In some embodiments, the bidirectional rail transit traction system further includes: a DC side switching device, which is arranged on the DC bus and is used to control the connection and disconnection between the converter module and the external load.

[0110] The 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 switch device to be disconnected so as to disconnect the converter module from the external load.

[0111] In some embodiments, the conversion module includes multiple IGBT modules, the short-circuit module includes a rectifier bridge circuit, the DC end of the rectifier bridge circuit is respectively connected to the positive DC bus and the negative DC bus, and the AC end of the rectifier bridge circuit is connected to the AC bus.

[0112] The rectifier bridge circuit is a phase-controlled rectifier circuit, and the short-circuit control method further includes: When it is detected that the current in the DC bus changes to a first current threshold, the on and off of the multiple IGBT modules in the converter module are controlled to perform the wave-by-wave current limiting; when the voltage at the DC end of the converter module drops to the uncontrolled rectification voltage of the anti-parallel diode of the IGBT module, the multiple IGBT modules in the converter module are controlled to be disconnected to perform uncontrolled rectification 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 an 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.

[0113] Alternatively, the rectifier bridge circuit is an uncontrolled rectifier circuit, and the short-circuit control method further includes: When it is detected that the current in the DC bus changes to a first current threshold, the on and off of the multiple IGBT modules in the converter module are controlled to perform the wave-by-wave current limiting; when the voltage at the DC end of the converter module drops to the uncontrolled rectifier voltage, the multiple IGBT modules in the converter module are controlled to be disconnected, so that the short-circuit current flows through the uncontrolled rectifier circuit bypass.

[0114] An embodiment of the present application further provides a computer-readable storage medium, which stores a computer program. When the computer program is executed, the aforementioned method steps are implemented.

[0115] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0116] The units described as separate components may or may not be physically separate, and 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 these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0117] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0118] In the above embodiments, all or part of the embodiments can be implemented using software, hardware, firmware, or any combination thereof. When implemented using software, all or part of the embodiments can be implemented 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, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any computer-readable medium or a data storage device such as a server or data center that integrates one or more computer-readable media. The available medium may be a magnetic medium (eg, a floppy disk, a hard disk, a magnetic tape), an optical medium (eg, a digital versatile disc (DVD)), or a semiconductor medium (eg, a solid state disk (SSD)).

[0119] The above is only a specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be covered by the scope of protection of the present application.

Claims

1. A bidirectional rail transit traction system, characterized in that: It includes 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 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 current conversion module and is used to control the current conversion module to perform wave-by-wave current limiting when detecting that the current in the DC bus changes to a first current threshold; The short-circuit module is used to: when an external load of the bidirectional rail transit traction system is short-circuited, allow the short-circuit current to bypass and flow through the short-circuit module; The AC bus coupled with the DC bus through the short-circuit module is defined as a first path, and the AC bus coupled with the DC bus through the converter module is defined as a second path. The impedance of the first path is smaller 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 further includes: A DC side switch device, provided on the DC bus, for controlling the on / off between the converter module and the external load; The controller is connected to the DC side switch device, and the controller is further used for: When the duration of the short-circuit current is greater than or equal to a first preset time, the DC side switch device is controlled to be disconnected, so as to disconnect 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, wherein a DC end of the rectifier bridge circuit is connected to the positive DC bus and the negative DC bus respectively, and an AC end of the rectifier bridge circuit 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 a plurality of IGBT modules, and the controller is further configured to: When detecting that the current in the DC bus changes to a first current threshold, controlling the on and off of multiple IGBT modules in the converter module to perform the wave-by-wave current limiting; When the voltage at the DC terminal of the converter module drops to the uncontrolled rectification voltage of the anti-parallel diode of the IGBT module, controlling the multiple IGBT modules in the converter module to be disconnected so as to perform uncontrolled rectification 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 an 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 in a bypass manner.

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 a plurality of IGBT modules, and the controller is further configured to: When detecting that the current in the DC bus changes to a first current threshold, controlling the on and off of multiple IGBT modules in the converter module to perform the wave-by-wave current limiting; When the voltage at the DC end of the converter module drops to the uncontrolled rectifier voltage, the multiple IGBT modules in the converter module are controlled to be disconnected, so that the short-circuit current flows through the uncontrolled rectifier circuit bypass.

6. The bidirectional rail transit traction system according to any one of claims 1 to 5, characterized in that: The converter module further includes: a common-mode inductor, the common-mode inductor being arranged between the DC terminal of the converter module and the DC bus, and being used to suppress circulating currents between different converter modules when the bidirectional rail transit traction system is operating, and, when the short-circuit current exists in the DC bus, serving as an impedance on the second path to consume the short-circuit current; The filter inductor is arranged between the AC end of the converter module and the AC bus, and is used to perform AC filtering when the bidirectional rail transit traction system is working, and to serve as an impedance on the second path to consume the short-circuit current.

7. The bidirectional rail transit traction system according to any one of claims 1 to 5, characterized in that: A 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 bidirectional rail transit traction system, characterized in that: 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 comprises: When detecting that the current in the DC bus changes to a first current threshold, controlling the current conversion module to perform wave-by-wave current limiting; In the event that an external load of the bidirectional rail transit traction system is short-circuited, the short-circuit current is shunted by the short-circuit module, so that the short-circuit current is bypassed and flows through the short-circuit module; The AC bus coupled with the DC bus through the short-circuit module is defined as a first path, and the AC bus coupled with the DC bus through the converter module is defined as a second path. The impedance of the first path is smaller 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 further includes: A DC side switch device, provided on the DC bus, for controlling the on / off between the converter module and the external load; The method further comprises: When the duration of the short-circuit current is greater than or equal to a first preset time, the DC side switch device is controlled to be disconnected, so as to disconnect the converter module from the external load.

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

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