A metro water-cooled bidirectional converter mutual feedback test system and test method

Abstract

This invention discloses a mutual feedback testing system and method for a water-cooled bidirectional converter in subway systems, relating to the field of rail transit traction power supply technology. The system includes a #1 converter cabinet, a #2 converter cabinet, a DC control cabinet, an AC circuit breaker protection circuit, and a water-cooled collaborative monitoring circuit. The #1 converter cabinet is the energy input terminal on the rectifier side, internally equipped with six independent power modules PU1 to PU6. Each power module is configured with an independent IGBT, a driver board, and a water-cooled heat sink. Unit switching is achieved by controlling the IGBT's on / off state via the driver board, simultaneously eliminating the long-term maintenance costs of heat dissipation equipment and balancing the advantages of one-time investment and long-term operating costs. It overcomes the shortcomings of resistive loads, which can only be tested in steady state, and grid-connected feedback, which cannot simulate extreme impact conditions, thus comprehensively improving the product's factory performance verification coverage. The addition of a unit voltage equalization control module addresses the long-standing industry bias that "multiple units connected in parallel will inevitably generate circulating current."

Description

Technical Field

[0001] This invention relates to the field of rail transit traction power supply technology, specifically to a mutual feedback test system and test method for a metro water-cooled bidirectional converter. Background Technology

[0002] The water-cooled bidirectional converter in the subway traction power supply system undertakes the core function of bidirectional energy conversion between the AC power grid and the DC traction network. Before leaving the factory, the equipment must undergo high-power load testing to verify the temperature rise of the devices, IGBT switching characteristics, overall protection logic, and water cooling heat dissipation matching performance under rated operating conditions. Currently, the mainstream testing methods in the industry are divided into two categories: resistive load energy consumption testing and external grid-connected feedback testing. Meanwhile, the existing mature feedback testing reference document CN113281928A discloses a back-to-back feedback test device for rail transit traction converters. This reference document is the closest to the prior art of this invention. The inherent defects will be explained one by one below in conjunction with the reference document and the two traditional testing schemes, and all defects can be completely solved by this invention.

[0003] The first traditional approach is the high-power resistive load testing method, which directly connects a high-power water-cooled resistor array to the DC side of the converter under test, with all test energy dissipated as heat. This requires a large-capacity cooling tower and a high-power resistor cabinet; a 6000kW test setup can occupy up to 74m². 2 The hardware has a high initial investment cost; in terms of energy consumption, the full-load test consumes 4340kWh per hour, and the electricity cost for batch factory testing is high, which does not meet the requirements of green manufacturing; in terms of testing functions, it only supports full-power steady-state testing of the whole machine, and cannot split power units to carry out half-power or single-module aging, cannot simulate transient power impact and graded overload conditions, and the testing coverage is narrow.

[0004] The second type of traditional solution is external grid-connected feedback testing, which uses a back-to-back structure of two converters, with the inverter side directly feeding power back to the plant's public power grid. This solution requires independent design of grid-connected control algorithms and harmonic filtering devices for the inverter branch, and the collaborative debugging logic of the two converters is complex and has a long debugging cycle. High-power energy switching is prone to voltage distortion and harmonic disturbances, polluting the plant's power grid, which is why most plants restrict this type of high-power grid-connected test. Furthermore, it only supports synchronous commissioning of the entire unit, lacks a power unit grouping switching architecture, and one set of equipment is only compatible with a single-capacity converter, resulting in poor versatility.

[0005] The closest prior art reference document, CN113281928A, discloses a back-to-back mutual feed test device for rail transit traction converters. However, this document only achieves full-power closed-loop mutual feed between two complete units, and has three inherent defects that cannot be overcome: The system lacks a power unit grouping and switching topology, requiring all power modules to start synchronously. This makes it impossible to perform 3-to-3 half-power graded testing and results in weak compatibility with various water-cooled converter specifications. Furthermore, the system lacks an independent voltage equalization control module for each unit. There is a common industry bias that multi-unit grouping and parallel operation will cause DC bus voltage imbalance and excessive circulating current. This comparative document relies solely on unified modulation of the entire system and cannot adapt to scenarios involving split units feeding each other. Additionally, the two converters lack a local closed-loop circuit on the AC side, requiring inverter energy to be connected to the public power grid for energy cycling. The power grid participates in the main power transmission throughout the process, leading to high system losses and grid harmonic interference issues.

[0006] To solve the above-mentioned technical problems, it is necessary to provide a mutual feedback test system and test method for subway water-cooled bidirectional converters. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a mutual feedback testing system and method for a water-cooled bidirectional converter in a subway, aiming to solve the aforementioned technical problems.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: a mutual feedback test system for a water-cooled bidirectional converter in a subway, comprising a No. 1 converter cabinet, a No. 2 converter cabinet, a DC control cabinet, an AC circuit breaker protection circuit, and a water-cooled collaborative monitoring circuit; The No. 1 converter cabinet is the energy input terminal on the rectifier side. It has six independent power modules PU1 to PU6 inside. Each power module is equipped with an independent IGBT, driver board and water cooling heat sink. The unit switching is realized by controlling the IGBT on and off through the driver board. The unit switching of each power module is also realized by controlling the IGBT through the driver board.

[0009] The DC sides of converter cabinets #1 and #2 are connected in parallel to the DC control cabinet via DC positive and DC negative busbars, respectively. The AC sides of converter cabinets #1 and #2 are connected in parallel to the isolation transformer or reactor, forming a local closed-loop branch. The AC sides of both are then connected in parallel to the external AC power grid via the AC main circuit breaker. The external AC power grid only serves as a supplementary source for system losses and does not participate in the main power cycle. The unit voltage equalization control module is used to collect the DC output voltage of each power module in real time and dynamically adjust the PWM modulation ratio of each power module to suppress the DC circulating current generated by the group operation of multiple units; the DC control cabinet integrates DC IGBT switches, bus pre-charge circuit, discharge resistor, bus voltage sensor and unit voltage equalization control module.

[0010] The water-cooled collaborative monitoring loop synchronously collects the water-cooled inlet and outlet water temperatures and coolant flow rates of all power modules in converter cabinets #1 and #2. The system is configured with two freely switchable group feed-in topologies: the first is a 3-unit to 3-unit half-power feed-in topology, where the controller activates the odd / even power modules of converter cabinet #1 as rectifier units, and simultaneously activates the corresponding odd / even power modules of converter cabinet #2 as inverter units, while the remaining power modules are disconnected and put into sleep mode; the second is a 6-unit full-power feed-in topology, where all six power modules of converter cabinets #1 and #2 are simultaneously put into operation. The system controller is equipped with independent rectifier power regulation channels and inverter power regulation channels, which can independently set the rectifier output power and inverter feedback power of converter cabinet #1 and converter cabinet #2. The rectifier and inverter roles of the two converter cabinets can be interchanged. It can be set to rectify in converter cabinet #1 and invert in converter cabinet #2, or vice versa. The power difference can be used to simulate various operating conditions such as traction rectification, braking inversion, short-term overload, and transient impact.

[0011] Another method for mutual feedback testing in this technical solution is direct mutual feedback testing on the AC side inside the cabinet: This solution eliminates the need for a power frequency isolation transformer. Instead, it directly connects corresponding phases on the AC output sides of the two converter cabinets using series reactors to form a mutual feed circuit. During testing, both converter cabinets operate in inverter mode. A synchronous control system synchronizes the PWM drive pulses of the two converter cabinets, ensuring that the output frequencies and amplitudes of the three-phase AC voltages are identical, with a 120° electrical angle phase difference between corresponding phases. Because the AC outputs on both sides are directly connected via reactors, and there is a 120° phase difference between the outputs of the two converter cabinets, a voltage difference is generated across the reactors, producing a circulating current limited by the reactors, thus enabling bidirectional energy exchange between the two converter cabinets. By adjusting the amplitude, phase, or frequency of the output voltages of the two converter cabinets, the magnitude and direction of the mutual feed power can be precisely controlled, thereby completing performance tests under different load conditions.

[0012] Compared with the mutual feeding method using power frequency isolation transformers, this AC side direct mutual feeding scheme eliminates the isolation transformer, reducing system size, weight and equipment cost. At the same time, it reduces additional losses such as transformer copper loss and iron loss, improves the overall efficiency of the test system, and has the advantages of simple structure, convenient wiring and high power density.

[0013] In a dual converter cabinet system with direct interconnection on the AC side, a circulating current will be generated on the AC side when there is an output voltage difference between the two converter cabinets. At this time, the IGBT mainly bears the increased current stress and conduction loss caused by the circulating current. During the IGBT turn-off process, the main inductance of the reactor on the AC side interacts with the rate of rapid change of current (di / dt), generating a significant induced electromotive force on the AC side. This electromotive force is directly superimposed on the two ends of the device and works together with the AC circulating current to make the IGBT bear twice the voltage.

[0014] Under this near-twice transient voltage stress, system reliability can be actively detected.

[0015] (1) To assess the effectiveness of the active clamping circuit: By applying twice the voltage stress, it can be verified whether the circuit operates accurately at the preset threshold and whether its energy absorption capacity meets the requirements of the working conditions.

[0016] (2) Evaluate the immunity of the gate drive circuit: Under extremely high dv / dt (caused by the rapid establishment of twice the voltage), test the negative voltage turn-off capability of the drive circuit and the common mode rejection ratio of the signal isolation layer to prevent the device from being falsely triggered by Miller capacitance coupling.

[0017] (3) Equivalent accelerated aging test: During the test phase, the power device is subjected to a short-time overvoltage withstand test using twice the voltage stress, which can accelerate the screening of modules with potential insulation defects and expose early failure risks in advance.

[0018] In addition, the AC side mutual feed method in this cabinet also supports flexible combination testing of different power units. Multiple power units can be combined into different mutual feed circuits according to test requirements to realize functional verification, performance testing and reliability testing under different power levels and different operating modes. It has high versatility and engineering application value.

[0019] Preferably, the bus pre-charge circuit is equipped with a 120Ω current-limiting resistor, and the pre-charge process takes 12 seconds, which can smoothly raise the DC bus to the rated voltage of 1690V, avoiding power surge damage to power devices.

[0020] Preferably, the unit voltage equalization control module controls the DC voltage difference between each parallel power module within ±5V, eliminating the potential risk of excessive circulating current in the unit under the grouped mutual feed topology.

[0021] Preferably, when the system is running at full power, the power loss supplemented by the external AC power grid accounts for 5% to 10% of the total rated power of the system, and the main power energy circulates in a closed loop within the No. 1 and No. 2 converter cabinets.

[0022] Preferably, the entire testing system occupies only 28m² of space. 2It eliminates the need for high-power resistive load arrays, large water-cooled heat dissipation units, and independent grid-connected harmonic filtering devices.

[0023] Preferably, the AC circuit breaker protection circuit is equipped with independent circuit breakers on the AC side of the No. 1 and No. 2 converter cabinets respectively. When an overcurrent, over-temperature, or over-voltage fault is detected, the power module pulse output is blocked first, and then the AC circuit breaker is disconnected and the bus discharge resistor is activated to quickly discharge the residual electrical energy.

[0024] Preferably, the number of power modules can be replaced with 4 or 8, while the group switching logic and unit voltage equalization control strategy remain unchanged; buffer capacitors or energy storage batteries can be added to the DC bus to further reduce bus voltage fluctuations.

[0025] A method for testing the mutual feedback of a metro water-cooled bidirectional converter based on the aforementioned metro water-cooled bidirectional converter mutual feedback test system, characterized by comprising the following steps: S1. Pre-test self-check of the whole machine: sequentially complete the water cooling circuit flow and temperature detection, AC / DC circuit breaker status detection, all power module IGBT drive communication self-test, and DC bus insulation withstand voltage test. S2. Enable the pre-charge circuit IGBT to connect the current limiting resistor, slowly raise the bus voltage to the rated value, and after the pre-charge is completed, block the pre-charge circuit IGBT to remove the current limiting resistor. S3. Group topology configuration: Select 3 units to 3 units according to test requirements; The controller sends switching signals to enable the corresponding power module IGBT through the driver board; S4. Multi-condition power regulation test: Independently adjust the power parameters of the rectifier side and the inverter side, and carry out light load, rated load, short-time overload and transient impact tests in sequence, while simultaneously collecting temperature rise, bus voltage, current and harmonic data of each power unit; S5, graded shutdown protection: start the discharge resistor to release the residual electrical energy of the bus; when a fault is triggered, execute the graded protection logic, sequentially blocking the IGBT drive pulse, disconnecting the AC circuit, and starting the bus rapid discharge. First, block the inverter unit IGBT drive pulse, and then block the rectifier unit IGBT drive pulse.

[0026] Preferably, the total rated test power in the 3-to-3 half-power mutual feedback mode is 3000kW, and the power consumption per hour is only 216kWh, which saves 91.2% of the power compared with the same power resistive load scheme.

[0027] Preferably, in the full-power mutual feedback mode of the 6-unit whole machine, the total rated test power is 6000kW, the external power grid supplements the loss power of 510kW, and the power consumption per hour is 510kWh, which saves 3830kWh per hour compared with the traditional resistive load.

[0028] In summary, this invention provides a mutual feedback testing system and method for a water-cooled bidirectional converter in a subway system, achieving the following technical effects: This invention constructs a closed-loop local energy system within the cabinet, with the external power grid only supplementing 5% to 10% of system losses, resulting in energy savings of over 90% compared to traditional resistive load solutions. A 6000kW unit tested to this extent consumed only 510kWh per hour, compared to 4340kWh per hour for a resistive load under the same operating conditions, leading to significant annual electricity cost savings for mass production lines. The entire system eliminates the need for high-power resistor arrays, large water-cooled heat dissipation units, and grid-connected filtering devices, occupying only 28m² of space. 2 Compared to resistive load solutions, it reduces factory space by 62%, lowers equipment hardware investment by 55%, and saves on long-term maintenance costs for heat dissipation equipment, balancing the advantages of one-time investment and long-term use costs.

[0029] This invention features a dual-mode topology of 3-to-3 and 6-to-6 units, allowing a single system to be compatible with various specifications of water-cooled bidirectional converters, including 1000kW single-module, 3000kW half-power, and 6000kW full-power converters. Relying on dual-channel independent power regulation, it can fully simulate all scenarios of traction, braking, overload, and transient impact, overcoming the shortcomings of resistive loads which can only be tested in steady state and grid-connected feedback which cannot simulate extreme impact conditions. This significantly improves the coverage of product factory performance verification.

[0030] This invention enables inverter energy to circulate only in a local AC closed-loop system between two converter cabinets, eliminating the need for high-power feedback to the public power grid. This avoids harmonic distortion and voltage fluctuation issues, and is not limited by plant grid connection restrictions. It eliminates complex grid connection control algorithms, simplifying the local closed-loop collaborative control logic and reducing equipment commissioning cycle by 60%. Furthermore, this invention adds a unit voltage equalization control module, addressing the long-standing industry bias that "multi-unit parallel connection inevitably generates circulating current." This unit grouping topology combined with the local AC closed-loop system is not disclosed in comparative document CN113281928A or traditional test schemes, producing unexpected collaborative technical effects and demonstrating significant substantive features and progress.

[0031] The system of this invention supports two AC side connection methods: mutual feeding between isolation transformers and direct mutual feeding between reactors. It can be flexibly selected according to the test scenario, taking into account the advantages of electrical isolation safety, equipment cost, and power density, and adapting to different test requirements and field conditions. Attached Figure Description

[0032] Figure 1 This is the main circuit topology diagram of the mutual feedback test system for the water-cooled bidirectional converter in the subway according to the present invention; Figure 2 This is an enlarged topology diagram of the No. 1 converter cabinet of the subway water-cooled bidirectional converter mutual feedback test system of the present invention; Figure 3 This is an enlarged topology diagram of the No. 2 converter cabinet of the subway water-cooled bidirectional converter mutual feedback test system of the present invention; Figure 4 This is a schematic diagram of the mutual feedback test method of the present invention, which is a direct mutual feedback test on the AC side inside the cabinet. Detailed Implementation

[0033] To make the inventive objectives, complete technical solutions, and outstanding beneficial effects compared to the prior art clearer and more detailed, and to facilitate the complete replication and implementation of this solution by those skilled in the art, the device structure, implementation steps, and supporting technical details disclosed in the embodiments of this application will be comprehensively, clearly, and completely described below with reference to the accompanying drawings corresponding to multiple embodiments of this application.

[0034] In actual testing, the connection method can be selected according to the requirements: for high-safety-level test scenarios that require strong and weak electrical isolation, the isolation transformer connection method should be selected; for scenarios that pursue low cost, high power density and operating efficiency, the reactor direct connection method should be selected.

[0035] Example 1: In this example, the rated power of a single power module is 1000kW, the total test power of the 3-unit combination is 3000kW, the rated voltage of the DC bus is 1690V, the rated inlet water temperature of the water cooling system is 32℃, and the rated flow rate of the coolant is 8m³ / h. 3 / h; The current-limiting resistor of the pre-charge circuit of the DC control cabinet is 120Ω, the pre-charge time is 12s, and the unit voltage equalization control module controls the voltage difference of each power module within ±3V.

[0036] Figure 1 The diagram shows the main circuit topology of the mutual feedback test system for a water-cooled bidirectional converter in a subway system. The water-cooled bidirectional converter consists of converter cabinet #1, converter cabinet #2, and a DC control cabinet. The two cabinets are connected via a DC positive bus and a DC negative bus, and share the same DC control cabinet. Both cabinets are connected in parallel to an isolation transformer or reactor, sharing the same AC power grid. Converter cabinet #1 contains power modules pu1 to pu6 (i.e., 6 power units), and converter cabinet #2 also contains power modules pu1 to pu6 (i.e., 6 power units).

[0037] Reference Figure 1 As shown, before powering on the system, the pre-test self-check procedure is performed: the water cooling system is started, and the water cooling circuit flow rate is checked and found to be stable at 8m³ / s. 3 / h, the communication of the water cooling outlet temperature sensor of each power module is normal; the controller collects the position feedback signals of all AC and DC circuit breakers to confirm that there is no fault disconnection; it traverses all PU1 to PU6 power modules of the two converter cabinets and completes the communication self-test of the IGBT driver board; it uses an insulation tester to test the insulation resistance of the DC bus to ground, and the insulation resistance is ≥10MΩ to determine that the self-test is qualified.

[0038] The controller enables the IGBT in the pre-charge circuit inside the DC control cabinet. A 120Ω current-limiting resistor is connected to the bus circuit to slowly raise the bus voltage. The entire process takes 12 seconds, and the bus voltage rises steadily to the rated value of 1690V. After the pre-charge is completed, the IGBT in the pre-charge circuit is blocked, and the current-limiting resistor is removed.

[0039] The host computer's human-machine interface selects a 3-to-3 unit configuration; the unit voltage equalization control module inside the DC control cabinet collects the DC output voltage of the six input power modules in real time, dynamically corrects the PWM modulation ratio of each unit, and stably controls the voltage difference between units within ±3V in real time, with no circulating current exceeding the standard. The controller enables the IGBTs of the three rectifier units PU1, PU3, and PU5 in the #1 converter cabinet through the driver board, and simultaneously enables the IGBTs of the three inverter units PU1, PU3, and PU5 in the #2 converter cabinet, while the remaining IGBTs of the power modules PU2, PU4, and PU6 remain in a locked and dormant state.

[0040] The system controller sets the target power through independent rectifier power regulation channels and inverter power regulation channels: rectifier side target power 3000kW, inverter side feedback power 2800kW, internal closed-loop circulation power 2800kW, and external AC grid only supplements 200kW of system losses, with losses accounting for 7.2% of the total power.

[0041] Three types of operating condition tests were conducted sequentially: 2 hours of continuous aging under 100% half-power rated load, 10 minutes of short-term overload of 1.1 times 3300kW, and 100ms 4000, releasing residual bus energy to a safe voltage within 30 seconds. Finally, the AC main circuit breaker was disconnected, completing the entire half-power mutual feed-in test. Subsequently, the discharge resistor circuit of the DC control cabinet was activated to first block the IGBT drive pulses of the three units on the inverter side, and then block the IGBT drive pulses of the unit on the rectifier side.

[0042] In this embodiment, the measured power consumption per hour was 216kWh, which is 91.2% lower than that of a resistor load solution with the same power. The system operated stably throughout the entire process without any DC circulating current or external network harmonic interference issues.

[0043] Example 2: In this example, the rated power of a single power module is 1000kW. All PU1 to PU6 power modules of both converter cabinets are put into operation simultaneously, with a total rated test power of 6000kW. The rated voltage of the DC bus is 1690V, the inlet water temperature of the water cooling system is 32℃, and the coolant flow rate is 8m³ / h. 3 / h, the hardware parameters of the DC control cabinet pre-charge circuit and voltage equalization control module are completely consistent with those of Example 1.

[0044] The unit voltage equalization control module synchronously collects the real-time DC voltage of 12 power modules, dynamically adjusts the PWM modulation ratio of each unit, and controls the voltage difference of all parallel units within ±5V to suppress multi-unit parallel circulating current. All IGBTs of the six rectifier units PU1 to PU6 in converter cabinet #1 are enabled, and the IGBTs of the six inverter units PU1 to PU6 in converter cabinet #2 are enabled synchronously.

[0045] The controller is independently configured with a rectifier-side rated power of 6000kW and an inverter feedback power of 5490kW. The external AC grid only supplements 510kW of loss power, with losses accounting for 8.5% of the total rated power. The test conditions cover 6000kW full load for 2 hours of continuous aging, 1.2 times 3600kW overload for 10 minutes, and multiple consecutive 100ms transient power impact tests. The water-cooled collaborative monitoring loop collects the temperature rise data of each power module in real time. The overvoltage, overcurrent, and overtemperature protection logic of the bidirectional converter can be accurately triggered, and the water-cooled heat dissipation temperature rise is always controlled within the design threshold.

[0046] Under the same 6000kW whole unit operating conditions, the traditional resistive load scheme consumes 4340kWh per hour, the comparative document CN113281928A whole unit mutual feed scheme consumes 412kWh per hour, and this embodiment consumes only 510kWh per hour for full power mutual feed, saving 3830kWh per hour; the entire test system occupies an area of ​​28㎡, without the need for additional high-power resistors and large heat dissipation units, reducing the overall hardware investment by 55%.

[0047] Finally, disconnect the main AC circuit breaker, eliminating the risk of damage to the equipment from power-on or power-off surges. Connect the bus discharge resistor to release residual energy and sequentially block the IGBT drive pulses of the inverter unit and rectifier unit.

[0048] The embodiments described in this invention are for illustrative purposes only and do not constitute a limitation on the scope of the claims. Other substantially equivalent substitutions that can be conceived by those skilled in the art are all within the scope of protection of this invention.

Claims

1. A mutual feedback test system for a water-cooled bidirectional converter in a subway, characterized in that, It includes converter cabinet #1, converter cabinet #2, DC control cabinet, AC circuit breaker protection circuit, and water-cooled collaborative monitoring circuit; Each power module is also controlled by the driver board to switch the IGBTs. Each power module is equipped with an independent IGBT, driver board and water cooling heat sink. The switching of the units is achieved by controlling the IGBTs to turn on and off through the driver board. The DC sides of converter cabinets #1 and #2 are connected in parallel to the DC control cabinet via DC positive and DC negative busbars, respectively. The AC sides of converter cabinets #1 and #2 are connected in parallel to the isolation transformer or reactor, forming a local closed-loop branch. The AC sides of both are then connected in parallel to the external AC power grid via the AC main circuit breaker. The external AC power grid only serves as a supplementary source for system losses and does not participate in the main power cycle. The unit voltage equalization control module is used to collect the DC output voltage of each power module in real time and dynamically adjust the PWM modulation ratio of each power module to suppress the DC circulating current generated by the group operation of multiple units; the DC control cabinet integrates DC IGBT switches, bus pre-charge circuit, discharge resistor, bus voltage sensor and unit voltage equalization control module. The water-cooled collaborative monitoring loop synchronously collects the water-cooled inlet and outlet water temperatures and coolant flow rates of all power modules in converter cabinets #1 and #2. The system is configured with two freely switchable group feed-in topologies: the first is a 3-unit to 3-unit half-power feed-in topology, where the controller activates the odd / even power modules of converter cabinet #1 as rectifier units, and simultaneously activates the corresponding odd / even power modules of converter cabinet #2 as inverter units, while the remaining power modules are disconnected and put into sleep mode; the second is a 6-unit full-power feed-in topology, where all six power modules of converter cabinets #1 and #2 are simultaneously put into operation. The system controller is equipped with independent rectifier power regulation channels and inverter power regulation channels, which can independently set the rectifier output power and inverter feedback power of converter cabinet #1 and converter cabinet #2. The rectifier and inverter roles of the two converter cabinets can be interchanged. It can be set to rectify in converter cabinet #1 and invert in converter cabinet #2, or vice versa. The power difference can be used to simulate various operating conditions such as traction rectification, braking inversion, short-term overload, and transient impact.

2. The mutual feedback test system for a subway water-cooled bidirectional converter according to claim 1, characterized in that, The bus pre-charge circuit is equipped with a 120Ω current-limiting resistor. The pre-charge process takes 12 seconds and can smoothly raise the DC bus to the rated voltage of 1690V, avoiding power surge damage to power devices.

3. The mutual feedback test system for a subway water-cooled bidirectional converter according to claim 1, characterized in that, The unit voltage equalization control module controls the DC voltage difference between each parallel power module within ±5V, eliminating the potential risk of excessive circulating current in the unit under the grouped mutual feed topology.

4. The mutual feedback test system for a subway water-cooled bidirectional converter according to claim 1, characterized in that, When the system is running at full power, the power loss supplemented by the external AC power grid accounts for 5% to 10% of the total rated power of the system, and the main power energy circulates in a closed loop within the No. 1 and No. 2 converter cabinets.

5. The mutual feedback test system for a subway water-cooled bidirectional converter according to claim 1, characterized in that, The entire testing system occupies only 28m² of space. 2 It eliminates the need for high-power resistive load arrays, large water-cooled heat dissipation units, and independent grid-connected harmonic filtering devices.

6. The mutual feedback test system for a subway water-cooled bidirectional converter according to claim 1, characterized in that, The AC circuit breaking protection circuit is equipped with independent circuit breakers on the AC side of the No. 1 and No. 2 converter cabinets respectively. When an overcurrent, over-temperature, or over-voltage fault is detected, the power module pulse output is blocked first, then the AC circuit breaker is disconnected and the bus discharge resistor is activated to quickly discharge the residual electrical energy.

7. The mutual feedback test system for a subway water-cooled bidirectional converter according to claim 1, characterized in that, The number of power modules can be replaced with 4 or 8, while the group switching logic and unit voltage equalization control strategy remain unchanged; buffer capacitors or energy storage batteries can be added to the DC bus to further reduce bus voltage fluctuations.

8. A method for testing the mutual feedback of a subway water-cooled bidirectional converter based on the system described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Pre-test self-check of the whole machine: sequentially complete the water cooling circuit flow and temperature detection, AC / DC circuit breaker status detection, all power module IGBT drive communication self-test, and DC bus insulation withstand voltage test. S2. Enable the pre-charge circuit IGBT to connect the current limiting resistor, slowly raise the bus voltage to the rated value, and after the pre-charge is completed, block the pre-charge circuit IGBT to remove the current limiting resistor. S3. Group topology configuration: Select 3 units to 3 units according to test requirements; The controller sends switching signals to enable the corresponding power module IGBT through the driver board; S4. Multi-condition power regulation test: Independently adjust the power parameters of the rectifier side and the inverter side, and carry out light load, rated load, short-time overload and transient impact tests in sequence, while simultaneously collecting temperature rise, bus voltage, current and harmonic data of each power unit; S5, graded shutdown protection: start the discharge resistor to release the residual electrical energy of the bus; when a fault is triggered, execute the graded protection logic, sequentially blocking the IGBT drive pulse, disconnecting the AC circuit, and starting the bus rapid discharge. First, block the inverter unit IGBT drive pulse, and then block the rectifier unit IGBT drive pulse.

9. The mutual feedback test method for a water-cooled bidirectional converter in a subway according to claim 8, characterized in that, In the 3-to-3 half-power mutual feedback mode, the total rated test power is 3000kW, and the power consumption per hour is only 216kWh, which saves 91.2% of the power compared with the same power resistive load scheme.

10. The mutual feedback test method for a water-cooled bidirectional converter in a subway according to claim 8, characterized in that, The total rated test power of the 6-unit whole unit in full power mutual feedback mode is 6000kW, the power loss of external power grid is 510kW, the power consumption per hour is 510kWh, which saves 3830kWh per hour compared with traditional resistive load.

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