Bidirectional converter of rail transit traction power supply system and control method of bidirectional converter

Abstract

The invention discloses a bidirectional converter of a rail transit traction power supply system and a control method of the bidirectional converter, and relates to the technical field of bidirectional converters, and the bidirectional converter has high reliability: a modular power unit and redundancy design enable a single-point fault not to affect the overall operation of the system; a three-layer protection mechanism can quickly and accurately isolate faults; meanwhile, the control performance is excellent, active and reactive independent accurate control is achieved through double-closed-loop decoupling control, and the network voltage stabilizing effect is good; one set of system has two functions of bidirectional energy flow and reactive compensation, so that the utilization rate of equipment is improved; the power module adopts a plug-in design, so that the power module can be quickly replaced after a fault occurs, and the maintenance time is greatly shortened; and the train braking energy can be efficiently fed back to a power grid, so that the operation energy consumption is reduced.

Description

Technical Field

[0001] This invention belongs to the field of bidirectional converter technology, specifically a bidirectional converter and its control method for rail transit traction power supply systems. Background Technology

[0002] Currently, urban rail transit traction power supply systems generally use uncontrolled rectifier units, where energy can only flow unidirectionally from the AC grid to the DC traction grid. When the train brakes, the regenerative energy causes the DC grid voltage to rise. The traditional method is to use resistor energy dissipation devices or regenerative energy absorption devices with only inverter functions, but this has problems such as energy waste, large grid voltage fluctuations, poor voltage quality, and large line losses.

[0003] To address these issues, existing technologies have developed converters capable of bidirectional energy flow. However, these devices often suffer from shortcomings in system reliability, control precision, protection completeness, and modular maintenance. For example, they lack rapid hierarchical protection mechanisms, making them prone to equipment damage during faults; their control strategies are not flexible enough to accommodate multiple functions such as traction, braking energy feedback, and reactive power compensation; and their power unit structures are complex, making maintenance inconvenient.

[0004] Therefore, there is an urgent need in this field for a high-performance, highly reliable, and easy-to-maintain bidirectional converter system. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art; Therefore, this invention proposes a control method for a bidirectional converter in a rail transit traction power supply system, comprising: S1: Steps for acquiring operating parameters, including real-time synchronous acquisition of device status signals, module unit status signals, and system-level electrical quantity signals; S2: Layered collaborative protection execution steps. Based on the signal collected by S1, a three-level collaborative protection method consisting of device level, module level and system level is executed, and corresponding protection instructions are generated and executed within the preset time threshold. S3: Dual-mode control steps. Based on the external mode command, execute either the bidirectional converter control method or the reactive power compensation control method. The bidirectional converter control method controls the converter to operate in inverter or rectifier mode based on the comparison result between the DC bus voltage and the preset threshold, and adopts a dual closed-loop decoupling control method based on a synchronous rotating coordinate system. The reactive power compensation control method executes a reactive power outer loop and current inner loop control method based on a synchronous rotating coordinate system based on the reactive power reference value.

[0006] Furthermore, the device-level protection method includes: when the instantaneous current of any IGBT exceeds a first current threshold or the temperature exceeds a first temperature threshold, generating a first protection command and locking the IGBT within a first time threshold.

[0007] Furthermore, the module-level protection method includes: when the DC voltage difference of the module is detected to continuously exceed a percentage threshold of the rated voltage, or the communication heartbeat signal is lost for more than a second time threshold, and the device-level protection does not operate, a second protection command is generated within a third time threshold and the module is locked, and then the system performs derating operation.

[0008] Furthermore, the system-level protection method includes: when the DC bus voltage continuously exceeds the second voltage threshold, or the grid voltage continuously falls below the third voltage threshold, and the module-level protection fails to operate effectively, generating a third protection command within a fourth time threshold and performing a system-level shutdown or mode switching operation.

[0009] Furthermore, in the bidirectional converter control method, the outer loop is a DC voltage loop and the inner loop is a current loop, and a PI controller is used to realize independent control of active current and reactive current.

[0010] Furthermore, the bidirectional converter control method introduces an adaptive PI parameter tuning method: when the DC voltage change rate is detected to exceed a preset threshold, it automatically switches to a more aggressive PI parameter, and restores the original value after the system stabilizes.

[0011] Furthermore, it also includes: an accident recollection and data recording method that automatically saves the data sequence of all key operating parameters for a period of time before and after any protection action is triggered.

[0012] Furthermore, it also includes a method for smooth mode switching, specifically: When switching from bidirectional converter mode to reactive power compensation mode, the active current reference value is gradually reduced to zero, while the reactive current reference value is gradually reduced from zero to the target value to achieve a seamless switching.

[0013] Furthermore, the module-level protection method also includes module power output balance judgment: when the output current of any module continuously deviates from the average current value by more than a set ratio, a second protection command is generated and it is preemptively blocked.

[0014] A bidirectional converter for a rail transit traction power supply system includes a power cabinet and a control start cabinet, the control start cabinet being configured to execute the aforementioned control method.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This application features high reliability: modular power units and redundant design ensure that a single point of failure does not affect the overall system operation; a three-layer protection mechanism can quickly and accurately isolate faults; at the same time, it has excellent control performance: dual closed-loop decoupling control realizes independent and precise control of active and reactive power, resulting in good grid voltage stability.

[0016] Moreover, it has a high degree of functional integration: a single system has both bidirectional energy flow and reactive power compensation functions, which improves equipment utilization; this application is easy to maintain: the power module adopts a plug-in design, which can be quickly replaced after a failure, greatly shortening the maintenance time; and it can efficiently feed the train braking energy back to the power grid, reducing operating energy consumption. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the main wiring topology of the bidirectional converter system of the present invention; Figure 2 This is a block diagram illustrating the control principle of the system of the present invention; Figure 3 This is a block diagram of the AC overvoltage protection logic of the present invention; Figure 4 This is a block diagram of the AC undervoltage protection logic of the present invention; Figure 5 This is a block diagram of the overcurrent protection logic of the present invention. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figures 1-5 This application provides a bidirectional converter and its control method for a rail transit traction power supply system; As an embodiment of this application, it specifically includes: S1: Steps for obtaining runtime parameters; The system's three types of operating parameters are acquired in real time and synchronously through the signal acquisition module: Device status signals include collector-emitter voltage (Vce) of each IGBT switch and current information fed back from the drive circuit, used to detect overcurrent and desaturation faults; and temperature sensor signals mounted on the IGBT heat sink, used to monitor overheating.

[0020] Module unit status signals: including the DC side positive and negative bus voltages of each power module (used to calculate voltage balance), and the communication heartbeat signal between the module and the control master station.

[0021] System-level electrical quantity signals include the voltage and current of the common DC bus, as well as the AC grid voltage, current, and frequency acquired through grid-side voltage transformers (PTs) and current transformers (CTs).

[0022] S2: Hierarchical collaborative protection execution steps; This step executes a three-tiered collaborative protection method based on the signals acquired by S101: S201, Device-level Protection Method: When the instantaneous current value of any IGBT exceeds 2000A, or the temperature exceeds 85℃, the protection logic processing module generates the first protection command within 10 microseconds. This method directly acts on the drive circuit of the IGBT, immediately locking it to prevent device damage.

[0023] S202, Module-level Protection Method: When the positive and negative DC voltage difference of a module is detected to be greater than 10% of the rated voltage (1700V) (i.e., 170V) for 5ms or more, or the communication heartbeat signal is lost for more than 100ms, and provided that the device-level protection has not been activated, a second protection command is generated within 100 microseconds to 10 milliseconds. This method blocks all IGBTs of the faulty module, causing it to take off. Subsequently, the system executes a derating operation method: the main control device recalculates the maximum output power of the system (e.g., from 4MW to 3.5MW) based on the number of remaining healthy modules (e.g., 7 out of 8), and adjusts the total power reference value.

[0024] S203, System-level Protection Method: When the DC bus voltage is detected to be continuously higher than 2000V, or the grid voltage (for a 10kV system) is continuously lower than 9kV for 200ms, and the module-level protection has not been effectively activated, a third protection command is generated within 5ms to 10 seconds. This method performs system-level operations, such as complete shutdown, or switching from bidirectional converter mode to reactive power compensation mode.

[0025] S3: Dual-mode control steps The main control unit receives an external mode command and executes one of the following two control methods: Bidirectional converter control method (first mode): The collected DC bus voltage (Vdc) is compared with a preset threshold: if Vdc > 1750V, the control system operates in inverter mode; if Vdc < 1600V, it operates in rectification mode.

[0026] Execution of the control algorithm: A dual-closed-loop decoupling control method based on a synchronous rotating coordinate system (dq axis) is adopted.

[0027] The outer loop is a DC voltage loop, and its PI controller parameters are set as follows: Kpv=0.5, Tiv=0.1s; the inner loop is a current loop, and its PI controller parameters are set as follows: Kpi=1.0, Tii=0.01s. This method realizes independent control of active current and reactive current.

[0028] Reactive power compensation control method (second mode, SVG mode): Receives external or preset reactive power reference values ​​(Qref), ranging from -1Mvar to +1Mvar.

[0029] A reactive power outer loop and current inner loop control method based on a synchronous rotating coordinate system is implemented. The PI controller parameters for the reactive power outer loop are set as follows: Kpq = 0.2, Tiq = 0.05s.

[0030] Example 2; Based on Example 1, this embodiment optimizes the control method for scenarios where frequent train starts and stops cause severe fluctuations in DC bus voltage.

[0031] In S2 (hierarchical collaborative protection execution step), the module-level protection method is strengthened: Add "module power output balance judgment" as a protection trigger condition.

[0032] This method continuously calculates the output current of each parallel module. When the current of any module deviates from the average current value by more than 20%, even if its voltage and communication are normal, a second protection command is generated to preemptively block it, preventing cascading failures caused by current sharing failure.

[0033] In S3 (dual-mode control step), the bidirectional converter control method is optimized: An adaptive PI parameter tuning method is introduced: the PI parameters of the DC voltage loop are no longer fixed. When the DC voltage change rate (dVdc / dt) exceeds a preset threshold, it automatically switches to a more aggressive set of parameters (e.g., Kp_v is temporarily increased to 0.8, and Ti_v is decreased to 0.05s) to provide a faster dynamic response and quickly suppress voltage fluctuations. After the system stabilizes, the parameters return to their original values.

[0034] Example 3; This embodiment adds advanced functional methods to support system monitoring and maintenance, based on Embodiment 1.

[0035] S4: Accident Recall and Data Recording Method (an extension of S1) The monitoring backend continuously acquires and caches system parameter sequences from the main control device via Ethernet (IEC 61850MMS protocol); when any layer of protection action is triggered, this method is automatically activated, and the data sequence (including all key voltages, currents, power, and status words) recorded at a sampling rate of 1kHz within 10 seconds before the protection action to 5 seconds after the action is permanently saved to the local database; this method provides a complete data chain for subsequent fault analysis.

[0036] S5: Smooth mode switching method (integrated into S3) When the system needs to switch from "bidirectional converter mode" to "SVG mode", a smooth, non-disruptive switching method is implemented. This method first gradually reduces the active current reference value (ld_ref) of the inner current loop to zero over 2-3 grid cycles, while simultaneously gradually reducing the reactive current reference value (lq_ref) from zero to the target value. This method avoids current surges during mode switching and ensures stable grid operation.

[0037] Example 4; As another embodiment of this application, this embodiment provides a bidirectional converter device for a rail transit traction power supply system, the device being configured to perform the control method as described in any one of embodiments one to three; See Figure 1 The bidirectional converter device mainly includes: a connecting transformer (1), a power cabinet (2), and a control start cabinet (3).

[0038] Transformer (1): Its primary side is connected to a 10kV or 35kV AC power grid, and its secondary side outputs 950V AC power. This transformer achieves electrical isolation and voltage matching, providing a safe interface environment for the entire device.

[0039] Power cabinet (2): Its internal structure is modular and parallel, and it is the execution unit for energy conversion.

[0040] Control start cabinet (3): It is connected to each module unit in the power cabinet (2) through multiple optical fibers (4) and is the control core of the device.

[0041] The detailed structure of the power cabinet (2) is as follows: The power cabinet (2) contains N (e.g., N=8) power module units (21) connected in parallel. Each power module unit (21) is physically independent and includes: IGBT full-bridge circuit (211): It consists of six IGBT switching transistors (S1-S6) forming a three-phase full-bridge topology, serving as the core of AC / DC and DC / AC conversion.

[0042] DC support capacitor (212): Directly connected in parallel to the DC side of the IGBT full-bridge circuit (211) to filter voltage ripple and stabilize DC voltage. In this embodiment, each capacitor has a capacitance of 1000uF and a withstand voltage rating of not less than 2000V. Interface reactor (213): Connected in series at the AC side outlet of the IGBT full-bridge circuit (211) to filter switching harmonic current and suppress current surges.

[0043] Local driver and sampling board (214): Installed inside the module, responsible for driving the IGBT to turn on and off, and collecting device status signals such as current, voltage and temperature of the module in real time. This board receives drive signals from the control start cabinet (3) through optical fiber (4) and uploads the sampling data.

[0044] The AC side of all power module units (21) is connected in parallel to the common AC bus (22) through the interface reactor (213); their DC side is connected in parallel to the common DC bus (23). This parallel structure is the basis for realizing power expansion and operational redundancy.

[0045] The hardware configuration and functional modules of the control starter cabinet (3) are as follows: The control cabinet (3) integrates a main control device (31) based on a high-performance UAPC platform, such as a controller of model PCS-9566. This main control device (31) is configured at the hardware level to include the following functional modules: Signal acquisition module (311): This module has multiple analog input channels and digital input channels. It is configured as follows: Receive device status signals (such as IGBT Vce voltage and junction temperature) reported by the power module unit (21) via optical fiber; Receive module unit status signals (such as module DC voltage) from sensors inside the cabinet; Receive system-level electrical quantity signals (such as DC bus voltage, AC grid voltage and current) from system-level instrument transformers.

[0046] Protection logic processing module (312): This module is jointly implemented by high-speed logic circuits (such as FPGA) and microprocessors (such as DSP). It is configured to execute the hierarchical collaborative protection method described above: based on the input of the signal acquisition module (311), it independently generates first, second, or third protection instructions within different time thresholds corresponding to the device level, module level, and system level.

[0047] Control instruction generation module (313): The core of this module is a microprocessor (such as a DSP), which is configured as follows: Run a dual closed-loop decoupling control algorithm (such as PI control based on a synchronous rotating coordinate system).

[0048] According to the operating mode (bidirectional converter or SVG) and the instructions of the protection logic processing module (312), the corresponding PWM drive signal is generated.

[0049] The PWM drive signal is distributed to the local drive board (214) of each power module unit (21) via the fiber optic interface.

[0050] The extended functional units of the device are: The device may also optionally include: The monitoring backend (32) is an independent host computer system that communicates with the main control device (31) via Ethernet. It can be physically located in the control start cabinet (3) or in a remote control room. It is configured to perform an accident recall method, that is, to continuously and cyclically record system parameters and permanently save the data sequence from 10 seconds before the fault to 5 seconds after the fault when the protection action is triggered. The communication protocol adopts the standard IEC 61850 MMS protocol.

[0051] Brief description of the device's workflow; When the device is powered on, the signal acquisition module (311) of the control start cabinet (3) continuously acquires system data. The protection logic processing module (312) analyzes the data in parallel and immediately processes it according to the level once a fault is detected. At the same time, the control command generation module (313) calculates and sends PWM drive signals in real time according to the current mode and system status, controlling the IGBT full-bridge circuit (211) in the power cabinet (2) to perform precise power conversion. The monitoring background (32) records the entire process, realizing operation visualization and fault traceability.

[0052] The above embodiments are only used to illustrate the technical methods of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical methods of the present invention without departing from the spirit and scope of the technical methods of the present invention.

Claims

1. A control method for a bidirectional converter in a rail transit traction power supply system, characterized in that, include: S1: Steps for acquiring operating parameters, including real-time synchronous acquisition of device status signals, module unit status signals, and system-level electrical quantity signals; S2: Layered collaborative protection execution steps. Based on the signal collected by S1, a three-level collaborative protection method consisting of device level, module level and system level is executed, and corresponding protection instructions are generated and executed within the preset time threshold. S3: Dual-mode control steps. Based on the external mode command, execute either the bidirectional converter control method or the reactive power compensation control method. The bidirectional converter control method controls the converter to operate in inverter or rectifier mode based on the comparison result between the DC bus voltage and the preset threshold, and adopts a dual closed-loop decoupling control method based on a synchronous rotating coordinate system. The reactive power compensation control method executes a reactive power outer loop and current inner loop control method based on a synchronous rotating coordinate system based on the reactive power reference value.

2. The control method for the bidirectional converter of the rail transit traction power supply system according to claim 1, characterized in that, The device-level protection method includes: when the instantaneous current of any IGBT exceeds a first current threshold or the temperature exceeds a first temperature threshold, generating a first protection command and locking the IGBT within a first time threshold.

3. The control method for the bidirectional converter of the rail transit traction power supply system according to claim 1, characterized in that, The module-level protection method includes: when the DC voltage difference of the module is detected to continuously exceed the percentage threshold of the rated voltage, or the communication heartbeat signal is lost for more than a second time threshold, and the device-level protection does not operate, a second protection command is generated within a third time threshold and the module is locked, and then the system performs derating operation.

4. The control method for the bidirectional converter of the rail transit traction power supply system according to claim 1, characterized in that, The system-level protection method includes: when the DC bus voltage continuously exceeds the second voltage threshold, or the grid voltage continuously falls below the third voltage threshold, and the module-level protection fails to operate effectively, generating a third protection command within a fourth time threshold and performing a system-level shutdown or mode switching operation.

5. The control method for the bidirectional converter of the rail transit traction power supply system according to claim 1, characterized in that, In the bidirectional converter control method, the outer loop is a DC voltage loop and the inner loop is a current loop. A PI controller is used to achieve independent control of active current and reactive current.

6. The control method for the bidirectional converter of the rail transit traction power supply system according to claim 5, characterized in that, The bidirectional converter control method introduces an adaptive PI parameter tuning method: when the DC voltage change rate is detected to exceed a preset threshold, it automatically switches to a more aggressive PI parameter, and restores the original value after the system stabilizes.

7. The control method for the bidirectional converter of the rail transit traction power supply system according to claim 1, characterized in that, Also includes: The accident recap and data recording method automatically saves the data sequence of all key operating parameters for a period of time before and after any protection action is triggered.

8. The control method for the bidirectional converter of the rail transit traction power supply system according to claim 1, characterized in that, It also includes a method for smooth mode switching, specifically: When switching from bidirectional converter mode to reactive power compensation mode, the active current reference value is gradually reduced to zero, while the reactive current reference value is gradually reduced from zero to the target value to achieve a seamless switching.

9. The control method for the bidirectional converter of the rail transit traction power supply system according to claim 1, characterized in that, The module-level protection method also includes module power output balance judgment: when the output current of any module continuously deviates from the average current value by more than a set ratio, a second protection command is generated and it is pre-judged and blocked.

10. A bidirectional converter for a rail transit traction power supply system, characterized in that, It includes a power cabinet and a control start cabinet, the control start cabinet being configured to perform the control method as described in any one of claims 1 to 9.

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