A bidirectional converter applied to a power supply system of urban rail transit and a control method thereof

Abstract

The application discloses a bidirectional converter applied to a city rail transit power supply system and a control method, and relates to the technical field of city rail transit direct-current traction power supply. The bidirectional converter comprises a transformer, a converter, a rectifying unit and a control unit. The alternating current end of the converter and the alternating current end of the rectifying unit are connected to an alternating current power grid through the transformer. The direct current end of the converter and the direct current end of the rectifying unit are connected with a direct current contact net. The rectifying unit is used for converting alternating current of the alternating current power grid into direct current and supplying power for the direct current contact net. The control unit is used for monitoring contact net voltage of the direct current contact net, determining whether the contact net voltage is higher than a preset power feedback starting voltage threshold value, and when the contact net voltage is higher than the power feedback starting voltage threshold value, controlling the converter to deliver electric energy at the direct current contact net to the alternating current power grid to perform power feedback to the alternating current power grid. The above scheme can improve the electric energy utilization rate of the rail transit system.

Description

Technical Field

[0001] This invention relates to the field of DC traction power supply technology for urban rail transit, and in particular to a bidirectional converter and control method for use in urban rail transit power supply systems. Background Technology

[0002] In the urban rail transit sector, improving energy efficiency is a critical issue that the industry urgently needs to address. Traditional rail transit power supply systems use diode rectifiers to obtain power from the AC grid to supply power to the DC contact network, ensuring the power needs of train traction operation.

[0003] However, diode rectifiers can only achieve unidirectional energy conversion from alternating current to direct current, and cannot achieve reverse energy flow. Therefore, a large amount of regenerative energy generated at the DC contact network during train braking cannot be recovered and can only be consumed through onboard resistors. This not only causes serious energy waste in the rail transit system but also leads to a sudden voltage spike in the DC contact network, affecting the power supply stability of the rail transit system. Summary of the Invention

[0004] In view of this, this application provides a bidirectional converter and control method for use in urban rail transit power supply systems, with the main purpose of solving the technical problem of low power utilization rate in rail transit systems.

[0005] According to a first aspect of the present invention, a bidirectional converter for use in an urban rail transit power supply system is provided, the bidirectional converter being connected between an AC power grid and a DC contact network, the bidirectional converter comprising a transformer, a converter, a rectifier unit, and a control unit; The AC terminals of the converter and the rectifier unit are respectively connected to the AC power grid via the transformer, and the DC terminals of the converter and the rectifier unit are respectively connected to the DC contact network. The rectifier unit is used to convert the AC power from the AC power grid into DC power and to supply power to the DC contact network. The control unit is used to monitor the contact voltage of the DC contact network and determine whether the contact voltage is higher than a preset power feedback start voltage threshold. When the contact voltage is higher than the power feedback start voltage threshold, the control unit controls the converter to transmit the electrical energy at the DC contact network to the AC power grid to provide power feedback to the AC power grid.

[0006] In an optional embodiment, the rectifier unit includes a first rectifier unit and a second rectifier unit; the transformer is a four-winding transformer; the high-voltage winding of the four-winding transformer is connected to the AC power grid; the AC terminal of the first rectifier unit is connected to the first low-voltage winding of the four-winding transformer, the positive terminal of the first rectifier unit is connected to the DC contact network, and the negative terminal of the first rectifier unit is connected to the vehicle rail; the AC terminal of the second rectifier unit is connected to the second low-voltage winding of the four-winding transformer, the positive terminal of the second rectifier unit is connected to the DC contact network, and the negative terminal of the second rectifier unit is connected to the vehicle rail; the AC terminal of the converter is connected to the third low-voltage winding of the four-winding transformer, the positive terminal of the converter is connected to the DC contact network, and the negative terminal of the converter is connected to the vehicle rail.

[0007] In an optional embodiment, the control unit is configured to control the converter to start when the contact network voltage is higher than the power feedback start-up voltage threshold, and control the converter to output power to the AC grid for power feedback to the AC grid; the control unit is also configured to control the converter to be in standby mode when the contact network voltage is lower than the power feedback start-up voltage threshold.

[0008] In an optional embodiment, the method by which the control unit controls the converter to transmit electrical energy from the DC contact network to the AC power grid includes: the control unit determining a feedback power setpoint based on the contact network voltage and the power feedback start-up voltage threshold; and sending a power output command signal corresponding to the feedback power setpoint to the converter to control the converter to output the feedback power setpoint to the AC power grid.

[0009] In an optional embodiment, the method by which the control unit determines the feedback power setpoint based on the contact network voltage and the power feedback start-up voltage threshold includes: the control unit calculating the voltage difference between the contact network voltage and the power feedback start-up voltage threshold; and performing proportional-integral adjustment on the voltage difference to obtain the feedback power setpoint.

[0010] In an optional embodiment, the method by which the control unit sends a power output command signal corresponding to the feedback power setpoint to the converter to control the converter to output the feedback power setpoint to the AC grid includes: the control unit performing dq transformation on the grid voltage and grid current of the AC grid to obtain d-axis voltage, d-axis current, and q-axis current values; performing voltage outer loop control on the feedback power setpoint using the d-axis voltage value to obtain a d-axis current target value, and determining a d-axis current deviation signal based on the difference between the d-axis current target value and the d-axis current value; performing current loop control on the d-axis current deviation signal and the q-axis current value to obtain active power control quantity and reactive power control quantity, and performing dq inverse transformation on the active power control quantity and the reactive power control quantity to obtain a specified value for phase A voltage, a specified value for phase B voltage, and a specified value for phase C voltage; generating a power output command signal based on the specified values ​​for phase A voltage, phase B voltage, and phase C voltage, and controlling the feedback power output by the converter to the AC grid based on the power output command signal.

[0011] In an optional embodiment, the power output command signal is a pulse width modulation signal; the method by which the control unit generates the power output command signal based on the specified values ​​of phase A voltage, phase B voltage, and phase C voltage includes: the control unit comparing the specified values ​​of phase A voltage, phase B voltage, and phase C voltage with a preset carrier signal, and generating pulse width modulation signals corresponding to the specified values ​​of phase A voltage, phase B voltage, and phase C voltage respectively according to the comparison results.

[0012] In an optional embodiment, the high-voltage winding, the second low-voltage winding, and the third low-voltage winding of the four-winding transformer are connected in a delta configuration, and the first low-voltage winding is connected in a star configuration.

[0013] In an optional embodiment, the first rectifier unit and the second rectifier unit are both three-phase six-pulse rectifier units.

[0014] According to a second aspect of the present invention, a control method is provided, the method being applied to a control unit in a bidirectional converter used in an urban rail transit power supply system as described above, the method comprising: Monitor the contact network voltage of the DC contact network and determine whether the contact network voltage is higher than the preset power feedback start voltage threshold; When the contact network voltage is higher than the power feedback start-up voltage threshold, the converter is controlled to transmit the electrical energy at the DC contact network to the AC power grid to provide power feedback to the AC power grid.

[0015] This invention provides a bidirectional converter and control method for urban rail transit power supply systems. Through the combined design of rectifier unit and converter, and with the voltage monitoring and power feedback control strategy of control unit, the regenerative energy generated by train braking can be fed back to the AC grid while ensuring stable power supply to the DC contact network and meeting the power demand of train traction. This effectively reduces the energy waste caused by traditional resistor energy consumption and significantly improves the energy utilization rate of rail transit systems. At the same time, it can also avoid the problem of sudden voltage rise in DC contact network caused by the accumulation of regenerative energy, ensuring the operational stability of the entire power supply system.

[0016] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This invention provides a schematic diagram of the structure of a bidirectional converter applied to an urban rail transit power supply system. Figure 2 This invention provides a schematic diagram of another bidirectional converter applied to an urban rail transit power supply system. Figure 3 This diagram illustrates a method for calculating a setpoint for feedback power according to an embodiment of the present invention. Figure 4 A schematic diagram illustrating a calculation method for a power output command signal provided by an embodiment of the present invention is shown; Figure 5 This diagram illustrates a method for calculating the target value of d-axis current according to an embodiment of the present invention. Figure 6 This diagram illustrates a calculation method for active power control quantities and reactive power control quantities provided by an embodiment of the present invention. Figure 7 A schematic diagram of a converter topology provided in an embodiment of the present invention is shown; Figure 8 A schematic diagram of a control unit provided in an embodiment of the present invention is shown. Detailed Implementation

[0018] The present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the present application can be combined with each other.

[0019] Currently, improving energy efficiency is a critical issue that the urban rail transit industry urgently needs to address. Traditional rail transit power supply systems use diode rectifiers to obtain power from the AC grid to supply power to the DC contact network, ensuring the energy needs of train traction. However, diode rectifiers can only achieve unidirectional energy conversion from AC to DC, and cannot achieve reverse energy flow. Therefore, a large amount of regenerative energy generated at the DC contact network during train braking cannot be recovered and can only be consumed through onboard resistors. This not only causes serious energy waste in the rail transit system but also leads to a sudden voltage spike in the DC contact network, affecting the power supply stability of the rail transit system. To address the above problems, in one embodiment, such as Figure 1 As shown, a bidirectional converter for use in urban rail transit power supply systems is provided. This bidirectional converter connects the AC power grid 500 and the DC contact network 600 in the rail transit system. It includes a transformer 100, a converter 200, a rectifier unit 300, and a control unit 400. The converter 200 can be a bidirectional converter or a bidirectional power converter, enabling bidirectional energy flow between the AC power grid 500 and the DC contact network 600. Furthermore, the control unit 400 can be a computer terminal or other computer equipment.

[0020] Specifically, the AC terminals of the converter 200 and the rectifier unit 300 are connected to the AC power grid 500 via the transformer 100, and the DC terminals of the converter 200 and the rectifier unit 300 are connected to the DC contact network 600.

[0021] Furthermore, the rectifier unit 300 is used to convert the AC power from the AC grid 500 into DC power and transmit the DC power to the DC contact network 600 to supply power to the DC contact network 600. Here, when the train starts or accelerates, the rectifier unit 300 transmits electrical energy from the AC grid 500 to the DC contact network 600 under load, so that the train can absorb energy from the DC contact network 600.

[0022] Furthermore, the control unit 400 is used to monitor the contact network voltage of the DC contact network 600 and determine whether the contact network voltage is higher than a preset power feedback start-up voltage threshold. The power feedback start-up voltage threshold is preset and is used to determine whether the voltage value at the DC contact network 600 has excessively increased due to the presence of regenerative energy; its specific value can be determined according to actual conditions. Specifically, a voltage sensor can be installed at the DC contact network 600 to collect the contact network voltage and send the voltage value to the control unit.

[0023] Furthermore, when the contact network voltage is higher than the power feedback start voltage threshold, the control unit 400 controls the converter 200 to transmit the electrical energy at the DC contact network 600 to the AC power grid 500 to provide power feedback to the AC power grid 500. This can effectively prevent the waste of regenerated electrical energy and improve the power utilization rate of the rail transit system.

[0024] The bidirectional converter provided in this embodiment for use in urban rail transit power supply systems can, through the combined design of rectifier units and converters, and in conjunction with the voltage monitoring and power feedback control strategy of the control unit, feed back the regenerative energy generated by train braking to the AC grid while ensuring stable power supply to the DC contact network and meeting the power demand of train traction. This effectively reduces the energy waste caused by traditional resistor energy consumption and significantly improves the energy utilization rate of the rail transit system. At the same time, it can also avoid the problem of sudden voltage rise in the DC contact network caused by the accumulation of regenerative energy, ensuring the operational stability of the entire power supply system.

[0025] In an optional embodiment, such as Figure 2 As shown, the rectifier unit includes a first rectifier unit 310 and a second rectifier unit 320; wherein the first rectifier unit 310 and the second rectifier unit 320 are three-phase six-pulse rectifier units, each rectifier unit has a set of six-pulse rectifier circuits, and the first rectifier unit 310 and the second rectifier unit 320 can form a 12-pulse rectifier circuit to achieve 12 pulses, thereby reducing the harmonic content of the DC-side output voltage of the rectifier unit.

[0026] Furthermore, the transformer 100 is a four-winding transformer, with its high-voltage winding connected to the AC power grid 500. The high-voltage winding of the four-winding transformer is connected in a delta configuration (three-phase delta connection). Furthermore, the AC terminal of the first rectifier unit 310 is connected to the first low-voltage winding of the four-winding transformer, the positive terminal of the first rectifier unit 310 is connected to the DC contact network 600, and the negative terminal of the first rectifier unit 310 is connected to the rail 700. Here, the first low-voltage winding of the four-winding transformer is connected in a star configuration (three-phase Y connection). Furthermore, the rail 700 is the steel rail on which the train travels in the rail transit system.

[0027] Furthermore, the AC terminal of the second rectifier unit 320 is connected to the second low-voltage winding of the four-winding transformer, the positive terminal of the second rectifier unit 320 is connected to the DC contact network 600, and the negative terminal of the second rectifier unit 320 is connected to the rail 700. Furthermore, the AC terminal of the converter 200 is connected to the third low-voltage winding of the four-winding transformer, the positive terminal of the converter 200 is connected to the DC contact network 600, and the negative terminal of the converter 200 is connected to the rail 700. The second and third low-voltage windings of the four-winding transformer are both connected in a delta configuration (three-phase Δ connection).

[0028] Here, the negative terminals of the first rectifier unit 310, the second rectifier unit 320, and the converter 200 are all connected to the rail 700, so that the DC contact network 600 acts as the positive terminal to supply power to the train. The electrical energy consumed by the train is conducted to the rail 700 through its wheels and eventually flows back to the power source, forming a closed loop for powering the train.

[0029] The embodiments provided in this application use two three-phase six-pulse rectifier units in conjunction with the low-voltage windings of a four-winding transformer with different connections to form a twelve-pulse rectifier circuit. This can significantly reduce the harmonic content of the DC output voltage to the rail transit system, improve the power supply stability of the DC contact network, and reduce harmonic interference to the power grid and on-board equipment. Furthermore, the rectifier units and the converter share a rail as the negative return line, forming a simple closed-loop power supply circuit that takes into account both train traction power supply and regenerative energy feedback functions, thereby improving energy utilization efficiency.

[0030] In an optional embodiment, the control unit is used to control the converter to start when the contact network voltage is higher than the power feedback start voltage threshold, and to control the converter to output power to the AC grid for power feedback. In actual operation, if the train brakes, the regenerative energy generated by braking flows from the train into the DC contact network. At this time, because the rectifier unit can only achieve unidirectional power transmission from the AC grid to the DC contact network, the regenerative energy generated by the train braking cannot be fed back to the AC grid, thus causing the voltage at the DC contact network to rise.

[0031] Furthermore, when the voltage of the DC contact network is too high, if there is a train starting or accelerating within the DC contact network, the regenerative energy generated by the braking of the train will be directly supplied to the train starting or accelerating. Conversely, when there is no train starting or accelerating within the DC contact network, the contact network voltage will continue to rise because the energy generated by the train braking cannot be absorbed. When the DC contact network voltage exceeds the preset power feedback start-up voltage threshold, the control unit controls the converter to start, performing power feedback, so that energy flows from the DC contact network to the AC grid, preventing energy waste.

[0032] Furthermore, the control unit is also used to control the converter to enter standby mode when the contact wire voltage is lower than the power feedback start-up voltage threshold. Specifically, after the converter starts, the contact wire voltage at the DC contact wire will decrease and tend to approach the set power feedback start-up voltage threshold. After the braking train stops braking or switches to acceleration mode, the DC contact wire voltage decreases. When the contact wire voltage is lower than the power feedback start-up voltage threshold, the converter exits and enters standby mode, stopping power feedback to the AC grid.

[0033] The embodiments provided in this application enable the control unit to control the start-up and shutdown of the converter based on the numerical relationship between the contact network voltage and the power feedback start-up voltage threshold, thereby achieving precise recovery and utilization of regenerative energy. When the contact network voltage is too high, the converter starts to feed the braking energy back to the AC grid, avoiding energy waste; when the contact network voltage falls below the power feedback start-up voltage threshold, the converter is controlled to be in standby mode to save energy.

[0034] In an optional embodiment, the control unit controls the manner in which the converter delivers electrical energy from the DC contact network to the AC power grid, including: First, the control unit can determine the setpoint for the feedback power based on the contact network voltage and the power feedback start-up voltage threshold; specifically, such as... Figure 3 As shown, the control unit first calculates the voltage difference between the contact network voltage Udc and the power feedback start-up voltage threshold Usetup. The voltage difference is obtained by subtracting the power feedback start-up voltage threshold Usetup from the contact network voltage Udc using comparator 311. Then, the voltage difference can be proportional-integral (P / I) adjustment based on the proportional-integral module 312. The result of the P / I adjustment is amplified by the gain control module 313, and the amplitude of the amplified signal is limited by the limiting module 314 to obtain the feedback power setpoint P_ref.

[0035] Then, a power output command signal corresponding to the given feedback power value is sent to the converter to control the converter to output the given feedback power value to the AC grid. The embodiments provided in this application can accurately generate the given power feedback value through a closed-loop control process of voltage difference calculation, PI regulation, gain amplification, and limiting, ensuring that the converter output power matches the contact network voltage. This effectively avoids power feedback overload or underload problems, stabilizes the contact network voltage, and improves the efficiency of regenerative energy feedback.

[0036] In an optional embodiment, the control unit sends a power output command signal corresponding to the feedback power setpoint to the converter, thereby controlling the converter to output feedback power of the feedback power setpoint to the AC grid in the following manner: First, such as Figure 4 As shown, the control unit performs dq transformation on the grid voltage and grid current of the AC grid (including phase A voltage UA, phase A current IA, phase B voltage UB, phase B current IB, phase C voltage UC, and phase C current IC) to obtain the d-axis voltage value Ud, the q-axis voltage value Uq, the d-axis current value Id, and the q-axis current value Iq. Here, the AC voltage phase angle Wt can also be determined based on the phase A voltage UA, phase B voltage UB, and phase C voltage UC of the AC voltage for use during dq transformation and inverse dq transformation.

[0037] Furthermore, the feedback power setpoint P_ref is controlled by the d-axis voltage value Ud to obtain the d-axis current target value Id_ref, and the d-axis current deviation signal is determined based on the difference between the d-axis current target value Id_ref and the d-axis current value Id.

[0038] Here, as Figure 5 As shown, the feedback power setpoint P_ref can be amplified with a gain of 1, and the amplified result is multiplied by 2 / 3 through multiplier 340. The multiplication result is then divided by the d-axis voltage value Ud through divider 350. The result after division is filtered by the first filter 421 to obtain the d-axis current target value Id_ref.

[0039] Furthermore, such as Figure 4 As shown, based on the d-axis voltage value Ud and the q-axis voltage value Uq, current loop control is performed on the d-axis current deviation signal and the q-axis current value Iq to obtain the active power control quantity Ud_ref and the reactive power control quantity Uq_ref. Then, the active power control quantity Ud_ref and the reactive power control quantity Uq_ref are subjected to dq inverse transformation to obtain the specified values ​​of phase A voltage, phase B voltage, and phase C voltage.

[0040] Here, the target value of the q-axis current Iq_ref can be set to zero, and the difference between the target value of the q-axis current Iq_ref and the q-axis current value Iq can be calculated. If the difference between the target value of the q-axis current Iq_ref and the q-axis current value Iq is still equal to the q-axis current value Iq, then current loop control can be directly performed based on the q-axis current value Iq and the d-axis current deviation signal to obtain the active power control quantity Ud_ref and the reactive power control quantity Uq_ref.

[0041] Here, Figure 6 The flowcharts for calculating the active power control quantity Ud_ref and the reactive power control quantity Uq_ref are given, as follows: Figure 6 As shown, the d-axis current target value Id_ref and the d-axis current value Id can be subtracted based on the first subtractor 411, and the resulting difference can be adjusted by the first proportional-integral module 431 to obtain the d-axis current process value. Further, the q-axis current value Iq is calculated based on the first inductor voltage calculation module 451. By multiplying the q-axis current value Iq with the AC voltage phase angle Wt and the grid-side inductance value of the converter, the q-axis inductor voltage drop value is obtained. Further, after the d-axis voltage value Ud is filtered by the second filter 422, the filtered d-axis voltage value Ud is added to the q-axis inductor voltage drop value by the third subtractor 413 and then the d-axis current process value is subtracted to obtain the active power control quantity Ud_ref used for dq inverse transformation.

[0042] Similarly, the target value of the q-axis current Iq and the q-axis current value Iq can be subtracted based on the second subtractor 412, and the resulting difference can be adjusted by the second proportional-integral module 432 to obtain the process value of the q-axis current. Further, the inductor voltage is calculated based on the second inductor voltage calculation module 452 for the d-axis current value Id. By multiplying the d-axis current value Id with the AC voltage phase angle Wt and the grid-side inductance value of the converter, the d-axis inductor voltage drop value is obtained. Further, after the q-axis voltage value Uq is filtered by the third filter 423, the filtered q-axis voltage value Uq is added to the d-axis inductor voltage drop value by the fourth subtractor 414 and then the q-axis current process value is subtracted to obtain the reactive power control quantity Uq_ref used for dq inverse transformation.

[0043] Finally, a power output command signal is generated based on the specified values ​​of phase A voltage, phase B voltage, and phase C voltage, and the power output command signal is used to control the feedback power output by the converter to the AC grid.

[0044] Here, the power output command signal is a pulse width modulation (PWM) signal. Furthermore, the method by which the control unit generates the power output command signal based on the specified values ​​of phase A voltage, phase B voltage, and phase C voltage includes: the control unit compares the specified values ​​of phase A voltage, phase B voltage, and phase C voltage with a preset carrier signal, and generates pulse width modulation signals corresponding to the specified values ​​of phase A voltage, phase B voltage, and phase C voltage respectively based on the comparison results.

[0045] Specifically, the control unit can have a built-in three-phase voltage output command generation module and a carrier signal generation module. The carrier signal generation module continuously outputs a carrier signal with a preset frequency and amplitude. Furthermore, the control unit compares the specified values ​​of phase A voltage, phase B voltage, and phase C voltage with the carrier signal in real time. When the specified voltage value of a certain phase is greater than the amplitude of the carrier signal, the pulse width modulation signal corresponding to that phase voltage is a high-level signal; when the specified voltage value of a certain phase is less than the amplitude of the carrier signal, the pulse width modulation signal corresponding to that phase voltage is a low-level signal. Furthermore, based on the alternating high and low level signals of the specified voltage values ​​of phase A, phase B, and phase C, pulse width modulation signals corresponding to phases A, B, and C are generated respectively. These pulse width modulation signals are used to drive the power switching devices inside the converter to turn on and off, thereby precisely controlling the amplitude and frequency of the three-phase voltage supplied by the converter to the AC grid to achieve power feedback.

[0046] Furthermore, the topology of the inverter used to generate alternating current in the converter is as follows: Figure 7As shown, the switching transistors in the bridge arm of the inverter that generate the A-phase voltage include a first A-phase switch Q1A, a second A-phase switch Q2A, a third A-phase switch Q3A, a fourth A-phase switch Q4A, a fifth A-phase switch Q5A, and a sixth A-phase switch Q6A. The fifth A-phase switch Q5A is switched on or off with the first A-phase switch Q1A, and the sixth A-phase switch Q6A is switched on or off with the fourth A-phase switch Q4A. Further, the switching transistors in the bridge arm of the inverter that generate the B-phase voltage include a first B-phase switch Q1B, a second B-phase switch Q2B, a third B-phase switch Q3B, a fourth B-phase switch Q4B, a fifth B-phase switch Q5B, and a sixth B-phase switch Q6B. The fifth B-phase switch Q5B is switched on or off with the first B-phase switch Q1B, and the sixth B-phase switch Q6B is switched on or off with the fourth B-phase switch Q4B. Furthermore, the switching transistors in the bridge arm that generates the C-phase voltage in the inverter include a first C-phase switch Q1C, a second C-phase switch Q2C, a third C-phase switch Q3C, a fourth C-phase switch Q4C, a fifth C-phase switch Q5C, and a sixth C-phase switch Q6C. The fifth C-phase switch Q5C is switched on or off with the first C-phase switch Q1C, and the sixth C-phase switch Q6C is switched on or off with the fourth C-phase switch Q4C. All of these switching transistors can be insulated-gate bipolar transistors (IGBTs).

[0047] Taking the generation of phase A voltage as an example, the pulse width modulation signal corresponding to the specified value of phase A voltage can be sent to the gate terminals of the first phase A switch Q1A and the second phase A switch Q2A. After inverting the pulse width modulation signal, it is sent to the gate terminals of the third phase A switch Q3A and the fourth phase A switch Q4A, so that this bridge arm generates the phase A voltage corresponding to the specified value of phase A voltage. Similarly, the converter can generate the phase B voltage corresponding to the specified value of phase B voltage and the phase C voltage corresponding to the specified value of phase C voltage, and transmit the phase A, phase B, and phase C voltages to the AC grid. By controlling the converter to output AC voltage to the AC grid, feedback power is output to the AC grid to provide power feedback.

[0048] The embodiments provided in this application can precisely adjust the output power of the converter through dq transformation combined with a dual closed-loop control strategy, so as to stably feed regenerated power back to the AC grid and improve the power utilization rate of the rail transit system.

[0049] Furthermore, such as Figure 8 As shown in the figure, this application also provides a structural diagram of a control unit, which includes a liquid crystal display, a processor, a power supply, and an output circuit. The liquid crystal display, processor, power supply, and output circuit interact with each other via a communication bus.

[0050] Here, the LCD screen displays the operating parameters of the bidirectional converter used in the urban rail transit power supply system, and supports setting system parameters and setpoints. Furthermore, the processor integrates a data acquisition module, a calculation module, and a control module. The data acquisition module acquires the actual DC voltage of the DC contact network and the AC voltage and current of the AC power grid. The calculation module calculates and outputs the feedback power setpoint P_ref based on the acquired information. The control module further calculates the power feedback start voltage threshold to generate a pulse width adjustment signal. Furthermore, the memory stores the device's operating system, computer programs, and operating data. Furthermore, the power supply provides power to all modules of the device. Furthermore, the output circuit is responsible for acquiring and controlling switching signals and interacting with the converter.

[0051] The bidirectional converter provided in this application for urban rail transit power supply systems can effectively reduce power supply harmonic interference by combining a rectifier unit with a bidirectional converter and using a four-winding transformer to form a 12-pulse rectifier circuit. At the same time, the converter start-stop control based on voltage threshold and the dq conversion dual closed-loop strategy can achieve accurate recovery and stable feedback of regenerated energy, which can improve the energy utilization rate of the rail transit system, avoid waste, and ensure the stable and reliable operation of the power supply system.

[0052] Furthermore, this application also provides a control method applied to a control unit in a bidirectional converter used in an urban rail transit power supply system as described above, the method comprising: First, monitor the contact voltage of the DC contact network and determine whether the contact voltage is higher than the preset power feedback start voltage threshold. Then, when the contact network voltage is higher than the power feedback start voltage threshold, the converter is controlled to transmit the electrical energy at the DC contact network to the AC power grid to provide power feedback to the AC power grid.

[0053] The serial numbers in this application are for descriptive purposes only and do not represent the superiority or inferiority of any particular implementation scenario. The above disclosures are merely a few specific implementation scenarios of this application; however, this application is not limited thereto, and any variations conceived by those skilled in the art should fall within the protection scope of this application.

Claims

1. A bidirectional converter for use in urban rail transit power supply systems, wherein the bidirectional converter is connected between an AC power grid and a DC contact network, characterized in that, The bidirectional converter includes a transformer, a converter, a rectifier unit, and a control unit; The AC terminals of the converter and the rectifier unit are respectively connected to the AC power grid via the transformer, and the DC terminals of the converter and the rectifier unit are respectively connected to the DC contact network. The rectifier unit is used to convert the AC power from the AC power grid into DC power and to supply power to the DC contact network. The control unit is used to monitor the contact voltage of the DC contact network and determine whether the contact voltage is higher than a preset power feedback start voltage threshold. When the contact voltage is higher than the power feedback start voltage threshold, the control unit controls the converter to transmit the electrical energy at the DC contact network to the AC power grid to provide power feedback to the AC power grid.

2. The bidirectional converter for urban rail transit power supply systems according to claim 1, characterized in that, The rectifier unit includes a first rectifier unit and a second rectifier unit; the transformer is a four-winding transformer; The high-voltage winding of the four-winding transformer is connected to the AC power grid; The AC terminal of the first rectifier unit is connected to the first low-voltage winding of the four-winding transformer, the positive terminal of the first rectifier unit is connected to the DC contact network, and the negative terminal of the first rectifier unit is connected to the vehicle rail. The AC terminal of the second rectifier unit is connected to the second low-voltage winding of the four-winding transformer, the positive terminal of the second rectifier unit is connected to the DC contact network, and the negative terminal of the second rectifier unit is connected to the vehicle rail. The AC terminal of the converter is connected to the third low-voltage winding of the four-winding transformer, the positive terminal of the converter is connected to the DC contact network, and the negative terminal of the converter is connected to the vehicle rail.

3. The bidirectional converter for urban rail transit power supply systems according to claim 1, characterized in that, The control unit is used to control the converter to start when the contact network voltage is higher than the power feedback start voltage threshold, and to control the converter to output power to the AC grid so as to provide power feedback to the AC grid; The control unit is also used to control the converter to be in standby mode when the contact network voltage is less than the power feedback start-up voltage threshold.

4. The bidirectional converter for urban rail transit power supply systems according to claim 1, characterized in that, The control unit controls the converter to transmit electrical energy from the DC contact network to the AC power grid in the following ways: The control unit determines the setpoint value of the feedback power based on the contact network voltage and the power feedback start voltage threshold. Send a power output command signal corresponding to the feedback power setpoint to the converter to control the converter to output the feedback power setpoint to the AC grid.

5. The bidirectional converter for urban rail transit power supply systems according to claim 4, characterized in that, The control unit determines the feedback power setpoint based on the contact network voltage and the power feedback start voltage threshold in the following ways: The control unit calculates the voltage difference between the contact network voltage and the power feedback start-up voltage threshold; The voltage difference is adjusted proportionally and integrally to obtain the feedback power setpoint.

6. The bidirectional converter for urban rail transit power supply systems according to claim 4, characterized in that, The control unit sends a power output command signal corresponding to the feedback power setpoint to the converter, in order to control the converter to output the feedback power setpoint to the AC grid in the following manner: The control unit performs dq transformation on the grid voltage and grid current of the AC grid to obtain d-axis voltage value, d-axis current value and q-axis current value; The feedback power setpoint is controlled by the d-axis voltage value through an outer loop to obtain the d-axis current target value, and the d-axis current deviation signal is determined based on the difference between the d-axis current target value and the d-axis current value. The d-axis current deviation signal and the q-axis current value are subjected to current loop control to obtain active power control quantity and reactive power control quantity. The active power control quantity and the reactive power control quantity are subjected to dq inverse transformation to obtain the specified value of phase A voltage, the specified value of phase B voltage and the specified value of phase C voltage. A power output command signal is generated based on the specified values ​​of phase A voltage, phase B voltage, and phase C voltage, and the power output feedback power of the converter to the AC grid is controlled based on the power output command signal.

7. The bidirectional converter for urban rail transit power supply systems according to claim 6, characterized in that, The power output command signal is a pulse width modulation signal; The method by which the control unit generates a power output command signal based on the specified values ​​of phase A voltage, phase B voltage, and phase C voltage includes: The control unit compares the specified values ​​of phase A voltage, phase B voltage, and phase C voltage with a preset carrier signal, and generates pulse width modulation signals corresponding to the specified values ​​of phase A voltage, phase B voltage, and phase C voltage based on the comparison results.

8. The bidirectional converter applied to the power supply system of urban rail transit according to claim 2, characterized in that, The high-voltage winding, the second low-voltage winding, and the third low-voltage winding of the four-winding transformer are connected in a delta configuration, while the first low-voltage winding is connected in a star configuration.

9. The bidirectional converter applied to the power supply system of urban rail transit according to claim 2, characterized in that, The first rectifier unit and the second rectifier unit are both three-phase six-pulse rectifier units.

10. A control method, characterized in that, The method is applied to a control unit in a bidirectional converter used in an urban rail transit power supply system as described in any one of claims 1 to 9, and the method includes: Monitor the contact network voltage of the DC contact network and determine whether the contact network voltage is higher than the preset power feedback start voltage threshold; When the contact network voltage is higher than the power feedback start-up voltage threshold, the converter is controlled to transmit the electrical energy at the DC contact network to the AC power grid to provide power feedback to the AC power grid.

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