Power unit for rail transit, and control method

Abstract

Provided is a traction power supply system for rail transit, specifically a power unit for rail transit, and a control method. Distinguished from the architecture of a conventional traction power supply system for rail transit, a modularization-based power unit main circuit and a control method therefor are provided. The power unit main circuit comprises a high-voltage switch module, high-voltage modules, high-frequency transformers, low-voltage modules and an intermediate direct-current module. On the basis of a modular design concept, electrical isolation between high and low voltages and level conversion are implemented, thereby effectively reducing the difficulty in insulation design of a system and also improving the degree of redundancy and maintainability of the system. Furthermore, with regard to the phenomenon of voltage unbalance of multiple cascaded modules caused by differences in device parameters, a voltage equalization start logic and a control method are provided to effectively resolve the phenomenon of voltage unbalance between the cascaded modules, thereby reducing the impact of starting currents and improving the reliability of the system.

Description

A power unit and control method for rail transportation

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number 202311724699.1 and application date of December 14, 2023, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby incorporated into this disclosure by introduction. Technical Field

[0003] The present disclosure relates to a rail transit traction power supply system, and in particular to a power unit for rail transit and a control method thereof. Background Art

[0004] The rail transit industry demands fast, efficient, and reliable train operations. Therefore, the train's traction power supply system is crucial to the stability and reliability of the locomotive. Research has shown that the application of high-power power pack integration, high-efficiency traction components, and energy-saving control technologies can reduce the weight of traction equipment, save installation space, and lower overall vehicle traction energy consumption. Specifically, the power unit, based on novel devices and a new topology, utilizes high-frequency power electronics technology to replace the traditional onboard power frequency transformer, rectifier, traction auxiliary inverter, and DC / DC converter. Compared to traditional traction power supply systems, it offers the following advantages: 1. Small size, light weight, and no transformer oil pollution, making it environmentally friendly; 2. A modular, simplified, and highly redundant design improves system reliability and facilitates maintenance; 3. Adjustable grid-side power factor effectively reduces grid harmonic pollution; 4. A wide range of power interfaces, including high and low voltage AC and DC interfaces; 5. High power density and efficiency. In summary, the power unit based on new devices and new topology is in line with the development trend of small, lightweight, low-carbon and energy-saving electrical equipment in the rail transit field, and has broad prospects for promotion and application at home and abroad.

[0005] With the continuous advancement of technology and the continuous improvement of train operation reliability, the power unit is required to be miniaturized, lightweight, green and intelligent. It can also achieve high and low voltage electrical isolation and level conversion through modular design concepts, effectively reducing the difficulty of system insulation design, while improving system redundancy and maintainability; it can also effectively solve the voltage imbalance caused by differences in device parameters of multi-cascade modules, reduce starting current impact, and improve system reliability.

[0006] Summary of the Invention

[0007] This disclosure is different from the traditional traction power supply system architecture of rail transit, and proposes a modular power unit main circuit and its control method. It can replace traditional on-board transformers and converters, and realize the miniaturization, lightweight, green and intelligentization of equipment. Through the modular design concept, high and low voltage electrical isolation and level conversion are achieved, effectively reducing the difficulty of system insulation design, while improving system redundancy and maintainability; further, in response to the voltage imbalance phenomenon caused by the difference in device parameters of multi-cascade modules, a voltage-equalizing starting logic and control method are proposed to effectively solve the voltage imbalance phenomenon between cascade modules, reduce the starting current impact, and improve system reliability.

[0008] The power unit for rail transit described in the present disclosure is realized by adopting the following technical solution: the main circuit of the power unit includes a high-voltage switch module, a high-voltage module, a high-frequency transformer, a low-voltage module, and an intermediate DC module;

[0009] The high-voltage switch module is configured to connect the high-voltage power supply network and the high-voltage module, connect the single-phase high-voltage AC power to the high-voltage module, and realize the pre-charging process and the high-voltage module redundancy switching function through the internal mechanical switch and the bidirectional power switch device;

[0010] The high-voltage module is configured to complete AC / DC and DC / AC conversion of electric energy, converting low-frequency high-voltage sinusoidal alternating current into high-frequency high-voltage pulsed alternating current; the input ports of each high-voltage module are connected in series through a high-voltage switch module, while achieving the functions of isolating the faulty module and switching in the redundant module; the output ports of each high-voltage module are connected to the input port of the high-frequency transformer;

[0011] The high-frequency transformer is configured to achieve high-voltage and low-voltage electrical isolation and level conversion functions, converting high-frequency and high-voltage pulsed alternating current into high-frequency and low-voltage pulsed alternating current. The input port of the high-frequency transformer is connected to the output port of each high-voltage module, and the output port of the high-frequency transformer is connected to the input port of the low-voltage module;

[0012] The low-voltage module is configured to complete AC / DC conversion of electric energy, converting high-frequency low-voltage pulsed alternating current into low-voltage direct current; the low-voltage module input port is connected to the high-frequency transformer output port, and the output ports of each low-voltage module are connected in parallel to the input port of the intermediate DC module;

[0013] The intermediate DC module is configured to implement a ground detection function, an overvoltage protection function, and a slow discharge function, and its output port is connected to a load.

[0014] In an optional embodiment of the present disclosure, a high-voltage module includes two H-full bridges connected in series, one H-full bridge serving as an input end and one H-full bridge serving as an output end; a low-voltage module includes at least two H-full bridges connected in parallel, wherein one H-full bridge in the low-voltage module corresponds to one high-voltage module, and one H-full bridge in the low-voltage module is connected to the H-full bridge at the output end of the corresponding high-voltage module via a high-frequency transformer; the electrical circuit consisting of the H-full bridge at the output end of a high-voltage module, the high-frequency transformer, and the H-full bridge in a low-voltage module is collectively referred to as a resonant circuit;

[0015] Cascade H-bridge circuit: The input H-bridges of all high-voltage modules are electrically connected in series. This electrical circuit is collectively referred to as a cascade H-bridge circuit.

[0016] Subunit: A high-voltage module, a high-frequency transformer and an H-full bridge in the corresponding low-voltage module are called a subunit;

[0017] The output port of the high-voltage module is connected in series with a resonant capacitor Cr; each H-bridge output port of the low-voltage module is connected in parallel with a capacitor C l ;The high voltage switch module contains a pre-charge resistor.

[0018] The present disclosure discloses a voltage-equalizing startup logic and control method for a power unit for rail transit, comprising the following steps: (1) firstly charging the capacitor in the high-voltage module through a pre-charging resistor and an uncontrolled rectifier bridge;

[0019] (2) When the average value of the capacitor voltage in the high-voltage module is greater than the threshold value U th1 And after a delay of Δt1, the pre-charge resistor is cut off;

[0020] (3) When the average value of the capacitor voltage in the high-voltage module is greater than the threshold value U th2 After a delay of Δt2, the drive pulse generated by the voltage-balanced soft-start control method is used to control the action of the power switch device in the resonant circuit to pre-charge the capacitor in the low-voltage module. During the pre-charging process, the capacitor voltages in each high-voltage module will be clamped to the same voltage level, effectively solving the capacitor voltage imbalance problem in the high-voltage module.

[0021] (4) When the capacitor voltage in the low voltage module is greater than U th3 After a delay of Δt3, the capacitor pre-charging process in the low-voltage module is completed, and the resonant circuit enters the normal working stage;

[0022] (5) After the resonant circuit works normally and the delay Δt4, the cascade H-bridge circuit enters the controlled rectification state from the uncontrolled rectification state, and uses the dual closed-loop voltage-sharing control method and the carrier phase-shift modulation method to generate driving pulses to control the action of the power switching devices in the cascade H-bridge circuit, raising the capacitance of each high-voltage module to the desired threshold value U th4 ; At the same time, the output voltage is equal to the threshold Uth5 , the cascade H-bridge startup is completed; the entire power unit starts normally.

[0023] The modular power unit main circuit and control method proposed in the technical solution disclosed in the present invention are different from traditional traction power supply systems. They have the characteristics of small size, light weight, high power density, green and efficient, and high power factor. They meet the development trend of small, lightweight, low-carbon and energy-saving on-board electrical equipment in the rail transit field, and can also expand into new energy fields such as wind power, photovoltaics, and energy storage, and have broad prospects for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG1 is a schematic diagram of the main circuit structure of the power unit disclosed in the present invention.

[0025] Figure 2 Schematic diagram of the high-voltage switch module circuit topology.

[0026] Figure 3 Schematic diagram of high-voltage module circuit topology.

[0027] Figure 4 Schematic diagram of low-voltage module circuit topology.

[0028] Figure 5: Schematic diagram of the intermediate DC module circuit topology.

[0029] Figure 6: Voltage equalization startup logic diagram.

[0030] Figure 7 is a schematic diagram of a resonant circuit voltage-sharing soft-start control method.

[0031] Figure 8 is a schematic diagram of the cascaded H-bridge dual closed-loop voltage-sharing control method.

[0032] Figure 9 Carrier phase shift modulation method. DETAILED DESCRIPTION

[0033] The present disclosure will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] The main circuit of the power unit of the present disclosure is shown in FIG1 , and is mainly composed of a high-voltage switch module, a high-voltage module, a high-frequency transformer, a low-voltage module and an intermediate DC module.

[0035] The circuit topology of the high-voltage switch module is shown in Figure 2. It mainly consists of a current sensor (TA-ig), a network voltage transformer (TV-vg), an inductor (l s )、Mechanical switch (k0), pre-charge resistor (R pr ), bidirectional power switch devices k connected in sequence pr 、k1-k n , composed of. The voltage and current sensors are mainly responsible for collecting the grid-side input voltage and current. Pre-charge resistor R pr Connected to the bidirectional power switch device k prAt both ends of the circuit, the inductor cooperates with the high-voltage module to complete the power exchange and realize voltage pumping. On the other hand, it plays the role of filtering the harmonics on the AC side. The pre-charge resistor can reduce the current impact at the beginning of the pre-charge. pr The output terminal is connected to the first high voltage module M h1 The first input terminal of k1 is connected to the first high voltage module M h1 The second input terminal and the second high voltage module M h2 The first input terminal of k is connected to the n The output end of the last high voltage module M hn The output end of the high voltage switch module circuit is connected to the wheel rail (ie grounded); the bidirectional power switch device is driven by the drive signal (g pr 、g k1 -g kn ) to control the opening and closing, and is mainly responsible for circuit power supply, isolation of faulty modules and switching of redundant modules.

[0036] Under normal working conditions:

[0037] (1) Under normal working conditions, the high voltage module M h1 ~M h(n-1) Normal operation, driving signal g k1 ~g k(n-1) It is in the untriggered state and the power switch device is in the open circuit state. hn As a redundant unit, drive signal g kn Trigger conduction, the power switch device is in short circuit state, the spare module M hn bypass.

[0038] (2) During the pre-charging process, the mechanical switch k0 is closed. The electric energy flows from the high voltage power supply network through the pre-charging resistor R pr Input to each high-voltage module to pre-charge the capacitors in the high-voltage module.

[0039] (3) After the pre-charge is completed, the driving pulse g pr Trigger k pr It is turned on, bypassing the pre-charge resistor and completing the pre-charge process.

[0040] Under abnormal working conditions: If the high voltage module M h1 Fault occurs, drive pulse g k1 Triggering k1 conduction will bypass the faulty module. At the same time, drive pulse g kn Trigger k n Shut down and turn on the high voltage standby module M hn Put into use, replace the faulty module M h1 , ensure the normal operation of the system and improve the redundancy of the entire system.

[0041] The circuit topology of a single high-voltage module is shown in Figure 3. It mainly consists of two H-bridges composed of power switching devices, requiring a total of 8 drive pulses, namely g h1-11 、g h1-12、 g h1-21 、g h1-22 、g h1-31 、g h1-32 、g h1-41 and g h1-42 The middle is the support capacitor C h1 And voltage sensor TV-h1, a resonant capacitor C is connected in series with the output port r1 , the output port is connected to the corresponding high-frequency transformer input port.

[0042] The circuit topology of a single low-voltage module is shown in Figure 4. It mainly consists of two H-bridges composed of power switching devices, requiring a total of 8 drive pulses, namely g l1-11 、g l1-12 、g l1-21 、g l1-22 、g l2-11 、g l2-12 、g l2-21 、g l2-22 The two H-bridge output terminals are equipped with two output support capacitors C l1 and C l2 , connected in parallel. It's important to note that a single low-voltage module isn't limited to two H-bridges in parallel; it can also consist of n (n>2) H-bridges in parallel. The only electrical connection is to ensure that the output H-bridge in the high-voltage module corresponds to one H-bridge in the low-voltage module. The output and input ports of both are electrically connected via a high-frequency transformer, achieving high- and low-voltage isolation and level conversion.

[0043] The intermediate DC module circuit topology is shown in Figure 5, which mainly consists of a slow-discharge resistor R mf , voltage / current sensors TA-zo, TV-zo, TA-zb, 1 / 2 ground detection circuit, overvoltage suppression circuit. The current sensor TA-zo is connected to the positive pole of the intermediate DC module bus, and the slow-discharge resistor R mf The voltage sensor TV-zo is connected in parallel between the positive and negative poles of the busbar of the intermediate DC module. The 1 / 2 ground detection circuit includes two resistors R connected in series between the positive and negative poles of the busbar of the intermediate DC module. gnd1 and R gnd2 , also includes the resistor R gnd2 The capacitor and voltage sensor TV-gnd are connected in parallel, and one end of the voltage sensor TV-gnd is grounded; the overvoltage suppression circuit includes an H full bridge composed of four power devices and resistors R respectively connected to the two midpoints of the H full bridge. zb1 and Rzb2 , resistor R zb1 and R zb2 The other end is connected to the negative pole of the busbar of the intermediate DC module; the current sensor TA-zb is connected to the two midpoints of the H full bridge and the resistor R zb1 and R zb2 The slow-discharge resistor dissipates residual energy in the DC circuit during shutdown. The ground detection circuit provides a zero-level reference point and can be configured to detect ground faults in downstream loads. The overvoltage suppression circuit suppresses transient overvoltages and ensures stable intermediate DC voltage.

[0044] Taking three sub-units as an example, the power unit pressure equalization startup logic is shown in Figure 6:

[0045] 1. Mechanical switch k0 is closed. Electric energy flows from the grid side through the pre-charge resistor R pr Input to each high voltage module, the capacitor C in the high voltage module h1 、C h2 、C h3 Due to the parameter differences between the components in the high voltage module, the U dc1 、U dc2 、U dc3 Voltage imbalance.

[0046] 2.When U dc1 、U dc2 、U dc3 Voltage average value Greater than U th1 And after delay Δt1, g pr Triggering conduction, the pre-charge resistor is bypassed to complete the pre-charge process.

[0047] 3.When U dc1 、U dc2 、U dc3 Voltage average value Greater than U th2 And after a delay of Δt2, l1 、C l2 and C l3 Precharge, U zo The output voltage starts to be output. The driving pulse generated by the voltage-balanced soft start control method is used to control the action of the power devices in the resonant circuit. The control method is detailed in Figure 7. After the pre-charge is completed, U dc1 、U dc2 、U dc3 will be clamped to the same voltage level.

[0048] 4.When U zo Output voltage is greater than U th3After a delay of Δt3, the capacitor pre-charging process in the low-voltage module is completed, and the resonant circuit enters the normal working stage. The control method is detailed in FIG7 .

[0049] 5. After the resonant circuit starts normally and the delay Δt4 is reached, the cascade H-bridge circuit is started, using a dual closed-loop voltage-sharing control method and a carrier phase-shift modulation method. The control method is detailed in Figure 8.

[0050] 6.When U dc1 、U dc2 、U dc3 Voltage average value Equal to U th4 , and U zo The output voltage is equal to U th5 , the cascade H-bridge startup is completed, and the entire power unit startup is completed.

[0051] Resonant circuit voltage-balanced start-up control method

[0052] The resonant circuit voltage-sharing soft-start control method is shown in Figure 7:

[0053] (1) The carrier count value is generated by the triangular carrier generator, and the modulation wave count value is generated by the counter. The triangular carrier generator and the counter can be implemented by software programming or by building a hardware circuit.

[0054] (2) Calculate the triangular carrier period value (PRD value) based on the rated resonant frequency of the resonant circuit. The calculation formula is as follows:

[0055] Where C r is the resonant capacitance value in the high voltage module, L r is the equivalent leakage inductance of the high-frequency transformer, T clk is the time base frequency of the triangle carrier generator.

[0056] (3) According to the dead zone of the power device in the resonant circuit and the control logic requirements, the initial phase value of the modulation wave (PHS value) is set, and the PHS value is less than the PRD value.

[0057] (4) When the carrier count value is equal to PRD, an interrupt will be triggered. At each interruption moment, the modulation wave count value will accumulate n until the value is equal to 1 / 2PRD, and the modulation wave count value remains unchanged.

[0058] (5) When the modulation wave count value is equal to 1 / 2PRD, the capacitor pre-charging in the low-voltage module is completed. According to the circuit topology, during the pre-charging process, the capacitor voltages in the cascaded H-bridge will be clamped to the same voltage level.

[0059] (6) In each interrupt cycle, the carrier count value and the modulation wave count value are compared to produce a drive pulse 1. The drive pulse follows the following principles:

[0060] 1) Carrier wave count value ≥ modulation wave count value, the drive pulse output is low level;

[0061] 2) Carrier wave count value < modulation wave count value, the drive pulse output is high level;

[0062] (7) Driving pulse 2 is the complementary pulse of driving pulse 1. At the same time, dead time needs to be added to avoid direct conduction of the upper and lower tubes of the half bridge.

[0063] (8) Driving pulse 1 acts on g hn-31 、g hn-42 、g lx-11 、g lx-22 , driving pulse 2 acts on g hn-32 、g hn-41 、g lx-12 、g lx-21 ; The g hn-31 、g hn-32 、g hn-41 、g hn-42 The four power devices of the H full bridge at the output end of a high-voltage module, g lx-11 、g lx-12 、g lx-21 、g lx-22 These are four power devices of an H-full bridge of a low-voltage module connected to the aforementioned high-voltage module via a high-frequency transformer.

[0064] (9) When the duty cycle of driving pulses 1 and 2 increases to 50%, the capacitance C of the resonant circuit is ln When the pre-charging is completed, the duty cycle is kept unchanged and the resonant circuit is started.

[0065] (10) The purpose of the resonant circuit operating in a resonant state is to reduce the on- and off-current of the power device and improve the system efficiency.

[0066] Cascade H-bridge dual closed-loop voltage-sharing startup control method

[0067] The cascaded H-bridge dual closed-loop voltage-sharing control method is shown in Figure 8:

[0068] (1) The cascaded H-bridge control method includes outer-loop DC side voltage control and inner-loop AC current control. The control objectives are to achieve unity power factor operation on the grid side and stabilize the DC side voltage of the high-voltage module.

[0069] (2) The outer loop of the control system is the DC side voltage control loop. First, the DC side voltage U of n-1 high-voltage modules is collected. dc1 ~U dc(n-1) , and take the average value to get The DC voltage is given as a signal After being compared with the actual DC voltage average value, it is sent to the PI regulator. The output of the PI regulator is the DC current command signal i d ,i d The size of is proportional to the amplitude of the AC input current. In order to speed up the control response, a current feedforward link is added here. The proportional coefficient k of the feedforward link is calculated as follows:

[0070] Assume that the output DC voltage of the low voltage module is U o , the DC module input current is i o , according to the law of conservation of power:

[0071] U g i g =U o i o Formula (3)

[0072] Therefore, the ratio of input current to load current is: Therefore, the ratio of input current to load current is:

[0073] (3) Add the load current feedforward value to the voltage loop PI output as the AC current command value The amplitude of The phase is given by the phase-locked loop.

[0074] (4) The current inner loop adopts PR controller, and the command value The feedback value of the AC current i g The error value passes through the PR controller, and the PR controller output is equal to the grid side voltage signal U g The modulated signal is obtained by subtracting

[0075] (5) In order to reduce the high-order harmonic content in the grid-side current, carrier phase-shift modulation is adopted. The carrier phase-shift modulation method is shown in Figure 9.

[0076] Carrier phase shift modulation method

[0077] The carrier phase shift modulation method is shown in FIG9 .

[0078] (1) In order to achieve voltage equalization control, the entire cascade H bridge shares the same modulation wave

[0079] (2) In the carrier phase-shift modulation method, a cascaded H-bridge consisting of N high-voltage modules requires 2N triangular carriers. The frequency and amplitude of each triangular carrier are the same, but there is a fixed phase shift of 360° / 2N between any two adjacent carriers. The modulated signal is compared with each of the 2N carriers to generate the switching signal for the cascaded H-bridge.

[0080] The following is an example of a cascaded H-bridge consisting of two high-voltage modules.

[0081] (3) The cascaded H-bridge composed of two high-voltage modules requires four triangular carriers, namely: U cr1 、U cr2 、U cr3 、U cr4 .

[0082] (4) Triangular carrier U cr1 and U cr3 With the same modulation wave Compare and generate two gate switching signals g h1-11 and g h2-11 , which are used to drive the upper switch tubes of the two left bridge arms of the full bridge. When the driving signal g h1-11 When the power device is high, it turns on; otherwise, it turns off. When the driving signal g h2-11 If it is high level, the power device is turned on, otherwise it is turned off.

[0083] (5) Triangular carrier U cr2 and U cr4 With triangular carrier U cr1 and U cr3 There are Phase shift, same modulation wave Compare and generate two gate switching signals g h1-21 and g h2-21 , which are used to drive the upper switch tubes of the two right arms of the full bridge. When the driving signal g h1-21 When the power device is high, it turns on; otherwise, it turns off. When the driving signal g h2-21 If it is high level, the power device is turned on, otherwise it is turned off.

[0084] (6) For the same bridge arm, the upper and lower switch tubes are complementary and turned on, and the switching signal of the lower switch tube of each bridge arm is no longer given.

[0085] (7) Driving signal g h1-11 、g h1-21 Control high voltage module M h1 The medium power device is in action, and the high voltage module Mh1 The input terminal generates a voltage U H1 .

[0086] (8) Driving signal g h2-11 、g h2-21 Control high voltage module M h2 The medium power device is in action, and the high voltage module M h2 The input terminal generates a voltage U H2 .

[0087] (9) Finally, the cascade H-bridge composed of two high-voltage modules generates a voltage U at the grid-side input terminal. H1 +U H2 , forming a 5-level rectifier circuit, which can output phase voltages with 5 different levels, as shown in Figure 9.

Claims

1. A power unit for rail transit, wherein: The main circuit of the power unit includes a high-voltage switch module, a high-voltage module, a high-frequency transformer, a low-voltage module, and an intermediate DC module; The high-voltage switch module is configured to connect the high-voltage power supply network and the high-voltage module, connect the single-phase high-voltage alternating current to the high-voltage module, and realize the pre-charging process and the high-voltage module redundant switching function through the internal mechanical switch and the bidirectional power switch device; The high-voltage module is configured to complete the AC / DC and DC / AC conversion of electric energy, converting low-frequency high-voltage sinusoidal alternating current into high-frequency high-voltage pulsed alternating current; the input ports of each high-voltage module are connected in series through the high-voltage switch module, and the fault module isolation and redundant module switching functions are realized at the same time; the output ports of each high-voltage module are connected to the input port of the high-frequency transformer; The high-frequency transformer is configured to realize high-low voltage electrical isolation and level conversion functions, converting high-frequency high-voltage pulsed alternating current into high-frequency low-voltage pulsed alternating current, the high-frequency transformer input port is connected to each high-voltage module output port, and the high-frequency transformer output port is connected to the low-voltage module input port; The low-voltage module is configured to complete the AC / DC conversion of electric energy, converting high-frequency low-voltage pulsed alternating current into low-voltage direct current; the input port of the low-voltage module is connected to the output port of the high-frequency transformer, and the output ports of each low-voltage module are connected to the input port of the intermediate direct current module in parallel; The intermediate DC module is configured to realize a ground detection function, an overvoltage protection function, and a slow discharge function, and its output port is connected to a load.

2. A rail transit power unit as claimed in claim 1, wherein: A high-voltage module includes two H full bridges connected in series, one H full bridge is used as the input end, and the other H full bridge is used as the output end; a low-voltage module includes at least two H full bridges connected in parallel, wherein one H full bridge in the low-voltage module corresponds to one high-voltage module, and one H full bridge in the low-voltage module is connected to the output end H full bridge of the corresponding high-voltage module through a high-frequency transformer; the electrical circuit composed of the output end H full bridge in a high-voltage module, the high-frequency transformer and the H full bridge in a low-voltage module is collectively referred to as a resonant circuit; Cascade H-bridge circuit: All H-bridges at the input end of the high-voltage module are electrically connected in series. The electrical circuit is collectively called a cascade H-bridge circuit. Subunit: A high voltage module, a high frequency transformer and an H full bridge in the corresponding low voltage module are called a subunit; The output port of the high-voltage module is connected in series with a resonant capacitor Cr; each H-bridge output end of the low-voltage module is connected in parallel with a capacitor C l ; The high voltage switch module contains a pre-charge resistor.

3. A rail transit power unit as claimed in claim 2, wherein: The high voltage switch module circuit includes a current sensor TA-ig, a voltage transformer TV-vg, an inductor l s , mechanical switch k0, pre-charge resistor R pr , bidirectional power switch devices k connected in sequence pr , k1-k n , pre-charge resistor R pr Connected to the bidirectional power switch device k pr The voltage and current sensors are configured to collect the grid-side input voltage and current; the bidirectional power switch device is driven by the signal g pr , g k1 -g kn To control the opening and closing, configured for circuit power supply, isolation of faulty modules and switching of redundant modules; Normal working condition Down: (1) High voltage module M h1 ~M h(n-1) Normal operation, driving signal g k1 ~g k(n-1) The power switch device is in the disconnected state; the high voltage module M hn As a redundant unit, drive signal g kn The trigger is turned on, the power switch device is in a short-circuit state, and the standby module M hn bypass; (2) During the pre-charging process, the mechanical switch k0 is closed; The electric energy is transferred from the high voltage power supply network through the pre-charge resistor R pr Input to each high-voltage module to pre-charge the capacitor in the high-voltage module; (3) After the pre-charge is completed, the driving pulse g pr Trigger k pr It is turned on, bypassing the pre-charging resistor and completing the pre-charging process; Under abnormal working conditions: If the high voltage module M h1 Fault occurs, drive pulse g k1 Trigger k1 to conduct, bypassing the faulty module; at the same time, drive pulse g kn Trigger k n Shut down and connect the high voltage standby module M hn Put into use, replace the faulty module M h1 , ensure the normal operation of the system and improve the redundancy of the entire system.

4. A rail transit power unit as claimed in claim 2, wherein: A supporting capacitor C is also connected between the two H full bridges of the high voltage module. h and voltage sensor TV-h.

5. A rail transit power unit as claimed in claim 2, wherein: The intermediate DC module circuit includes a slow-release resistor R mf , voltage / current sensor TA-zo, TV-zo, TA-zb, 1 / 2 ground detection circuit, overvoltage suppression circuit; current sensor TA-zo is connected to the positive pole of the intermediate DC module bus, slow discharge resistor R mf The voltage sensor TV-zo is connected in parallel between the positive and negative poles of the busbar of the intermediate DC module. The 1 / 2 ground detection circuit includes two resistors R connected in series between the positive and negative poles of the busbar of the intermediate DC module. gnd1 and R gnd2 , also includes the resistor R gnd2 A capacitor and a voltage sensor TV-gnd are connected in parallel, and one end of the voltage sensor TV-gnd is grounded; the overvoltage suppression circuit includes an H full bridge composed of four power devices and resistors R respectively connected to the two midpoints of the H full bridge zb1 and R zb2 , resistor R zb1 and R zb2 The other end is connected to the negative pole of the busbar of the intermediate DC module; the current sensor TA-zb is connected to the two midpoints of the H full bridge and the resistor R zb1 and R zb2 between.

6. A pressure equalization start logic and control method for a power unit for rail transit, wherein: The method comprises the following steps: (1) firstly charging the capacitor in the high voltage module through a pre-charging resistor and an uncontrolled rectifier bridge; (2) When the average value of the capacitor voltage in the high-voltage module is greater than the threshold value U th1 And after a delay of Δt1, the pre-charge resistor is cut off; (3) When the average value of the capacitor voltage in the high-voltage module is greater than the threshold value U th2 After a delay of Δt2, the driving pulse generated by the voltage-balanced soft-start control method is used to control the action of the power switch device in the resonant circuit to pre-charge the capacitor in the low-voltage module. During the pre-charging process, the capacitor voltages in each high-voltage module will be clamped to the same voltage level, effectively solving the capacitor voltage imbalance problem in the high-voltage module. (4) When the capacitor voltage in the low voltage module is greater than U th3 After a delay of Δt3, the capacitor pre-charging process in the low-voltage module is completed, and the resonant circuit enters the normal working stage; (5) After the resonant circuit works normally and the delay Δt4, the cascaded H-bridge circuit enters the controlled rectification state from the uncontrolled rectification state, and uses the double closed-loop voltage-sharing control method and the carrier phase-shift modulation method to generate driving pulses to control the action of the power switching devices in the cascaded H-bridge circuit, raising the capacitance in each high-voltage module to the desired threshold value U th4 ; At the same time, the output voltage is equal to the threshold U th5 , the cascade H-bridge startup is completed; entire The power unit starts normally.

7. A voltage-equalizing start-up logic and control method for a power unit for rail transit as claimed in claim 6, wherein: The voltage-balanced soft-start control method comprises the following steps: (1) The carrier count value is generated by the triangular carrier generator, and the modulation wave count value is generated by the counter; (2) Calculate the triangular carrier period value, i.e., the PRD value, according to the rated resonant frequency of the resonant circuit. The calculation formula is as follows: In the formula, C r is the resonant capacitance value in the high voltage module, L r is the equivalent leakage inductance of the high-frequency transformer, T clk is the time base frequency of the triangle carrier generator; (3) According to the dead zone of the power device in the resonant circuit and the control logic requirements, the initial phase value of the modulation wave, i.e., the PHS value, is set, and the PHS value is less than the PRD value; (4) When the carrier count value is equal to PRD, an interrupt will be triggered. At each interruption moment, the modulation wave count value will be accumulated by n until the value is equal to 1 / 2PRD, and the modulation wave count value remains unchanged; (5) When the modulation wave count value is equal to 1 / 2PRD, the capacitor pre-charging in the low-voltage module is completed. According to the circuit topology, during the pre-charging process, the capacitor voltage in the cascaded H-bridge will be clamped to the same voltage level. (6) In each interrupt cycle, the carrier count value and the modulation wave count value are compared to generate a drive pulse 1. The drive pulse follows the following principles: 1) Carrier count value ≥ modulation wave count value, the drive pulse output is low level; 2) Carrier count value < modulation wave count value, the drive pulse outputs high level; (7) Driving pulse 2 is the complementary pulse of driving pulse 1, and dead time needs to be added to avoid direct conduction of the upper and lower tubes of the half bridge; (8) Drive pulse 1 acts on g hn-31 , g hn-42 , g lx-11 , g lx-22 , driving pulse 2 acts on g hn-32 , g hn-41 , g lx-12 , g lx-21 ; The g hn-31 , g hn-32 , g hn-41 , g hn-42 For a high pressure mold The output end of the block H full bridge has four power devices, g lx-11 , g lx-12 , g lx-21 , g lx-22 Four power devices of an H full bridge of a low voltage module connected to the aforementioned high voltage module via a high frequency transformer; (9) When the duty cycle of driving pulses 1 and 2 increases to 50%, the capacitance C of the low-voltage module in the resonant circuit ln The moment when pre-charging is completed; the duty cycle is kept unchanged and the resonant circuit is started.

8. A voltage-equalizing start-up logic and control method for a power unit for rail transit as claimed in claim 6, wherein: The dual closed-loop voltage-sharing control method in step (5) adopts the following method: (1) It includes outer loop DC side voltage control and inner loop AC current control, and the control goal is to achieve grid-side unity power factor operation and stabilize the DC side voltage of the high-voltage module; (2) The outer loop of the control system is the DC side voltage control loop. First, the DC side voltage U of n-1 high-voltage modules is collected. dc1 ~U dc(n-1) , and take the average value to get The DC voltage is given as a signal After being compared with the actual DC voltage average value, it is sent to the PI regulator. The output of the PI regulator is the DC current command signal i d ,i d The size of is proportional to the amplitude of the AC input current; in order to speed up the control response speed, a current feedforward link is added here, and the proportional coefficient k of the feedforward link is calculated as follows: Assume that the output DC voltage of the low voltage module is U o , the DC module input current is i o , according to the power conservation law: U g i g = U o i o Equation (2) Therefore, the ratio of input current to load current is: Therefore, the ratio of input current to load current is: (3) Add the load current feedforward value to the voltage loop PI output as the AC current command value The amplitude of The phase of is given by the phase-locked loop; (4) The current inner loop control adopts PR controller, and the command value The feedback value of the AC current i g The error value passes through the PR controller, and the PR controller output is equal to the grid-side voltage signal U g The modulated signal is obtained by subtracting (5) In order to reduce the high-order harmonic content in the grid-side current, carrier phase shift modulation is adopted.

9. A method for controlling a power unit for rail transit as claimed in claim 6 or 8, wherein: The carrier phase shift modulation method comprises the following steps: (1) To achieve voltage equalization control, the entire cascaded H-bridge shares the same modulation wave (2) In the carrier phase-shift modulation method, a cascaded H-bridge consisting of N high-voltage modules requires 2N triangular carriers. The frequency and amplitude of each triangular carrier are the same, but there is a fixed phase shift between any two adjacent carriers, and its value is 360° / 2N. The modulated signal is compared with the 2N carriers respectively, and finally the switching signal of the cascaded H-bridge is generated.

10. A method for controlling a power unit for rail transit as claimed in claim 6, wherein: The triangular carrier generator and counter in step (1) can be implemented by software programming or by building a hardware circuit.

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