Auxiliary converter, control method, controller and rail transit equipment

Abstract

The invention provides an auxiliary converter, a control method, a controller and rail transit equipment, and relates to the power electronic technology. The auxiliary converter comprises at least two groups of DC-DC conversion circuits which are connected in parallel; any group of DC-DC conversion circuit comprises a three-level buck conversion circuit and two LLC resonant converters; wherein the input end of the three-level step-down conversion circuit is connected to the direct-current power supply end of the traction power supply system, and the output end of the three-level step-down conversion circuit is connected with the input ends of the two LLC resonant converters; the input ends of the two LLC resonant converters are connected in parallel and then connected to the output end of the three-level buck conversion circuit, and the output ends are connected in series and then connected to the input end of the inverter. According to the auxiliary converter, the light weight of the rail transit equipment carrying the auxiliary converter can be realized.

Description

Technical Field

[0001] The present application relates to power electronics technology, and in particular to an auxiliary converter, a control method, a controller, and rail transit equipment. Background Art

[0002] In the electrification system of modern rail transit equipment, auxiliary converters, as the core power conversion device of the auxiliary power supply system, play a critical role in providing stable energy to various auxiliary equipment, including air conditioners, lighting equipment, cooling fans, and brake compressor fans on rail vehicles.

[0003] Currently, the typical circuit topologies for auxiliary converters used in mainline locomotives and EMUs can be categorized into two types: AC-DC-AC (AC-DC-AC) and DC-AC (DC-AC). The AC-DC-AC auxiliary converter draws power from the auxiliary winding of the traction transformer, converting it to DC through a rectifier and then to AC output through an auxiliary inverter. The DC-AC auxiliary converter draws power from the intermediate DC circuit of the traction transformer, converting it from DC to AC through an auxiliary inverter and then stepping it down through a power-frequency transformer for AC output.

[0004] However, the above two types of auxiliary converters affect the volume and weight of the rail transit equipment equipped with the auxiliary converters to varying degrees, which is not conducive to achieving lightweight rail transit equipment. Summary of the Invention

[0005] The present application provides an auxiliary converter, a control method, a controller, and rail transit equipment, for achieving lightweight rail transit equipment equipped with the auxiliary converter.

[0006] In a first aspect, the present application provides an auxiliary converter, the auxiliary converter comprising at least two groups of DC-DC conversion circuits connected in parallel; each group of DC-DC conversion circuits comprises a three-level buck conversion circuit and two LLC resonant converters;

[0007] The input end of the three-level buck conversion circuit is connected to the DC power supply end of the traction power supply system, and the output end is connected to the input ends of the two LLC resonant converters;

[0008] The input ends of the two LLC resonant converters are connected in parallel and then connected to the output end of the three-level buck conversion circuit, and the output ends are connected in series and then connected to the input end of the inverter.

[0009] In another possible implementation, the three-level buck conversion circuit includes a voltage divider network, a power switch module, and an output network;

[0010] The voltage divider network includes a first capacitor and a second capacitor, the first capacitor and the second capacitor are connected in series and then connected across the DC power supply terminal, and the midpoint potential between the first capacitor and the second capacitor is half of the input voltage;

[0011] The power switch module includes a first switching tube and a second switching tube connected in series, and a third switching tube and a fourth switching tube connected in series, wherein the collector of the first switching tube is connected to the connection point between the DC power supply terminal and the first capacitor, and the emitter of the second switching tube is connected to the connection point between the first capacitor and the second capacitor; the collector of the third switching tube is connected to the emitter of the second switching tube, and the emitter of the fourth switching tube is connected to the connection point between the DC voltage source and the second capacitor;

[0012] The power switch module also includes four diodes, which are anti-parallel connected to the emitter and collector of each switch tube;

[0013] The output network includes a first inductor and a third capacitor, wherein a first end of the first inductor is connected to a connection point between the first switching tube and the second switching tube, a second end of the first inductor is connected to an input end of the LLC resonant converter, a first end of the third capacitor is connected to a connection point between the first inductor and the LLC resonant converter, and a second end of the third capacitor is connected to a connection point between the fourth switching tube and the third switching tube.

[0014] In another possible implementation, the LLC resonant converter includes a single-phase full-bridge inverter circuit, an LLC resonant circuit, a high-frequency transformer, and a single-phase uncontrolled rectifier bridge;

[0015] The input end of the single-phase full-bridge inverter circuit is connected to the output end of the three-level buck converter circuit, and the output end of the single-phase full-bridge inverter circuit is connected to the input end of the LLC resonant circuit.

[0016] The output end of the LLC resonant circuit is connected to the input end of the high-frequency transformer, the output end of the high-frequency transformer is connected to the single-phase uncontrolled rectifier bridge, and the output end of the single-phase uncontrolled rectifier bridge is connected to the input end of the inverter.

[0017] In another possible implementation, the single-phase full-bridge inverter circuit includes: a fifth switching tube and a sixth switching tube connected in series, and a seventh switching tube and an eighth switching tube connected in series, wherein the collectors of the fifth switching tube and the eighth switching tube are connected to the positive output terminal of the three-level buck conversion circuit, and the emitters of the sixth switching tube and the seventh switching tube are connected to the negative output terminal of the three-level buck conversion circuit; a first input terminal of the LLC resonant circuit is connected to the connection point of the fifth switching tube and the sixth switching tube, and a second input terminal is connected to the connection point of the seventh switching tube and the eighth switching tube;

[0018] The single-phase full-bridge inverter circuit further includes four diodes, which are respectively connected in anti-parallel to the emitter and collector of each switching tube.

[0019] In another possible implementation, the LLC resonant circuit includes the leakage inductance, excitation inductance and resonant capacitor of the high-frequency transformer; the first end of the leakage inductance is connected to the connection point of the fifth switching tube and the sixth switching tube, the second end of the leakage inductance is connected to the first end of the excitation inductance, forming a resonant inductance branch, the second end of the excitation inductance is connected to the first end of the resonant capacitor, and the second end of the resonant capacitor is connected to the connection point of the seventh switching tube and the eighth switching tube.

[0020] In another possible implementation, the single-phase uncontrolled rectifier bridge includes a single-phase rectifier bridge circuit and a fourth capacitor; the input end of the single-phase rectifier bridge circuit is connected to the output end of the high-frequency transformer, the output end of the single-phase rectifier bridge circuit is connected to the input end of the fourth capacitor, and the output end of the fourth capacitor serves as the output end of the LLC resonant converter.

[0021] In a second aspect, the present application provides a control method, applied to the auxiliary converter as described in any one of the first aspects above; the method comprises:

[0022] For any group of DC-DC conversion circuits, feedback control is performed on a first output voltage of the DC-DC conversion circuit based on a desired output voltage of the DC-DC conversion circuit to compensate for the first output voltage of the DC-DC conversion circuit to obtain a second output voltage;

[0023] Determining a second given reference voltage of the three-level buck converter circuit using the current sharing control strategy based on the second output voltage and the first given reference voltage of the DC-DC converter circuit;

[0024] The output voltage of the three-level buck conversion circuit is controlled based on the second given reference voltage and the current output voltage of the three-level buck conversion circuit.

[0025] In a third aspect, the present application provides a control device, applied to the auxiliary converter as described in any one of the first aspects above; the device comprises:

[0026] a first control module configured to, for any group of DC-DC conversion circuits, perform feedback control on a first output voltage of the DC-DC conversion circuit based on a desired output voltage of the DC-DC conversion circuit, so as to compensate the first output voltage of the DC-DC conversion circuit to obtain a second output voltage;

[0027] a second control module, configured to determine a second given reference voltage of the three-level buck converter circuit by adopting the current sharing control strategy based on the second output voltage and the first given reference voltage of the DC-DC converter circuit;

[0028] A third control module is configured to control the output voltage of the three-level buck conversion circuit based on the second given reference voltage and the current output voltage of the three-level buck conversion circuit.

[0029] In a fourth aspect, the present application provides a controller, comprising: at least one processor and a memory;

[0030] The memory stores computer-executable instructions;

[0031] The at least one processor executes the computer-executable instructions stored in the memory, so that the at least one processor performs the method as described in any one of the second aspects above.

[0032] In a fifth aspect, the present application provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer-executable instructions, and when the computer-executable instructions are executed by a central processing unit, they are used to implement the method described in any one of the second aspects above.

[0033] In a sixth aspect, the present application provides a computer program product, comprising a computer program, which, when executed by a central processing unit, implements the method as described in any one of the second aspects.

[0034] In a seventh aspect, the present application provides a rail transit equipment, which includes the auxiliary converter as described in any one of the first aspects above, and the controller as described in the fourth aspect above.

[0035] The present application provides an auxiliary converter, control method, controller, and rail transit equipment. The auxiliary converter provided herein includes at least two sets of parallel-connected DC-DC conversion circuits, and each set of DC-DC conversion circuits includes a three-level step-down converter circuit and an LLC resonant converter with two parallel input terminals and series output terminals. The three-level step-down converter circuit draws power from the intermediate DC circuit of the tractor, converts it into a suitable DC voltage, and then inputs it into the LLC resonant converter. An inverter used in conjunction with the auxiliary converter then converts it into the required AC power for use by electrical equipment in the rail transit vehicle. In this auxiliary converter, because the LLC resonant converter uses a high-frequency transformer and eliminates the need for an industrial frequency transformer during the entire conversion process, the volume and weight of the rail transit equipment equipped with the auxiliary converter are effectively reduced, thereby facilitating lightweight rail transit equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0037] Figure 1 A schematic diagram of an application scenario of an auxiliary converter provided in an embodiment of the present application;

[0038] Figure 2 A circuit block diagram of an auxiliary converter provided in an embodiment of the present application;

[0039] Figure 3 A circuit block diagram of a DC-DC conversion circuit provided in an embodiment of the present application;

[0040] Figure 4 A circuit schematic diagram of a DC-DC conversion circuit provided in an embodiment of the present application;

[0041] Figure 5 A flow chart of a control method provided in an embodiment of the present application;

[0042] Figure 6A A control principle diagram of a control method provided in an embodiment of the present application;

[0043] Figure 6B A control block diagram of a feedforward control provided in an embodiment of the present application;

[0044] Figure 7 A schematic structural diagram of a control device provided in an embodiment of the present application;

[0045] Figure 8 A schematic diagram of the structure of a controller provided in an embodiment of the present application.

[0046] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0047] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0048] In the electrification system of modern rail transit equipment, auxiliary converters, as the core hub of the auxiliary power supply system, perform crucial functions in power conversion and distribution. Their core mission is to meet the power demands of a wide range of auxiliary equipment within rail transit vehicles, such as air conditioning systems, lighting, cooling fans, and compressor fans. Through precise regulation and efficient conversion, auxiliary converters ensure stable output and adherence to standard power parameters, building a reliable power support system for rail transit vehicles' auxiliary power supply systems. This ensures the continuous and stable operation of various auxiliary equipment during rail transit operation, playing an indispensable role in improving the safety, comfort, and operational efficiency of rail transit systems.

[0049] Currently, the typical circuit topologies of auxiliary converters used in mainline rail transit equipment such as locomotives and EMUs are mainly divided into two types: AC-DC-AC and DC-AC. The AC-DC-AC auxiliary converter typically draws power from the auxiliary winding of the traction transformer, first converting the AC power to DC through a rectifier, and then converting the DC to AC output through an auxiliary inverter. This topology is suitable for scenarios requiring flexible adjustment of output voltage and frequency, but the multi-stage conversion leads to high efficiency losses and increased circuit complexity. The DC-AC auxiliary converter draws power from the intermediate DC circuit of the traction converter, first converting DC to AC through an auxiliary inverter, and then stepping down the AC output through a power frequency transformer. This structure is relatively simple because it eliminates the rectification stage, but the power frequency transformer is large and heavy, which is not conducive to lightweight design and integration of equipment.

[0050] As can be seen from the above, the AC-DC-AC auxiliary converter in the known technology needs to use the auxiliary winding of the traction transformer to draw power, and may require a larger capacity winding to meet the power supply needs of the auxiliary converter, thereby increasing the size and weight of the traction transformer. The DC-AC auxiliary converter requires the use of a large and heavy power frequency transformer for isolation, which is also not conducive to achieving the miniaturization and lightweighting of the auxiliary converter. Both types of auxiliary converters affect the size and weight of the rail transit equipment equipped with the auxiliary converter to varying degrees, and are therefore not conducive to achieving the lightweighting of rail transit equipment.

[0051] Therefore, embodiments of the present application provide an auxiliary converter, control method, controller, and rail transit equipment to address the aforementioned issues. Specifically, the auxiliary converter of the present application includes at least two parallel-connected DC-DC converter circuits, with each DC-DC converter group comprising a three-level step-down converter circuit and an LLC resonant converter with two parallel-connected input terminals and a series-connected output terminal. It should be understood that the LLC resonant converter utilizes a high-frequency transformer.

[0052] It should be noted that the auxiliary converter of the present application can be applied to any rail transportation equipment of a rail transportation vehicle. As an example, Figure 1 This is a schematic diagram of an application scenario of an auxiliary converter provided in an embodiment of the present application. Figure 1 As shown, the auxiliary converter of the present application can be used in a train's traction locomotive. Specifically, during train operation, the pantograph on the train's roof contacts the catenary, drawing high-voltage AC power from the catenary into the train's interior. After a series of conversions and processing, it is transmitted to the traction converter. A three-level step-down converter circuit draws power from the traction converter's intermediate DC circuit and converts the high-voltage DC power into a suitable DC voltage. Subsequently, an LLC resonant converter, with two input terminals connected in parallel and the output terminal connected in series, further converts the DC voltage output by the three-level step-down converter circuit.

[0053] In traction locomotives, the power output from the auxiliary converters powers a variety of auxiliary equipment, including air conditioners, lighting, cooling fans, and brake compressor fans. Multiple parallel DC-DC converter circuits work together to provide power tailored to the needs of various auxiliary devices. If a DC-DC converter circuit fails, the remaining circuits can take on more of the load, maintaining the operation of the auxiliary power supply system.

[0054] The following specific embodiments describe in detail the technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0055] The embodiment of the present application provides an auxiliary converter, Figure 2 A circuit block diagram of an auxiliary converter provided in an embodiment of the present application is shown in FIG. Figure 2 As shown, the auxiliary converter of this embodiment includes at least two groups of DC-DC conversion circuits connected in parallel. Each group of DC-DC conversion circuits includes a three-level buck conversion circuit and two LLC resonant converters.

[0056] like Figure 2 As shown, in this embodiment, the input of the three-level buck converter circuit is connected to the DC power supply of the traction power supply system, and the output is connected to the inputs of two LLC resonant converters. The inputs of the two LLC resonant converters are connected in parallel and then connected to the output of the three-level buck converter circuit. The outputs are then connected in series and then connected to the input of the inverter.

[0057] In this embodiment, the three-level step-down converter circuit is connected to the DC bus output from the traction substation via relevant input interfaces and circuit components, such as filter capacitors and input reactors, and receives DC power from the traction substation via this DC bus. It should be understood that this DC bus provides a stable DC voltage for the intermediate DC link of the entire traction power supply system. The voltage level generally varies depending on the rail transit system, with common voltages such as DC1500V or DC750V being common.

[0058] In this embodiment, the input terminals (Vin1, Vin2) of the two LLC resonant converters are respectively connected in parallel to the output terminals (Vdc+, Vdc-) of the three-level buck converter circuit, and the output terminals (Vo1+, Vo1-) of each LLC resonant converter are connected in series to form a superimposed output voltage (e.g., DC700V).

[0059] In this embodiment, the number of DC-DC converter circuits included in the auxiliary converter is not limited, as long as each group of DC-DC converter circuits is connected in parallel. In actual applications, the number of DC-DC converter circuits can be appropriately increased or decreased based on specific power requirements and power supply redundancy requirements.

[0060] The auxiliary converter provided in this embodiment includes at least two parallel-connected DC-DC conversion circuits. Each DC-DC conversion circuit employs a two-stage "three-level buck + LLC resonant" topology. The first-stage three-level buck conversion circuit draws DC power from the DC power supply of the traction power supply system, converts it to a suitable DC voltage, and then feeds it into the LLC resonant converter. The inverter used in conjunction with the auxiliary converter further converts the DC power into the required AC power for use by the electrical equipment in the rail transit vehicle.

[0061] The auxiliary converter provided in this embodiment only uses the high-frequency transformer in the LLC resonant converter during the entire process. No industrial frequency transformer is required during the entire conversion process, thereby effectively reducing the volume and weight of the auxiliary converter. At the same time, the volume and weight of the rail transit equipment equipped with the auxiliary converter are reduced, which is conducive to achieving lightweight rail transit equipment.

[0062] In addition, in the above-mentioned auxiliary converter, multiple groups of DC-DC conversion circuits are connected in parallel, making the circuit layout more flexible. During application, the positions of various circuit modules can be reasonably arranged according to actual space requirements, the design of the circuit board can be optimized, and unnecessary space occupation can be reduced, thereby reducing the weight of the entire auxiliary converter to a certain extent. This parallel structure also facilitates the use of modular design. Each module can be independently designed and manufactured, which is conducive to the selection of lighter materials and the optimization of manufacturing processes, further achieving the goal of lightweighting. At the same time, this parallel connection method can further improve the power and power supply redundancy of the auxiliary converter. When a single group of DC-DC conversion circuits fails, the remaining circuits can still ensure the continued stable operation of the system.

[0063] As a further illustration, Figure 3 This is a circuit block diagram of a DC-DC conversion circuit provided in an embodiment of the present application. Figure 3 As shown, the three-level step-down converter circuit in this embodiment includes a voltage divider network, a power switch module, and an output network. The LLC resonant converter includes a single-phase full-bridge inverter circuit, an LLC resonant circuit, a high-frequency transformer, and a single-phase uncontrolled rectifier bridge. To further understand its operating mechanism, the following details the design and function of each module in the DC-DC converter circuit.

[0064] Among them, the input end of the voltage divider network is connected to the DC power supply end of the traction power supply system, the output end is connected to the input end of the power switch module, the output end of the power switch module is connected to the input end of the output network, and the output end of the output network serves as the output end of the three-level step-down conversion circuit.

[0065] Specifically, Figure 4 This is a circuit diagram of a DC-DC converter circuit provided in an embodiment of the present application. Figure 4 As shown, in this embodiment, the voltage divider network includes a first capacitor and a second capacitor, which are connected in series and then connected across the DC power supply terminal. The midpoint potential between the first capacitor and the second capacitor is half of the input voltage.

[0066] It should be understood that the above-mentioned voltage divider network can divide the input voltage into smaller voltage segments, so that the midpoint potential is half of the input voltage, so that each switching device in the power switching module only needs to withstand part of the input voltage instead of the entire input voltage, thereby reducing the voltage stress of the switching device.

[0067] like Figure 4 As shown, in this embodiment, the power switch module includes a first switching transistor and a second switching transistor connected in series, as well as a third switching transistor and a fourth switching transistor connected in series. The collector of the first switching transistor is connected to the connection point between the DC power supply terminal and the first capacitor, and the emitter of the second switching transistor is connected to the connection point between the first capacitor and the second capacitor; the collector of the third switching transistor is connected to the emitter of the second switching transistor, and the emitter of the fourth switching transistor is connected to the connection point between the DC voltage source and the second capacitor. In addition, the power switch module also includes four diodes, respectively connected in anti-parallel to the emitter and collector of each switching transistor.

[0068] In this embodiment, the power switch module adopts a full-bridge structure, achieving a three-level output through the combined control of four switching tubes. Specifically, the first and second switching tubes, and the third and fourth switching tubes are connected in series to form two bridge arms. By controlling the conduction and shutdown of the switching tubes, different voltage levels can be obtained at the output end, thereby achieving a three-level output. This structure not only reduces the voltage stress on each switching tube, but also improves the efficiency and reliability of the circuit. In addition, when the switching tube is turned off, the anti-parallel diode can provide a freewheeling channel for the inductor current, preventing overvoltage from damaging the switching tube and playing a protective role in the circuit.

[0069] like Figure 4 As shown, in this embodiment, the output network includes a first inductor and a third capacitor, the first end of the first inductor is connected to the connection point of the first switching tube and the second switching tube, the second end of the first inductor is connected to the input end of the LLC resonant converter, the first end of the third capacitor is connected to the connection point of the first inductor and the LLC resonant converter, and the second end of the third capacitor is connected to the connection point of the fourth switching tube and the third switching tube.

[0070] It should be understood that the first inductor and third capacitor in the output network of this embodiment together form an LC filter, which is used to smooth the output voltage, reduce voltage ripple, and ensure output voltage stability. This filter design can effectively reduce output voltage ripple, improve the output quality of the power supply, and provide a stable input voltage for the subsequent LLC resonant converter.

[0071] The above configuration enables the three-level step-down converter circuit to operate over a wide input voltage range (e.g., DC1000V-3000V) and regulate it to a constant DC bus voltage. Furthermore, the reduced voltage stress allows the use of switching transistors with lower withstand voltages, further reducing size and improving efficiency. Furthermore, the reduced switching losses and thermal stress extend the device's lifespan.

[0072] After being processed by the three-level buck converter circuit, the output constant DC bus voltage becomes the input of the LLC resonant converter. Figure 3 As shown, in this embodiment, the input end of the single-phase full-bridge inverter circuit of the LLC resonant converter is connected to the output end of the three-level buck conversion circuit, and the output end of the single-phase full-bridge inverter circuit is connected to the input end of the LLC resonant circuit; the output end of the LLC resonant circuit is connected to the input end of the high-frequency transformer, the output end of the high-frequency transformer is connected to the single-phase uncontrolled rectifier bridge, and the output end of the single-phase uncontrolled rectifier bridge is connected to the input end of the inverter.

[0073] In this embodiment, the LLC resonant converter utilizes a single-phase full-bridge inverter circuit, coupled with an LLC resonant circuit, a high-frequency transformer, and a single-phase uncontrolled rectifier bridge, to achieve efficient energy conversion and voltage conversion. Specifically, the single-phase full-bridge inverter circuit is used to convert DC voltage into AC voltage for supply to the LLC resonant circuit. The LLC resonant circuit is designed to operate at the resonant frequency through precise design of resonant elements (including resonant inductors and resonant capacitors), minimizing switching losses and improving conversion efficiency. The high-frequency transformer is used for voltage conversion and isolation, ensuring the stability and safety of the output voltage. The single-phase uncontrolled rectifier bridge rectifies the AC voltage output by the LLC resonant circuit into DC voltage through the rectification action of four diodes. The output voltage is further smoothed by a subsequent filter circuit, providing a stable DC output, reducing voltage ripple, and ensuring high output voltage stability.

[0074] Through the above configuration, the modules in the LLC resonant converter form a parallel input and series output structure. Combined with its fixed resonant frequency operation, it can output a stable 700V DC voltage for the constant DC bus voltage output by the three-level step-down converter circuit. This allows the DC-DC converter circuit to adapt to diverse input voltage ranges while also providing efficient and stable output voltage, making it suitable for a wide range of power electronics applications. The overall system design fully considers efficiency, reliability, and volume optimization, resulting in significant advantages in practical applications.

[0075] In addition, the LLC resonant converter in this embodiment specifically adopts a single-phase full-bridge inverter circuit, which has higher output power capability, better soft switching characteristics, lower current stress, and more flexible design parameters compared to a single-phase half-bridge inverter circuit.

[0076] In practical applications, when the output power requirement is not high and the cost is relatively sensitive, the LLC resonant converter may also adopt a single-phase half-bridge inverter circuit provided that the requirement is met. This is not limited in this embodiment.

[0077] Specifically, such as Figure 4As shown, in this embodiment, the single-phase full-bridge inverter circuit includes: a fifth switch tube and a sixth switch tube connected in series, and a seventh switch tube and an eighth switch tube connected in series, and the collectors of the fifth switch tube and the eighth switch tube are connected to the output end of the three-level buck conversion circuit with a positive polarity, and the emitters of the sixth switch tube and the seventh switch tube are connected to the output end of the three-level buck conversion circuit with a negative polarity; the first input end of the LLC resonant circuit is connected to the connection point of the fifth switch tube and the sixth switch tube, and the second input end is connected to the connection point of the seventh switch tube and the eighth switch tube; the single-phase full-bridge inverter circuit also includes four diodes, which are respectively anti-parallel connected to the emitter and collector of each switch tube.

[0078] It should be understood that the single-phase full-bridge inverter circuit consists of two sets of switching transistors connected in series, forming a full-bridge structure. By controlling the conduction and shutdown of the fifth, sixth, seventh, and eighth switching transistors, the single-phase full-bridge inverter circuit converts the DC voltage output by the three-level buck converter circuit into AC voltage, which is then supplied to the LLC resonant circuit. Furthermore, the anti-parallel diode provides a freewheeling path, ensuring that current continues to flow when the switch is turned off, thereby reducing voltage spikes and switching losses.

[0079] like Figure 4 As shown, in this embodiment, the LLC resonant circuit includes the leakage inductance, excitation inductance and resonant capacitor of the high-frequency transformer; the first end of the leakage inductance is connected to the connection point of the fifth switching tube and the sixth switching tube, the second end of the leakage inductance is connected to the first end of the excitation inductance, forming a resonant inductance branch, the second end of the excitation inductance is connected to the first end of the resonant capacitor, and the second end of the resonant capacitor is connected to the connection point of the seventh switching tube and the eighth switching tube.

[0080] In this embodiment, the LLC resonant circuit utilizes the principle of resonance, achieving efficient energy transfer through the matching of a resonant inductor and a resonant capacitor, and performs voltage conversion via a high-frequency transformer. The combination of the high-frequency transformer's leakage inductance, magnetizing inductance, and resonant capacitor enables the LLC resonant circuit to operate at the resonant frequency, reducing switching losses and improving conversion efficiency.

[0081] Specifically, in this embodiment, when preparing the auxiliary converter, the operating frequency of the LLC resonant converter is controlled to be slightly lower than the resonant frequency. By utilizing the resonant characteristics of the high-frequency transformer's primary magnetizing inductance and the resonant capacitor, the parasitic capacitance of the switch is fully discharged to zero by the resonant current before the switch turns on, achieving zero voltage switching (ZVS). Furthermore, by properly adjusting the dead time of the switch, the resonant current passes through zero during the switch's turn-off process, thereby achieving zero current switching (ZCS) of the rectifier diode, significantly reducing switching losses.

[0082] like Figure 4 As shown, in this embodiment, the single-phase uncontrolled rectifier bridge includes a single-phase rectifier bridge circuit and a fourth capacitor; the input end of the single-phase rectifier bridge circuit is connected to the output end of the high-frequency transformer, the output end of the single-phase rectifier bridge circuit is connected to the input end of the fourth capacitor, and the output end of the fourth capacitor serves as the output end of the LLC resonant converter.

[0083] In this embodiment, a single-phase uncontrolled rectifier bridge rectifies the AC voltage output by the LLC resonant circuit into a DC voltage, which is then filtered by a fourth capacitor to provide a stable DC output. The design of the rectifier bridge ensures output voltage stability and low ripple characteristics. Furthermore, the high-frequency transformer operates at a high frequency, and the AC voltage output to the single-phase uncontrolled rectifier bridge has a relatively high frequency. Because the rectifier bridge is composed of diodes, the diodes achieve rectification under high-frequency AC voltage input based on their unidirectional conductivity, eliminating the use of controllable switching devices and thus eliminating switching losses associated with these devices. Furthermore, the high-frequency characteristics of the high-frequency transformer enable a smaller size while maintaining the same power transmission requirements. Combined with the rectifier bridge design, heating of the diodes during the rectification process is reduced, eliminating the need for a large heat sink and effectively reducing the overall circuit size. Furthermore, the improved output voltage stability of the rectifier bridge reduces the requirements for filter capacitors. Therefore, smaller capacitors (such as ceramic or film capacitors) can be used to achieve the same filtering effect, thereby reducing cost and size.

[0084] It should be noted that the switch tube used in this embodiment is specifically an IGBT. In actual applications, the switch tube can also be a MOS tube, which is not limited in this embodiment. It should be understood that different types of switch tubes have their own advantages in actual applications. In application scenarios such as rail transit that have high power and reliability requirements, selecting a suitable switch tube is crucial to the performance of the entire auxiliary converter. For example, in some situations where efficiency and switching speed are required to be high, MOS tubes may have more advantages; in high-power, high-voltage applications, IGBTs exhibit good voltage resistance and high current handling capabilities.

[0085] From the above content, it can be seen that the auxiliary converter provided in this application, by using a three-level step-down conversion circuit, not only reduces the voltage stress of the switching device, but also increases the equivalent switching frequency of the circuit, so that the inductance value of the chopper inductor is reduced, thereby greatly reducing the volume and weight of the inductor; at the same time, a full-bridge LLC resonant converter is used to achieve a high switching frequency of the switching device, so that the transformer can be high-frequency, and its volume and weight are small, thereby realizing the miniaturization and lightweight of rail transit equipment equipped with the auxiliary converter.

[0086] In addition, the auxiliary converter of the present application can be extended to be applied to the output parallel power supply of multiple groups of DC-DC conversion circuits, thereby further improving the power and power supply redundancy of the auxiliary converter.

[0087] The present application also provides a control method, which is applied to the auxiliary converter in the aforementioned embodiment and is specifically executed by any controller. Figure 5 A flow chart of a control method provided in an embodiment of the present application is shown as follows: Figure 5 As shown, the method of this embodiment includes:

[0088] S501, for any group of DC-DC conversion circuits, based on the desired output voltage of the DC-DC conversion circuit, feedback control is performed on the first output voltage of the DC-DC conversion circuit to compensate the first output voltage of the DC-DC conversion circuit to obtain a second output voltage.

[0089] In this embodiment, feedback control of the first output voltage is performed based on the desired output voltage of the DC-DC converter circuit, specifically by constructing a closed-loop feedback control system. The controller collects the first output voltage of the DC-DC converter circuit in real time, compares it with the desired output voltage, and inputs the difference between the two into the proportional (Kp) regulator. The Kp regulator is based on the formula The corresponding compensation amount is calculated and added to the original control signal, thereby achieving dynamic adjustment of the first output voltage to obtain a more stable second output voltage, effectively suppressing the deviation of the output voltage caused by load changes or input voltage fluctuations. is the output control quantity, is the proportionality coefficient, is the difference between the expected output voltage and the first output voltage. It can be understood that, The value of will affect the system response characteristics. A larger value may cause output overshoot or oscillation, while a smaller value may slow down the regulation speed.

[0090] In practical applications, the controller may also input the difference between the two into a proportional-integral (PI) regulator, so that the PI regulator calculates a corresponding compensation amount according to the difference, which is not limited in this embodiment.

[0091] S502 : Based on the second output voltage and the first given reference voltage of the DC-DC converter circuit, determine a second given reference voltage of the three-level buck converter circuit by adopting a current sharing control strategy.

[0092] It should be understood that the current sharing control strategy specifically performs current sharing control on the output currents of at least two groups of DC-DC conversion circuits. Since there is no communication between the at least two groups of DC-DC conversion circuits, the current sharing control strategy should be any control strategy applicable to the current sharing control scenario without interconnection lines, such as the master-slave current sharing method, the average current sharing method, the droop control method, etc.

[0093] As an example, if the master-slave current balancing method is adopted, a group of DC-DC converter circuits is set as the master module, its output current is used as the reference current, and the remaining modules are used as slave modules. The slave module detects the difference between its own output current and the master module's reference current, and corrects the first given reference voltage after PI adjustment to obtain the second given reference voltage, so that the output current of each slave module tends to be consistent with that of the master module. If the average current balancing method is adopted, the controller summarizes the output current of all DC-DC converter circuits, calculates the average current value, and processes the difference between the actual output current of each module and the average current through the control algorithm. The first given reference voltage is adjusted to obtain the second given reference voltage, thereby achieving current balancing control between the modules and ensuring stable operation of the auxiliary converter.

[0094] S503 : Control the output voltage of the three-level buck converter circuit based on the second given reference voltage and the current output voltage of the three-level buck converter circuit.

[0095] Specifically, the controller determines a first PWM drive signal for the first switch tube and the fourth switch tube based on a second given reference voltage and the current output voltage of the three-level buck conversion circuit to determine a second PWM drive signal for the second switch tube and the third switch tube; controls the first switch tube and the fourth switch tube according to the first PWM drive signal, and controls the second switch tube and the third switch tube according to the second PWM drive signal to control the output voltage of the three-level buck conversion circuit.

[0096] In this embodiment, the controller utilizes the principle of voltage closed-loop control to determine the first PWM drive signals for the first and fourth switching transistors. Specifically, the controller compares a second given reference voltage with the current output voltage of the three-level buck converter circuit. The resulting error signal is processed by a voltage regulator (such as a PI regulator) to generate a voltage control signal. This voltage control signal is combined with a carrier signal and pulse-width modulation technology to generate the first PWM drive signal, which controls the on and off time of the first and fourth switching transistors.

[0097] At the same time, based on the operating characteristics of the three-level topology, to ensure the normal operation of the circuit and achieve three-level output, the second PWM drive signals of the second and third switch tubes have a specific logical relationship with the first PWM drive signal, that is, they are generated through complementary or phase-shifting methods to ensure that the upper and lower switches in the same bridge arm are not turned on at the same time, avoiding the risk of short circuit, thereby accurately controlling the output voltage of the three-level buck converter circuit so that it stably tracks the second given reference voltage.

[0098] In the control method provided in this embodiment, for any group of DC-DC conversion circuits in the aforementioned auxiliary converter, the controller first performs feedback control on the first output voltage of the DC-DC conversion circuit based on the desired output voltage of the DC-DC conversion circuit to obtain a second output voltage; secondly, based on the second output voltage and the first given reference voltage of the DC-DC conversion circuit, a current sharing control strategy is adopted to determine the second given reference voltage of the three-level buck conversion circuit; finally, based on the second given reference voltage and the current output voltage of the three-level buck conversion circuit, the output voltage of the three-level buck conversion circuit is controlled.

[0099] Through the control method of this embodiment, the auxiliary converter achieves precise voltage regulation and current sharing control, ensuring coordinated operation among multiple DC-DC conversion circuit modules. Through closed-loop feedback and precise control of PWM signals, the system provides stable output voltage across a wide input voltage range, improving efficiency and reliability. Furthermore, the flexible control strategy adapts to diverse application requirements, enhancing the system's adaptability and safety.

[0100] As a further illustration, Figure 6A A control principle diagram of a control method provided in an embodiment of the present application is shown in FIG. Figure 6A As shown, the specific current sharing control strategy of this embodiment is a droop control strategy. When determining the second output voltage, a Kp regulator is specifically used.

[0101] It should be understood that according to the equivalent circuit of the DC-DC conversion circuits connected in parallel, the following formula can be obtained: , where m is used to represent the number of DC-DC converter circuits in the auxiliary converter, and Km is used to represent the droop coefficient (usually in V / A), which is used to adjust the rate of change of the output voltage with the current. Used to represent the line impedance of the mth group of DC-DC conversion circuits (in Ω), Used to represent the output current of the mth group of DC-DC conversion circuits, Used to represent the second output voltage of the mth group of DC-DC conversion circuits. Used to represent the second given reference voltage of the mth group of DC-DC conversion circuits.

[0102] From the above formula, we can know that to achieve power sharing, it is necessary to meet the requirements of any group of DC-DC conversion circuits. In addition, it should be understood that increasing the droop coefficient will increase the current sharing accuracy, but will cause the output voltage of the DC-DC converter circuit to decrease. It represents the second output voltage of the mth group of DC-DC conversion circuits, and its specific expression is: ,in, Used to indicate the first given reference voltage of the DC-DC conversion circuit.

[0103] On this basis, after droop control, the second given reference voltage of the three-level buck converter circuit is obtained by the following formula: .in, Used to indicate the second given reference voltage, It is obtained based on the droop control strategy.

[0104] As a further design, Figure 6A As shown, in this embodiment, when the second given reference voltage of the three-level buck converter circuit is obtained, a feedforward control strategy is further adopted based on the second given reference voltage to determine the target given reference voltage after feedforward compensation; based on the target given reference voltage and the current output voltage, the output voltage of the three-level buck converter circuit is controlled.

[0105] In this embodiment, Figure 6B A control block diagram of a feedforward control provided in an embodiment of the present application is shown as follows: Figure 6B As shown, G vd (s) is the transfer function from duty cycle to output voltage of the three-level buck converter circuit, G PI (s) is the transfer function of the PI controller, K f is the feedforward coefficient. Based on the control block diagram, the transfer function of the process is: .in, , U c3 Used to indicate the output voltage of the three-level step-down converter circuit, U c1 Used to represent the output voltage of the first capacitor, U c2 Used to represent the output voltage of the second capacitor.

[0106] In this embodiment, feedforward control is introduced to incorporate disturbance factors such as input voltage and load current into the pre-compensation mechanism. By detecting changes in the traction power supply system's input voltage and load current, a feedforward compensation term is generated and superimposed on a second given reference voltage, forming a dual-closed-loop collaborative architecture with voltage feedback control. This design enables the auxiliary converter to proactively respond to input fluctuations and sudden load changes, effectively mitigating output voltage fluctuations caused by input voltage changes. It also reduces the system's sensitivity to PI parameters and simplifies the commissioning process.

[0107] As a preferred example, Figure 6A As shown, in this embodiment, the controller also uses a voltage balancing control strategy to control the output voltage of the three-level buck converter circuit. Specifically, the controller calculates the deviation between the current voltage of the first capacitor and the current voltage of the second capacitor. Based on this deviation and a given deviation reference value, the controller uses a proportional-integral control strategy to update the first PWM drive signal and the second PWM drive signal.

[0108] More specifically, in this embodiment, the controller performs PI adjustment on the output voltage deviation between the first capacitor and the second capacitor, and then adds the PI result to the PWM drive signal of each switch of the three-level buck converter circuit. By adjusting the charging and discharging process of the two capacitors, the input capacitor voltage is balanced. Specifically, this process is expressed as follows: ,in, represents the output voltage of the first capacitor, represents the output voltage of the second capacitor, Used to indicate the output of the voltage equalizing loop PI regulation.

[0109] Through the above settings, the problem of voltage imbalance of the voltage divider capacitor in the three-level step-down conversion circuit can be effectively solved, ensuring that the voltage deviation between the first capacitor and the second capacitor is always maintained within a very small range, avoiding excessive voltage stress on the switching device due to uneven capacitor voltage, and extending the service life of the device. During the PI adjustment process, the proportional coefficient Kp can achieve a rapid response to the voltage deviation, and the integral coefficient Ki can eliminate the steady-state error. The two work together to keep the capacitor voltage balanced under both dynamic and static conditions. In practical applications, this voltage equalization control strategy can significantly reduce the output voltage ripple, improve the stability and reliability of the auxiliary converter output voltage, and enhance the operational safety of the three-level topology structure. It provides a stable and balanced DC bus voltage input for the subsequent LLC resonant converter, ensuring the efficient and stable operation of the entire auxiliary converter system. It is particularly suitable for rail transit power supply scenarios with strict requirements on voltage stability.

[0110] As can be seen from the foregoing, the control method provided in this application, combined with input capacitor voltage balancing and output voltage feedforward control of a three-level buck converter circuit, enables parallel power supply and output current balancing (power sharing) of at least two groups of DC-DC converter circuits, thereby improving the high-power and power supply redundancy capabilities of the auxiliary converter. Furthermore, since there is no communication between the at least two groups of DC-DC converter circuits, this application utilizes droop control to achieve current balancing of the at least two groups of DC-DC converters. A control strategy is also provided to address the output voltage drop of the DC-DC converter circuits caused by droop control.

[0111] The embodiment of the present application also provides a control device, Figure 7A schematic diagram of the structure of a control device provided in an embodiment of the present application is shown in FIG. Figure 7 As shown, the device includes:

[0112] a first control module 71 configured to perform feedback control on a first output voltage of any group of DC-DC conversion circuits based on a desired output voltage of the DC-DC conversion circuits, so as to compensate for the first output voltage of the DC-DC conversion circuits and obtain a second output voltage;

[0113] A second control module 72 is configured to determine a second given reference voltage of the three-level buck converter circuit using a current sharing control strategy based on the second output voltage and the first given reference voltage of the DC-DC converter circuit;

[0114] The third control module 73 is configured to control the output voltage of the three-level buck conversion circuit based on the second given reference voltage and the current output voltage of the three-level buck conversion circuit.

[0115] In another possible implementation of the embodiment of the present application, the current sharing control strategy is a droop control strategy.

[0116] In another possible implementation of the embodiment of the present application, the third control module 73 is specifically configured to:

[0117] Based on the second given reference voltage, a feedforward control strategy is adopted to determine a target given reference voltage after feedforward compensation;

[0118] The output voltage of the three-level buck converter circuit is controlled based on the target given reference voltage and the current output voltage.

[0119] In another possible implementation of the embodiment of the present application, the third control module 73 is specifically configured to:

[0120] Determine first PWM drive signals for the first switching tube and the fourth switching tube to determine PWM drive signals for the second switching tube and the third switching tube;

[0121] The first switch tube and the fourth switch tube are controlled according to the first PWM drive signal, and the second switch tube and the third switch tube are controlled according to the second PWM drive signal to control the output voltage of the three-level buck conversion circuit.

[0122] In another possible implementation of the embodiment of the present application, the third control module 73 is further configured to:

[0123] Calculating a deviation between a current voltage of the first capacitor and a current voltage of the second capacitor;

[0124] Based on the deviation value and a given deviation reference value, a proportional-integral control strategy is adopted to update the first PWM drive signal and the second PWM drive signal.

[0125] A control device provided in an embodiment of the present application is applicable to the above-mentioned method embodiment and will not be described in detail here.

[0126] In an embodiment of the present application, a controller is provided. Figure 8 A schematic diagram of the structure of a controller provided in an embodiment of the present application is shown in FIG. Figure 8 As shown, Figure 8 The controller shown includes a processor 81 and a memory 82. The processor 81 and the memory 82 are connected, for example, via a bus 83. Optionally, the controller may also include a transceiver 84. It should be noted that in practice, the number of transceivers 84 is not limited to one, and the structure of the controller does not constitute a limitation on the embodiments of the present application.

[0127] The processor 81 may be a central processing unit (CPU), a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic device, transistor logic device, hardware component, or any combination thereof. It may implement or execute the various exemplary logic blocks, modules, and circuits described in conjunction with the disclosure of this application. The processor 81 may also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, etc.

[0128] Bus 83 may include a path for transmitting information between the above components. Bus 83 may be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus. Bus 83 may be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Figure 8 Only one thick line is used in the figure, but it does not mean that there is only one bus 83 or one type of bus 83.

[0129] The memory 82 may be a read-only memory (ROM) or other type of static storage device that can store static information and instructions, a random access memory (RAM) or other type of dynamic storage device that can store information and instructions, or an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compact discs, laser discs, optical discs, digital versatile discs, Blu-ray discs, etc.), a magnetic disk storage medium or other magnetic storage device, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and can be accessed by a computer, but is not limited to these.

[0130] The memory 82 is used to store application code for executing the solution of the present application, and the execution is controlled by the processor 81. The processor 81 is used to execute the application code stored in the memory 82 to implement the content shown in the above method embodiment.

[0131] The present application also provides a computer-readable storage medium, which may include: a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a disk or an optical disk, and other media that can store program code. Specifically, the computer-readable storage medium stores program instructions, and the program instructions are used to implement the methods in the above embodiments.

[0132] A computer program product is also provided in an embodiment of the present application, including a computer program. When the computer program is executed by a processor, the technical solution of the above-mentioned method embodiment is implemented. Its implementation principle and technical effect are similar and will not be repeated here.

[0133] An embodiment of the present application further provides a rail transit equipment, which includes the auxiliary converter in the aforementioned embodiment and the controller in the aforementioned embodiment.

[0134] It should be noted that for the aforementioned method embodiments, for the sake of simplicity, they are all expressed as a series of action combinations, but those skilled in the art should be aware that this application is not limited by the order of the actions described, because according to this application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in this specification are all optional embodiments, and the actions and modules involved are not necessarily required by this application.

[0135] It should be understood that the above-described device embodiments are merely illustrative, and the devices of the present application may also be implemented in other ways. For example, the system / module division in the above-described embodiments is merely a logical functional division, and actual implementations may employ other division methods. For example, multiple units, modules, or components may be combined or integrated into another system, or some features may be omitted or not implemented.

[0136] In the above embodiments, the description of each embodiment has its own emphasis. For parts not described in detail in a particular embodiment, please refer to the relevant description of other embodiments. The technical features of the above embodiments can be combined in any way. To keep the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0137] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of the present application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, and the true scope and spirit of the present application are indicated by the following claims.

[0138] It should be understood that the present application is not limited to the exact structure described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. An auxiliary converter, characterized in that: The auxiliary converter includes at least two groups of DC-DC conversion circuits connected in parallel; any one group of DC-DC conversion circuits includes a three-level buck conversion circuit and two LLC resonant converters; The input end of the three-level buck conversion circuit is connected to the DC power supply end of the traction power supply system, and the output end is connected to the input ends of the two LLC resonant converters; The input ends of the two LLC resonant converters are connected in parallel and then connected to the output end of the three-level buck conversion circuit, and the output ends are connected in series and then connected to the input end of the inverter.

2. The auxiliary converter according to claim 1, characterized in that The three-level buck conversion circuit includes a voltage divider network, a power switch module and an output network; The voltage divider network includes a first capacitor and a second capacitor, the first capacitor and the second capacitor are connected in series and then connected across the DC power supply terminal, and the midpoint potential between the first capacitor and the second capacitor is half of the input voltage; The power switch module includes a first switching tube and a second switching tube connected in series, and a third switching tube and a fourth switching tube connected in series, wherein the collector of the first switching tube is connected to the connection point between the DC power supply terminal and the first capacitor, and the emitter of the second switching tube is connected to the connection point between the first capacitor and the second capacitor; the collector of the third switching tube is connected to the emitter of the second switching tube, and the emitter of the fourth switching tube is connected to the connection point between the DC voltage source and the second capacitor; The power switch module also includes four diodes, which are anti-parallel connected to the emitter and collector of each switch tube; The output network includes a first inductor and a third capacitor, wherein a first end of the first inductor is connected to a connection point between the first switching tube and the second switching tube, a second end of the first inductor is connected to an input end of the LLC resonant converter, a first end of the third capacitor is connected to a connection point between the first inductor and the LLC resonant converter, and a second end of the third capacitor is connected to a connection point between the fourth switching tube and the third switching tube.

3. The auxiliary converter according to claim 1 or 2, characterized in that: The LLC resonant converter includes a single-phase full-bridge inverter circuit, an LLC resonant circuit, a high-frequency transformer and a single-phase uncontrolled rectifier bridge; The input end of the single-phase full-bridge inverter circuit is connected to the output end of the three-level buck converter circuit, and the output end of the single-phase full-bridge inverter circuit is connected to the input end of the LLC resonant circuit. The output end of the LLC resonant circuit is connected to the input end of the high-frequency transformer, the output end of the high-frequency transformer is connected to the single-phase uncontrolled rectifier bridge, and the output end of the single-phase uncontrolled rectifier bridge is connected to the input end of the inverter.

4. The auxiliary converter according to claim 3, characterized in that The single-phase full-bridge inverter circuit includes: a fifth switching tube and a sixth switching tube connected in series, and a seventh switching tube and an eighth switching tube connected in series, wherein the collectors of the fifth switching tube and the eighth switching tube are connected to the positive output terminal of the three-level buck conversion circuit, and the emitters of the sixth switching tube and the seventh switching tube are connected to the negative output terminal of the three-level buck conversion circuit; a first input terminal of the LLC resonant circuit is connected to the connection point of the fifth switching tube and the sixth switching tube, and a second input terminal is connected to the connection point of the seventh switching tube and the eighth switching tube; The single-phase full-bridge inverter circuit further includes four diodes, which are respectively connected in anti-parallel to the emitter and collector of each switching tube.

5. The auxiliary converter according to claim 4, characterized in that The LLC resonant circuit includes the leakage inductance, excitation inductance and resonant capacitor of the high-frequency transformer; the first end of the leakage inductance is connected to the connection point of the fifth switching tube and the sixth switching tube, the second end of the leakage inductance is connected to the first end of the excitation inductance, forming a resonant inductance branch, the second end of the excitation inductance is connected to the first end of the resonant capacitor, and the second end of the resonant capacitor is connected to the connection point of the seventh switching tube and the eighth switching tube.

6. The auxiliary converter according to claim 3, characterized in that The single-phase uncontrolled rectifier bridge includes a single-phase rectifier bridge circuit and a fourth capacitor; the input end of the single-phase rectifier bridge circuit is connected to the output end of the high-frequency transformer, the output end of the single-phase rectifier bridge circuit is connected to the input end of the fourth capacitor, and the output end of the fourth capacitor serves as the output end of the LLC resonant converter.

7. A control method, characterized in that: Applied to the auxiliary converter according to any one of claims 1 to 6; the method comprising: For any group of DC-DC conversion circuits, feedback control is performed on a first output voltage of the DC-DC conversion circuit based on a desired output voltage of the DC-DC conversion circuit to compensate for the first output voltage of the DC-DC conversion circuit to obtain a second output voltage; Determining a second given reference voltage of the three-level buck converter circuit by adopting a current sharing control strategy based on the second output voltage and the first given reference voltage of the DC-DC converter circuit; The output voltage of the three-level buck conversion circuit is controlled based on the second given reference voltage and the current output voltage of the three-level buck conversion circuit.

8. The method according to claim 7, characterized in that The current sharing control strategy is a droop control strategy.

9. The method according to claim 7 or 8, characterized in that The controlling the output voltage of the three-level buck converter circuit based on the second given reference voltage and the current output voltage of the three-level buck converter circuit includes: Based on the second given reference voltage, a feedforward control strategy is adopted to determine a target given reference voltage after feedforward compensation; Based on the target given reference voltage and the current output voltage, the output voltage of the three-level buck conversion circuit is controlled.

10. The method according to claim 7 or 8, characterized in that The controlling the output voltage of the three-level buck conversion circuit comprises: Determine a first PWM drive signal for the first switching tube and the fourth switching tube to determine a second PWM drive signal for the second switching tube and the third switching tube; The first switch tube and the fourth switch tube are controlled according to the first PWM drive signal, and the second switch tube and the third switch tube are controlled according to the second PWM drive signal to control the output voltage of the three-level buck conversion circuit.

11. The method according to claim 10, characterized in that The method further comprises: Calculating a deviation between a current voltage of the first capacitor and a current voltage of the second capacitor; Based on the deviation value and a given deviation reference value, a proportional-integral control strategy is adopted to update the first PWM drive signal and the second PWM drive signal.

12. A controller, characterized in that: The controller includes: at least one processor and a memory; The memory stores computer-executable instructions; The at least one processor executes the computer-executable instructions stored in the memory, so that the at least one processor performs the method according to any one of claims 7 to 11.

13. A rail transit equipment, characterized in that: The rail transit equipment includes the auxiliary converter according to any one of claims 1 to 6, and the controller according to claim 12.

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