Train auxiliary converter and three-level chopper unit thereof

Abstract

The present application relates to train auxiliary converter and its three-level chopper unit, three-level chopper unit control method and computer readable storage medium.The three-level chopper unit includes two voltage division capacitors, two step-down switch tubes, two freewheeling diodes, a chopper inductor, a filter capacitor, a step-up switch tube and an anti-reverse diode.Two step-down switch tubes are adapted to be turned on in step-down mode and step-up / down mode to realize step-down output in cooperation with two voltage division capacitors, two freewheeling diodes, a chopper inductor and a filter capacitor, and are adapted to be always turned on in step-up mode.The one end of the step-up switch tube is arranged at the rear end of the chopper inductor, and the other end of the step-up switch tube is connected to the other end of the filter capacitor through the anti-reverse diode.The step-up switch tube is adapted to be turned on in step-up mode and step-up / down mode to realize step-up output in cooperation with two voltage division capacitors, a chopper inductor, an anti-reverse diode and a filter capacitor, and is adapted to be always turned off in step-down mode.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of converters, in particular to a three-level chopping unit of a train auxiliary converter, a control method of the three-level chopping unit, and an auxiliary converter of a train. BACKGROUND

[0002] The conventional low-floor high-frequency auxiliary converter is mainly applied in the DC 750V power supply system of urban rail transit, and has a power supply range of DC 500V-DC 900V, and a narrow input range. However, in some scenarios, the owner may require a higher input voltage range, such as a rated pantograph DC 1500V (DC 900V-DC 1800V) input voltage, or a storage yard maintenance voltage of DC 500V of the power supply system during storage yard maintenance. Due to the limitation of the circuit topology architecture, the existing high-frequency auxiliary converter cannot meet the application requirements beyond its input voltage range.

[0003] Please refer to Figure 1 , Figure 1 a circuit schematic diagram of a conventional high-frequency auxiliary converter topology is shown.

[0004] As Figure 1 shown, the existing high-frequency auxiliary converter can be composed of a three-level chopping unit 11, a high-frequency isolation unit 12, and a three-phase inverter unit 13. In the urban rail DC 750V power supply system, the input voltage of the high-frequency auxiliary converter is DC 750V. The input voltage can be converted to an intermediate voltage of DC 450V by the three-level chopping unit 11. The intermediate voltage can be converted to a DC 700V direct current voltage by the isolation transformation of the high-frequency isolation unit 12, and then output three-way AC 380V alternating current by the three-phase inverter unit 13.

[0005] In the scenario where the input voltage range is DC 500V-DC 1800V, the conventional auxiliary converter may have the following problems:

[0006] 1. If the intermediate voltage is set below 500V, the system efficiency of the auxiliary converter will be significantly reduced due to the too low voltage reduction ratio of the chopping unit 11 under the rated pantograph voltage of DC 1500V.

[0007] 2. If the intermediate voltage is set above 500V, since the existing three-level chopping unit 11 only has the function of voltage reduction and chopping, it cannot raise the input voltage of DC 500V to the set intermediate voltage, and an additional boost chopping converter is needed, thereby increasing the volume and weight of the system.

[0008] In order to overcome the above-mentioned defects of the prior art, the technical field urgently needs a three-level chopping technology for determining a corresponding voltage conversion mode according to a value of an input voltage, thereby meeting the application requirement of a wide range of input, improving the efficiency of a converter, and reducing the volume and weight of the converter. SUMMARY

[0009] The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

[0010] In order to overcome the above-mentioned defects of the prior art, the present application provides a three-level chopping unit of a train auxiliary converter, a control method of a three-level chopping unit, an auxiliary converter of a train, and a computer readable storage medium for determining a corresponding voltage conversion mode according to a value of an input voltage, thereby meeting the application requirement of a wide range of input, improving the efficiency of a converter, and reducing the volume and weight of the converter.

[0011] The three-level chopping unit of the train auxiliary converter provided by the present application comprises two voltage dividing capacitors, two voltage reducing switch tubes, two freewheeling diodes, a chopping inductor, a filter capacitor, a voltage increasing switch tube, and an anti-reverse diode. The two voltage reducing switch tubes are adapted to be turned on in a voltage reducing mode and a voltage increasing and reducing mode to cooperate with the two voltage dividing capacitors, the two freewheeling diodes, the chopping inductor, and the filter capacitor to realize voltage reducing output, and are adapted to be always turned on in a voltage increasing mode. One end of the voltage increasing switch tube is arranged at a rear end of the chopping inductor, and the other end of the voltage increasing switch tube is connected to the other end of the filter capacitor through the anti-reverse diode. The voltage increasing switch tube is adapted to be turned on in the voltage increasing mode and the voltage increasing and reducing mode to cooperate with the two voltage dividing capacitors, the chopping inductor, the anti-reverse diode, and the filter capacitor to realize voltage increasing output, and is adapted to be always turned off in the voltage reducing mode.

[0012] Optionally, in some embodiments of the present application, an output end of the three-level chopping unit can be connected to an isolation voltage conversion unit of the auxiliary converter, and is adapted to supply power to an inverter unit of the auxiliary converter through the isolation voltage conversion unit to realize alternating current output of the auxiliary converter. The output end of the three-level chopping unit can be connected to a charger unit of the auxiliary converter, and is adapted to realize direct current output of the auxiliary converter through the charger unit.

[0013] Preferably, in some embodiments of the present application, the three-level buck unit can further comprise a processor. The processor can be communicatively connected to the two buck switch tubes and the boost switch tube, and configured to: detect an input voltage of the auxiliary converter; determine a working mode of the three-level buck unit according to the input voltage and a preset target intermediate voltage, wherein the working mode comprises the buck mode, the boost mode and the buck-boost mode; in response to the input voltage being higher than a preset first voltage threshold, determine that the working mode of the three-level buck unit is the buck mode, and control the two buck switch tubes to realize the buck output; in response to the input voltage being lower than a preset second voltage threshold, determine that the working mode of the three-level buck unit is the boost mode, and control the boost switch tube to realize the boost output; and in response to the input voltage being between the first voltage threshold and the second voltage threshold, determine that the working mode of the three-level buck unit is the buck-boost mode, and control the two buck switch tubes and the boost switch tube to realize the buck-boost output.

[0014] Preferably, in some embodiments of the present application, the processor can be further configured to: in the boost mode, determine a duty cycle of the boost switch tube according to the target intermediate voltage and the input voltage; and control the boost switch tube to be turned on according to the duty cycle, so as to realize the boost output.

[0015] Optionally, in some embodiments of the present application, the processor can be further configured to: in the buck-boost mode, determine duty cycles of the two buck switch tubes according to the target intermediate voltage, the input voltage and a fixed duty cycle of the boost switch tube; control the boost switch tube to be turned on according to the fixed duty cycle; and control the two buck switch tubes to be turned on in opposite phase according to the determined duty cycles, so as to realize the buck-boost output.

[0016] Optionally, in some embodiments of the present application, the processor can be further configured to: in the buck mode, determine duty cycles of the two buck switch tubes according to a ratio of the target intermediate voltage to the input voltage; and control the two buck switch tubes to be turned on in opposite phase by 180° according to the duty cycles, so as to realize the buck output.

[0017] Preferably, in some embodiments of the present application, the target intermediate voltage can be not lower than 1 / 2 of an upper limit of the input voltage, so as to ensure that a buck ratio in the buck mode is not lower than 1 / 2; and the target intermediate voltage can be not higher than 2 times of a lower limit of the input voltage, so as to ensure that a boost ratio in the boost mode is less than 2.

[0018] Preferably, in some embodiments of the present application, the first voltage threshold can be the sum of the target intermediate voltage and a preset transition voltage width, and the second voltage threshold can be the difference between the target intermediate voltage and the transition voltage width. The transition voltage width indicates the fluctuation amplitude of the input voltage in normal working condition.

[0019] According to another aspect of the present application, a control method of a three-level chopper unit is also provided herein.

[0020] In the control method of the three-level chopper unit provided by the present application, the three-level chopper unit comprises two voltage dividing capacitors, two step-down switch tubes, two freewheeling diodes, a chopper inductor, a filter capacitor, a step-up switch tube and an anti-reverse diode. The control method comprises the steps of: detecting an input voltage of the auxiliary converter; determining a working mode of the three-level chopper unit according to the input voltage and a preset target intermediate voltage, wherein the working mode comprises a step-down mode, a step-up mode and a step-up / down mode; and controlling the two step-down switch tubes and / or the step-up switch tube to realize a step-down output, a step-up output or a step-up / down output according to the working mode.

[0021] Preferably, in some embodiments of the present application, the step of realizing the step-down output, the step-up output or the step-up / down output can comprise: in response to the input voltage being higher than a preset first voltage threshold, determining that the working mode of the three-level chopper unit is the step-down mode, controlling the step-up switch tube to be always off, and controlling the two step-down switch tubes to realize the step-down output in cooperation with the two voltage dividing capacitors, the two freewheeling diodes, the chopper inductor and the filter capacitor; in response to the input voltage being lower than a preset second voltage threshold, determining that the working mode of the three-level chopper unit is the step-up mode, controlling the two step-down switch tubes to be always on, and controlling the step-up switch tube to realize the step-up output in cooperation with the two voltage dividing capacitors, the chopper inductor, the anti-reverse diode and the filter capacitor; and in response to the input voltage being between the first voltage threshold and the second voltage threshold, determining that the working mode of the three-level chopper unit is the step-up / down mode, and controlling the two step-down switch tubes and the step-up switch tube to realize the step-up / down output in cooperation.

[0022] Preferably, in some embodiments of the present application, the step of realizing the step-up output can further comprise: in the step-up mode, determining a duty cycle of the step-up switch tube according to the target intermediate voltage and the input voltage; and controlling the step-up switch tube to be turned on according to the duty cycle, so as to realize the step-up output.

[0023] Optionally, in some embodiments of the present application, the step of achieving the step-up / down output can further comprise: determining duty cycles of the two step-down switching tubes according to the target intermediate voltage, the input voltage and a fixed duty cycle of the step-up switching tube in the step-up / down mode; and controlling the step-up switching tube to be turned on according to the fixed duty cycle and controlling the two step-down switching tubes to be turned on in opposite phase according to the determined duty cycles, so as to achieve the step-up / down output.

[0024] Optionally, in some embodiments of the present application, the step of achieving the step-down output can further comprise: determining duty cycles of the two step-down switching tubes according to a ratio of the target intermediate voltage to the input voltage in the step-down mode; and controlling the two step-down switching tubes to be turned on in opposite phase by 180° according to the duty cycles, so as to achieve the step-down output.

[0025] Preferably, in some embodiments of the present application, the control method can further comprise the step of: setting the target intermediate voltage to be not lower than 1 / 2 of an upper limit of the input voltage and not higher than 2 times of a lower limit of the input voltage, so as to ensure that a step-down ratio in the step-down mode is not lower than 1 / 2 and a step-up ratio in the step-up mode is less than 2.

[0026] Preferably, in some embodiments of the present application, the control method can further comprise the steps of: setting a sum of the target intermediate voltage and a preset transition voltage width as the first voltage threshold, the transition voltage width indicating a fluctuation amplitude of the input voltage in a normal working condition; and setting a difference between the target intermediate voltage and the transition voltage width as the second voltage threshold.

[0027] According to another aspect of the present application, a train auxiliary converter is also provided herein.

[0028] The train auxiliary converter provided by the present application can comprise the three-level chopping unit, the isolation transformer unit and the inverter unit provided by any one of the above embodiments. The isolation transformer unit is connected to the output end of the three-level chopping unit. The inverter unit is connected to the output end of the isolation transformer unit and is adapted to achieve an AC output of the auxiliary converter under power supply of the isolation transformer unit.

[0029] Preferably, in some embodiments of the present application, the auxiliary converter can further comprise a charger unit. The charger unit is connected to the output end of the three-level chopping unit and is adapted to achieve a DC output of the auxiliary converter under power supply of the three-level chopping unit.

[0030] According to another aspect of the present application, a computer readable storage medium is also provided herein.

[0031] The computer-readable storage medium provided by this invention stores computer instructions thereon. When the computer instructions are executed by a processor, the control method of the three-level chopper unit provided in any of the above embodiments can be implemented to determine the corresponding transformation mode according to the value of the input voltage, thereby meeting the application requirements of a wide range of inputs, improving the efficiency of the converter, and reducing the size and weight of the converter. Attached Figure Description

[0032] The above-described features and advantages of the present invention will be better understood after reading the following detailed description of embodiments of the present disclosure in conjunction with the accompanying drawings. In the drawings, components are not necessarily drawn to scale, and components having similar related characteristics or features may have the same or similar reference numerals.

[0033] Figure 1 A circuit diagram of a conventional high-frequency auxiliary converter topology is shown.

[0034] Figure 2 A circuit diagram of a three-level chopper unit provided according to some embodiments of the present invention is shown.

[0035] Figure 3 A flowchart illustrating a control method for a three-level chopper unit according to some embodiments of the present invention is shown.

[0036] Figure 4A and Figure 4B Equivalent circuit diagrams for buck and boost modes provided according to some embodiments of the present invention are shown respectively.

[0037] Figures 5A-5C Schematic diagrams of electrical parameters for buck mode, boost mode, and buck-boost mode provided according to some embodiments of the present invention are shown respectively.

[0038] Figure 6 A schematic diagram of the architecture of a train auxiliary converter provided according to some embodiments of the present invention is shown. Detailed Implementation

[0039] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a thorough understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description.

[0040] As described above, the three-level chopping unit 11 of the existing high-frequency auxiliary converter has the defect of significant reduction of system efficiency in the case of excessively high input voltage; and the defect of the need of additional boost chopping converter in the case of excessively low input voltage, thereby increasing the volume and weight of the system.

[0041] In order to overcome the above defects of the prior art, the present application provides a three-level chopping unit of a train auxiliary converter, a control method of a three-level chopping unit, an auxiliary converter of a train, and a computer readable storage medium, for determining the corresponding voltage conversion mode according to the value of the input voltage, thereby meeting the application requirements of wide range input, improving the efficiency of the converter, and reducing the volume and weight of the converter.

[0042] Please refer to Figure 2 , Figure 2 The circuit schematic diagram of the three-level chopping unit according to some embodiments of the present application is shown.

[0043] As Figure 2 shown, in some embodiments of the present application, the three-level chopping unit 20 of the train auxiliary converter can include two voltage dividing capacitors C1-C2, two step-down switch tubes V1-V2, two freewheeling diodes D1-D2, a chopping inductor L102, filter capacitors C3-C4, a boost switch tube V9, and an anti-reverse diode D9.

[0044] The above two voltage dividing capacitors C1-C2 can be arranged at the input end of the three-level chopping unit 20, and a capacitor with large capacity and equal capacitance value is selected to ensure that each voltage dividing capacitor C1 and C2 carries half of the input voltage, i.e. 1 / 2Vin.

[0045] The above two step-down switch tubes V1-V2 can be arranged at the high voltage end and the low voltage end of the three-level chopping unit 20, respectively. In some embodiments, the two step-down switch tubes V1-V2 are adapted to work in the step-down mode and the step-up / down mode, and cooperate with the two voltage dividing capacitors C1-C2, the two freewheeling diodes D1-D2, the chopping inductor L102, and the filter capacitors C3-C4 to realize the step-down output of the three-level chopping unit 20. In some embodiments, they are also adapted to be always on in the step-up mode to be equivalent to a short circuit state. In some embodiments, both of the two step-down switch tubes V1-V2 can be selected to be an Insulated Gate Bipolar Transistor (IGBT) with a switching frequency of 10 kHz.

[0046] The above two freewheeling diodes D1-D2 can be connected in parallel to the two voltage dividing capacitors C1-C2, respectively, for assisting the two step-down switch tubes V1-V2 to realize the step-down output of the three-level chopping unit 20.

[0047] The above-mentioned chopper inductance L102 can be arranged at the high-voltage end of the three-level chopping unit 20, for maintaining the instantaneous current at the high-voltage end to realize the step-up output, step-down output and step-up and step-down output of the three-level chopping unit 20. In some embodiments, the chopper inductance L102 can be selected as a 1 mH inductance element.

[0048] The above-mentioned filter capacitors C3-C4 can be arranged at the output end of the three-level chopping unit 20, and are adapted to cooperate with the chopper inductance L102 to stabilize and filter the output voltage of the three-level chopping unit 20. In some embodiments, the filter capacitors C3-C4 can include filter capacitors C3 and C4 with equal capacitance values. The rear-stage unit of the train auxiliary converter can take power from between the two filter capacitors C3-C4 to achieve the effect of taking power in both positive and negative directions.

[0049] The above-mentioned anti-reverse diode D9 can be connected in series between the chopper inductance L102 and the filter capacitors C3-C4, and is adapted to reverse-isolate the high voltage at the ends of the filter capacitors C3-C4 to realize the step-up output of the three-level chopping unit 20.

[0050] The collector of the above-mentioned step-up switch tube V9 can be connected to the rear end of the chopper inductance L102, and the high-voltage end of the filter capacitors C3-C4 through the anti-reverse diode D9, and its emitter can be connected to the low-voltage end of the filter capacitors C3-C4. In some embodiments, the step-up switch tube V9 is adapted to work in step-up mode and step-up and step-down mode, and cooperates with the two voltage dividing capacitors C1-C2, the chopper inductance L102, the anti-reverse diode D9 and the filter capacitors C3-C4 to realize the step-up output of the three-level chopping unit 20. In some embodiments, the step-up switch tube V9 is adapted to be always off in step-down mode to be equivalent to an open circuit state. In some embodiments, the step-up switch tube V9 can be selected as an IGBT with a switching frequency of 10 kHz.

[0051] In some embodiments of the present application, the three-level chopping unit 20 can further include a processor. The processor can be communicatively connected to the gates of the switch tubes V1-V2 and V9, and is adapted to control the switch tubes V1-V2 and V9 to be turned on and off in a time sequence by outputting control signals, so as to realize the step-down output in the above-mentioned step-down mode, the step-up output in the above-mentioned step-up mode, and the step-up output and the step-down output in the above-mentioned step-up and step-down mode of the three-level chopping unit 20.

[0052] The working principle of the control method of the three-level chopping unit 20 will be described below in combination with some embodiments of the control method. The control method can be implemented by the processor of the three-level chopping unit 20 by executing computer instructions. It can be understood that the control methods are only some non-limiting embodiments, which are intended to clearly show the main idea of the present application and provide some specific solutions for facilitating the public to implement, rather than to limit the protection scope of the present application.

[0053] Please refer to Figure 3 , Figure 3 The flowchart of the control method of the three-level chopping unit according to some embodiments of the present application is shown.

[0054] As Figure 3 shown, the control method of the three-level chopping unit provided by the present application can include the step 301 of detecting the input voltage of the auxiliary converter.

[0055] As described above, the three-level chopping unit 21 can be arranged at the input end of the train auxiliary converter, which is adapted to convert any input voltage Vin in a wider input voltage range (for example: DC500V-DC1800V) into a specified intermediate voltage Vmid, and plays a role of pre-stabilization when the input voltage Vin changes, so as to provide a voltage suitable for the normal operation of the rear-end isolation transformer unit, the inverter unit and the charger unit.

[0056] In some embodiments of the present application, the processor can use the voltage sensor to monitor the voltage across the voltage dividing capacitors C1-C2 in real time to determine the input voltage Vin of the auxiliary converter.

[0057] As Figure 3 shown, the control method of the three-level chopping unit provided by the present application can further include the step 302 of determining the working mode of the three-level chopping unit according to the input voltage and the preset target intermediate voltage.

[0058] In some embodiments of the present application, the target value of the intermediate voltage Vmid outputted by the three-level chopper unit 20, i.e. the target intermediate voltage, can be designed according to the input range of the input voltage Vin of the auxiliary converter. Specifically, the processor can first acquire the application scenario data of the train to determine the input voltage range that the auxiliary converter can involve. For example, if the train works at the rated overhead line DC 1500V (the input voltage is between DC 900V and DC 1800V) on a daily basis, and occasionally involves the power supply system of the depot maintenance voltage DC 500V when entering the depot for maintenance, the processor can determine that the input voltage Vin of the auxiliary converter ranges from DC 500V to DC 1800V. In some embodiments, the processor can set the target intermediate voltage Vmid to a voltage value that is greater than 1 / 2 of the upper limit of the input voltage DC 1800V and less than 2 times the lower limit of the input voltage DC 500V, i.e. DC 900V to DC 1000V.

[0059] By setting the target intermediate voltage Vmid to be greater than 1 / 2 of the upper limit of the input voltage DC 1800V, the target intermediate voltage Vmid will not be lower than 1 / 2 of the input voltage Vin no matter what input voltage Vin is provided to the three-level chopper unit 20. By ensuring that the target intermediate voltage Vmid is higher than 1 / 2 of the input voltage Vin, it can be ensured that the duty cycle of the two buck switch tubes V1-V2 in the buck mode is not lower than 1 / 2. At this time, the buck ratio of the three-level chopper unit 20 is greater than 0.5, and the loss of the buck switch tubes V1-V2 and the chopper inductor L102 is small, so the energy utilization efficiency of the three-level chopper unit 20 can be improved.

[0060] By setting the target intermediate voltage Vmid to be less than 2 times the lower limit of the input voltage DC 500V, the target intermediate voltage Vmid will not be higher than 2 times the input voltage Vin no matter what input voltage Vin is provided to the three-level chopper unit 20. By ensuring that the target intermediate voltage Vmid is lower than 2 times the input voltage Vin, it can be ensured that the boost ratio in the boost mode is not higher than 2, thereby improving the energy utilization efficiency of the three-level chopper unit 20.

[0061] Since the above-mentioned three-level chopper unit 20 provided by the present application is suitable for use in a wide range of input scenarios from DC 500V to DC 1800V, the input voltage Vin of the auxiliary converter can be higher than the target intermediate voltage Vmid, lower than the target intermediate voltage Vmid, or similar to the target intermediate voltage Vmid. In some embodiments, after detecting the input voltage Vin of the auxiliary converter, the processor can compare the input voltage Vin with the target intermediate voltage Vmid, and determine the working mode of bucking, boosting or buck-boosting for three-level chopping according to the comparison result.

[0062] Specifically, in some embodiments, the processor can set the fluctuation range of the input voltage Vin under normal working conditions of the train (e.g., 100V) as the transition voltage width ΔV, and set the sum of the target intermediate voltage Vmid and the transition voltage width ΔV (i.e., Vmid+ΔV) as the first voltage threshold. In response to the input voltage Vin being higher than the first voltage threshold, the processor can determine that the input voltage Vin is higher than the target intermediate voltage Vmid, and the three-level buck unit 20 is adapted to adopt the step-down mode to step down the input voltage Vin to obtain the set target intermediate voltage Vmid.

[0063] In the above embodiments, the processor can also set the difference between the target intermediate voltage Vmid and the transition voltage width ΔV (i.e., Vmid-ΔV) as the second voltage threshold. In response to the input voltage Vin being lower than the second voltage threshold, the processor can determine that the input voltage Vin is lower than the target intermediate voltage Vmid, and the three-level buck unit 20 is adapted to adopt the step-up mode to step up the input voltage Vin to obtain the set target intermediate voltage Vmid.

[0064] In the above embodiments, in response to the input voltage Vin being between the first voltage threshold and the second voltage threshold, the processor can also determine that the input voltage Vin is similar to the target intermediate voltage Vmid, and the three-level buck unit 20 is adapted to adopt the step-up / down mode to step up and step down the input voltage Vin to obtain the set target intermediate voltage Vmid.

[0065] Those skilled in the art can understand that, although the above embodiments describe the operations of setting the target intermediate voltage Vmid, determining the first voltage threshold, and determining the second voltage threshold as being implemented by the processor, this does not mean that these steps must be performed in the control process of the three-level buck unit 20. Alternatively, in other embodiments, those skilled in the art can also determine the values of the target intermediate voltage Vmid, the first voltage threshold, and the second voltage threshold in advance according to the upper limit of the input voltage and the fluctuation range of the input voltage under normal working conditions, and preset them in the processor of the three-level buck unit 20 to achieve the same control effect.

[0066] As shown in FIG. 3, the control method of the three-level buck unit provided by the present application can further include the following steps. Figure 3

[0067] ​As mentioned above, the processor of the three-level chopping unit 20 can determine the working mode of the three-level chopping unit 20 according to the high or low of the input voltage Vin and the target intermediate voltage Vmid. After determining the working mode of the three-level chopping unit 20, the processor can further control the switches V1-V2, V9 of the three-level chopping unit 20 to work in time sequence according to the determined working mode, so as to convert the input voltage Vin into the specified intermediate voltage Vmid.

[0068] Specifically, in some embodiments, in response to detecting that the input voltage Vin is DC 1500V, the processor can determine that the input voltage Vin is higher than the first voltage threshold, and thus determine that the three-level chopping unit 20 is suitable for adopting the step-down mode to perform step-down processing on the input voltage Vin.

[0069] In the step-down mode, the processor can determine the duty cycle of the two step-down switches V1-V2 according to the ratio of the target intermediate voltage Vmid to the input voltage Vin, i.e. At the same time, the processor can set the duty cycle of the step-up switch V9 to zero (i.e. d9=0), so that the step-up switch V9 is in a constant-off state.

[0070] Please refer to Figure 4A and Figure 5A , Figure 4A shows an equivalent circuit schematic diagram of the step-down mode according to some embodiments of the present application, Figure 5A shows an electrical parameter schematic diagram of the step-down mode according to some embodiments of the present application.

[0071] As Figure 4A shown, in the step-down mode, by keeping the step-up switch V9 in a constant-off state, its two ends are equivalent to an open circuit structure, and the circuit topology of the three-level chopping unit 20 can be equivalent to a three-level step-down chopping circuit. In this embodiment, the processor can control the two step-down switches V1-V2 to conduct in the above-mentioned duty cycle d1=d2=0.6 and out of phase by 180°, so as to obtain an intermediate voltage Vmid of 60% Vin, i.e. DC 900V, across the filter capacitors C3-C4.

[0072] As Figure 5AAs shown, in the above embodiment with duty cycle d1=d2=0.6, the three-level chopper unit 20 can include three switching modes. In the period of t1-t2, the buck switch V1 is on while the buck switch V2 is off, the voltage-dividing capacitor C2 is disconnected by the buck switch V2, the divided voltage Vin / 2 on the voltage-dividing capacitor C1 is connected to the two ends of the filter capacitor C3-C4 through the freewheeling diode D2, and the current on the chopper inductor L102 decreases linearly with time. In the period of t2-t3, both buck switches V1-V2 are on, the complete input voltage Vin is directly connected to the two ends of the filter capacitor C3-C4, and the current on the chopper inductor L102 increases linearly with time. In the period of t3-t4, the buck switch V2 is on while the buck switch V1 is off, the voltage-dividing capacitor C1 is disconnected by the buck switch V1, the divided voltage Vin / 2 on the voltage-dividing capacitor C2 is connected to the two ends of the filter capacitor C3-C4 through the freewheeling diode D1, and the current on the chopper inductor L102 decreases linearly with time again. Due to the presence of the chopper inductor L102, the current flowing into the filter capacitor C3-C4 cannot be abruptly changed, and the intermediate voltage Vmid across the filter capacitor C3-C4 will adapt to the duty cycle d1=d2=0.6 of the buck switches V1-V2, and be maintained at the voltage level of 60% Vin, thereby achieving the effect of voltage reduction.

[0073] By increasing the intermediate voltage from DC 450V in the prior art to DC 900V, the present application can ensure that the voltage reduction ratio of the three-level chopper unit 20 is maintained at 0.5 or above. In the embodiment with input voltage Vin=DC 1500V, compared with the voltage reduction ratio less than 0.3 in the prior art, the voltage reduction ratio of the three-level chopper unit 20 is increased to 0.6, thereby increasing its energy efficiency from 0.975 in the prior art to 0.985. In addition, as shown, by maintaining the voltage reduction ratio of the three-level chopper unit 20 at 0.5 or above, the ripple ratio of the inductor current is also successfully reduced to less than 20%, which is less than the ripple generated when the voltage reduction ratio is 0.3 in the prior art. Figure 5A

[0074] In some embodiments, in response to detecting that the input voltage Vin is DC 500V, the processor can determine that the input voltage Vin is lower than the second voltage threshold, and thus determine that the three-level chopper unit 20 is suitable for adopting the boost mode to boost the input voltage Vin.

[0075] In the boost mode, the processor can set the duty cycle of the two buck switches V1-V2 to 1, i.e., d1=d2=1, so that the two buck switches V1-V2 are in a constant-on state. At the same time, the processor can determine the duty cycle of the boost switch V9 according to the following relationship (1):

[0076] ​

[0077] Please refer to Figure 4B and Figure 5B , Figure 4B The equivalent circuit schematic diagram of the boost mode provided by some embodiments of the present application is shown, Figure 5B The electrical parameter schematic diagram of the boost mode provided by some embodiments of the present application is shown.

[0078] As Figure 4B shown, in the boost mode, by keeping the two buck switch tubes V1-V2 in the state of always-on, the two buck switch tubes V1-V2 can be equivalent to a wire, and the circuit topology of the three-level chopping unit 20 can be equivalent to a three-level boost chopping circuit. In this embodiment, the processor can control the boost switch tube V9 to be turned on with the above-mentioned duty ratio d9=0.44, so as to obtain the intermediate voltage Vmid of 1.8Vin at both ends of the filter capacitor C3-C4, i.e. DC 900V.

[0079] As Figure 5B shown, in the above-mentioned embodiment with the duty ratio d9=0.44, the three-level chopping unit 20 can include two kinds of switching modes. In the period of t5-t6, the boost switch tube V9 is turned on, the voltage dividing capacitor C1-C2 is grounded through the chopping inductor L102, the current on the chopping inductor L102 rises with time, and the intermediate voltage Vmid is maintained at the original voltage due to the voltage clamping of the anti-reverse diode D9. In the period of t6-t7, the boost switch tube V9 is turned off, the chopping inductor L102 charges the filter capacitor C3-C4 through the anti-reverse diode D9 to increase the intermediate voltage Vmid. At the same time, the current on the chopping inductor L102 decreases with time. Due to the presence of the chopping inductor L102, the current flowing into the filter capacitor C3-C4 cannot be suddenly changed, and the intermediate voltage Vmid at both ends of the filter capacitor C3-C4 will adapt to the duty ratio d9=0.44 of the boost switch tube V9, and be maintained at the voltage level of 1.8Vin, thereby achieving the effect of boost output.

[0080] By adopting Figure 2 the circuit topology structure of the three-level chopping unit 20 as shown, even if the input voltage Vin is lower than the preset intermediate voltage Vmid, the three-level chopping unit 20 can also perform boost output on the input voltage Vin, thereby avoiding the trouble of increasing an additional boost converter in the prior art. Compared with the prior art which needs to adopt a set of buck converter and an additional set of boost converter to cope with the application scenario of low input voltage, the present application can realize the multiplexing of the chopping inductor L102 and the filter capacitor C3-C4, thereby reducing the volume and weight of the converter system. In addition, as Figure 5B shown, when the three-level chopping unit 20 is used for boost output, the ripple ratio of the inductor current is controlled to be below 20%, which has good system steady-state performance.

[0081] By comparison Figure 5A and Figure 5B It can be seen that the ripple in the buck mode is smaller than that in the boost mode. In some embodiments, the minimum value DC900V can be selected as the target intermediate voltage Vmid within the range of the above intermediate voltage (i.e. DC900V-DC1000V), so that the three-level chopping unit 20 works more in the buck mode to reduce power loss.

[0082] In some embodiments, in response to detecting that the input voltage Vin is DC800V, the processor can determine that the input voltage Vin is between the first voltage threshold and the second voltage threshold, so as to determine that the three-level chopping unit 20 is suitable for adopting the boost-buck mode to perform boost processing and buck processing on the input voltage Vin, respectively.

[0083] In the boost-buck mode, the processor can first determine the duty ratio of the boost switch tube V9 according to the preset fixed duty ratio d fix , for example, d9=d fix =0.2. Then, the processor can determine the duty ratios of the two buck switch tubes V1-V2 according to the following relationship (2):

[0084]

[0085] Please refer to Figure 2 and Figure 5C , Figure 5C show the electrical parameter diagram of the boost-buck mode according to some embodiments of the present application.

[0086] As shown in Figure 2 , in the boost-buck mode, the processor can control the two buck switch tubes V1-V2 to conduct according to the above duty ratios d1=d2=0.9 and out of phase by 180°, and control the boost switch tube V9 to conduct according to the above duty ratio d9=d fix =0.2, so as to obtain an intermediate voltage Vmid of 1.125Vin, i.e. DC900V, across the two ends of the filter capacitor C3-C4.

[0087] As shown in Figure 5C , in the above duty ratios d1=d2=0.9 and d9=d fixIn the embodiment of d1 = d2 = d9 = 0.2, the three-level chopping unit 20 can include five kinds of switching modes. In the period of t8-t9, two buck switch tubes V1-V2 are turned on and the boost switch tube V9 is turned on, the divided voltage capacitors C1-C2 are grounded through the chopping inductor L102, the current on the chopping inductor L102 rises with time, and the intermediate voltage Vmid is kept at the original voltage by the voltage clamping of the anti-reverse diode D9. In the period of t9-t10, two buck switch tubes V1-V2 are turned on and the boost switch tube V9 is turned off, the chopping inductor L102 charges to the filter capacitors C3-C4 through the anti-reverse diode D9 to increase the intermediate voltage Vmid. Meanwhile, the current on the chopping inductor L102 falls with time. In the period of t10-t11, the boost switch tube V9 is turned off, the buck switch tube V1 is turned on and the buck switch tube V2 is turned off, the divided voltage capacitor C2 is disconnected by the buck switch tube V2, the divided voltage Vin / 2 on the divided voltage capacitor C1 is connected to the two ends of the filter capacitors C3-C4 through the freewheeling diode D2, and the current on the chopping inductor L102 falls rapidly with time. In the period of t11-t12, the boost switch tube V9 is turned off and two buck switch tubes V1-V2 are turned on simultaneously, and the complete input voltage Vin is directly connected to the two ends of the filter capacitors C3-C4. Since the input voltage Vin = 800V is slightly less than the intermediate voltage Vmid = 900V, the current on the chopping inductor L102 falls slowly with time. In the period of t12-t13, the buck switch tube V2 is turned on and the buck switch tube V1 is turned off, the divided voltage capacitor C1 is disconnected by the buck switch tube V1, the divided voltage Vin / 2 on the divided voltage capacitor C2 is connected to the two ends of the filter capacitors C3-C4 through the freewheeling diode D1, and the current on the chopping inductor L102 falls rapidly with time again. Due to the existence of the chopping inductor L102, the current flowing into the filter capacitors C3-C4 cannot be abrupt, and the intermediate voltage Vmid across the filter capacitors C3-C4 will adapt to the duty ratios d1 = d2 = 0.9 of the buck switch tubes V1-V2 and the duty ratio d9 = d fix = 0.2, respectively achieving the effect of boost output and the effect of buck output, thereby maintaining the voltage level of 1.125Vin.

[0088] By using the fluctuation range of the input voltage Vin under the daily working condition of the train as the transition voltage width AV to set the first voltage threshold and the second voltage threshold, and by using the above-mentioned boost-buck mode when the output voltage Vin is between the first voltage threshold and the second voltage threshold, the present application can ensure that the train uniformly uses the boost-buck mode for three-level chopping under the daily normal working condition. By using the above-mentioned boost-buck mode, even if the input voltage Vin fluctuates near the intermediate voltage Vmid, the present application can provide a good transition between the boost mode and the buck mode, thereby avoiding frequent switching of the working mode. In addition, as Figure 5CAs shown, when the three-level chopper unit 20 is used for step-up / down output, the inductor current ripple is controlled to be less than 20%, and the system has good steady-state performance.

[0089] Those skilled in the art can understand that the above method of first determining the fixed duty cycle d fix The duty cycle d9 of the step-up switch tube V9 is determined, and then the target intermediate voltage Vmid, the input voltage Vin and the fixed duty cycle d fix The scheme of determining the duty cycles d1-d2 of the two step-down switch tubes is only a non-limiting embodiment of the present application, which aims to demonstrate the main concept of the present application and provide a specific scheme for the public to implement, rather than to limit the protection scope of the present application. Alternatively, in other embodiments, the processor can also first determine the fixed duty cycle d fix The duty cycles d1-d2 of the two step-down switch tubes are determined, and then the target intermediate voltage Vmid, the input voltage Vin and the fixed duty cycle d fix The duty cycle d9 of the step-up switch tube V9 is determined, thereby achieving the same technical effect in the present application.

[0090] Those skilled in the art can also understand that although the above embodiment describes the processor as an element of the three-level chopper unit 20, this does not mean that the processor must be arranged in the three-level chopper unit 20 or must be used alone by the three-level chopper unit 20. Alternatively, in other embodiments, the processor can also be a processing unit of an auxiliary converter or a control system of a train, and can be arranged in an auxiliary converter or a device compartment of a train.

[0091] Although the above methods are illustrated and described as a series of actions for the sake of simplicity of explanation, it should be understood and appreciated that these methods are not limited by the order of actions, because according to one or more embodiments, some actions can occur in different orders and / or concurrently with other actions illustrated and described herein or not illustrated and described herein but can be understood by those skilled in the art.

[0092] According to another aspect of the present application, a train auxiliary converter is also provided herein.

[0093] Please refer to Figure 6 , Figure 6 The architecture schematic diagram of the train auxiliary converter provided according to some embodiments of the present application is shown.

[0094] As Figure 6 shown, the above train auxiliary converter provided by the present application can include the three-level chopper unit 61, the isolation transformer unit 62 and the inverter unit 63 provided by any one of the above embodiments.

[0095] The aforementioned isolation transformer unit 62 can be a high-frequency isolation transformer circuit with LLC series resonance. The input terminal of the isolation transformer unit 62 is connected to the output terminal of the three-level chopper unit 61, which is suitable for converting the DC900V voltage output by the three-level chopper unit 61 into a DC700V DC voltage.

[0096] The inverter unit 63 mentioned above can be a three-phase half-bridge inverter circuit. Its input terminal can be connected to the output terminal of the isolation transformer unit 62, which is suitable for converting the DC700V DC voltage output by the isolation transformer unit 62 into three AC380V AC voltages, thereby realizing the AC output of the auxiliary converter at the three output terminals U, V, and W.

[0097] like Figure 6 As shown, in some embodiments, the auxiliary converter may further include a charger unit 64. This charger unit 64 may be an isolated half-bridge DC / DC circuit, suitable for connecting to the output of the three-level chopper unit 61 to obtain its intermediate output voltage Vmid. In some embodiments, the three-level chopper unit 61 may include two series-connected filter capacitors C3 to C4, where C3 = C4 = 600μF. The charger unit 64 can utilize the isolated half-bridge DC / DC circuit to draw power from the middle of the two filter capacitors C3 to C4 to obtain a ±DC450V DC voltage, and convert it to a DC110V or DC24V DC voltage to achieve the DC output of the auxiliary converter.

[0098] Thanks to the use of the three-level chopper unit 61 provided by this invention, the auxiliary converter can meet the application requirements of a wide input range of DC500V to DC1800V. Furthermore, compared to traditional train high-frequency auxiliary converters, the auxiliary converter provided by this invention has higher energy efficiency and a smaller size and lighter weight.

[0099] According to another aspect of the invention, a computer-readable storage medium is also provided herein.

[0100] The computer-readable storage medium provided by this invention stores computer instructions thereon. When these computer instructions are executed by a processor, the control method of the three-level chopper unit provided in any of the above embodiments can be implemented, and the corresponding transformation mode can be determined according to the value of the input voltage Vin, thereby meeting the application requirements of a wide range of inputs, improving the efficiency of the converter, and reducing the size and weight of the converter.

[0101] While the processor described in the above embodiments is implemented by a combination of software and hardware to control the method, it is understood that the processor can be implemented in software or hardware alone. For hardware implementation, the processor can be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DAPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described above, or a combination of the above. For software implementation, the processor can be implemented by separate software modules such as procedures and functions, which perform one or more of the functions and operations described herein, running on a general purpose chip.

[0102] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-level chopper cell of a train auxiliary converter, characterized by, The three-level chopping unit comprises a voltage dividing capacitor C1, a voltage dividing capacitor C2, a step-down switch V1, a step-down switch V2, a freewheeling diode D1, a freewheeling diode D2, a chopping inductor L 102 , a filter capacitor C3, a filter capacitor C4, a step-up switch V9, an anti-reverse diode D9, and a processor, wherein one end of the voltage dividing capacitor C1 is connected to a high-voltage end of an input end of the three-level chopping unit and a collector of the step-down switch V1, a first end of the voltage dividing capacitor C2 is connected to a low-voltage end of the three-level chopping unit and an emitter of the step-down switch V2, the emitter of the step-down switch V1 is connected to a negative electrode of the freewheeling diode D1, a collector of the step-down switch V2 is connected to a positive electrode of the freewheeling diode D2, a second end of the voltage dividing capacitor C1, a second end of the voltage dividing capacitor C2, a positive electrode of the freewheeling diode D1, and a negative electrode of the freewheeling diode D2 are connected, the negative electrode of the freewheeling diode D1 is further connected to a first end of the chopping inductor L 102 , a second end of the chopping inductor L 102 is connected to a positive electrode of the anti-reverse diode D9 and a collector of the step-up switch V9, a negative electrode of the anti-reverse diode D9 is connected to a high-voltage end of a series branch of the filter capacitor C3 and the filter capacitor C4, an emitter of the step-up switch V9 is connected to a low-voltage end of the series branch of the filter capacitor C3 and the filter capacitor C4, the processor is communicatively connected to the step-down switch V1, the step-down switch V2, and the step-up switch V9, and is configured to: detecting an input voltage of the auxiliary converter; determining a working mode of the three-level chopper unit according to the input voltage and a preset target intermediate voltage, wherein the working mode at least includes a buck-boost mode; determining a first voltage threshold and a second voltage threshold according to the target intermediate voltage and a preset transition voltage width, wherein the first voltage threshold is a sum of the target intermediate voltage and the transition voltage width, the second voltage threshold is a difference between the target intermediate voltage and the transition voltage width, and the transition voltage width indicates a fluctuation range of the input voltage in a normal working condition; determining the working mode of the three-level chopper unit as the buck-boost mode in response to the input voltage being between the first voltage threshold and the second voltage threshold, and determining duty cycles of the buck switch tubes V1 and V2 according to the target intermediate voltage, the input voltage and a fixed duty cycle of the boost switch tube V9; and controlling the boost switch tube V9 to be turned on according to the fixed duty cycle, and controlling the buck switch tubes V1 and V2 to be turned on in opposite phases according to the determined duty cycles, so as to control the buck switch tubes V1 and V2 and the boost switch tube V9 to cooperatively realize buck-boost output.

2. The three-level chopper cell of claim 1, wherein, an output end of the three-level chopper unit is connected to an isolation transformer unit of the auxiliary converter, and is adapted to supply power to an inverter unit of the auxiliary converter through the isolation transformer unit, so as to realize AC output of the auxiliary converter, and / or an output end of the three-level chopper unit is connected to a charger unit of the auxiliary converter, and is adapted to realize DC output of the auxiliary converter through the charger unit.

3. The three-level chopper cell of claim 1, wherein, The working mode further includes a buck mode and a boost mode, and the processor is further configured to: determine the working mode of the three-level chopper unit as the buck mode in response to the input voltage being higher than the first voltage threshold, and control the buck switch tubes V1 and V2 to realize buck output; and determine the working mode of the three-level chopper unit as the boost mode in response to the input voltage being lower than the second voltage threshold, and control the boost switch tube V9 to realize boost output.

4. The three-level chopper cell of claim 3, wherein, The processor is further configured to: determine a duty cycle of the boost switch tube V9 according to the target intermediate voltage and the input voltage in the boost mode; and control the boost switch tube V9 to be turned on according to the duty cycle, so as to realize the boost output. The processor is further configured to:

5. The three-level chopper cell of claim 3, wherein, determine duty cycles of the two buck switch tubes V1 and V2 according to a ratio of the target intermediate voltage to the input voltage in the buck mode; and control the two buck switch tubes V1 and V2 to be turned on in opposite phases by 180° according to the duty cycles, so as to realize the buck output. The target intermediate voltage is not lower than 1 / 2 of an upper limit of the input voltage, and is not higher than 2 times of a lower limit of the input voltage.

6. The three-level chopper cell of claim 5, wherein, detecting an input voltage of the auxiliary converter; 7. A control method of a three-level chopper unit, characterized by, The three-level chopping unit comprises a voltage division capacitor C1, a voltage division capacitor C2, a voltage reduction switch tube V1, a voltage reduction switch tube V2, a freewheeling diode D1, a freewheeling diode D2, a chopping inductor L 102 , a filter capacitor C3, a filter capacitor C4, a voltage increase switch tube V9, an anti-reverse diode D9 and a processor, and the control method comprises the following steps: ​ According to the input voltage and a preset target intermediate voltage, a working mode of the three-level chopping unit is determined, wherein one end of the voltage dividing capacitor C1 is connected to a high voltage end of an input end of the three-level chopping unit and a collector of the step-down switch tube V1, a first end of the voltage dividing capacitor C2 is connected to a low voltage end of the three-level chopping unit and an emitter of the step-down switch tube V2, the emitter of the step-down switch tube V1 is connected to a negative electrode of the freewheeling diode D1, a collector of the step-down switch tube V2 is connected to a positive electrode of the freewheeling diode D2, a second end of the voltage dividing capacitor C1, a second end of the voltage dividing capacitor C2, a positive electrode of the freewheeling diode D1 and a negative electrode of the freewheeling diode D2 are connected, and a negative electrode of the freewheeling diode D1 is further connected to a first end of the chopping inductor L 102 A second end of the chopping inductor L 102 is connected to a positive electrode of the anti-reverse diode D9 and a collector of the step-up switch tube V9, a negative electrode of the anti-reverse diode D9 is connected to a high voltage end of a series branch of the filter capacitor C3 and the filter capacitor C4, an emitter of the step-up switch tube V9 is connected to a low voltage end of the series branch of the filter capacitor C3 and the filter capacitor C4, and the working mode at least includes a step-up and step-down mode. determining a first voltage threshold and a second voltage threshold according to the target intermediate voltage and a preset transition voltage width, wherein the first voltage threshold is a sum of the target intermediate voltage and the transition voltage width, and the second voltage threshold is a difference between the target intermediate voltage and the transition voltage width, and the transition voltage width indicates a fluctuation range of the input voltage in a normal working condition; determining a working mode of the three-level chopper unit as the boost-buck mode in response to the input voltage being between the first voltage threshold and the second voltage threshold, and determining duty cycles of the buck switch tubes V1 and V2 according to the target intermediate voltage, the input voltage and a fixed duty cycle of the boost switch tube V9; and controlling the boost switch tube V9 to be turned on according to the fixed duty cycle, and controlling the buck switch tubes V1 and V2 to be turned on in opposite phase according to the determined duty cycles, so as to control the buck switch tubes V1 and V2 and the boost switch tube V9 to cooperate to realize the boost-buck output.

8. The control method according to claim 7, characterized by, The working mode further comprises a buck mode and a boost mode, and the control method further comprises the following steps: In response to the input voltage being higher than the first voltage threshold, determining the working mode of the three-level chopper unit to be the step-down mode, controlling the step-up switch V9 to be always off, and controlling the step-down switches V1 and V2 to cooperate with the voltage division capacitors C1 and C2, the freewheeling diodes D1 and D2, the chopper inductor L 102 and the filter capacitors C3 and C4 to achieve step-down output; and In response to the input voltage being lower than the second voltage threshold, it is determined that the working mode of the three-level chopper unit is the boost mode, the buck switch V1 and V2 are controlled to be always on, and the boost switch V9 is controlled to cooperate with the voltage division capacitor C1 and C2, the chopper inductor L 102 , the anti-reverse diode D9 and the filter capacitor C3 and C4 to realize boost output.

9. The control method according to claim 8, characterized by, The step of realizing the boost output further comprises: in the boost mode, determining a duty cycle of the boost switch tube V9 according to the target intermediate voltage and the input voltage; and controlling the boost switch tube V9 to be turned on according to the duty cycle, so as to realize the boost output.

10. The control method according to claim 8, characterized by, The step of realizing the buck output further comprises: in the buck mode, determining duty cycles of the buck switch tubes V1 and V2 according to a ratio of the target intermediate voltage to the input voltage; and controlling the buck switch tubes V1 and V2 to be turned on in opposite phase by 180° according to the duty cycles, so as to realize the buck output.

11. The control method according to claim 10, characterized by, The control method further comprises the following steps: setting the target intermediate voltage to be not lower than 1 / 2 of an upper limit of the input voltage and not higher than 2 times of a lower limit of the input voltage.

12. The control method according to claim 11, characterized by The control method further comprises the following steps: taking a sum of the target intermediate voltage and a preset transition voltage width as the first voltage threshold, and taking a difference between the target intermediate voltage and the transition voltage width as the second voltage threshold, and the transition voltage width indicates a fluctuation range of the input voltage in a normal working condition. The control method comprises:

13. An auxiliary converter for a train, characterized by a three-level chopper unit as claimed in any one of claims 1-6; an isolation transformer unit connected to an output end of the three-level chopper unit; and an inverter unit connected to an output end of the isolation transformer unit and adapted to realize an alternating current output of the auxiliary inverter under power supply of the isolation transformer unit. The control method further comprises:

14. The auxiliary converter of claim 13, wherein, a charging machine unit connected to the output end of the three-level chopper unit and adapted to realize a direct current output of the auxiliary inverter under power supply of the three-level chopper unit. The computer instructions are executed by the processor to implement the control method as claimed in any one of claims 8-12.

15. A computer readable storage medium having stored thereon computer instructions, wherein, ​

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