Bidirectional traction converter, method of controlling its output and power supply system for a metro train

Abstract

The application provides a bidirectional traction converter, a method for controlling the output of the bidirectional traction converter and a power supply system of a city rail train. The bidirectional traction converter comprises a first capacitor, a second capacitor and a three-phase bridge arm unit. The positive electrode of the first capacitor is connected with the first terminal of each phase bridge arm unit to serve as the positive electrode of a DC bus. The third terminal of each phase bridge arm unit is a three-phase AC bus. The fourth terminal of each phase bridge arm unit is connected with the positive electrode of the second capacitor. The negative electrode of the second capacitor is connected with the fifth terminal of each phase bridge arm unit to serve as the negative electrode of the DC bus. A control unit is used for controlling the switching tube of each phase bridge arm unit to switch between different switching states corresponding to different DC output levels and different AC output levels, so that the bidirectional traction converter has different DC side outputs and different AC side outputs, is suitable for working with a diode rectifier and other step-down rectification topologies in a common winding, and does not increase the cost of additional equipment and land occupation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of urban rail train technology, in particular to a bidirectional traction converter, a method for controlling output of the bidirectional traction converter and an urban rail train power supply system. BACKGROUND

[0002] At present, the bidirectional traction converter used in urban rail transit is usually a two-level or three-level converter. Since the rectification peak power is usually significantly higher than the inversion peak power in urban rail transit occasions, a diode rectifier with higher power is usually required to be set to meet the demand of rectification peak power. However, the AC voltage level of the diode rectifier does not match the AC voltage level of the bidirectional traction converter, for example, for a 1500V DC voltage level, the diode rectifier usually selects an AC voltage of about 1180V, while the bidirectional traction converter usually selects an AC voltage of about 950V at most. The difference between the AC voltages of the two converters makes the two converters not suitable for being connected to the same winding of the traction transformer for use, and thus independent transformers need to be set for the two converters, thereby increasing the additional equipment cost and equipment footprint. SUMMARY

[0003] The present application aims to at least solve one of the technical problems existing in the prior art.

[0004] To this end, one object of the present application is to provide a bidirectional traction converter, which can work under the condition that the DC side voltage is lower than the peak value of the AC side voltage, thereby being suitable for co-winding work with a diode rectifier and other step-down rectification topologies, without increasing additional equipment cost and footprint.

[0005] A second object of the present application is to provide a method for controlling output of the bidirectional traction converter.

[0006] A third object of the present application is to provide an urban rail train power supply system.

[0007] In order to achieve the above objects, a first aspect of the present application provides a bidirectional traction converter, comprising: a first capacitor, a second capacitor and a three-phase bridge arm unit.

[0008] The positive electrode of the first capacitor is connected to the first terminal of each phase bridge arm unit as a DC bus positive electrode, the second terminal of each phase bridge arm unit is connected to the negative electrode of the first capacitor after connection, the third terminal of each phase bridge arm unit is a three-phase AC bus respectively, the fourth terminal of each phase bridge arm unit is connected to the positive electrode of the second capacitor after connection, and the negative electrode of the second capacitor is connected to the fifth terminal of each phase bridge arm unit as a DC bus negative electrode.

[0009] The each-phase bridge arm unit comprises a plurality of switch tubes, and the each-phase bridge arm unit can output different direct current output levels and different alternating current output levels according to switch states of the plurality of switch tubes.

[0010] The control unit is connected with the each-phase bridge arm unit, and is configured to control the switch tubes of the each-phase bridge arm unit to switch between the switch states corresponding to the different direct current output levels and the different alternating current output levels according to the received upper-layer control signal, so that the bidirectional traction converter has different direct current side outputs and different alternating current side outputs.

[0011] The bidirectional traction converter provided in the embodiment of the present application has a novel structure, and is based on a novel structure in which a first capacitor, a second capacitor and three-phase bridge arm units are connected. A control unit controls on / off of switch tubes of each-phase bridge arm units, so that each-phase bridge arm units can output different direct current output levels and different alternating current output levels, and the bidirectional traction converter has different direct current side outputs and different alternating current side outputs. Therefore, the bidirectional traction converter can independently control direct current side outputs and alternating current side outputs, and the instantaneous value of the output alternating current voltage can be greater than or equal to the output direct current voltage. That is, the bidirectional traction converter can still work normally when the peak value of the alternating current side voltage is higher than the direct current side voltage, and the alternating current side output voltage is not limited by the direct current side voltage. Therefore, the alternating current voltage grade of the bidirectional traction converter can be matched with the alternating current voltage grade of a step-down converter such as a diode converter, the difference between the alternating current voltages of the two can be reduced, the same alternating current side voltage can be selected according to the requirement of the diode converter on the alternating current side voltage, the requirement of co-winding operation with the diode converter can be met, and there is no need to separately arrange independent transformers to condition the voltages of the two, so that the additional equipment cost and land occupation are not increased.

[0012] In some embodiments, the control unit is further configured to control time ratios of different direct current output levels and time ratios of different alternating current output levels respectively, so that the bidirectional traction converter has different direct current side outputs and different alternating current side outputs.

[0013] In some embodiments, each-phase bridge arm unit comprises:

[0014] The first switch tube has a first end as a first terminal of the bridge arm unit, a second end connected with a first end of the second switch tube, and a control end connected with the control unit; and the second switch tube has a second end as a second terminal of the bridge arm unit and a control end connected with the control unit.

[0015] The first inductor has a first end connected with the second end of the first switch tube and the first end of the second switch tube respectively.

[0016] The second end of the third switch tube is connected with the second end of the first inductor, the second end of the third switch tube is connected with the first end of the fifth switch tube, the control end of the third switch tube is connected with the control unit, the first end of the fourth switch tube is connected with the second end of the first inductor, the second end of the fourth switch tube is connected with the second end of the eighth switch tube and the second end of the sixth switch tube respectively, the control end of the fourth switch tube is connected with the control unit, the first end of the fifth switch tube is connected with the first end of the third switch tube, the second end of the fifth switch tube is connected with the second end of the sixth switch tube, and the first common end is taken as the third terminal of the bridge arm unit, the first end of the seventh switch tube is connected with the second end of the third switch tube and the first end of the fifth switch tube respectively, the second end of the seventh switch tube is connected with the first end of the eighth switch tube, the control end of the seventh switch tube is connected with the control unit, and the control end of the eighth switch tube is connected with the control unit.

[0017] The second end of the second inductor is connected with the second end of the seventh switch tube and the first end of the eighth switch tube respectively.

[0018] The first end of the ninth switch tube is taken as the fourth terminal of the bridge arm unit, the second end of the ninth switch tube is connected with the first end of the second inductor, the control end of the ninth switch tube is connected with the control unit, the first end of the tenth switch tube is connected with the second end of the ninth switch tube and the first end of the second inductor respectively, the second end of the tenth switch tube is taken as the fifth terminal of the bridge arm unit, and the control end of the tenth switch tube is connected with the control unit.

[0019] The positive electrode of the third capacitor is connected with the first end of the third switch tube and the first end of the fifth switch tube respectively, and the negative electrode of the third capacitor is connected with the second end of the fourth switch tube, the second end of the eighth switch tube and the second end of the sixth switch tube respectively.

[0020] In some embodiments, the direct-current output level includes E and 2E, and the alternating-current output level includes -E, 0 and E; wherein E is the average voltage value of the first capacitor, the second capacitor and the third capacitor.

[0021] In some embodiments, the value of E satisfies the following formula:

[0022] E < Udc < 2E, E > sqrt(2) * Uac / 2, (1+m)E > Udc / 2 + sqrt(2) * Uac / 2.

[0023] Wherein, Udc is the target direct current voltage, Uac is the target alternating current voltage, and m is the modulation ratio.

[0024] In some embodiments, the control unit is configured to obtain, according to the upper-layer control signal, switching states of the switching tubes of each phase bridge arm unit corresponding to different direct current output levels and different alternating current output levels from a switching state table.

[0025] In some embodiments, the switching state table comprises the following table of closed switching tubes corresponding to each of the direct current output levels and each of the alternating current output levels.

[0026]

[0027] Wherein, S1 is the first switching tube, S2 is the second switching tube, S3 is the third switching tube, S4 is the fourth switching tube, S5 is the fifth switching tube, S6 is the sixth switching tube, S7 is the seventh switching tube, S8 is the eighth switching tube, S9 is the ninth switching tube, and S10 is the tenth switching tube.

[0028] In some embodiments, the first capacitor and the second capacitor are clamping capacitors.

[0029] To achieve the above-mentioned purpose, the method for controlling the output of the bidirectional traction converter according to the second aspect of the present application is used for the bidirectional traction converter, and the method comprises: receiving an upper-layer control signal; and controlling the switching tubes of each phase bridge arm unit to switch between switching states corresponding to different direct current output levels and different alternating current output levels according to the upper-layer control signal.

[0030] According to the method for controlling the output of the bidirectional traction converter, the switching tubes of each phase bridge arm unit are controlled to be turned on or turned off based on the bidirectional traction converter with the novel structure of the above embodiments, so that each phase bridge arm unit can output different direct current output levels and different alternating current output levels, and the bidirectional traction converter has different direct current side outputs and different alternating current side outputs, thereby the direct current side output and the alternating current side output can be independently controlled, the instantaneous value of the output alternating current voltage can be greater than or equal to the output direct current voltage, and the bidirectional traction converter can still work normally when the peak value of the alternating current side voltage is higher than that of the direct current side voltage, thereby the alternating current voltage grade of the bidirectional traction converter can be matched, the difference between the alternating current voltages of the two can be reduced, the same alternating current side voltage can be selected according to the requirement of the diode converter on the alternating current side voltage, and the bidirectional traction converter can be operated in the same winding without the need of setting an independent transformer, thereby the additional equipment cost and land occupation can be reduced.

[0031] In some embodiments, the method further comprises:

[0032] The time ratio of different direct current output levels and the time ratio of different alternating current output levels are controlled respectively, so that the bidirectional traction converter has different direct current side outputs and different alternating current side outputs.

[0033] To achieve the above object, the third aspect of the present application provides a power supply system for a city train, comprising: a traction transformer; a bidirectional traction converter, whose positive and negative direct current buses are connected to the positive and negative poles of a catenary respectively, and whose three-phase alternating current buses are connected to the three-phase windings of the traction transformer; and a rectifier, which is connected to the same winding of the traction transformer as the bidirectional traction converter.

[0034] According to the power supply system for a city train of the present application, the bidirectional traction converter of the above embodiment is used, which can work under the condition that the direct current side voltage is lower than the peak value of the alternating current side voltage, so that the alternating current voltage level of the rectifier can be matched, and the rectifier such as a diode rectifier, a thyristor rectifier and other step-down rectifier topologies can work in the same winding, so that the equipment cost and equipment footprint are not increased.

[0035] Additional aspects and advantages of the present application will be described in the following description and part will become apparent from the following description or will be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0036] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0037] Figure 1 is a schematic diagram of a three-level bidirectional converter in the related art;

[0038] Figure 2 is a schematic diagram of a mixed use mode of a bidirectional converter and a diode rectifier in the related art;

[0039] Figure 3 is a schematic diagram of a bidirectional traction converter according to an embodiment of the present application;

[0040] Figure 4 is a circuit schematic diagram of each phase bridge arm unit according to an embodiment of the present application. DETAILED DESCRIPTION

[0041] The embodiments of the present application are described in detail below, and the embodiments described with reference to the accompanying drawings are exemplary, and the embodiments of the present application are described in detail below.

[0042] Figure 1 is a schematic diagram of a three-level converter structure in the related art, Figure 2As a schematic diagram of a mixed use mode of a bidirectional converter and a diode rectifier in the related art, in the related art, due to different AC voltage level requirements of the three-level converter and the diode rectifier, an independent transformer needs to be provided, thereby increasing additional equipment cost and equipment occupation.

[0043] The embodiment of the present application proposes a brand-new bidirectional traction converter structure, which can work under the condition that the DC side voltage is lower than the peak value of the AC side voltage, thereby being applicable to co-winding work with a diode rectifier and other step-down rectifier topologies, without increasing additional equipment cost and occupation.

[0044] Reference will be made below to Figure 3 and Figure 4 a bidirectional traction converter according to the first aspect of the present application.

[0045] Figure 3 is a schematic diagram of a bidirectional traction converter according to an embodiment of the present application, as Figure 3 shown, the bidirectional traction converter 10 includes a first capacitor C+, a second capacitor C-, a control unit (not shown in the figure) and three-phase bridge arm units such as LA, LB and LC in the figure.

[0046] Among them, the positive electrode of the first capacitor C+ is connected with the first terminal T1 of each phase bridge arm unit as the positive electrode DC+ of the DC bus, the second terminal T2 of each phase bridge arm unit is connected with the negative electrode of the first capacitor C+ after connection, the third terminal T3 of each phase bridge arm unit is respectively three-phase AC bus such as ACU, ACV and ACW, the fourth terminal T4 of each phase bridge arm unit is connected with the positive electrode of the second capacitor C- after connection, and the negative electrode of the second capacitor C- is connected with the fifth terminal T5 of each phase bridge arm unit as the negative electrode DC- of the DC bus.

[0047] When the urban rail transit power supply system works, the upper controller will send an upper control signal to the bidirectional traction converter 10 according to the operation condition, and make the bidirectional traction converter 10 output stably in the target voltage range by adjusting, for example, D-Q modulation.

[0048] Each phase bridge arm unit includes a plurality of switching tubes, and each phase bridge arm unit can output different DC output levels and different AC output levels according to the switching states of the plurality of switching tubes;

[0049] The control unit is connected with each phase bridge arm unit, used for receiving the upper control signal, and controlling the switching tubes of each phase bridge arm unit to switch between the switching states corresponding to different DC output levels and different AC output levels according to the upper control signal, so that the bidirectional traction converter has different DC side outputs and different AC side outputs.

[0050] The bidirectional traction converter 10 of the embodiment of the application proposes a brand-new structure, based on a brand-new structure of connection of the first capacitor C+, the second capacitor C- and the three-phase bridge arm unit, the control unit controls the on or off of the switch tube of each phase bridge arm unit, so that the output of each phase bridge arm unit can output different DC output levels and different AC output levels, so that the bidirectional traction converter has different DC side outputs and different AC side outputs, so that the bidirectional traction converter can independently control the DC side output and the AC side output, so that the instantaneous value of the output AC voltage can be greater than or equal to the DC side output voltage, that is, when the AC side voltage peak is higher than the DC side voltage, it can still work normally, so that the AC voltage level of the bidirectional traction converter can be matched with the AC voltage level of the diode converter, the difference between the AC voltages of the two can be reduced, the same AC side voltage can be selected according to the requirement of the diode converter on the AC side voltage, and the bidirectional traction converter is suitable for common winding operation with the diode converter, without the need to set an independent transformer, without increasing the cost of additional equipment and land occupation.

[0051] In the embodiment, the control unit is further configured to control the time ratio of different DC output levels and the time ratio of different AC output levels respectively, so that the bidirectional traction converter has different DC side outputs and different AC side outputs.

[0052] Further, in the embodiment, as shown in Figure 4 each phase bridge arm unit includes a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, a fifth switch tube S5, a sixth switch tube S6, a seventh switch tube S7, an eighth switch tube S8, a ninth switch tube S9 and a tenth switch tube S10, a first inductor Lu, a second inductor L1 and a third capacitor C.

[0053] The first end of the first switch tube S1 is used as the first terminal T1 of the bridge arm unit, the second end of the first switch tube S1 is connected with the first end of the second switch tube S2, the second end of the second switch tube S2 is used as the second terminal T2 of the bridge arm unit, the control end of the first switch tube S1 is connected with the control unit, and the control end of the second switch tube S2 is connected with the control unit.

[0054] The first end of the first inductor Lu is connected with the second end of the first switch tube S1 and the first end of the second switch tube S2 respectively.

[0055] The second end of the third switch tube S3 is connected with the second end of the first inductor Lu, the second end of the third switch tube S3 is connected with the first end of the fifth switch tube S5, the control end of the third switch tube S3 is connected with the control unit, the first end of the fourth switch tube S4 is connected with the second end of the first inductor Lu, the second end of the fourth switch tube S4 is connected with the second end of the eighth switch tube S8 and the second end of the sixth switch tube S6 respectively, the control end of the fourth switch tube S4 is connected with the control unit, the first end of the fifth switch tube S5 is connected with the first end of the third switch tube S3, the second end of the fifth switch tube S5 is connected with the first common end of the first end of the sixth switch tube S6 as the third terminal T3 of the bridge arm unit, the first end of the seventh switch tube S7 is connected with the first end of the third switch tube S3 and the first end of the fifth switch tube S5 respectively, the second end of the seventh switch tube S7 is connected with the first end of the eighth switch tube S8, the control end of the seventh switch tube S7 is connected with the control unit, and the control end of the eighth switch tube S8 is connected with the control unit.

[0056] The second end of the second inductor L1 is connected with the second end of the seventh switch tube S7 and the first end of the eighth switch tube S8 respectively.

[0057] The first end of the ninth switch tube S9 is the fourth terminal T4 of the bridge arm unit, the second end of the ninth switch tube S9 is connected with the first end of the second inductor L1, the control end of the ninth switch tube S9 is connected with the control unit, the first end of the tenth switch tube S10 is connected with the second end of the ninth switch tube S9 and the first end of the second inductor L1 respectively, the second end of the tenth switch tube S10 is the fifth terminal T5 of the bridge arm unit, and the control end of the tenth switch tube S10 is connected with the control unit.

[0058] The positive electrode of the third capacitor C is connected with the first end of the third switch tube S3 and the first end of the fifth switch tube S5 respectively, and the negative electrode of the third capacitor C is connected with the second end of the fourth switch tube S4, the second end of the eighth switch tube S8 and the second end of the sixth switch tube S6 respectively.

[0059] The embodiment of the present application proposes Figure 4 The novel bridge arm unit structure shown in the figure, the control unit controls the on or off of the switch tube of each phase bridge arm unit, so that the output of each phase bridge arm unit can output different direct current output levels and different alternating current output levels, so that the bidirectional traction converter has different direct current side outputs and different alternating current side outputs, the alternating current side output voltage of the bidirectional traction converter 10 is not limited by the direct current side voltage, can match the alternating current side voltage demand of the diode converter, is suitable for working with the diode converter in a common winding, and does not need to independently set a transformer.

[0060] In some embodiments, the DC output level of each phase bridge arm unit of the bidirectional traction converter includes E and 2E, and the AC output level includes -E, 0 and E, i.e. the control unit controls the switching of the switching tubes in each phase bridge arm unit to switch states corresponding to E and 2E and switch states corresponding to -E, 0 and E, so as to obtain a target DC side output voltage and a target AC side output voltage, and wherein the instantaneous value of the target AC side output voltage can be higher than the target DC side output voltage, so as to match the AC voltage level of the diode converter and realize the common winding operation of the two. Wherein E is the average voltage value of the first capacitor C+, the second capacitor C- and the third capacitor C.

[0061] Specifically, during normal operation, the voltages of the first capacitor C+, the second capacitor C- and the third capacitor C of each phase bridge arm unit of the bidirectional traction converter 10 are close to each other, and the average value is E. By selecting the closed switching tubes, the output voltage (output DC voltage) between the T1 and T5 terminals of each phase bridge arm unit can be switched between E and 2E, and the voltage (output AC voltage) between the T3 terminal and the DC side midpoint can be switched between E, 0 and -E.

[0062] In some embodiments, for Figure 4 For the structure of each phase bridge arm unit shown in the figure, the value of E can satisfy the following formula:

[0063] E < Udc < 2E, E > sqrt(2) * Uac / 2, (1+m)E > Udc / 2 + sqrt(2) * Uac / 2;

[0064] Wherein Udc is the target DC side output voltage, Uac is the target AC side output voltage, and m is the modulation ratio.

[0065] By selecting a suitable voltage E, the proposed bidirectional traction converter 10 can operate under an AC voltage suitable for a diode rectifier, and effectively control the AC current and DC current.

[0066] In an embodiment, the control unit is configured to obtain, according to an upper control signal, the switching states of the switching tubes of each phase bridge arm unit corresponding to different DC output levels and different AC output levels from a switching state table. The switching state table includes the closed switching tubes corresponding to each DC output level and each AC output level as shown in Table 1.

[0067] Since for any combination of AC output level and DC output level, at least two switching states can be realized, by switching between different switching states, the DC voltage output and the AC voltage output of the bidirectional traction converter can be independently adjusted within the range of E-2E and -E-E, respectively; and by selecting different switching states corresponding to a certain output voltage, the voltage balance between the capacitors can be realized.

[0068] Table 1

[0069]

[0070] Wherein, S1 is the first switch, S2 is the second switch, S3 is the third switch, S4 is the fourth switch, S5 is the fifth switch, S6 is the sixth switch, S7 is the seventh switch, S8 is the eighth switch, S9 is the ninth switch, and S10 is the tenth switch.

[0071] The following reference Figure 3 and Figure 4 For example, such as Figure 3 As shown, the DC+ and DC- of the bidirectional traction converter 10 are connected to the positive and negative terminals of the 1500V urban rail contact network, respectively, and ACU, ACV and ACW are connected to the 1180V three-phase windings of the traction transformer, respectively.

[0072] To ensure a modulation ratio below 0.9 when the DC voltage rises to 1700V (after third harmonic injection), a rated capacitor voltage E of 890V can be selected. Under this rated capacitor voltage, the target DC output voltage range is 890V to 1780V, the instantaneous target AC output voltage range is -890V to 890V, and the maximum effective value of the AC line voltage output is 1254V. This ensures that the maximum effective value of the AC side output voltage is 1254V. During the operation of the bidirectional traction converter 10, the DC side voltage can be controlled by adjusting the ratio of the time occupied by the 890V and 1780V output states. For example, for a switching frequency of 1500Hz and a DC side output voltage of 1500V, each phase bridge arm unit can sequentially output 890V for 210μs and 1780V for 457μs. After filtering by the first inductor Lu and the second inductor L1 in the bridge arm, a stable 1500V voltage can be obtained.

[0073] Similarly, by adjusting the proportion of time occupied by the switching states of -890V, 0V, and 890V on the AC side output, the AC side voltage can be controlled to meet the requirements for operation with the diode converter via a common winding. Furthermore, the active and reactive power at the AC port can be controlled through current control loops and power control loops. The current drawn from and injected into the bidirectional traction converter 10 by the urban rail train causes the capacitor voltage of the bidirectional traction converter 10 to decrease and increase, respectively. By controlling the active power at the AC port, the capacitor voltage of the converter can be kept constant around 890V. Thus, effective control of both the AC and DC sides is achieved.

[0074] In summary, the bidirectional traction converter 10 of the embodiment of the present application has its AC side output voltage not limited by the DC side output voltage, and thus can work under the condition that the DC side output voltage is lower than the peak value of the AC side output voltage, and thus is suitable for working in the same winding with a diode rectifier, a thyristor rectifier or other step-down rectifier topologies, without the need of setting an independent transformer, and without increasing the additional equipment cost and equipment footprint.

[0075] Based on the bidirectional traction converter of the above embodiment, the method for controlling the output of the bidirectional traction converter according to the second aspect of the present application is described below.

[0076] The method of the embodiment of the present application is used for the bidirectional traction converter of the above embodiment, and at least includes: receiving an upper control signal, controlling the switching of the switching tubes of each phase bridge arm unit between the switching states corresponding to the DC output levels according to the upper control signal, and controlling the switching of the switching tubes in each phase bridge arm unit between the switching states corresponding to the AC output levels.

[0077] The method for controlling the output of the bidirectional traction converter according to the embodiment of the present application is based on the bidirectional traction converter of the above embodiment with a brand-new structure, and controls the on or off of the switching tubes of each phase bridge arm unit, so that the instantaneous value of the output AC signal is greater than or equal to the target DC signal, and thus the AC voltage level of the step-down converter such as a diode converter can be matched, and the bidirectional traction converter can still work normally when the peak value of the AC side voltage is higher than the DC side voltage, and the same AC side voltage can be selected according to the requirement of the diode converter on the AC side voltage, so that the bidirectional traction converter can work in the same winding with the diode converter, without the need of setting an independent transformer, and without increasing the additional equipment cost and footprint.

[0078] By selecting a suitable voltage E, the proposed bidirectional traction converter can work at the AC voltage suitable for the diode rectifier, and the effective control of the AC current and the DC current can be realized.

[0079] In the embodiment, before controlling the switching of the switching tubes of each phase bridge arm unit, the method further includes: obtaining the switching states of the switching tubes of each phase bridge arm unit corresponding to each DC output level and the AC output level from a switching state table according to the upper control signal; and wherein the switching state table includes the closed switching tubes corresponding to each DC output level and each AC output level as shown in Table 1. As shown in Table 1, for any combination of the AC output voltage and the DC output voltage, at least two switching states can be realized, and thus the DC voltage output and the AC voltage output of the bidirectional traction converter can be independently adjusted in the range of E-2E and -E-E respectively by switching between different switching states; and by selecting different switching states corresponding to a certain output voltage, the balance of the voltage between the capacitors can be realized.

[0080] In an embodiment, the method further comprises controlling the time ratio of different DC output levels and the time ratio of different AC output levels respectively so that the bidirectional traction converter has different DC side outputs and different AC side outputs.

[0081] A power supply system of a metro train according to a third aspect of the present application is described as follows. The power supply system of the metro train according to the embodiment of the present application comprises a traction transformer, the bidirectional traction converter according to the above embodiment and a rectifier.

[0082] The positive pole and the negative pole of the DC bus of the bidirectional traction converter are connected to the positive pole and the negative pole of the catenary respectively, and the three-phase AC bus of the bidirectional traction converter is connected to the three-phase winding of the traction transformer respectively; the rectifier is connected to the same winding of the traction transformer as the bidirectional traction converter.

[0083] According to the power supply system of the metro train according to the embodiment of the present application, the bidirectional traction converter according to the above embodiment is adopted, which can work under the condition that the DC side voltage is lower than the peak value of the AC side voltage, so that the AC voltage level of the rectifier can be matched, and the rectifier such as the diode rectifier, the thyristor rectifier and the like voltage reduction rectifier topology can work in the same winding, so that the equipment cost and the equipment footprint are not increased.

[0084] In the description of the present specification, the description of the terms “one embodiment”, “some embodiments”, “exemplary embodiment”, “example”, “specific example” or “some examples” and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example.

[0085] Although the embodiments of the present application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. A bridge arm unit characterized by, Comprise: The first switch tube, the second switch tube, the first inductor, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube, the eighth switch tube, the second inductor, the ninth switch tube, the tenth switch tube and the third capacitor; Wherein, the second end of the first switch tube is connected with the first end of the second switch tube, the first end of the first inductor is connected with the second end of the first switch tube and the first end of the second switch tube respectively, the second end of the third switch tube is connected with the second end of the first inductor, the first end of the fourth switch tube is connected with the second end of the first inductor, the second end of the fourth switch tube is connected with the second end of the eighth switch tube and the second end of the sixth switch tube respectively, the first end of the fifth switch tube is connected with the first end of the third switch tube, the second end of the fifth switch tube is connected with the first end of the sixth switch tube as the first common end, the first end of the seventh switch tube is connected with the first end of the third switch tube and the first end of the fifth switch tube respectively, the second end of the seventh switch tube is connected with the first end of the eighth switch tube, the second end of the second inductor is connected with the second end of the seventh switch tube and the first end of the eighth switch tube respectively, the second end of the ninth switch tube is connected with the first end of the second inductor, the first end of the tenth switch tube is connected with the second end of the ninth switch tube and the first end of the second inductor respectively, the positive pole of the third capacitor is connected with the first end of the third switch tube and the first end of the fifth switch tube respectively, and the negative pole of the third capacitor is connected with the second end of the fourth switch tube, the second end of the eighth switch tube and the second end of the sixth switch tube respectively.

2. A bidirectional traction converter, characterized in that Comprise: The three-phase bridge arm unit, each phase bridge arm unit of the three-phase bridge arm unit is the bridge arm unit of claim 1, in each phase bridge arm unit, the first end of the first switch tube as the first terminal of the bridge arm unit, the second end of the second switch tube as the second terminal of the bridge arm unit, the first common end of the second end of the fifth switch tube and the first end of the sixth switch tube as the third terminal of the bridge arm unit, the first end of the ninth switch tube as the fourth terminal of the bridge arm unit, the second end of the tenth switch tube as the fifth terminal of the bridge arm unit; The first capacitor and the second capacitor, the positive pole of the first capacitor is connected with the first terminal of each phase bridge arm unit as the positive pole of the direct current bus, the second terminal of each phase bridge arm unit is connected after being connected with the negative pole of the first capacitor, the third terminal of each phase bridge arm unit is three-phase alternating current bus respectively, the fourth terminal of each phase bridge arm unit is connected after being connected with the positive pole of the second capacitor, and the negative pole of the second capacitor is connected with the fifth terminal of each phase bridge arm unit as the negative pole of the direct current bus; The control unit is connected with the control end of the switch tube of each phase bridge arm unit, and is used for controlling the switch tube of each phase bridge arm unit to switch between the switching states corresponding to different direct current output levels and different alternating current output levels according to the received upper layer control signal, so that the bidirectional traction converter has different direct current side outputs and different alternating current side outputs.

3. The bidirectional traction converter of claim 2, wherein, The control unit is also used for controlling the time ratio of different direct current output levels and the time ratio of different alternating current output levels respectively, so that the bidirectional traction converter has different direct current side outputs and different alternating current side outputs. The control unit is also used for controlling the time ratio of different direct current output levels and the time ratio of different alternating current output levels respectively, so that the bidirectional traction converter has different direct current side outputs and different alternating current side outputs.

4. The bidirectional traction converter of claim 2, wherein, the DC output levels include E and 2E, and the AC output levels include -E, 0 and E; wherein E is an average voltage value of the first capacitor, the second capacitor and the third capacitor.

5. A bidirectional traction converter according to claim 4, characterized in that, the value of E satisfies the following formula: E < Udc < 2E, E > sqrt(2) * Uac / 2, (1+m)E > Udc / 2 + sqrt(2) * Uac / 2; wherein Udc is a target DC side output voltage, Uac is a target AC side output voltage, and m is a modulation ratio.

6. The bidirectional traction converter of claim 4, wherein, the control unit is configured to obtain, according to the upper control signal, a switch state of a switch tube of each phase bridge arm unit corresponding to different DC output levels and different AC output levels from a switch state table; wherein the switch tubes in a closed state corresponding to each of the DC output levels and each of the AC output levels are as follows: wherein S1 is a first switch tube, S2 is a second switch tube, S3 is a third switch tube, S4 is a fourth switch tube, S5 is a fifth switch tube, S6 is a sixth switch tube, S7 is a seventh switch tube, S8 is an eighth switch tube, S9 is a ninth switch tube, and S10 is a tenth switch tube.

7. The bidirectional traction converter of claim 2, wherein, The first capacitor and the second capacitor are clamping capacitors.

8. A method of controlling the output of a bidirectional traction converter, characterized by, The method for the bidirectional traction converter of any one of claims 2-7, the method comprising: receiving an upper control signal; controlling a switch tube of each phase bridge arm unit to switch between switch states corresponding to different DC output levels and different AC output levels according to the upper control signal.

9. The method of controlling a bidirectional traction converter output of claim 8, wherein, The method further comprises: controlling a time ratio of different DC output levels and a time ratio of different AC output levels respectively so that the bidirectional traction converter has different DC side outputs and different AC side outputs.

10. A power supply system for a city train, characterized in that, comprising: a traction transformer; The bidirectional traction converter of any one of claims 2-7, a positive DC bus and a negative DC bus of the bidirectional traction converter are connected to a positive pole and a negative pole of a catenary respectively, and three-phase AC buses of the bidirectional traction converter are connected to three-phase windings of the traction transformer respectively; a rectifier connected to the same winding of the traction transformer as the bidirectional traction converter.

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