Comprehensive management device and comprehensive management method for urban rail transit traction power supply system

Abstract

A comprehensive management device and a comprehensive management method for an urban rail transit traction power supply system, wherein the AC side of a PWM rectifier unit is connected to the AC side of a diode rectifier and the low voltage side of a rectifier transformer, and the DC side of the PWM rectifier unit is connected to the DC side of the diode rectifier and a DC traction network through a bidirectional DC / DC unit; during vehicle traction operation, the comprehensive management device is used to compensate for reactive power and harmonic current of the diode rectifier, and it is proposed that the output DC voltage of the diode rectifier is stabilized by providing capacitive reactive current to the rectifier transformer, and when the capacity of the diode rectifier is insufficient, the comprehensive management device and the diode rectifier are used to jointly provide power to the DC traction network; during vehicle braking operation, the comprehensive management device can transmit regenerated energy back to the AC medium voltage power grid; the present invention also proposes to eliminate the circulation problem between the comprehensive management device and the diode rectifier by controlling the current of two energy storage inductors in the bidirectional DC / DC unit.

Description

Technical Field

[0001] The invention belongs to the field of urban rail transit traction power supply control, and relates to a comprehensive management device and a comprehensive management method applied to an urban rail transit traction power supply system. Background Art

[0002] The traction network of the urban rail transit traction power supply system adopts DC power supply, and the most commonly used voltage levels are DC750V and DC1500V. The traction substation first steps down the AC10kV or AC35kV to 590V or 1180V AC, and then converts it into DC power through diode rectification to supply the DC traction network. Figure 1 and Figure 2 The following are the main circuit diagrams of commonly used 12-pulse and 24-pulse rectification. Figure 3 yes Figure 1 and Figure 2 The internal circuit diagram of the diode rectifier unit. This multi-pulse rectifier power supply system has the advantages of simple structure, high efficiency, good reliability, easy maintenance, small current distortion on the AC side, and small voltage ripple on the DC side. It has been used until today. However, it also has the following disadvantages:

[0003] First, the distance between urban rail vehicle stations is short, and starting and braking are frequent, which generates a large amount of regenerative braking energy. Because the energy of the diode rectifier can only flow from the AC side to the DC side, part of the regenerative energy is absorbed by other traction vehicles on the line, and the rest of the regenerative energy is consumed by the on-board or ground braking resistors and released into the atmosphere.

[0004] Second, the diode rectifier cannot control the output voltage. As the load current increases, the commutation overlap angle of the diode rectifier increases, causing DC rectifier voltage loss. At the same time, the increase in the commutation overlap angle will lead to a decrease in the power factor, causing a voltage drop on the AC side of the rectifier transformer, accelerating the voltage drop of the DC traction network, increasing the contact network current, and increasing the contact network line loss.

[0005] Third, although 12 or 24-pulse rectification can ensure the power quality of the AC current on the primary side of the rectifier transformer, the low-voltage side winding of the rectifier transformer contains a large amount of harmonic current, which increases the loss and noise of the transformer and affects the life of the transformer.

[0006] In recent years, people have begun to use energy feedback or energy storage devices to absorb vehicle regenerative braking energy. The energy feedback device uses a PWM rectifier, which is usually implemented in two forms: one form is to add another energy feedback device to feed back the regenerative braking energy to the medium voltage or 400V low voltage AC power grid, such as Figure 4 As shown; another form is to use PWM rectifier to replace the traditional diode rectifier, which can control the bidirectional flow of energy in the AC power grid and DC traction network, meeting the traction and braking energy flow requirements.

[0007] like Figure 4 The figure shows the structure of the traction power supply system with a medium voltage energy feed device based on the original 24-pulse rectifier. The energy feed device is connected in parallel with the diode rectifier on the DC side and the medium voltage AC side. BR_PWM1 and BR_PWM2 in the energy feed device are PWM rectifier units, and their internal structure is as follows: Figure 5 As shown, it includes a three-phase inverter, a DC filter inductor Ld and AC connection inductors La, Lb and Lc. Figure 5 The PWM rectifier unit shown can realize bidirectional energy conversion, that is, it has the dual functions of rectification and inversion: when rectifying, the energy on the AC side is sent to the DC side; when inverting, the energy on the DC side can be sent to the AC side. Regardless of rectification or inversion, the power factor on the AC side can be controlled, and the current on the AC side can be controlled to have a smaller distortion rate. However, because the efficiency during rectification is lower than that of diode rectification, the existing energy feeding device usually only converts the regenerated energy from the DC side to the AC side when the train brakes, and sends it to the medium-voltage AC power grid through the transformer TR3. When the rectifier transformer TR3 in the energy feeding device is connected to the medium-voltage power grid, electrical equipment such as circuit breakers and disconnectors must be configured, which increases the volume and equipment cost of the energy feeding device, especially the increase in equipment volume requires an increase in installation space, which increases civil engineering costs.

[0008] like Figure 6 Another energy feeding scheme is shown, where the PWM rectifier unit is directly connected in parallel with the diode rectifier. The diode rectifier transfers energy from the AC side to the DC side when the vehicle is towing, and the PWM rectifier feeds energy back to the AC side when the vehicle is braking, and the energy is sent to the medium-voltage AC grid by the rectifier transformer TR. This can save the energy feeding transformer and medium-voltage electrical switches, greatly reducing the size and equipment cost of the energy feeding device. However, this structural energy feeding device also has two problems:

[0009] First, the PWM rectifier unit is connected in parallel with the AC and DC sides of the diode rectifier. When the PWM rectifier unit is working, it will cause circulating current, increase losses, and affect the capacity of the PWM rectifier unit.

[0010] Secondly, to ensure that the PWM rectifier unit can work normally, the inverter AC voltage must be greater than the input AC voltage. Therefore, overmodulation or injection of inductive reactive power into the grid is required to meet this working condition.

[0011] In view of the above two factors, this solution has not been applied in practice. Summary of the invention

[0012] In view of the problem that the scheme of directly connecting a PWM rectifier unit in parallel with the AC and DC sides of the diode rectifier of the urban rail transit traction power supply system has complex control and difficult circulation control, which makes it impossible to carry out practical application, the present invention proposes a comprehensive management device connected in parallel with the diode rectifier, and adds a three-level bidirectional DC / DC unit with a symmetrical structure on the DC side of the PWM rectifier unit and then connects it to the DC side of the diode rectifier, and a circulation control unit is provided to eliminate the circulation between the comprehensive management device and the diode rectifier connected in parallel; in addition, based on the device proposed by the present invention, a corresponding comprehensive management method is also proposed. When the vehicle is towed, the comprehensive management device can compensate for the harmonics and reactive power generated by the diode rectifier and can maintain the stability of the DC traction power grid. At the same time, the bidirectional DC / DC unit working in the buck mode can also make the PWM rectifier unit and the diode rectifier work together to transfer energy from the AC traction power grid to the DC traction network; when the vehicle is braked, the bidirectional DC / DC unit working in the boost mode can make the PWM rectifier unit feed back the vehicle regenerative braking energy to the AC traction power grid, and the present invention can be realized in practical application in combination with the circulation control.

[0013] The technical solution of the comprehensive treatment device proposed by the present invention is:

[0014] A comprehensive management device for an urban rail transit traction power supply system, the comprehensive management device is connected in parallel between the AC side and the DC side of a diode rectifier in the urban rail transit traction power supply system, the comprehensive management device comprises a PWM rectifier unit, a bidirectional DC / DC unit and a circulating current control unit, the AC side of the PWM rectifier unit is connected to the AC side of the diode rectifier and the low-voltage side of a rectifier transformer in the urban rail transit traction power supply system, the DC side thereof is connected to the high-voltage side of the bidirectional DC / DC unit, and the low-voltage side of the bidirectional DC / DC unit is connected to the DC side of the diode rectifier and a DC traction network;

[0015] When the urban rail transit traction power supply system operates in vehicle traction conditions, the AC side of the PWM rectifier unit in the comprehensive treatment device outputs a compensation current, and the compensation current has the same magnitude and opposite phase to the fundamental reactive current and the harmonic current connected to the AC side of the diode rectifier connected in parallel with the comprehensive treatment device;

[0016] The PWM rectifier unit and the bidirectional DC / DC unit are also used to adjust the DC side voltage of the PWM rectifier unit, so that the DC side voltage of the PWM rectifier unit is stable, and the voltage value of the DC side voltage of the PWM rectifier unit is ensured to be higher than the AC side line voltage peak value of the PWM rectifier unit and the DC traction network voltage value, so as to ensure that the bidirectional DC / DC unit can operate in a step-down mode when the urban rail transit traction power supply system operates in a vehicle traction condition; the bidirectional DC / DC unit operates in a step-up mode when the urban rail transit traction power supply system operates in a vehicle braking condition;

[0017] The bidirectional DC / DC unit is a three-level structure that is symmetrical up and down, including a first energy storage inductor and a second energy storage inductor connected before its low-voltage side; the circulating current control unit ensures that the circulating current between the comprehensive management device and the diode rectifier connected in parallel with it is zero by controlling the current of the first energy storage inductor to be equal to the current of the second energy storage inductor and equal to the reference inductor current.

[0018] Specifically, the bidirectional DC / DC unit also includes a first capacitor, a second capacitor, a first switch tube, a second switch tube, a third switch tube and a fourth switch tube. The first capacitor and the second capacitor are connected in series and connected between the high-voltage sides of the bidirectional DC / DC unit; the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series in sequence and connected between the high-voltage sides of the bidirectional DC / DC unit, the series point of the first switch tube and the second switch tube is connected to one end of the first energy storage inductor, the series point of the second switch tube and the third switch tube is connected to the series point of the first capacitor and the second capacitor, the series point of the third switch tube and the fourth switch tube is connected to one end of the second energy storage inductor, and the other end of the first energy storage inductor and the other end of the second energy storage inductor are connected between the low-voltage sides of the bidirectional DC / DC unit.

[0019] Specifically, when the urban rail transit traction power supply system operates in a vehicle traction condition, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are turned off, and energy is only transmitted from the rectifier transformer to the DC traction network through the diode rectifier, and the circulating current between the comprehensive management device and the diode rectifier connected in parallel with it is zero.

[0020] Specifically, when the urban rail transit traction power supply system operates in vehicle traction conditions, the bidirectional DC / DC unit operates in a step-down mode, and the energy on the low-voltage side of the rectifier transformer is transmitted to the DC traction network through the diode rectifier and the comprehensive management device.

[0021] Specifically, when the bidirectional DC / DC unit operates in the buck mode or the boost mode, there is a circulating current between the comprehensive treatment device and the diode rectifier connected in parallel therewith, and the circulating current control unit is used to eliminate the circulating current between the comprehensive treatment device and the diode rectifier connected in parallel therewith;

[0022] The circulating current control unit includes a first adder, a second adder, a third adder, a first current regulator, a second current regulator, a third current regulator, a triangular wave generator, a first comparator, a second comparator, a first inverter and a second inverter.

[0023] The third adder is used for subtracting the current of the first energy storage inductor from the current of the second energy storage inductor and sending the subtracted current to the input end of the third current regulator;

[0024] The first adder is used for sending the result of subtracting the current of the first energy storage inductor and the output current of the third current regulator from the reference inductor current to the input end of the first current regulator;

[0025] The second adder is used for adding the output current of the third current regulator to the current obtained by subtracting the current of the second energy storage inductor from the reference inductor current and then sending the result to the input terminal of the second current regulator;

[0026] The first input end of the first comparator is connected to the first input end of the second comparator and the output end of the triangular wave generator, the second input end of the first comparator is connected to the output end of the first current regulator, and the output end of the first comparator is connected to the control end of the first switch tube on the one hand, and connected to the control end of the second switch tube on the other hand after passing through the first inverter;

[0027] The second input end of the second comparator is connected to the output end of the second current regulator, and the output end thereof is connected to the control end of the fourth switch tube on one hand, and is connected to the control end of the third switch tube on the other hand through the second inverter.

[0028] The technical solution of the comprehensive treatment method proposed by the present invention is:

[0029] A comprehensive management method for an urban rail transit traction power supply system, the urban rail transit traction power supply system comprising a diode rectifier connected between a low-voltage side of a rectifier transformer and a DC traction network, the comprehensive management method comprising the following steps:

[0030] Step 1: Setting a comprehensive treatment device, which includes a PWM rectifier unit, a bidirectional DC / DC unit and a circulating current control unit, wherein the AC side of the PWM rectifier unit is connected to the AC side of the diode rectifier and the low-voltage side of the rectifier transformer, and the DC side is connected to the high-voltage side of the bidirectional DC / DC unit, and the low-voltage side of the bidirectional DC / DC unit is connected to the DC side of the diode rectifier and the DC traction network;

[0031] Step 2: When the urban rail transit traction power supply system operates in a vehicle traction condition, the PWM rectifier unit of the comprehensive treatment device outputs a compensation current on the AC side. The compensation current is equal in magnitude to the fundamental reactive current and the harmonic current input on the AC side of the diode rectifier connected in parallel to the comprehensive treatment device, but opposite in phase, to ensure that only the fundamental active current is output from the low-voltage side of the rectifier transformer; at the same time, by adjusting the PWM rectifier unit and the bidirectional DC / DC unit, the DC side voltage of the PWM rectifier unit is stabilized, and the voltage value of the DC side voltage of the PWM rectifier unit is higher than the peak value of the AC side line voltage of the PWM rectifier unit and the voltage value of the DC traction network, to ensure that the bidirectional DC / DC unit can operate in a step-down mode, and the energy on the low-voltage side of the rectifier transformer is transmitted to the DC traction network through the diode rectifier, or the energy on the low-voltage side of the rectifier transformer is transmitted to the DC traction network through the diode rectifier and the comprehensive treatment device;

[0032] When the urban rail transit traction power supply system operates in a vehicle braking condition, the bidirectional DC / DC unit is controlled to operate in a boost mode, and the energy of the DC traction network is transmitted by the bidirectional DC / DC unit to the DC side of the PWM rectifier unit, and then transmitted to the low-voltage side of the rectifier transformer through the PWM rectifier unit;

[0033] Step three, when the DC / DC unit operates in the buck mode or the boost mode, there is a circulating current between the comprehensive management device and the diode rectifier connected in parallel with it, and the circulating current control unit is used to eliminate the circulating current between the comprehensive management device and the diode rectifier connected in parallel with it; the bidirectional DC / DC unit is a three-level structure symmetrical up and down, including a first energy storage inductor and a second energy storage inductor connected before its low-voltage side, and the circulating current control unit controls the current of the first energy storage inductor and the current of the second energy storage inductor to be equal to the reference inductor current, so that the circulating current between the comprehensive management device and the diode rectifier connected in parallel with it is zero.

[0034] Specifically, when the urban rail transit traction power supply system operates in a vehicle traction condition, a capacitive reactive current is provided to the rectifier transformer, so that the output voltage of the rectifier transformer remains unchanged when the load increases, thereby ensuring that the output DC voltage of the diode rectifier remains unchanged.

[0035] Specifically, the bidirectional DC / DC unit further includes a first capacitor, a second capacitor, a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, the first capacitor and the second capacitor are connected in series and connected between the high-voltage sides of the bidirectional DC / DC unit; the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series in sequence and connected between the high-voltage sides of the bidirectional DC / DC unit, the series point of the first switch tube and the second switch tube is connected to one end of the first energy storage inductor, the series point of the second switch tube and the third switch tube is connected to the series point of the first capacitor and the second capacitor, the series point of the third switch tube and the fourth switch tube is connected to one end of the second energy storage inductor, and the other end of the first energy storage inductor and the other end of the second energy storage inductor are connected between the low-voltage sides of the bidirectional DC / DC unit;

[0036] In the step 3, when the bidirectional DC / DC unit operates in the boost mode or the buck mode, the specific method of using the circulating current control unit to eliminate the circulating current between the comprehensive treatment device and the diode rectifier connected in parallel therewith is:

[0037] Sending the difference between the reference inductor current and the current of the first energy storage inductor to a first current regulator for calculation, and sending the difference between the reference inductor current and the current of the second energy storage inductor to a second current regulator for calculation;

[0038] Send the difference between the current of the first energy storage inductor and the current of the second energy storage inductor to the third current regulator for calculation, subtract the difference between the current of the reference inductor and the current of the first energy storage inductor from the current output of the third current regulator and send it to the first current regulator for calculation, add the difference between the current of the reference inductor and the current of the second energy storage inductor and send it to the second current regulator for calculation;

[0039] Compare the output signal of the first current regulator with the triangular wave signal and generate a first control signal according to the comparison result, wherein the first control signal is used to control the first switch tube, and the first control signal is inverted and used to control the second switch tube;

[0040] Compare the output signal of the second current regulator with the triangular wave signal and generate a second control signal according to the comparison result, wherein the second control signal is used to control the fourth switch tube, and the second control signal is inverted and used to control the third switch tube;

[0041] The current of the first energy storage inductor and the current of the second energy storage inductor are adjusted by controlling the on and off of the first to fourth switch tubes, so that the current of the first energy storage inductor is equal to the current of the second energy storage inductor and equal to the reference inductor current.

[0042] The beneficial effects of the present invention are:

[0043] 1. The comprehensive treatment device proposed in the present invention is connected in parallel with the diode rectifier and shares the rectifier transformer, eliminating the need for a dedicated energy-feed transformer and medium-voltage switchgear, saving equipment costs, greatly reducing equipment volume, and saving a large amount of equipment installation space, thereby saving civil engineering costs.

[0044] 2. When the vehicle is towing, the comprehensive treatment device can compensate for the harmonics and reactive power generated by the diode rectifier, improve the load power factor of the rectifier transformer, and improve the capacity utilization rate of the rectifier transformer (calculation shows that it can be improved by about 30%). At the same time, it also reduces the winding current of the rectifier transformer, especially the harmonic current, thereby reducing the additional iron loss (eddy current generated by the harmonic flux of the iron core) and copper loss (skin effect generated by the harmonic current) of the rectifier transformer due to the harmonic current (calculation shows that the loss can be reduced by about 50%). The DC traction network voltage is increased, the output current of the diode rectifier is reduced, the capacity utilization rate of the diode rectifier is improved, and the line loss of the contact network is also reduced.

[0045] 3. The bidirectional DC / DC unit is used to work in step-down mode during vehicle traction and in step-up mode during vehicle braking. It not only has the function of regenerative energy feedback, but also can reduce the burden of the diode rectifier in transmitting energy to the DC traction network. It can be implemented in the traction power supply system of newly built lines, and is also suitable for adding devices to the traction power supply system of existing lines, especially for lines with insufficient traction power supply system capacity and low DC traction network voltage after the increase in transportation volume.

[0046] 4. The present invention retains the advantages of the existing diode rectifier such as high efficiency, simplicity, reliability, and easy maintenance. Compared with the traditional PWM rectifier, only a bidirectional DC / DC unit is added. The energy storage inductor in the bidirectional DC / DC unit is equivalent to the line filter inductor Ld of the PWM rectifier. Therefore, the main increase is only the power switching device, which overcomes the problems of regenerative energy feedback of the diode rectifier and the large drop of DC voltage with load at a relatively low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a circuit diagram of a traditional 12-pulse rectifier. TR is a rectifier transformer, the primary of TR is connected to the medium voltage 10kV or 35kV grid, and the two secondary windings are 30° out of phase; BR1 and BR2 are three-phase diode rectifier units, and the internal structure is shown in Figure 3 .

[0048] Figure 2This is a circuit diagram of a traditional 24-pulse rectifier. TR1 and TR2 are rectifier transformers. The primary of TR1 and TR2 are connected to the medium voltage 10kV or 35kV power grid. The primary of TR1 and TR2 adopts the extended triangle connection method, so that the phase difference between the corresponding secondary of TR1 and TR2 is 15°; BR1-BR4 is a three-phase diode rectifier unit, and the internal structure is shown in Figure 3 .

[0049] Figure 3 This is the internal structure diagram of the three-phase diode rectifier unit. D1-D6 are diodes, and the three-phase AC is converted into DC after passing through the rectifier bridge.

[0050] Figure 4 This is a structural diagram of a power supply system equipped with a medium voltage energy feed device. TR1 and TR2 are rectifier transformers, the primary of TR1 and TR2 are connected to the medium voltage 10kV or 35kV power grid, TR3 is the energy feed transformer; BR1-BR4 are diode rectifier units, BR_PWM1 and BR_PWM2 are three-phase PWM rectifier units, and the internal structure of the three-phase PWM rectifier unit is shown in Figure 5 .

[0051] Figure 5 This is the internal structure diagram of the three-phase PWM rectifier unit. La, Lb and Lc are connected inductors, T1-T6 are 6 IGBTs that form a three-phase inverter; Cd is the inverter DC side support capacitor; Ld is the DC side line filter inductor; Ud is the inverter DC side voltage.

[0052] Figure 6 It is a structural diagram of the connection between the energy feeding device and the rectifier. TR is a rectifier transformer, the primary of TR is connected to the medium voltage 10kV or 35kV power grid, BR1 and BR2 are diode rectifier units; BR_PWM1 and BR_PWM2 are three-phase PWM rectifier units.

[0053] Figure 7 The schematic diagram of the structure of the embodiment in which the comprehensive treatment device proposed in the present invention is applied to the urban rail transit traction power supply system and connected in parallel with the diode rectifier. TR is a rectifier transformer, the primary of TR is connected to the medium voltage 10kV or 35kV power grid, BR1 and BR2 are diode rectifiers; U1 and U2 are the comprehensive treatment device proposed in the present invention, and the internal structure of the comprehensive treatment device is shown in FIG. Figure 8 .

[0054] Figure 8This is an internal implementation structure diagram of the comprehensive treatment device proposed in the present invention. Among them, La, Lb and Lc are connection inductors, T1-T6 are 6 IGBTs constituting a three-phase inverter; Cd is the DC side support capacitor of the inverter; T7-T10 are four IGBTs, L1 is the first energy storage inductor, L2 is the second energy storage inductor, the first capacitor Cd1 and the second capacitor Cd2 are voltage divider capacitors, H1 and H2 are current sensors, Cd1, Cd2, T7-T10, L1, L2, H1, H2 together constitute a three-level bidirectional DC / DC unit with a vertically symmetrical structure; Ud1 is the DC side voltage of the inverter; Ud2 is the DC traction network voltage.

[0055] Fig. 9 This is a schematic diagram of the internal structure of a circulating current control unit in a comprehensive management device for an urban rail transit traction power supply system proposed by the present invention, which is used to control the current of the first energy storage inductor L1 and the second energy storage inductor L2 in a bidirectional DC / DC unit. L_ref is the given reference inductor current, i L1 、i L2 They are the currents of the first energy storage inductor L1 and the second energy storage inductor L2 respectively; ADD1, ADD1 and ADD3 are adders; PI1, PI2 and PI3 are proportional integral current regulators; TRI is a triangle wave generator; COM1 and COM2 are comparators; NOT1 and NOT2 are inverters; PT7-PT10 correspond to the driving logic signals of T7-T10.

[0056] Fig.10 This is a circuit diagram for implementing the comprehensive treatment device proposed in the present invention when it is applied to the 24-pulse structure urban rail transit traction power supply system. TR1 and TR2 are rectifier transformers; BR1-BR4 are diode rectifiers; U1-U4 are the comprehensive treatment device proposed in the present invention. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0058] Based on the shortcomings of diode rectification in the urban rail transit traction power supply system, the present invention Figure 6 Based on the structure shown in FIG. 1 , the PWM rectifier unit is replaced by a comprehensive treatment device, such as Figure 7 As shown in FIG. 1 , the present invention connects the comprehensive treatment device in parallel between the AC side and the DC side of the diode rectifier in the urban rail transit traction power supply system. The comprehensive treatment device includes a PWM rectifier unit and a bidirectional DC / DC unit, such as Figure 8As shown, the present invention adds a bidirectional DC / DC unit on the DC side of the PWM rectifier unit, so that the DC side of the PWM rectifier unit is not directly connected to the DC traction network, and controls the PWM rectifier unit or the bidirectional DC / DC unit to make the DC side voltage Ud1 of the PWM rectifier unit stable, and the stable voltage value is higher than the peak value of the AC input voltage, thereby ensuring that the modulation degree of the PWM rectifier unit is not greater than 1; at the same time, Ud1 is controlled to be higher than the DC traction network voltage Ud2, ensuring that the bidirectional DC / DC unit can operate in the buck mode during traction, and the bidirectional DC / DC unit operates in the boost mode during braking.

[0059] The PWM rectifier unit can adopt a two-level inverter structure, such as Figure 8 As shown, of course, a three-level structure can also be used. The specific structure of the PWM rectifier unit is not used to limit the protection scope of the present invention. The symmetrical bidirectional DC / DC unit used in the present invention can only be a three-level bidirectional DC / DC structure with a top-bottom symmetrical structure, such as Figure 8 As shown, it includes a first energy storage inductor L1, a second energy storage inductor L2, a first capacitor Cd1, a second capacitor Cd2, a first switch tube T7, a second switch tube T8, a third switch tube T9 and a fourth switch tube T10. The first capacitor Cd1 and the second capacitor Cd2 are connected in series and connected between the high-voltage sides of the bidirectional DC / DC unit; the first switch tube T7, the second switch tube T8, the third switch tube T9 and the fourth switch tube T10 are connected in series in sequence and connected between the high-voltage sides of the bidirectional DC / DC unit, the series connection point of the first switch tube T7 and the second switch tube T8 is connected to one end of the first energy storage inductor L1, the series connection point of the second switch tube T8 and the third switch tube T9 is connected to the series connection point of the first capacitor Cd1 and the second capacitor Cd2, the series connection point of the third switch tube T9 and the fourth switch tube T10 is connected to one end of the second energy storage inductor L2, and the other end of the first energy storage inductor L1 and the other end of the second energy storage inductor L2 are connected between the low-voltage sides of the bidirectional DC / DC unit. The current sensors H1 and H2 are respectively connected to the first energy storage inductor L1 and the second energy storage inductor L2 to obtain the current of the first energy storage inductor L1 and the current of the second energy storage inductor L2 for output current and circulating current control.

[0060] The working principle and working process of the comprehensive management device proposed in the present invention are described in detail below in conjunction with the traction and braking conditions of vehicles in the urban rail transit traction power supply system. Figure 7 There are two diode rectifiers BR1 and BR2 and two comprehensive treatment devices U1 and U2, which have the same working principle. For convenience, the diode rectifier BR1 and the comprehensive treatment device U1 are described here.

[0061] 1) Vehicle traction conditions

[0062] When the vehicle is towing, the diode rectifier BR1 rectifies the three-phase AC from the low-voltage side of the rectifier transformer TR into DC, and outputs it to the DC traction network. The diode rectifier BR1 is a nonlinear load. In addition to the fundamental active current, the current it draws from the AC side of the rectifier transformer TR also absorbs the fundamental reactive current (because the fundamental current lags the fundamental voltage due to the commutation overlap angle of the diode rectifier) ​​and a large amount of harmonic current. If not compensated, the reactive power and harmonic current under load will cause the voltage on the low-voltage side of the rectifier transformer TR to decrease and distort, and the output voltage of the diode rectifier BR1 will decrease as the load power increases. The present invention utilizes the comprehensive treatment device U1 to compensate for the reactive power and harmonics of the diode rectifier BR1 connected in parallel therewith. The AC side of the PWM rectifier unit in the comprehensive treatment device U1 outputs a compensation current. The compensation current is a current with the same magnitude and opposite phase of the fundamental reactive current and the harmonic current input to the AC side of the diode rectifier BR1 connected in parallel with the comprehensive treatment device U1, so that the rectifier transformer TR provides only the fundamental active current. In this way, under the same load, the input and output currents of the rectifier transformer TR are reduced, and the output AC voltage drop is also reduced, so that the DC output voltage drop of the diode rectifier BR1 is also reduced.

[0063] In some embodiments, by providing leading reactive current (capacitive reactive current) to the rectifier transformer TR, the leakage reactance and resistance voltage drop of the rectifier transformer TR are fully compensated, so that the AC voltage of the rectifier transformer TR remains unchanged or slightly increases with the load, and the voltage drop of the diode rectifier BR1 due to the increase in load is compensated, and the output voltage drop of the diode rectifier BR1 is reduced or maintained unchanged, so as to keep the traction network voltage stable. Usually, compensating for inductive reactive power can reduce the voltage drop of the rectifier transformer AC voltage with the load, but the present invention proposes to compensate for leading reactive power to reduce the DC voltage drop of the rectifier, which solves the problem of controlling the DC voltage drop of rail transit rectification.

[0064] During operation, the comprehensive treatment device proposed in the present invention controls the PWM rectifier unit and / or the bidirectional DC / DC unit to keep the DC side voltage Ud1 of the PWM rectifier unit stable, and the Ud1 voltage is higher than the peak value of the AC side line voltage of the PWM rectifier unit, and also higher than the DC side input voltage value, that is, the low voltage side voltage Ud2 of the bidirectional DC / DC unit, to ensure that the PWM rectifier unit works in a controllable state with a modulation index not greater than 1, so that the bidirectional DC / DC unit can work in a buck mode under vehicle traction conditions. In this way, for some existing lines built in the early stage, due to the increase in line traffic in the later stage, the capacity of the transformer and the diode rectifier BR1 is insufficient. On the one hand, the output power factor is improved by reactive compensation current, thereby improving the capacity utilization rate of the transformer. On the other hand, the DC voltage is increased, the current of the diode rectifier is reduced, and its capacity utilization rate is improved. At the same time, the bidirectional DC / DC unit can also work in the buck buck mode, and the energy is transmitted from the rectifier transformer to the DC traction network through the PWM rectifier unit and the diode rectifier system, compensating for the insufficient capacity of the diode rectifier BR1.

[0065] If the integrated control device U1 is not required to feed energy to the DC traction grid, Figure 8 The first switch tube T7 to the fourth switch tube T10 in the bidirectional DC / DC unit are turned off. Because the voltage Ud1 is greater than Ud2, the anti-parallel diodes in the first switch tube T7 to the fourth switch tube T10 are cut off, and the DC side of the comprehensive management device U1 is isolated from the DC side of the diode rectifier BR1, and no circulating current will be generated between the two. If the comprehensive management device U1 needs to feed energy to the DC traction network, the diode rectifier BR1 and the AC side and DC side of the parallel-connected comprehensive management device U1 are directly connected in parallel, and a circulating current will be generated between the two. At this time, the circulating current control unit in the comprehensive management device U1 can be used to control the current i of the first energy storage inductor L1 in the bidirectional DC / DC unit. L1 and the current i of the second energy storage inductor L2 L2 , the circulating current between the diode rectifier BR1 and its parallel-connected integrated treatment device U1 is controlled to 0.

[0066] The principle of the circulating current control unit controlling the current in the bidirectional DC / DC unit is as follows Fig. 9 As shown, the current loop control target is: L1 =i L2 =i L_ref ,i L_ref is the reference inductor current, which is the externally given current command. The current i of the first energy storage inductor L1 is L1 and the current i of the second energy storage inductor L2 L2 Following the current command, the current i of the first energy storage inductor L1 L1 and the current i of the second energy storage inductor L2 L2Equal, the current i of the first energy storage inductor L1 L1 and the current i of the second energy storage inductor L2 L2 That is to say, the circulating current between the comprehensive treatment device U1 and the parallel diode rectifier BR1 is 0.

[0067] The three current regulators PI1-PI3 in the circulating current control unit proposed by the present invention respectively realize the current i of the first energy storage inductor L1 L1 For current command i L_ref Following, the current i of the second energy storage inductor L2 L2 For current command i L_ref Follow and i L1 -i L2 Following the 0 current command. The detailed control principle analysis is as follows:

[0068] The current i of the first energy storage inductor L1 L1 For current command i L_ref Follow control: i L_ref with i L1 After subtraction by the first adder ADD1, the difference is calculated by the first current regulator PI1, and the output is a triangular wave ratio generated by the first comparator COM1 and the triangular wave generator TRI to generate a trigger logic signal PT7 for the first switch T7 and a trigger logic signal PT8 for the second switch T8 through the first inverter NOT1.

[0069] The current i of the second energy storage inductor L2 L2 For current command i L_ref Follow control: i L_ref with i L2 After subtraction by the second adder ADD2, the difference is calculated by the second current regulator PI2, and the output is a triangular wave ratio generated by the second comparator COM2 and the triangular wave generator TRI to generate a trigger logic signal PT10 for the fourth switch T10 and a trigger logic signal PT9 for the third switch T9 through the second inverter NOT2.

[0070] i L1 -i L2 Follow-up control of 0 current command: i L1 with i L2 After the third adder ADD3 subtracts, the difference is calculated by the third current regulator PI3, and the current output by the third current regulator PI3 is added to the current in the first adder ADD1. L_ref and i L1 The difference between the current and the current is subtracted and sent to the first current regulator PI1 for calculation. The current output by the third current regulator PI3 is added to i in the second adder ADD2. L_ref and i L2The difference is added and sent to the second current regulator PI2 for calculation. The first comparator COM1 and the second comparator COM2 respectively compare the outputs of the first current regulator PI1 and the second current regulator PI2 with the triangular wave signal to control the on and off of the first switch tube T7 to the fourth switch tube 710 to adjust i L1 and i L2 , when i L1 -i L2 >0, it is equivalent to reducing the current command value of the first energy storage inductor L1 and increasing the current command value of the second energy storage inductor L2; when i L1 -i L2 >0, on the contrary, the output of the first current regulator PI1 increases the current command value of the first energy storage inductor L1, and the second current regulator PI2 reduces the current command value of the second energy storage inductor L2.

[0071] It can be seen that through the above control process, the two inductor currents can be made equal to the command current value, and the circulating current can be controlled to 0.

[0072] 2) Vehicle braking conditions

[0073] When the vehicle brakes, the vehicle transmits regenerative braking energy to the DC traction network, and the voltage of the DC traction network is raised. When the DC network voltage is higher than the peak voltage of the AC side of the diode rectifier BR1, the output current of the diode rectifier BR1 drops to 0. At this time, the rectifier transformer TR no longer needs the PWM rectifier unit to compensate for reactive power and harmonic current. When the DC traction network voltage is further raised to the set energy feedback threshold value, the bidirectional DC / DC unit of the comprehensive management device U1 proposed in the present invention operates in the boost mode, and transmits energy from the DC traction network side to the DC side of the PWM rectifier unit, and then transmits it to the low-voltage AC side of the rectifier transformer TR through the PWM rectifier unit, and finally the rectifier transformer TR boosts the voltage and sends it to the medium-voltage power grid.

[0074] When the vehicle brakes, the bidirectional DC / DC unit works in boost mode, the diode rectifier BR1 and the AC side and DC side of the integrated treatment device U1 are directly connected in parallel, and a circulating current will be generated between the two. At this time, according to the working principle of the circulating current control unit analyzed in the above vehicle traction condition, the circulating current control unit can be used to control the current of the first energy storage inductor L1 and the second energy storage inductor L2 of the bidirectional DC / DC unit respectively, and the circulating current is controlled to be close to 0. The circulating current control principle during braking is exactly the same as the control principle in the buck mode during traction, and will not be repeated here.

[0075] The working process of the overall traction power supply system when the comprehensive management device of the present invention is applied to the most typical 24-pulse rectified DC1500V urban rail traction power supply system is described in detail below in conjunction with the accompanying drawings.

[0076] like Fig.10 As shown, TR1 and TR2 are two primary extended triangle connected rectifier transformers. The voltage of the four low voltage windings of TR1 and TR2 is 1180V, and the corresponding voltage phase difference is 15 degrees. BR1-BR4 are four diode rectifiers. The internal structure is shown in Figure 3 , respectively connected to the four low-voltage windings of rectifier transformers TR1 and TR2; Figure 8 The four comprehensive treatment devices U1-U4 of the structure shown are respectively connected in parallel with the four diode rectifiers BR1-BR4.

[0077] During operation, the current direction on the supporting capacitor Cd in each comprehensive management device is controlled by controlling the PWM rectifier unit (or bidirectional DC / DC unit) in the comprehensive management device U1-U4, so that the DC measurement voltage of the PWM rectifier unit in the comprehensive management device U1-U4 is kept constant, and the stable voltage is higher than the peak value of the AC side line voltage and the voltage value of the DC traction network.

[0078] When the vehicle is towing, the diode rectifiers BR1-BR4 rectify and rectify the AC power into DC power to supply the DC traction network. At this time, the PWM rectifier unit in the comprehensive management device U1-U4 partially compensates for the reactive power and harmonic current on the AC side of the corresponding diode rectifier BR1-BR4, and can even increase the output of appropriate capacitive reactive current, so that the load current of the rectifier transformer has a visible capacity, compensates for the transformer leakage reactance and resistance voltage drop, reduces the voltage drop on the AC side of the diode rectifier, and thus reduces the voltage drop of the DC traction network. While increasing the voltage of the DC traction network, the transformer loss is also reduced due to the reduction of the transformer harmonics and reactive current, and the capacity utilization rate of the traction transformer is improved; the DC voltage is increased, the DC current is reduced, and the capacity utilization rate of the diode rectifier is also improved, while the loss of the contact network is reduced. When used in existing lines, as the line traffic increases, if the capacity of the diode rectifiers BR1-BR4 is insufficient, the bidirectional DC / DC units of the comprehensive management devices U1-U4 can be operated in buck mode to enable the comprehensive management devices U1-U4 to output power to the DC traction network, thereby reducing the burden on the diode rectifiers BR1-BR4.

[0079] When the vehicle brakes, the regenerative braking energy returns to the DC traction network and raises the voltage on the DC traction network side. When the voltage on the DC traction network side is higher than the peak value on the AC side of the diode rectifiers BR1-BR4, the output current of the diode rectifiers BR1-BR2 is 0 and no longer outputs power. As the voltage of the DC traction network further increases, when its value is higher than the set energy-feed voltage threshold, the bidirectional DC / DC unit in the comprehensive management device U1-U4 operates in boost mode, sending the energy of the DC traction network to the DC side of the PWM rectifier unit, which is then transmitted by the PWM rectifier unit to the low-voltage side of the rectifier transformer, and then transmitted to the medium-voltage AC grid through rectifier transformers TR1 and TR2.

[0080] When the bidirectional DC / DC unit is not working, the first switch tube T7 to the fourth switch tube T10 in the bidirectional DC / DC unit are in the off state, and the anti-parallel diodes in the first switch tube T7 to the fourth switch tube T10 isolate the comprehensive treatment device from the diode rectifier, and no circulating current is generated; when the bidirectional DC / DC unit is working, the circulating current control unit is used to control the circulating current of each comprehensive treatment device U1-U4 and the diode rectifier BR1-BR4 connected in parallel thereto to 0.

[0081] exist Fig.10 In the actual application shown, in order to ensure load balance among the four comprehensive treatment devices, information should be exchanged between them.

[0082] Combined with the above analysis, it can be known that the present invention directly connects the comprehensive management device and the diode rectifier in parallel on both the AC side and the DC side, and shares the rectifier transformer with the diode rectifier; the comprehensive management device sets a bidirectional three-level DC / DC unit with a vertically symmetrical structure on the DC side of the PWM rectifier unit, the high-voltage side of the bidirectional DC / DC unit is connected to the DC side of the PWM rectifier unit, and its low-voltage side is connected to the DC traction network, the bidirectional DC / DC unit can operate in buck step-down and boost step-up modes to achieve bidirectional energy flow between the high-voltage side and the low-voltage side, and the PWM rectifier unit can operate in rectification and inversion modes to achieve bidirectional energy flow between the AC side and the DC side.

[0083] During vehicle towing, the present invention compensates for the reactive power and harmonic current of the AC side of the diode rectifier connected in parallel therewith through the AC side of the PWM rectifier unit of the comprehensive management device, thereby increasing the voltage on the AC side of the diode rectifier, thereby reducing the voltage drop when the DC traction network is loaded, while reducing the current of the rectifier transformer and also reducing the loss of the rectifier transformer, thereby increasing the capacity utilization of the rectifier transformer and the diode rectifier; it also proposes to stabilize the output DC voltage of the diode rectifier by providing a capacitive reactive current to the rectifier transformer; in the case where the capacity of the diode rectifier is insufficient, the comprehensive management device can also provide power to the DC traction network to share part of the load of the diode rectifier.

[0084] When the vehicle brakes, the comprehensive management device can transmit the regenerated energy to the AC medium-voltage power grid. The bidirectional DC / DC unit transmits the DC traction network energy to the DC side of the PWM rectifier unit by boosting, and then the PWM rectifier transmits it to the AC side.

[0085] For the circulating current problem caused by the bidirectional DC / DC unit working in the buck and boost modes, the present invention also independently controls the current of the first energy storage inductor L1 and the second energy storage inductor L2 in the bidirectional DC / DC unit to achieve a circulating current close to 0 between the comprehensive management device and the diode rectifier connected in parallel. Therefore, the comprehensive management device proposed in the present invention can be used for newly built lines, which can reduce the installation space, save civil engineering costs, improve power supply performance, and obtain good comprehensive performance indicators; it is also suitable for the transformation of existing lines where the DC network voltage is low due to increased traffic volume, and the rectifier transformer and diode rectifier capacity are insufficient. It can install equipment within limited space, increase the output capacity of the rectifier power supply, increase the voltage of the DC traction network, and reduce the loss of the traction network.

[0086] A person skilled in the art may make various other specific modifications and combinations based on the technical inspirations disclosed in the present invention without departing from the essence of the present invention, and these modifications and combinations are still within the protection scope of the present invention.

Claims

1. A comprehensive management device for urban rail transit traction power supply system, characterized in that: The comprehensive treatment device is connected in parallel between the AC side and the DC side of the diode rectifier in the urban rail transit traction power supply system. The comprehensive treatment device includes a PWM rectifier unit, a bidirectional DC / DC unit and a circulating current control unit. The AC side of the PWM rectifier unit is connected to the AC side of the diode rectifier and the low-voltage side of the rectifier transformer in the urban rail transit traction power supply system, and the DC side is connected to the high-voltage side of the bidirectional DC / DC unit. The low-voltage side of the bidirectional DC / DC unit is connected to the DC side of the diode rectifier and the DC traction network. When the urban rail transit traction power supply system operates in vehicle traction conditions, the AC side of the PWM rectifier unit in the comprehensive treatment device outputs a compensation current, and the compensation current has the same magnitude and opposite phase to the fundamental wave reactive current and harmonic current input to the AC side of the diode rectifier connected in parallel with the comprehensive treatment device; The PWM rectifier unit and the bidirectional DC / DC unit are also used to adjust the DC side voltage of the PWM rectifier unit, so that the DC side voltage of the PWM rectifier unit is stable, and the voltage value of the DC side voltage of the PWM rectifier unit is ensured to be higher than the AC side line voltage peak value of the PWM rectifier unit and the DC traction network voltage value, so as to ensure that the bidirectional DC / DC unit can operate in a step-down mode when the urban rail transit traction power supply system operates in a vehicle traction condition; the bidirectional DC / DC unit operates in a step-up mode when the urban rail transit traction power supply system operates in a vehicle braking condition; The bidirectional DC / DC unit is a three-level structure that is symmetrical up and down, and includes a first energy storage inductor and a second energy storage inductor connected before its low-voltage side; the circulating current control unit ensures that the circulating current between the comprehensive treatment device and the diode rectifier connected in parallel with it is zero by controlling the current of the first energy storage inductor to be equal to the current of the second energy storage inductor and equal to the reference inductor current; The bidirectional DC / DC unit also includes a first capacitor, a second capacitor, a first switch tube, a second switch tube, a third switch tube and a fourth switch tube. The first capacitor and the second capacitor are connected in series and connected between the high-voltage sides of the bidirectional DC / DC unit; the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series in sequence and connected between the high-voltage sides of the bidirectional DC / DC unit, the series connection point of the first switch tube and the second switch tube is connected to one end of the first energy storage inductor, the series connection point of the second switch tube and the third switch tube is connected to the series connection point of the first capacitor and the second capacitor, the series connection point of the third switch tube and the fourth switch tube is connected to one end of the second energy storage inductor, and the other end of the first energy storage inductor and the other end of the second energy storage inductor are connected between the low-voltage sides of the bidirectional DC / DC unit; When the bidirectional DC / DC unit operates in a buck mode or a boost mode, there is a circulating current between the comprehensive treatment device and the diode rectifier connected in parallel therewith, and the circulating current control unit is used to eliminate the circulating current between the comprehensive treatment device and the diode rectifier connected in parallel therewith; The circulating current control unit includes a first adder, a second adder, a third adder, a first current regulator, a second current regulator, a third current regulator, a triangular wave generator, a first comparator, a second comparator, a first inverter and a second inverter. The third adder is used for subtracting the current of the first energy storage inductor from the current of the second energy storage inductor and sending the subtracted current to the input end of the third current regulator; The first adder is used for sending the result of subtracting the current of the first energy storage inductor and the output current of the third current regulator from the reference inductor current to the input end of the first current regulator; The second adder is used for adding the output current of the third current regulator to the current obtained by subtracting the current of the second energy storage inductor from the current of the reference inductor and then sending the result to the input terminal of the second current regulator; The first input end of the first comparator is connected to the first input end of the second comparator and the output end of the triangular wave generator, the second input end of the first comparator is connected to the output end of the first current regulator, and the output end of the first comparator is connected to the control end of the first switch tube on the one hand, and connected to the control end of the second switch tube on the other hand after passing through the first inverter; The second input end of the second comparator is connected to the output end of the second current regulator, and the output end thereof is connected to the control end of the fourth switch tube on one hand, and is connected to the control end of the third switch tube on the other hand through the second inverter.

2. The comprehensive management device for the urban rail transit traction power supply system according to claim 1 is characterized in that: When the urban rail transit traction power supply system operates in a vehicle traction condition, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are turned off, and energy is transmitted from the rectifier transformer to the DC traction network only through the diode rectifier, and the circulating current between the comprehensive management device and the diode rectifier connected in parallel with it is zero.

3. The comprehensive management device for the urban rail transit traction power supply system according to claim 2 is characterized in that: When the urban rail transit traction power supply system operates in vehicle traction conditions, the bidirectional DC / DC unit operates in a step-down mode, and the energy on the low-voltage side of the rectifier transformer is transmitted to the DC traction network through the diode rectifier and the comprehensive management device.

4. A comprehensive management method for urban rail transit traction power supply system, characterized in that: The urban rail transit traction power supply system includes a diode rectifier connected between the low-voltage side of the rectifier transformer and the DC traction network, and the comprehensive treatment method includes the following steps: Step 1: Setting a comprehensive treatment device, which includes a PWM rectifier unit, a bidirectional DC / DC unit and a circulating current control unit, wherein the AC side of the PWM rectifier unit is connected to the AC side of the diode rectifier and the low-voltage side of the rectifier transformer, and the DC side is connected to the high-voltage side of the bidirectional DC / DC unit, and the low-voltage side of the bidirectional DC / DC unit is connected to the DC side of the diode rectifier and the DC traction network; Step 2: When the urban rail transit traction power supply system operates in a vehicle traction condition, the PWM rectifier unit of the comprehensive treatment device outputs a compensation current on the AC side. The compensation current is equal in magnitude to the fundamental reactive current and the harmonic current input on the AC side of the diode rectifier connected in parallel to the comprehensive treatment device, but has an opposite phase, so as to ensure that the low-voltage side of the rectifier transformer only outputs a fundamental active current; at the same time, by adjusting the PWM rectifier unit and the bidirectional DC / DC unit, the DC side voltage of the PWM rectifier unit is stabilized, and the voltage value of the DC side voltage of the PWM rectifier unit is ensured to be higher than the peak value of the AC side line voltage of the PWM rectifier unit and the voltage value of the DC traction network, so as to ensure that the bidirectional DC / DC unit can operate in a step-down mode, and the energy on the low-voltage side of the rectifier transformer is transmitted to the DC traction network through the diode rectifier, or the energy on the low-voltage side of the rectifier transformer is transmitted to the DC traction network through the diode rectifier and the comprehensive treatment device; When the urban rail transit traction power supply system operates in a vehicle braking condition, the bidirectional DC / DC unit is controlled to operate in a boost mode, and the energy of the DC traction network is transmitted by the bidirectional DC / DC unit to the DC side of the PWM rectifier unit, and then transmitted to the low-voltage side of the rectifier transformer through the PWM rectifier unit; Step 3: When the DC / DC unit operates in a buck mode or a boost mode, there is a circulating current between the comprehensive treatment device and the diode rectifier connected in parallel therewith, and the circulating current control unit is used to eliminate the circulating current between the comprehensive treatment device and the diode rectifier connected in parallel therewith; the bidirectional DC / DC unit is a three-level structure symmetrical up and down, including a first energy storage inductor and a second energy storage inductor connected before its low-voltage side, and the circulating current control unit controls the current of the first energy storage inductor and the current of the second energy storage inductor to be equal to the reference inductor current, so that the circulating current between the comprehensive treatment device and the diode rectifier connected in parallel therewith is zero; The bidirectional DC / DC unit also includes a first capacitor, a second capacitor, a first switch tube, a second switch tube, a third switch tube and a fourth switch tube. The first capacitor and the second capacitor are connected in series and connected between the high-voltage sides of the bidirectional DC / DC unit; the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series in sequence and connected between the high-voltage sides of the bidirectional DC / DC unit, the series connection point of the first switch tube and the second switch tube is connected to one end of the first energy storage inductor, the series connection point of the second switch tube and the third switch tube is connected to the series connection point of the first capacitor and the second capacitor, the series connection point of the third switch tube and the fourth switch tube is connected to one end of the second energy storage inductor, and the other end of the first energy storage inductor and the other end of the second energy storage inductor are connected between the low-voltage sides of the bidirectional DC / DC unit; In the step 3, when the bidirectional DC / DC unit operates in the boost mode or the buck mode, the specific method of using the circulating current control unit to eliminate the circulating current between the comprehensive treatment device and the diode rectifier connected in parallel therewith is: Sending the difference between the reference inductor current and the current of the first energy storage inductor to a first current regulator for calculation, and sending the difference between the reference inductor current and the current of the second energy storage inductor to a second current regulator for calculation; Send the difference between the current of the first energy storage inductor and the current of the second energy storage inductor to the third current regulator for calculation, subtract the difference between the current of the reference inductor and the current of the first energy storage inductor from the current output of the third current regulator and send it to the first current regulator for calculation, add the difference between the current of the reference inductor and the current of the second energy storage inductor and send it to the second current regulator for calculation; Compare the output signal of the first current regulator with the triangular wave signal and generate a first control signal according to the comparison result, wherein the first control signal is used to control the first switch tube, and the first control signal is inverted and used to control the second switch tube; Compare the output signal of the second current regulator with the triangular wave signal and generate a second control signal according to the comparison result, wherein the second control signal is used to control the fourth switch tube, and the second control signal is inverted and used to control the third switch tube; The current of the first energy storage inductor and the current of the second energy storage inductor are adjusted by controlling the on and off of the first to fourth switch tubes, so that the current of the first energy storage inductor is equal to the current of the second energy storage inductor and equal to the reference inductor current.

5. The comprehensive management method of the urban rail transit traction power supply system according to claim 4 is characterized in that: When the urban rail transit traction power supply system operates in a vehicle traction condition, a capacitive reactive current is provided to the rectifier transformer, so that the output voltage of the rectifier transformer remains unchanged when the load increases, thereby ensuring that the output DC voltage of the diode rectifier remains unchanged.

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