A rail transit vehicle network voltage detection circuit and inrush current suppression method

Abstract

The present invention discloses a network voltage detection circuit and inrush current suppression method for rail transit vehicles. The network voltage detection circuit includes at least one high-voltage voltage transformer for monitoring the network voltage. The high-voltage voltage transformer includes multiple secondary windings connected to loads. Inrush current suppression is achieved by, on the one hand, balancing the equivalent loads corresponding to the multiple secondary windings, and on the other hand, optimizing the synchronous transformer within the traction converter. The inrush current suppression method for the network voltage detection circuit is simple, easy to implement, and highly economical, practical, and reliable.

Description

Technical Field

[0001] The present invention belongs to the field of rail transit network voltage detection and relates to the suppression of inrush current in a network voltage detection circuit. Background Art

[0002] Currently, rail vehicles generally utilize a high-voltage current collection system. Electric energy passes through pantographs, high-voltage disconnectors, and main circuit breakers, and then is stepped down by traction transformers before being supplied to EMUs. The high voltage voltages used can reach up to 25kV AC, and the currents can reach hundreds of amperes. The detection and protection of high-voltage circuits in rail vehicles is crucial for the safe operation of EMUs. Currently, the AC high-voltage catenary system for rail vehicles generally utilizes a segmented power supply system, with a de-energized zone between the segments, known as the phase-splitting zone. When a rail vehicle passes through a phase-splitting zone, the grid voltage detection circuit generates an inrush current. Excessive inrush current can cause the secondary fuse of the high-voltage voltage transformer to rapidly wear out or even blow, resulting in a no-grid voltage failure on the rail vehicle. This type of failure has occurred on various domestic EMUs. Designing an economical and practical grid voltage detection circuit to suppress inrush current during phase-splitting is crucial to enhancing the reliability of grid voltage detection.

[0003] Rail vehicles commonly implement overvoltage protection by installing lightning arresters on both sides of the main circuit breaker. These arresters provide general protection for electrical equipment (e.g., CN110907742A). During actual rail vehicle operation, under over-equalized operating conditions, the inrush current generated on the secondary side of the high-voltage transformer in the grid voltage detection circuit can still pose a significant risk to the secondary fuses, necessitating additional optimization measures. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a rail transit vehicle network voltage detection circuit and an inrush current suppression method to effectively suppress the inrush current of the network voltage detection circuit in view of the shortcomings of the existing technology.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a rail transit vehicle network voltage detection circuit, comprising:

[0006] At least one high-voltage voltage transformer for monitoring the grid voltage, the high-voltage voltage transformer comprising a plurality of secondary windings connected to loads;

[0007] The equivalent loads corresponding to the multiple secondary windings are balanced.

[0008] The present invention balances the load of the high-voltage voltage transformer output end (i.e., the secondary winding) of the grid voltage detection circuit, thereby increasing the minimum impedance of the high-voltage voltage transformer output end and effectively suppressing the inrush current of the grid voltage detection circuit from the circuit structure.

[0009] In the present invention, the load includes a plurality of traction converters and a grid voltage meter arranged in the driver's cab.

[0010] In the present invention, it should be noted that equivalent load balancing does not limit the load at the output of the high-voltage voltage transformer to absolute balance; relative balance also meets the design requirements of the present invention. In the present invention, the following structure can be used to ensure equivalent load balancing of multiple secondary windings.

[0011] Assume that the number of secondary windings is M and the number of traction converters is N; if the remainder of N / M is 0, each of the secondary windings is connected to N / M traction converters; if the remainder of N / M is not 0, then any L secondary windings are each connected to K+1 traction converters, and the remaining ML secondary windings are each connected to K traction converters; where K is the quotient of N / M and L is the remainder of N / M; any two secondary windings are each connected to one of the grid voltage meters.

[0012] Based on the relationship between the number of traction converters and the number of secondary windings, it is determined how to distribute the traction converters to each secondary winding to ensure load balance on the secondary windings of the high-voltage voltage transformer.

[0013] In the present invention, the number of the high-voltage voltage transformers is the same as the number of pantographs in rail transit vehicles, ensuring the reliability of the grid voltage detection circuit.

[0014] In the present invention, the number of secondary windings of each high-voltage voltage transformer is 2. This has strong practicality, low cost, and is more convenient for load balancing distribution.

[0015] In the present invention, the load further includes P electric energy meters for measuring the electric energy consumed by the train, wherein the electric energy meters are user-selectable devices.

[0016] In order to further ensure the load balance of the secondary winding of the high-voltage voltage transformer, if P<M, then any P secondary windings are connected to one electric energy meter; if P=M, then each secondary winding is connected to one electric energy meter.

[0017] In order to further ensure the load balance of the secondary winding of the high-voltage voltage transformer, when the remainder N / M is not 0, if P≤ML, then any P secondary windings among the ML secondary windings connected to the K traction converters are each connected to one of the electric energy meters; if P>ML, then any P secondary windings among the ML secondary windings connected to the K traction converters are each connected to one of the electric energy meters, and any P-(ML) secondary windings among the remaining L secondary windings are each connected to one of the electric energy meters.

[0018] In the present invention, the number of turns of the synchronous transformer used for voltage acquisition within the traction converter can also be appropriately increased to effectively suppress the inrush current in the grid voltage detection circuit under the requirements of grid voltage protection. The traction converter includes a synchronous transformer for voltage acquisition, which is connected to a high-voltage voltage transformer. After the number of turns of the synchronous transformer is increased, the primary winding resistance value R1 satisfies the following relationship: Among them, I t is the maximum allowable inrush current of the synchronous transformer, R0 is the primary winding resistance value before the number of turns of the synchronous transformer coil is increased, and I0 is the actual maximum inrush current.

[0019] In the present invention, the synchronous transformer meets the following conditions: 涌流 <I 涌流最大值 ,△U<△U m and △θ<△θ m ; Among them, I 涌流 is the inrush current of the synchronous transformer, △U is the absolute value of the voltage difference after the voltage drop at the synchronous transformer is converted to MkV level, △θ is the absolute value of the phase difference between the primary and secondary sides of the synchronous transformer, I 涌流最大值 is the maximum allowable inrush current of the synchronous transformer, △U m is the maximum error allowed by the grid voltage, △θ m is the maximum absolute value of the phase difference between the primary and secondary sides of the synchronous transformer. M is the voltage level selected in the test, for example, 25kV.

[0020] As an inventive concept, the present invention further provides a rail transit vehicle, which adopts the above-mentioned grid voltage detection circuit of the present invention.

[0021] As an inventive concept, the present invention also provides a method for suppressing inrush current in a rail transit vehicle grid voltage detection circuit, wherein the grid voltage detection circuit includes multiple high-voltage voltage transformers; the high-voltage voltage transformers include multiple secondary windings connected to loads; the loads include multiple traction converters and a grid voltage meter installed in a driver's cab; the traction converter includes a synchronous transformer for collecting voltage, and the synchronous transformer is connected to the high-voltage voltage transformer; the method includes: increasing the number of turns of the synchronous transformer coil.

[0022] In order to further ensure the inrush current suppression effect, in the present invention, the equivalent loads corresponding to the multiple secondary windings are balanced.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The measures for suppressing inrush current in the grid voltage detection circuit of the present invention are simple, easy to implement, and highly economical, practical, and reliable.

[0025] 2) The present invention effectively suppresses the inrush current of the grid voltage detection circuit under the requirement of grid voltage protection by appropriately increasing the number of turns of the synchronous transformer used for voltage collection inside the traction converter.

[0026] 3) The present invention balances the loads at the two output ends of the high-voltage voltage transformer of the balanced grid voltage detection circuit, thereby effectively suppressing the inrush current of the grid voltage detection circuit from the perspective of circuit structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : This is the secondary side equivalent circuit of the high voltage voltage transformer according to an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the testing principle of the inrush current suppression effect of the synchronous transformer according to an embodiment of the present invention;

[0029] Figure 3 This is a grid voltage detection circuit with four traction converters according to an embodiment of the present invention;

[0030] Figure 4 This is a grid voltage detection circuit with three traction converters according to an embodiment of the present invention;

[0031] Figure 5 An optimized analog circuit for the synchronous transformer according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In one implementation of the present invention, the grid voltage detection circuit includes a high-voltage voltage transformer, a grid voltage meter, an electric energy meter (whether to use it depends on the specific situation) and a traction converter. High-voltage AC current-collecting rail vehicles usually adopt a dual pantograph arrangement scheme, with a high-voltage voltage transformer arranged after each pantograph. In actual operation, one pantograph is raised and the other is on standby. After the pantograph is raised, the high-voltage voltage transformer at the raised end detects the grid voltage. The primary side (primary side) of the high-voltage voltage transformer is connected to the grid through the main circuit breaker, and the secondary side (secondary winding) is connected to the load in turn through a fuse and a switch (generally a relay contact). The load in the embodiment of the present invention includes the above-mentioned grid voltage meter, electric energy meter and traction converter.

[0033] In one implementation of the present invention, the measure for suppressing inrush current in the grid voltage detection circuit is to optimize the high-voltage detection circuit structure and balance the load on the secondary side of the high-voltage voltage transformer. After the rail vehicle pantograph is raised, the high-voltage voltage transformer at the pantograph end detects the grid voltage. A high-voltage voltage transformer secondary side has two output terminals, and the secondary side load includes a traction converter, a grid voltage meter, and an electric energy meter (as appropriate). By designing the equivalent load 1 and equivalent load 2 at the two output terminals of the high-voltage voltage transformer secondary side to be balanced, ensuring that the impedance of equivalent load 1 and the impedance of equivalent load 2 are equal or as close as possible, inrush current can be effectively suppressed from the circuit structure. When the number of traction converters is even, the grid voltage detection circuit adopts a symmetrical layout. The high-voltage voltage transformer output terminals 1 and 2 (the high-voltage voltage transformer output terminals are exactly the same, the names are only for convenience of distinction, and the output terminals are the secondary windings) are respectively connected to half of the traction converter and a grid voltage meter in the driver's cab at one end. If the rail vehicle has an electric energy meter, the electric energy meter should also be arranged in a balanced manner as much as possible. If the rail vehicle has one energy meter, the energy meter is connected to any output terminal of the high-voltage transformer. If the rail vehicle has two energy meters, one energy meter is connected to each of the output terminals 1 and 2 of the high-voltage voltage transformer. When the number of traction converters is odd, the high-voltage detection circuit adopts a layout with slightly less symmetry. One more traction converter is connected to the output terminal 1 of the high-voltage voltage transformer, and one less traction converter is connected to the output terminal 2 of the high-voltage voltage transformer. Most or all of the other loads (including the voltmeter and energy meter at the driver's cab end) are connected to the output terminal 2 of the high-voltage voltage transformer. The specific connection method of other loads can be determined based on the contribution of each load to the inrush current, and the equivalent load balance of the output terminals 1 and 2 of the high-voltage transformer is ensured as much as possible.

[0034] For example, if the number of traction converters is 3, the number of electric energy meters is 1, and the number of grid voltage meters is 2, then the output terminal 1 of the high-voltage voltage transformer can be connected to 2 traction converters and 1 grid voltage meter, and the output terminal 2 of the high-voltage voltage transformer can be connected to the electric energy meter, 1 traction converter and 1 grid voltage meter.

[0035] For example, if the number of traction converters is 3, the number of electricity meters is 2, and the number of grid voltage meters is 2, then the output terminal 1 of the high-voltage voltage transformer can be connected to 2 traction converters, 1 grid voltage meter, and 1 electricity meter, and the output terminal 2 of the high-voltage voltage transformer can be connected to 1 electricity meter, 1 traction converter, and 1 grid voltage meter.

[0036] In another implementation of the present invention, the measure for suppressing inrush current in the grid voltage detection circuit is to optimize the synchronous transformer used for voltage acquisition within the traction converter. During the phase separation process of a rail vehicle, inrush current is generated in the circuit between the high-voltage transformer in the grid voltage detection circuit and the synchronous transformer within the traction converter. Increasing the number of turns in the synchronous transformer used for voltage acquisition within the traction converter can effectively reduce the magnetizing inrush current. While increasing the number of turns in the synchronous transformer suppresses the inrush current, it also increases the winding resistance, leakage reactance, and magnetizing reactance, leading to increased error in the synchronous transformer. When optimizing a synchronous transformer by increasing the number of turns, the appropriate number of turns must be considered to control the accuracy of the synchronous transformer and meet the requirements for grid voltage detection and high-voltage protection. Furthermore, given that the resistance of the primary winding of a synchronous transformer is proportional to the number of turns, the primary winding resistance R is used to represent the number of turns. Given the characteristics of the synchronous transformer's magnetization curve, there is no analytical formula for calculating the error and inrush current of the synchronous transformer after increasing the number of turns. The appropriate primary winding R (i.e., the appropriate number of turns) for a synchronous transformer can be determined through simulation tests. The simulation test equipment includes a power supply, a main circuit breaker, a high-voltage voltage transformer, fuses, a switch, multiple synchronous transformers with increased turns, a traction control unit, and an oscilloscope. The test circuit is connected as follows: the power supply is first connected to a main circuit breaker, then to the primary of the high-voltage voltage transformer. One output terminal of the high-voltage voltage transformer's secondary is connected to the primary of the synchronous transformer via a fuse and a switch. Finally, the secondary of the synchronous transformer is connected to the traction control unit. The number of synchronous transformers connected in parallel after the high-voltage transformer is determined by the number of traction control units connected to the high-voltage transformers in the grid voltage measurement circuit; that is, the number of synchronous transformers and traction control units is the same. The test procedure involves supplying 25kV AC from the power supply, closing the switch between the high-voltage voltage transformer and the synchronous transformer, and then rapidly opening and closing the main circuit breaker to simulate the grid voltage detection circuit's operating conditions when a rail vehicle is over-phased. The primary winding resistance R0 of a synchronous transformer to be optimized is measured. The maximum inrush current I0 (equivalent to the actual maximum inrush current) generated during the test is measured using the simulation. Considering that the synchronous transformer core operates in the saturation region when the synchronous transformer generates inrush current, the optimized synchronous transformer primary winding satisfies the following inequality:

[0037]

[0038] In the above formula, I t is the maximum allowable inrush current of the synchronous transformer after optimization, and R1 is the primary winding resistance of the synchronous transformer after optimization.

[0039] Make the primary winding resistance R satisfy the above inequality and have the same magnitude as I0R0 / I t Several synchronous transformers are used as test samples. During the test, the peak value of the primary surge current of the synchronous transformer is 涌流Characterize the size of the inrush current; during the test, the absolute value of the voltage difference △U after the synchronous transformer terminal voltage drop is converted to 25kV level and the absolute value of the phase difference between the primary and secondary sides of the synchronous transformer △θ are used to characterize the voltage size and phase error. The table records the primary winding R, I of each synchronous transformer sample. 涌流 , △U and △θ. According to the inrush current value allowed for long-term stable operation of the secondary side fuse of the high-voltage transformer in the rail vehicle network voltage detection circuit, the maximum allowable inrush current of the synchronous transformer I is determined. 涌流最大值 , determine the maximum allowable error value of the network voltage △U according to the network voltage protection logic m The maximum value and the maximum absolute value of the phase difference between the primary and secondary sides (i.e. the primary side and the secondary side) △θ m . Select from the test samples that both meet I 涌流 <I 涌流最大值 ,△U<△U m and △θ<△θ m For a synchronous transformer, the number of turns corresponding to winding R is the appropriate number of turns (in actual testing, redundancy is appropriately considered for grid voltage measurement errors and inrush current). Tests have shown that when the number of turns is appropriately increased and the internal resistance is increased to a certain value, the synchronous transformer has a good inrush current suppression effect and meets accuracy requirements.

[0040] When designing the grid voltage detection circuit, an optimized synchronous transformer is selected. Furthermore, the grid voltage detection circuit connection is arranged to balance the equivalent load on the secondary side of the high-voltage voltage transformer. By combining the two implementation methods of the present invention, inrush current can be effectively suppressed in the rail vehicle grid voltage detection circuit, improving the reliability of grid voltage detection economically and practically.

[0041] Figure 1 This is the equivalent circuit of the secondary side of the high-voltage voltage transformer in an embodiment of the present invention. The layout of the grid voltage detection circuit balances load 1 and load 2, which can effectively suppress inrush current.

[0042] Figure 2 This is a schematic diagram of the principle of testing the inrush current suppression effect of a synchronous transformer according to an embodiment of the present invention. The number of synchronous transformers connected in parallel after the high-voltage transformer is determined by the number of traction control units connected to the high-voltage transformers of the grid voltage measurement circuit. Figure 2 The figure contains only one synchronous transformer, and the secondary side of the high-voltage voltage transformer only represents one output terminal, which is only used to illustrate the principle. Close the switch between the high-voltage voltage transformer and the synchronous transformer (the switch is connected between the fuse connected to the secondary winding of the high-voltage voltage transformer and the primary winding of the synchronous voltage transformer), and simulate the over-phase condition of the grid voltage detection circuit by closing and opening the main circuit breaker at high speed. Synchronous transformers with different coil turns are selected for testing, and the R of each synchronous transformer is recorded in the table. 内 , I 涌流, △U and △θ. Taking into account the actual grid voltage measurement circuit high-voltage protection grid voltage error requirements and the allowable range of inrush current (redundancy is appropriately considered for both grid voltage measurement error and inrush current), a synchronous transformer with an appropriate number of coil turns is selected from the test sample.

[0043] Figure 3 The network voltage detection circuit of this embodiment includes two high-voltage voltage transformers, relay contacts (i.e. Figure 3 The optimized grid voltage detection circuit structure adopts a symmetrical layout, with the two output terminals of the secondary side of the high-voltage voltage transformer each connected to two traction converters, a voltmeter, and an watt-hour meter. Output terminal 1 of high-voltage voltage transformer 1 is connected to traction converter 1, traction converter 2, voltmeter 1, and watt-hour meter 1; output terminal 2 of high-voltage voltage transformer 1 is connected to traction converter 3, traction converter 4, voltmeter 2, and watt-hour meter 2; output terminal 1 of high-voltage voltage transformer 2 is connected to traction converter 3, traction converter 4, voltmeter 2, and watt-hour meter 2; output terminal 2 of high-voltage voltage transformer 2 is connected to traction converter 1, traction converter 2, voltmeter 1, and watt-hour meter 1. When the pantograph at a certain high-voltage voltage transformer is raised, the switch at that pantograph terminal closes, and grid voltage detection begins.

[0044] Figure 4 This is a network voltage detection circuit with three traction converters according to an embodiment of the present invention. The circuit of this embodiment includes two high-voltage voltage transformers, relay contacts (i.e. Figure 4 The switch in the grid), three traction converters, two voltmeters and an electric energy meter. The optimized scheme for the grid voltage detection circuit structure is to adopt an asymmetric layout. One output end of the secondary side of the high-voltage voltage transformer is connected to two traction converters and a grid voltage meter, and the other output end is connected to a traction converter, a grid voltage meter and an electric energy meter. Output end 1 of high-voltage voltage transformer 1 is connected to traction converter 1, traction converter 3 and grid voltage meter 2; output end 2 of high-voltage voltage transformer 1 is connected to traction converter 2, grid voltage meter 1 and electric energy meter; output end 1 of high-voltage voltage transformer 2 is connected to traction converter 1, traction converter 3 and grid voltage meter 2; output end 2 of high-voltage voltage transformer 2 is connected to traction converter 2, grid voltage meter 1 and electric energy meter. When the pantograph at a certain high-voltage voltage transformer end is raised, the switch at the pantograph end is closed and the grid voltage is detected. The scheme of this embodiment is not necessarily the best and is for illustration only. The specific situation still needs to be analyzed according to the contribution of each load to the inrush current.

[0045] In the embodiment of the present invention, a certain type of EMU is composed of 6 motors and 2 tractions, the grid voltage detection circuit adopts a symmetrical layout, the secondary side of a high-voltage transformer is connected to three traction converters, and the synchronous transformer optimization analog circuit is as follows: Figure 5As shown. The inrush current of three synchronous transformers without optimization and with an internal resistance of 20Ω was measured by simulation test, and the test inrush current value was 1690mA. 100mA was taken as the maximum inrush current allowed by the optimized synchronous transformer. According to the range of winding resistance, synchronous transformers with internal resistances of 150 ohms and 300 ohms were made as test samples. Three synchronous transformers with internal resistances of 150 ohms and 300 ohms were taken, respectively. Figure 5 A simulation test was conducted using this connection method. The test data is shown in Table 1. The test showed that increasing the internal resistance of the synchronous transformer to 150 ohms achieved better inrush current suppression, and the voltage measurement error met the requirements. This example is for illustrative purposes only and does not necessarily represent optimal results.

[0046] Table 1 Test results of synchronous transformers with different number of turns

[0047]

Claims

1. A rail transit vehicle network voltage detection circuit, characterized in that: include: At least one high-voltage voltage transformer for monitoring the grid voltage, the high-voltage voltage transformer comprising a plurality of secondary windings connected to loads; The equivalent loads corresponding to the multiple secondary windings are balanced; The load includes a plurality of traction converters and a grid voltage meter arranged in the driver's cab; Assume that the number of secondary windings is M and the number of traction converters is N; if the remainder of N / M is 0, then each secondary winding is connected to N / M traction converters; if the remainder of N / M is not 0, then any L secondary windings are each connected to K+1 traction converters, and the remaining ML secondary windings are each connected to K traction converters; where K is the quotient of N / M and L is the remainder of N / M; any two secondary windings are each connected to one grid voltage meter; The load also includes P electric energy meters; If P < M, then any P secondary windings are each connected to one of the electric energy meters; if P = M, then each of the secondary windings is connected to one of the electric energy meters; When the remainder of N / M is not 0, if P≤ML, then any P secondary windings among the ML secondary windings connected to the K traction converters are each connected to one of the electric energy meters; if P>ML, then any P secondary windings among the ML secondary windings connected to the K traction converters are each connected to one of the electric energy meters, and any P-(ML) secondary windings among the remaining L secondary windings are each connected to one of the electric energy meters.

2. The rail transit vehicle network voltage detection circuit according to claim 1, characterized in that: The number of the high-voltage voltage transformers is the same as the number of pantographs on rail transit vehicles.

3. The rail transit vehicle network voltage detection circuit according to claim 1, characterized in that: The number of secondary windings of each high-voltage voltage transformer is 2.

4. The rail transit vehicle network voltage detection circuit according to any one of claims 1 to 3, characterized in that: The traction converter includes a synchronous transformer for collecting voltage, and the synchronous transformer is connected to a high-voltage voltage transformer. The number of turns of the synchronous transformer coil is increased, and the primary winding resistance value R1 after the number of turns of the synchronous transformer coil is increased satisfies the following relationship: Among them, I t is the maximum allowable inrush current of the synchronous transformer, R0 is the primary winding resistance value before the number of turns of the synchronous transformer coil is increased, and I0 is the actual maximum inrush current.

5. A rail transit vehicle, characterized in that: It adopts the grid voltage detection circuit described in any one of claims 1 to 4.

6. A method for suppressing inrush current in a network voltage detection circuit of a rail transit vehicle, wherein the network voltage detection circuit includes multiple high-voltage voltage transformers; the high-voltage voltage transformers include multiple secondary windings connected to loads; the loads include multiple traction converters and a network voltage meter disposed in a driver's cab; the traction converters include synchronous transformers for collecting voltage, the synchronous transformers being connected to the high-voltage voltage transformers; characterized in that: The method comprises: setting equivalent loads corresponding to the plurality of secondary windings to be balanced; Assume that the number of secondary windings is M and the number of traction converters is N; if the remainder of N / M is 0, then each secondary winding is connected to N / M traction converters; if the remainder of N / M is not 0, then any L secondary windings are each connected to K+1 traction converters, and the remaining ML secondary windings are each connected to K traction converters; where K is the quotient of N / M and L is the remainder of N / M; any two secondary windings are each connected to one grid voltage meter; The load also includes P electric energy meters; If P < M, then any P secondary windings are each connected to one of the electric energy meters; if P = M, then each of the secondary windings is connected to one of the electric energy meters; When the remainder of N / M is not 0, if P≤ML, then any P secondary windings among the ML secondary windings connected to the K traction converters are each connected to one of the electric energy meters; if P>ML, then any P secondary windings among the ML secondary windings connected to the K traction converters are each connected to one of the electric energy meters, and any P-(ML) secondary windings among the remaining L secondary windings are each connected to one of the electric energy meters.

7. The method according to claim 6, characterized in that The number of the high-voltage voltage transformers is the same as the number of pantographs on rail transit vehicles.

8. The method according to claim 6, characterized in that The number of secondary windings of each high-voltage voltage transformer is 2.

9. The method according to claim 6, characterized in that Also includes: Increase the number of turns of the synchronous transformer coil.

10. The method according to claim 9, characterized in that The primary winding resistance R1 of the synchronous transformer with increased turns satisfies the following relationship: Among them, I t is the maximum allowable inrush current of the synchronous transformer, R0 is the primary winding resistance value before the number of turns of the synchronous transformer coil is increased, and I0 is the actual maximum inrush current.

11. The method according to claim 10, characterized in that The synchronous transformer meets the following conditions: 涌流 <I 涌流最大值 ,△U<△U m and △θ<△θ m ; Among them, I 涌流 is the inrush current of the synchronous transformer, △U is the absolute value of the voltage difference after the voltage drop at the synchronous transformer is converted to MkV level, △θ is the absolute value of the phase difference between the primary and secondary sides of the synchronous transformer, I 涌流最大值 is the maximum allowable inrush current of the synchronous transformer, △U m is the maximum error allowed by the grid voltage, △θ m It is the maximum absolute value of the phase difference between the primary and secondary sides of the synchronous transformer.

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