阅读说明：本技术 一种基于多重Boost/Buck斩波器的多流制牵引传动系统 (multi-system traction transmission system based on multiple Boost/Buck choppers ) 是由 许加柱 项锦文 刘裕兴 于 2019-09-26 设计创作，主要内容包括：本发明公开一种基于多重Boost/Buck斩波器的多流制牵引传动系统,包括两个双向开关、N个储能电感、M个四象限变流器和稳压控制器；第一双向开关的固定端接入直流牵引网电源,第二双向开关的固定端与牵引逆变器的直流侧连接；两个双向开关的两个触点端相互交叉连接；所有N个储能电感的一端均与第一双向开关的第一触点端连接,另一端分别与N个桥臂中点一一对应连接；每个四象限变流器的桥臂第一共接点均与第一双向开关的第二触点端连接,桥臂第二共接点均接地；第二双向开关的固定端、每个储能电感分别所在支路以及四象限变流器的门极端口均与稳压控制器连接。本发明可以有效降低牵引网电压波动对系统性能的影响。(the invention discloses a multi-system traction transmission system based on a multiple Boost/Buck chopper, which comprises two bidirectional switches, N energy storage inductors, M four-quadrant converters and a voltage stabilizing controller, wherein the two bidirectional switches are connected with the N energy storage inductors; the fixed end of the first bidirectional switch is connected with a direct-current traction network power supply, and the fixed end of the second bidirectional switch is connected with the direct-current side of the traction inverter; two contact ends of the two bidirectional switches are connected with each other in a cross way; one end of each of the N energy storage inductors is connected with a first contact end of the first bidirectional switch, and the other end of each of the N energy storage inductors is connected with the middle points of the N bridge arms in a one-to-one correspondence manner; the first common contact of the bridge arms of each four-quadrant converter is connected with the second contact end of the first bidirectional switch, and the second common contact of the bridge arms is grounded; the fixed end of the second bidirectional switch, the branch where each energy storage inductor is respectively located and the gate port of the four-quadrant converter are connected with the voltage stabilizing controller. The invention can effectively reduce the influence of the voltage fluctuation of the traction network on the system performance.)

1. a multi-system traction transmission system based on multiple Boost/Buck choppers comprises a traction inverter (9) and a traction motor (10), and is characterized by further comprising multiple Boost/Buck choppers consisting of N Boost/Buck choppers, wherein each multiple Boost/Buck chopper comprises a first bidirectional switch S7, a second bidirectional switch S8, N energy storage inductors, M four-quadrant converters and a voltage stabilizing controller (14); wherein 2M is more than or equal to N, and M is more than or equal to 1;

The fixed end of the first bidirectional switch S7 is connected to a direct-current traction network power supply, and the fixed end of the second bidirectional switch S8 is connected with the direct-current side of the traction inverter;

A first contact terminal of the first bidirectional switch S7 is connected with a second contact terminal of the second bidirectional switch S8, and a second contact terminal of the first bidirectional switch S7 is connected with a first contact terminal of the second bidirectional switch S8; a first bidirectional switch S7 and a second bidirectional switch S8, both closed at respective first contact ends, or both closed at respective second contact ends;

One end of each of the N energy storage inductors is connected with a first contact end of the first bidirectional switch S7, and the other end of each of the N energy storage inductors is connected with the middle points of the N bridge arms of the M four-quadrant converters in a one-to-one correspondence manner; the first common contact of the bridge arms of each four-quadrant converter is connected with the second contact end of the first bidirectional switch S7, and the second common contact of the bridge arms is grounded;

The fixed end of the second bidirectional switch S8 and the branch where each energy storage inductor is located are connected with the input port of the voltage stabilizing controller (14) through the sensor, and the output port of the voltage stabilizing controller (14) is connected with the gate port of each four-quadrant converter.

2. The multi-flow traction drive system according to claim 1, wherein each four-quadrant converter comprises 2 legs and is a full-bridge structure composed of four fully-controlled devices with anti-parallel diodes.

3. The multiple-flow traction drive system as claimed in claim 2, wherein the fully controlled device is a MOSFET, an IGBT or an IGCT.

4. The multi-flow traction drive system according to claim 2, wherein the regulated pressure controller (14) comprises a sampling conditioning module, a DSP board module and a drive board module, both of which are connected to the DSP module;

the sampling conditioning module is used for collecting the output voltage of the fixed end of the second bidirectional switch S8 and the current of each energy storage inductor;

the DSP board module is used for processing the data collected by the sampling conditioning module and sending a control signal to the drive board module;

The driving board module is used for generating driving signals for controlling gate ports of four fully-controlled devices according to the control signals, and further controlling the duty ratio of the multiple Boost/Buck chopper.

5. Multiple-flow-regime traction drive system according to claim 2, wherein the regulated controller (14) employs dual PI closed-loop control of a voltage outer loop and a current inner loop.

6. The multi-modulation traction drive system of claim 1, wherein when the dc traction grid voltage is lower than the dc-side voltage of the traction inverter, both first and second bidirectional switches S7 and S8 are closed at respective first contact terminals, the multiple Boost/Buck chopper being a multiple Boost chopper; when the direct-current traction grid voltage is higher than the direct-current side voltage of the traction inverter, the first bidirectional switch S7 and the second bidirectional switch S8 are both closed at the respective second contact ends, and the multiple Boost/Buck chopper is a multiple Buck step-down chopper.

7. The multiple-mode traction drive system as claimed in claim 1, wherein the first and second bidirectional switches S7, S8 are of the type circuit breaker, air switch or contactor.

8. The multi-modulation traction drive system according to claim 1, further comprising an ac-modulation traction drive subsystem, wherein the four-quadrant converter in the multiple Boost/Buck chopper is multiplexed with the four-quadrant converter in the ac-modulation traction drive system through switching elements.

9. The multi-split traction drive system according to claim 8, further comprising a dc pantograph (2), a switch S2, a dc smoothing reactor (4), a switch S9, and a switch S10, wherein the ac traction drive subsystem comprises an ac pantograph (1), an ac input reactor (3), a traction transformer (5), a first four-quadrant converter (6), a second four-quadrant converter (7), a switch S3, a switch S4, a switch S5, and a switch S6;

the direct current pantograph (2), the switch S2 and the direct current smoothing reactor (4) are sequentially connected in series between the direct current traction network and the fixed end of the first bidirectional switch S7;

the switch S9 is connected in series between the first energy storage inductor (12) and the midpoint of the first bridge arm of the first four-quadrant converter (6), and the switch S10 is connected in series between the second energy storage inductor (13) and the midpoint of the second bridge arm of the first four-quadrant converter (6);

the alternating current pantograph (1), the switch S1, the alternating current input reactor (3) and a main side winding of the traction transformer are sequentially connected in series between an alternating current traction network and the ground;

two ends of a first traction winding of the traction transformer (5) are respectively connected with the middle point of a first bridge arm and the middle point of a second bridge arm of a first four-quadrant converter (6) through a switch S3 and a switch S4; the first common contact of the bridge arm of the first four-quadrant converter (6) is connected with the first contact end of the second bidirectional switch S8; a second common contact of a bridge arm of the first four-quadrant converter (6) is connected with a direct-current side ground end of the traction inverter (9);

Two ends of a second traction winding of the traction transformer (5) are respectively connected with the middle point of a first bridge arm and the middle point of a second bridge arm of a second four-quadrant converter (7) through a switch S5 and a switch S6; a first common contact of a bridge arm of the four-quadrant converter II (7) is connected with a first contact end of a second bidirectional switch S8; a second common contact of a bridge arm of the four-quadrant converter II (7) is connected with a direct current side ground end of the traction inverter (9);

A switch S11 is connected between the DC side ground end of the traction inverter (9) and the ground.

Technical Field

the invention relates to the technical field of rail transit traction transmission current transformation, in particular to a multi-system traction transmission system based on a multiple Boost/Buck chopper.

Background

multi-locomotive electric locomotives were first introduced in europe. The railway network in the European region has the remarkable characteristic of multiple traction power supply systems, so that the railway network can be conveniently managed by railway operation companies and reduce the trouble of passenger transfer at junctions, and a multi-system electric locomotive is necessary to be used for realizing the continuous operation of a single train on lines with the multiple power supply systems.

In recent years, research and development and production of multi-stream electric locomotives have been actively carried out by domestic electric locomotive manufacturing and research institutions. On one hand, due to the rapid development of urban groups in China, multi-system electric locomotives are needed to realize interconnection of trunk lines, intercity and urban rail transit lines; on the other hand, the railway technology in China speeds up the walking-out step, and products which can adapt to various foreign power supply systems need to be produced.

at present, the mainstream traction network power supply system comprises four types of alternating current 25kV/50Hz, alternating current 15kV/16.7Hz, direct current 3kV and direct current 1.5 kV. The traction transmission system of the multi-system electric locomotive can adapt to the two or more power supply systems. With the development of high-frequency high-power electronic devices, microcomputer technology and vector control technology, the combination of a high-power voltage source type traction inverter and a three-phase traction asynchronous motor becomes the standard configuration of the current electric traction transmission system, and is also the basis of the traction transmission system of a multi-flow electric locomotive. The method is guided by reducing the whole life cycle cost and improving the system reliability, and the voltage of the intermediate direct current link of the traction transmission system is expected to be stabilized at the same value no matter which power supply system the multi-system electric locomotive runs under.

under the AC power supply system, the pantograph is stepped down by an isolation transformer and then is connected to the DC side of the traction inverter by a four-quadrant rectifier, and under the condition of widely adopting 6.5kV IGBT, the voltage of a DC link is generally stably controlled to a certain value (such as the widely adopted 2800V intermediate DC link voltage level) between 2 kV and 3kV, so that the optimal power supply condition can be provided for the motor. However, in the dc power supply system, the dc traction network is directly connected to the dc side of the traction inverter after passing through the smoothing reactor, which brings about a problem that the voltage of the dc traction network is not matched with the voltage of the intermediate dc link in the ac power supply system, so that the traction motor in the dc power supply system cannot operate in the optimal operation state. Moreover, the voltage mismatch causes frequent fluctuation of the dc link voltage in the switching process of the power supply system, which is not favorable for safe and stable operation of the system. In addition, the dc traction network is directly connected to the dc side of the inverter, and the fluctuations in the network side voltage can affect the operating performance of the voltage source type traction inverter.

In view of the above problems, there is an urgent need for a method for matching the dc traction network voltage with the dc side voltage of the traction inverter, and it is required to add as few additional devices as possible to meet the development trend of integration, miniaturization and light weight of the traction transmission system of the multi-flow system electric locomotive.

Disclosure of Invention

the invention provides a multi-system traction transmission system based on a multi-Boost/Buck chopper, which can realize that the direct-current loop voltage of a traction inverter can be maintained at a desired value under different power supply systems so as to obtain better traction motor performance, higher overall efficiency and more reliable operation.

the purpose of the invention is realized by the following technical scheme:

A multi-system traction transmission system based on multiple Boost/Buck choppers comprises a traction inverter (9), a traction motor (10) and multiple Boost/Buck choppers consisting of N Boost/Buck choppers, wherein each multiple Boost/Buck chopper comprises a first bidirectional switch S7, a second bidirectional switch S8, N energy storage inductors, M four-quadrant converters and a voltage stabilizing controller (14); wherein 2M is more than or equal to N, and M is more than or equal to 1;

The fixed end of the first bidirectional switch S7 is connected to a direct-current traction network power supply, and the fixed end of the second bidirectional switch S8 is connected with the direct-current side of the traction inverter;

a first contact terminal of the first bidirectional switch S7 is connected with a second contact terminal of the second bidirectional switch S8, and a second contact terminal of the first bidirectional switch S7 is connected with a first contact terminal of the second bidirectional switch S8; a first bidirectional switch S7 and a second bidirectional switch S8, both closed at respective first contact ends, or both closed at respective second contact ends;

One end of each of the N energy storage inductors is connected with a first contact end of the first bidirectional switch S7, and the other end of each of the N energy storage inductors is connected with the middle points of the N bridge arms of the M four-quadrant converters in a one-to-one correspondence manner; the first common contact of the bridge arms of each four-quadrant converter is connected with the second contact end of the first bidirectional switch S7, and the second common contact of the bridge arms is grounded;

the fixed end of the second bidirectional switch S8 and the branch where each energy storage inductor is located are connected with the input port of the voltage stabilizing controller (14) through the sensor, and the output port of the voltage stabilizing controller (14) is connected with the gate port of each four-quadrant converter.

Furthermore, each four-quadrant converter comprises 2 bridge arms and is in a full-bridge structure formed by four fully-controlled devices with anti-parallel diodes.

Further, the full-control device is a MOSFET, an IGBT or an IGCT.

further, the voltage stabilizing controller (14) comprises a sampling and conditioning module, a DSP board module and a drive board module, wherein the sampling and conditioning module and the drive board module are connected with the DSP module;

The sampling conditioning module is used for collecting the output voltage of the fixed end of the second bidirectional switch S8 and the current of each energy storage inductor;

the DSP board module is used for processing the data collected by the sampling conditioning module and sending a control signal to the drive board module;

the driving board module is used for generating driving signals for controlling gate ports of four fully-controlled devices according to the control signals, and further controlling the duty ratio of the multiple Boost/Buck chopper.

Further, the voltage stabilizing controller (14) adopts double PI closed loop control of a voltage outer loop and a current inner loop.

Further, when the voltage of the direct-current traction network is lower than the voltage of the direct-current side of the traction inverter, the first bidirectional switch S7 and the second bidirectional switch S8 are both closed at respective first contact ends, and the multiple Boost/Buck chopper is a multiple Boost chopper; when the direct-current traction grid voltage is higher than the direct-current side voltage of the traction inverter, the first bidirectional switch S7 and the second bidirectional switch S8 are both closed at the respective second contact ends, and the multiple Boost/Buck chopper is a multiple Buck step-down chopper.

Further, the first and second bidirectional switches S7 and S8 are of the type of circuit breaker, air switch or contactor.

Further, the system also comprises an AC traction transmission subsystem, and a four-quadrant converter in the multiple Boost/Buck chopper is multiplexed with a four-quadrant converter in the AC traction transmission system through a switching element.

Further, the system comprises a direct current pantograph (2), a switch S2, a direct current smoothing reactor (4), a switch S9 and a switch S10, wherein the alternating current system traction transmission subsystem comprises an alternating current pantograph (1), an alternating current input reactor (3), a traction transformer (5), a four-quadrant converter I (6), a four-quadrant converter II (7), a switch S3, a switch S4, a switch S5 and a switch S6;

The direct current pantograph (2), the switch S2 and the direct current smoothing reactor (4) are sequentially connected in series between the direct current traction network and the fixed end of the first bidirectional switch S7;

the switch S9 is connected in series between the first energy storage inductor (12) and the midpoint of the first bridge arm of the first four-quadrant converter (6), and the switch S10 is connected in series between the second energy storage inductor (13) and the midpoint of the second bridge arm of the first four-quadrant converter (6);

The alternating current pantograph (1), the switch S1, the alternating current input reactor (3) and a main side winding of the traction transformer are sequentially connected between an alternating current traction network and the ground in series;

two ends of a first traction winding of the traction transformer (5) are respectively connected with the middle point of a first bridge arm and the middle point of a second bridge arm of a first four-quadrant converter (6) through a switch S3 and a switch S4; the first common contact of the bridge arm of the first four-quadrant converter (6) is connected with the first contact end of the second bidirectional switch S8; a second common contact of a bridge arm of the first four-quadrant converter (6) is connected with a direct-current side ground end of the traction inverter (9);

Two ends of a second traction winding of the traction transformer (5) are respectively connected with the middle point of a first bridge arm and the middle point of a second bridge arm of a second four-quadrant converter (7) through a switch S5 and a switch S6; a first common contact of a bridge arm of the four-quadrant converter II (7) is connected with a first contact end of a second bidirectional switch S8; a second common contact of a bridge arm of the four-quadrant converter II (7) is connected with a direct current side ground end of the traction inverter (9);

A switch S11 is connected between the DC side ground end of the traction inverter (9) and the ground.

Advantageous effects

The invention provides a multi-system traction transmission system based on a multiple Boost/Buck chopper, which is based on the topology of a traction traditional system of an alternating current power supply system and multiplexes a four-quadrant converter I in the alternating current power supply system in the direct current power supply system based on the idea of equipment multiplexing to form a front-end Buck-Boost chopper. When the voltage of the direct current traction network is lower than the set voltage of the middle direct current link (namely the direct current side voltage of the traction inverter), a step-up chopper is formed, and when the voltage of the direct current traction network is higher than the set voltage of the middle direct current link, a step-down chopper is formed, so that the direct current side voltage of the traction inverter can be maintained at a desired value under different power supply system conditions; and different voltage requirements on the direct current side of the traction inverter can be met, so that the multi-system traction transmission system has a wider application range.

In addition, under any direct current power supply system, the voltage of a traction network is connected with the direct current side of the traction inverter after being regulated and modulated by the front-end buck-boost chopper, so that under the condition of voltage fluctuation of the traction network, the voltage of the direct current side of the traction inverter of the multi-system traction transmission system can be kept stable, a traction motor can always work in the optimal state, the whole life cycle cost of the system is reduced, and the running stability of the system is improved.

in addition, the choppers are connected in a staggered and parallel mode, ripple current can be effectively reduced, the size of passive equipment is further saved, and the electric energy quality is improved. The invention has less added equipment and meets the requirements of miniaturization, light weight and integration of a multi-system traction transmission system.

Drawings

FIG. 1 is a schematic view of an improved multi-flow traction drive system;

FIG. 2 is a schematic diagram of a system with a dual Boost chopper for a 1.5kV power system;

FIG. 3 is a schematic diagram of a system with a double Buck chopper for a 3kV power supply system;

FIG. 4 is a control block diagram of a voltage stabilizing controller of the dual Boost/Buck chopper;

Fig. 5 shows a driving pulse signal and a working current waveform in the dual Boost mode.

description of reference numerals: the synchronous control system comprises a 1-alternating current pantograph, a 2-direct current pantograph, a 3-alternating current input reactor, a 4-direct current filter reactor, a 5-traction transformer, a 6-four-quadrant converter I, a 7-four-quadrant converter II, an 8-direct current link capacitor, a 9-traction inverter, a 10-three-phase asynchronous motor, 11-wheel rails, 12-first energy storage inductors, 13-second energy storage inductors, a 14-voltage stabilizing controller, S1-S6-one-way switches, S9-S11-one-way switches, and S7-S8-two-way switches.

Detailed Description

the present invention will be described in detail below with reference to the drawings and examples.

The invention provides a multi-system traction transmission system based on multiple Boost/Buck choppers, wherein the multiple Boost/Buck choppers are composed of N Boost/Buck choppers, and the specific value of N can be specifically determined according to the voltage grade of a direct-current traction network power supply which is actually connected and the voltage withstanding grade of devices in the traction transmission system. In this embodiment, taking the dc side voltage class of the traction inverter of the multi-system traction transmission system as 2800V, N is 2, and M is 1 as an example, a step-up chopper is required in the dc 1.5kV traction power supply system, and a step-down chopper is required in the dc 3kV traction power supply system. Since N is 2 in this embodiment, the multiple Boost/Buck chopper in this embodiment is a dual Boost/Buck chopper, which is specifically explained in detail as follows.

in this embodiment, a multi-system traction transmission system based on a dual Boost/Buck chopper is shown in fig. 1, and includes an ac pantograph 1, a dc pantograph 2, an ac input reactor 3, a dc smoothing reactor 4, a traction transformer 5, a first four-quadrant converter 6, a second four-quadrant converter 7, a dc link capacitor 8, a traction inverter 9, a three-phase asynchronous motor 10, a wheel rail 11, a first energy storage inductor 12, a second energy storage inductor 13, a voltage stabilizing controller 14, unidirectional switches S1 to S6, first bidirectional switches S7 to S8, and unidirectional switches S9 to S11.

The four-quadrant converter I6 is a full-bridge structure formed by four fully-controlled devices V1-V4 with anti-parallel diodes D1-D4, wherein the fully-controlled devices can be MOSFETs, IGBTs or IGCTs, and the IGBTs are taken as an example in the embodiment. The four-quadrant converter I6 comprises a first bridge arm and a second bridge arm, each bridge arm is a half bridge formed by two fully-controlled devices, and the connecting point of the two fully-controlled devices on the same bridge arm is the middle point of the bridge arm; in order to explain the technical scheme more clearly, one of the two common connection points is named as a first common connection point of the bridge arm of the four-quadrant converter, the other one is named as a second common connection point of the bridge arm of the four-quadrant converter, and other connection points are named differently and have the same substantial circuit structure, so that the invention is also within the protection scope. In this embodiment, as shown in fig. 2 and 3, a connection point of the full-control devices V1 and V3 is a middle point of the first bridge arm, a connection point of the full-control devices V2 and V4 is a middle point of the second bridge arm, a connection point of the full-control devices V1 and V2 is a first common point of the bridge arms of the four-quadrant converter, and a connection point of the full-control devices V3 and V4 is a second common point of the bridge arms of the four-quadrant converter. The four-quadrant converter two 7 has the same structure as the four-quadrant converter one 6, and is not described herein again.

the switches S1-S11 may be of the type that is automatic switches such as circuit breakers, air switches, contactors, and the like.

the alternating current pantograph 1 is connected with an alternating current traction network, sequentially passes through a one-way switch S1 and an alternating current input reactor 3 and then is connected with a main side winding of a traction transformer 5; the primary winding of the traction transformer is also connected to the wheel rail 11. Two ends of a first traction winding of the traction transformer 5 are respectively connected with the middle point of a first bridge arm and the middle point of a second bridge arm of the four-quadrant converter I6 through a one-way switch S3 and a one-way switch S4; the first common contact of the bridge arms of the first four-quadrant converter 6 is connected with the first contact end of the second bidirectional switch S8; and a second common contact of a bridge arm of the first four-quadrant converter 6 is connected with a direct-current side ground end of the traction inverter 9. Two ends of a second traction winding of the traction transformer 5 are respectively connected with the middle point of a first bridge arm and the middle point of a second bridge arm of the four-quadrant converter II 7 through a one-way switch S5 and a one-way switch S6; the first common contact of the bridge arm of the four-quadrant converter II 7 is connected with the first contact end of the second bidirectional switch S8; and a second common contact of a bridge arm of the second four-quadrant converter 7 is connected with a direct-current side ground end of the traction inverter 9.

the direct current pantograph 2 is connected with a direct current traction network, and is connected with the fixed end of a first bidirectional switch S7 through a unidirectional switch S1 and a direct current smoothing reactor 4 in sequence. The fixed end of the second bidirectional switch S8 is connected in parallel through the dc link capacitor 8 and then connected to the dc side of the traction inverter 9, and the ac side of the traction inverter 9 is connected to the three-phase asynchronous motor 10. The middle point of the first bridge arm of the four-quadrant converter I6 is simultaneously connected with the first contact end of the first bidirectional switch S7 and the second contact end of the second bidirectional switch S8 after passing through the unidirectional switch S9 and the first energy storage inductor 12; the middle point of the second bridge arm of the first four-quadrant converter 6 is connected with the first contact end of the first bidirectional switch S7 and the second contact end of the second bidirectional switch S8 through the unidirectional switch S10 and the second energy storage inductor 12; a first common point of a bridge arm of the four-quadrant converter I6 is simultaneously connected with a first contact end of the second bidirectional switch S8 and a second contact end of the first bidirectional switch S7; and a second common connection point of a bridge arm of the fourth quadrant converter 6, a common connection point of the direct-current link capacitor 8 and a direct-current side ground end of the traction inverter 9 are connected with the wheel rail 11 through a one-way switch S11.

the voltage stabilizing controller comprises a sampling conditioning module, a DSP board module and a driving board module, wherein the sampling conditioning module is connected with a voltage sensor on the direct current side of the traction inverter and used for collecting output voltage of the fixed end of a second bidirectional switch S8, namely voltage u _c at two ends of a direct current link capacitor 8, a Hall element is arranged on a branch where a first energy storage inductor 12 is located, the sampling conditioning module is connected with a Hoel element and used for collecting current i _L1 of the first energy storage inductor 12, a Hall element is arranged on a branch where a second energy storage inductor 13 is located, the sampling conditioning module is connected with the Hall element and used for collecting current i _L2 of a second energy storage inductor 13, the DSP board module is connected with the sampling conditioning module and used for processing collected voltage and current data and sending control signals to the driving board module, and the driving board module is used for generating control signals for controlling gate ports of four fully-controlled devices according to the control signals and further controlling the duty ratio of the dual Boost/Buck chopper.

the multi-system traction transmission system can work in two alternating current power supply systems, and under the alternating current power supply system, the one-way switches S1, S3, S4, S5 and S6 are required to be closed, the one-way switches S2, S9, S10, S11 and the first two-way switch S7 are all opened, and the second two-way switch is closed at the first contact end. The multi-system traction transmission system can also stably work in a direct-current power supply system, and requires that the one-way switches S1, S3, S4, S5 and S6 are all opened and the one-way switches S2, S9, S10 and S11 are closed. This embodiment exemplifies two dc power supply systems of dc 1.5kV and dc 3 kV.

Under the direct current 1.5kV power supply system, the direct current 1.5kV is lower than the direct current side voltage of the traction inverter by 2.8kV, as shown in a schematic diagram of a multi-system traction transmission system in fig. 2, a first bidirectional switch S7 and a second bidirectional switch S8 are both closed at a first contact terminal. At the moment, a first Boost chopper is formed by the first energy storage inductor 12, the IGBT of the full-control device V3 of the four-quadrant converter I6 and the anti-parallel diode D1 of the full-control device V1, a second Boost chopper is formed by the second energy storage inductor 13, the IGBT of the full-control device V4 of the four-quadrant converter I6 and the anti-parallel diode D2 of the full-control device V2, the two Boost choppers are connected in parallel, the duty ratios of driving pulses of the two Boost choppers are equal, the phases are staggered by half a period, a double Boost chopper is formed, and the level of the 1.5kV direct current voltage is increased to the expected value of the middle direct current link under the action of the voltage stabilizing controller.

in a direct current 1.5kV power supply system, the system works in a dual Boost mode, fully-controlled devices V3 and V4 work according to duty ratios, and the fully-controlled devices V1 and V2 are driven in a locking mode. Because the traction power is larger, the average value of the current flowing through the energy storage inductor is larger, and when the value of the energy storage inductor meets the requirement of current ripple, the chopper can work in an inductive current continuous mode. The calculation method of the value of the energy storage inductor will be described below. The duty ratios of the fully-controlled devices V3 and V4 are equal to each other and are D, the switching period is T, and the two energy storage inductance values are equal to each other and are L. Taking the duty ratio 0< D ≦ 0.5 in one period of V3 and V4 as an example, the dual Boost chopper can be divided into four stages in one working period, and the driving pulse signal and the working current waveform of each stage are shown in FIG. 5.

In the first phase (t ₀ -t ₁), the IGBT of the fully-controlled device V3 is turned on, and the IGBT of the fully-controlled device V4 is turned off, the current i _L1 flowing through the first energy storage inductor 12 charges the first energy storage inductor 12 and stores energy, the current i _L2 flowing through the second energy storage inductor 13 freewheels through the diode D2, and the second energy storage inductor 13 releases energy, so that at this time:

In the second stage (t ₁ -t ₂), the IGBT of the fully-controlled device V3 is turned off, and the IGBT of the fully-controlled device V4 is turned off, the current i _L1 flowing through the first energy-storage inductor 12 and the current i _L2 flowing through the second energy-storage inductor 13 freewheel through the diode D1 and the diode D2, respectively, and the first energy-storage inductor 12 and the second energy-storage inductor 13 both release energy, at this time:

in the third phase (t ₂ -t ₃), the IGBT of the fully-controlled device V3 is turned off, and the IGBT of the fully-controlled device V4 is turned on, the current i _L1 flowing through the first energy storage inductor 12 freewheels through the diode D1, the first energy storage inductor 12 releases energy, and the current i _L2 flowing through the second energy storage inductor 13 charges the second energy storage inductor 13 and stores energy, in this case:

In the fourth stage, the IGBT of the fully-controlled device V3 is turned off, and the IGBT of the fully-controlled device V4 is turned off, the current i _L1 flowing through the first energy-storage inductor 12 and the current i _L2 flowing through the second energy-storage inductor 13 freewheel through the diode D1 and the diode D2 at the same time, and both the first energy-storage inductor 12 and the second energy-storage inductor 13 release energy, at this time:

According to fig. 5 and the volt-second balance principle, the increment and decrement of the inductor current in one period T at the steady state are equal, that is, the current ripple magnitude, the current ripples Δ i _L1 and Δ i _L2 of the two energy storage inductors, the total grid-side current ripple Δ i _in after overlapping, and the voltage gain a _u expression can be obtained as follows:

Since the increase amount of the inductor current i _L1 in the switch on period DT is equal to the decrease amount of the switch off period T-DT, there are:

namely:

The following can be obtained:

Defining m (d) as an equation for the ratio of the input total current ripple magnitude Δ i _in to the one-phase inductor current ripple magnitude Δ i _L1 as a function of duty cycle, thus having:

since 0< D ≦ 0.5, the value of M (D) is less than 1. When D is more than 0.5 and less than or equal to 1, the value of M (D) is less than 1 by repeating the analysis process. Therefore, the ripple wave size of the input total current is always smaller than that of the one-phase inductive current due to the staggered parallel offsetting effect, and the electric energy quality is effectively improved.

As shown in fig. 4, the voltage regulator controller samples the output voltage and the energy storage inductor current, and adopts a dual PI closed loop with a voltage outer loop and a current inner loop, and the two phases of inductor currents connected in parallel in a staggered manner are controlled independently. The voltage outer ring can adjust different direct current traction network voltages into an expected value of the intermediate direct current link voltage, and the direct current link voltage can be kept stable under the condition of traction network voltage fluctuation or load change. The current inner ring can limit the current amplitude so as to play a role in protection, and can accelerate the response speed of the controller. In addition, the problem of current imbalance caused by inconsistent circuit parameters can be reduced by independently controlling the two-phase inductive current.

in a direct current 3kV power supply system, the direct current 3kV is higher than the direct current side voltage of the traction inverter by 2.8kV, and as shown in fig. 3 of the schematic diagram of the multi-system traction transmission system, the first bidirectional switch S7 and the second bidirectional switch S8 are both closed at the second contact end. The first energy storage inductor 12, the IGBT of the full-control device V1 of the four-quadrant converter I6 and the anti-parallel diode D3 of the full-control device V3 form a first Buck step-down chopper, the second energy storage inductor 13, the IGBT of the full-control device V2 of the four-quadrant converter I6 and the anti-parallel diode D4 of the full-control device V4 form a second Buck step-down chopper, the two Buck step-down choppers are connected in parallel, the duty ratios of driving pulses are equal, the phases are staggered by a half period, a double Buck step-down chopper is formed, and the 3kV direct-current voltage level is reduced to the expected value of the middle direct-current link under the action of the voltage stabilizing controller 14.

When the direct current 3kV power supply system is in a double Buck mode, the fully-controlled devices V1 and V2 work according to duty ratios, and the fully-controlled devices V3 and V4 are driven in a locking mode. Since the dual Buck mode and the dual Boost mode are similar in control concept and working waveform, the above analysis process can be referred to, and is not described herein again. Only the various working phases thereof will be described. Taking the example that the duty ratio D of the fully-controlled devices V1 and V2 in one period is less than or equal to 0.5, the double Buck chopper can be divided into four stages in one working period.

in the first phase, the IGBT of the full device type V1 is turned on and the IGBT of the full device type V2 is turned off, the current i _L1 flowing through the first energy storage inductor 12 charges the first energy storage inductor 12 and stores energy, the current i _L2 flowing through the second energy storage inductor 13 freewheels through the diode D4, and the second energy storage inductor 13 releases energy, and there are:

In the second stage, the IGBT of the full device type device V1 is turned off, and the IGBT of the full device type device V2 is turned off, the current i _L1 flowing through the first energy storage inductor 12 and the current i _L2 flowing through the second energy storage inductor 13 freewheel through the diode D3 and the diode D4, respectively, and the first energy storage inductor 12 and the second energy storage inductor 13 both release energy, at this time:

in the third phase, the IGBT of the full device type device V1 is turned off, and the IGBT of the full device type device V2 is turned on, the current i _L1 flowing through the first energy storage inductor 12 freewheels through the diode D3, the first energy storage inductor 12 releases energy, and the current i _L2 flowing through the second energy storage inductor 13 charges the second energy storage inductor 13 and stores energy.

In the fourth stage, the IGBT of the full device type device V1 is turned off, and the IGBT of the full device type device V2 is turned off, the current i _L1 flowing through the first energy storage inductor 12 and the current i _L2 flowing through the second energy storage inductor 13 freewheel simultaneously through the diode D3 and the diode D4, and the first energy storage inductor 12 and the second energy storage inductor 13 both release energy, at this time:

the voltage gain expression is as follows:

The energy storage inductor plays a role in storing and converting energy in the chopper circuit. Therefore, the reasonable selection of the inductor is directly related to the performance of the chopper circuit. According to the above analysis, the ripple magnitude of the Boost circuit inductive current is:

Generally, Δ i _L is 10% -20% of the average value, if Δ i _L is too large, the power loss on the inductor is increased, and if Δ i _L is too small, the cost of the required inductor is increased, therefore, an inductor with a proper size can be selected to obtain a current ripple Δ i _L meeting the requirement, and a calculation formula of the value of each phase of the inductor of the Boost circuit is as follows:

Similarly, for the Buck circuit, in a working period, the inductor current is also a pulsating quantity, and the ripple magnitude of the inductor current can be calculated as follows:

Further, a calculation formula of each phase inductance value of the Buck circuit can be obtained:

on one hand, when the direct current traction network with different voltage grades (higher or lower than the direct current side voltage of the traction inverter) supplies power, two structural modes of voltage boosting and voltage reducing can be realized through switching of a switching element, so that the voltage grades are converted, and the direct current side voltage of the system traction inverter is stabilized at an expected value; on the other hand, in the case of the possible fluctuation situation of the voltage of the direct current traction network and the situation of the load waveform, the direct current side voltage of the traction inverter can be quickly maintained to be stable by performing closed-loop control on the output voltage through the voltage stabilizing controller. Therefore, the method can effectively reduce the influence of the voltage fluctuation of the traction network on the system performance, ensure that the traction motor works under the optimal operation condition, and effectively improve the system efficiency, the reliability and the network side electric energy quality.

the above is only a description of the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above examples, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. Various modifications, additions and substitutions for the specific embodiments described herein may be made by those skilled in the art without departing from the spirit and principles of the invention.