Protection circuit and method for permanent magnet traction system

Abstract

The present disclosure relates to a permanent magnet electric motor traction system, and specifically relates to a protection circuit and method for a permanent magnet traction system. The technical problem of a fault inside a converter being expanded due to the persistence of a short-circuit current when an existing permanent magnet electric motor uses an isolation contactor as protection, a short-circuit working condition occurs in the converter and engagement occurs in a three-pole isolation contactor is thus solved. In the present disclosure, on the basis of the protection of the existing three-pole isolation contactor, a protection switch is added. Specifically, a short-circuit contactor is added at the front end of a permanent magnet contactor, and is configured to realize three-phase short-circuit protection of a permanent magnet electric motor. The protection switch is configured to perform emergency disposal when two phases are short-circuited inside the converter; and a short-circuit current of the permanent magnet electric motor is reduced by means of short-circuiting three phases of the permanent magnet electric motor, such that a vehicle can be kept in a safe state to move to a nearby station. Permanent magnet direct-drive technology is the development direction of future converters. The successful implementation of the present invention lays a good foundation for occupying the converter market in the future.

Description

A permanent magnet traction system protection circuit and method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number CN202311723041.9 and application date December 15, 2023, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby incorporated into this disclosure by introduction. Technical Field

[0003] The present disclosure relates to a permanent magnet motor traction system, and in particular to a permanent magnet traction system protection circuit and method. Background Art

[0004] In recent years, green, safe and energy-saving have become the key development directions of rail transit vehicle equipment. Compared with the traditional asynchronous motor electric transmission system, the permanent magnet direct drive electric transmission system has obvious energy-saving effects under all working conditions, solves the problems of transmission loss, noise and maintenance caused by gear transmission, avoids the environmental pollution problems caused by the use of gearbox lubricating grease, further improves the traction transmission efficiency, and is the development direction of future traction systems.

[0005] Permanent magnet motors require protection during operation. Prior art installations employ a three-pole isolation contactor between the traction converter inverter output and the permanent magnet motor. This isolation contactor isolates and protects the circuit, while also controlling the contactor's on / off state to control the permanent magnet motor's operating state. However, if a short circuit occurs within the converter and the three-pole isolation contactor becomes engaged, the continued short-circuit current can escalate the converter's internal faults and even cause a fire, effectively failing to protect the electrical equipment. Summary of the Invention

[0006] The present disclosure provides a permanent magnet traction system protection circuit and method to solve the technical problem that when a short circuit occurs inside the converter and the three-pole isolation contactor is engaged when the existing permanent magnet motor uses an isolation contactor as protection, the internal fault of the converter will be amplified as the short circuit current continues.

[0007] The permanent magnet traction system protection circuit described in the present invention is implemented by the following technical solution: it includes a permanent magnet motor and a traction converter system connected to the permanent magnet motor, a three-pole isolation contactor is connected between the permanent magnet motor and the traction converter system; a short-circuit protection switch is added between the three-pole isolation contactor and the permanent magnet motor; the three-pole switches of the three-pole isolation contactor all lead to independent feedback contacts connected to the control unit.

[0008] This disclosure adds a protective switch to the existing three-pole isolation contactor protection. Specifically, a short-circuit contactor is added to the front end of the permanent magnet contactor, configured to provide three-phase short-circuit protection for the permanent magnet motor. The protective switch is manually controlled and configured to provide emergency response in the event of a two-phase short circuit within the converter. By short-circuiting the three phases of the permanent magnet motor, the short-circuit current is reduced, allowing the vehicle to maintain safe operation to the nearest station.

[0009] The present disclosure discloses a permanent magnet traction system protection method using the following technical solution: the three-pole switches in the three-level isolation contactor each lead out independent feedback contacts connected to the control unit. The control unit determines the operating status of the contactor by detecting the status of the feedback contacts of each pole of the three-level isolation contactor and combining it with the operating current. The specific detection method is:

[0010] 1. Under normal working conditions, there is no need to operate the protection switch;

[0011] 2. When a single-phase engagement occurs, the permanent magnet motor does not form a closed current loop. In this operating condition, the protection switch does not operate.

[0012] 3. When two-phase and three-phase engagement occurs, the current sensor detects the current between the inverter and the traction motor. When the current exceeds a certain limit, the protection switch is activated;

[0013] 4. When the protection switch is closed, the permanent magnet motor operates under three-phase short-circuit conditions and can maintain operation.

[0014] The beneficial effects of the present disclosure are: 1) providing an electric transmission system solution for high-power freight permanent magnet direct-drive electric locomotives, meeting the requirements of electric locomotive traction characteristics;

[0015] 2) In view of the back EMF characteristics of permanent magnet motors, a protection method for traction inverter short-circuit conditions is added to the existing ones;

[0016] 3). Further improve the main circuit topology of the permanent magnet traction system to improve the availability and reliability of the permanent magnet traction system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG1 is a schematic diagram of the structure of the present disclosure.

[0018] FIG2 is a block diagram of an implementation of the method described in the present disclosure.

[0019] FIG3 is a schematic diagram of a traction converter system in an embodiment. DETAILED DESCRIPTION

[0020] Example 1 As shown in Figure 1, a permanent magnet traction system protection circuit includes a permanent magnet motor and a traction converter system connected to the permanent magnet motor, a three-pole isolation contactor is connected between the permanent magnet motor and the traction converter system; a short-circuit protection switch is added between the three-pole isolation contactor and the permanent magnet motor; the three-pole switches of the three-pole isolation contactor all lead to independent feedback contacts connected to the control unit; a current sensor is provided between the three poles of the three-pole isolation contactor and the traction converter system as a feedback contact; the protection switch is a manually controlled switch.

[0021] As shown in FIG2 , a permanent magnet traction system protection method adopts the following technical solution: the three-pole switches in the three-level isolation contactor each lead out independent feedback contacts connected to the control unit. The control unit determines the working state of the contactor by detecting the state of the feedback contact of each pole of the three-level isolation contactor and combining it with the working current. The specific detection method is:

[0022] 1. Under normal working conditions, there is no need to operate the protection switch;

[0023] 2. When a single-phase engagement occurs, the permanent magnet motor does not form a closed current loop. In this operating condition, the protection switch does not operate.

[0024] 3. When two-phase and three-phase engagement occurs, the current sensor detects the current between the inverter and the traction motor. When the current exceeds a certain limit, the protection switch is activated;

[0025] 4. When the protection switch is closed, the permanent magnet motor operates under three-phase short-circuit conditions and can maintain operation.

[0026] As shown in Figure 3, the traction converter system includes a pre-charging circuit, a four-quadrant power module, an intermediate DC circuit and a three-phase inverter; the three-phase inverter is connected to the permanent magnet motor through a three-pole isolation contactor; the pre-charging circuit includes a main contactor and an input current sensor; the four-quadrant power module is composed of four groups of IGBT half-bridge modules, two of which are connected in parallel to one end of the main contactor in the pre-charging circuit through a copper bus, and the other two parallel half-bridge circuits in the four-quadrant power module are connected to the input current sensor CT (IN) 1, and the other end of the input current sensor CT (IN) 1 is connected to the secondary winding of the transformer, and the secondary winding of the transformer connected to the pre-charging circuit is the two ends of the same winding; the intermediate DC circuit includes a voltage transformer PT11 connected between the two ends of the four-quadrant power module, and after being connected in series, The resistor HR1 and the indicator light HD1 are connected in parallel with the voltage transformer PT11, and the resistors RGe11 and RGe12 are connected in series in parallel with the voltage transformer PT11. A capacitor GC1 is connected between the midpoint of the resistors RGe11 and RGe12 and the other end of RGe12, and the midpoint of the resistors RGe11 and RGe12 is grounded. The voltage transformer PT12 is also connected between the two ends of the capacitor GC1. The three-phase inverter also includes a parallel resistor DR11 and a support capacitor FC11. The three-phase inverter includes four groups of IGBT half-bridge modules, the midpoint of the first group of IGBT half-bridge modules is connected to the other end of RGe12 through the resistor OVR1 and the current transformer OVCT1, and the midpoints of the remaining three groups of IGBT half-bridge modules are connected to the permanent magnet motor through a three-pole isolation contactor, and current sensors are respectively connected between the midpoints of the three groups of IGBT half-bridge modules and the three-pole isolation contactors.

[0027] This disclosure relates to a method and device for controlling the impact of the high back-electromotive force of permanent magnet motors on traction converters during the operation of permanent magnet systems in rail transit high-power converters. This method primarily protects the permanent magnet system from abnormal operating conditions by adding an isolation contactor and protective switch at the inverter output.

[0028] In this specific embodiment, the traction converter cabinet houses two traction units. Each unit consists of a pre-charging circuit, a four-quadrant module, a four-quadrant + chopper module, an intermediate DC link, and a three-phase inverter, driving a permanent magnet synchronous motor (axis-controlled). The schematic diagram of the traction converter system is shown in Figure 3. The electrical principles and structures of the two traction units are identical, and their cooling systems are independent, increasing system redundancy.

[0029] The four-quadrant power module consists of four half-bridge IGBT modules. Two parallel half-bridge circuits in the module are connected to one end of the main contactor in the pre-charge circuit via a copper busbar. The two parallel half-bridge circuits in the module are connected to the input circuit sensor, while the other end of the input current sensor is connected to the transformer secondary winding. The transformer secondary winding connected to the pre-charge circuit is the same winding at both ends. The four-quadrant rectifier is configured to rectify the AC power from the transformer secondary into DC power for the intermediate DC circuit. The intermediate voltage amplitude must meet the specification of 1800V±5%, and the AC side current and voltage must be in phase, thereby maintaining a grid-side power factor close to 1.0.

[0030] The intermediate DC circuit consists of a storage circuit, measurement, and protection circuits. The storage circuit, comprised of supporting capacitors, stabilizes the intermediate circuit voltage and filters the higher harmonics generated by the four-quadrant pulse rectifier and motor inverter. The measurement and protection circuitry includes a grounding measurement circuit, an intermediate voltage sensor, and a voltage detection board.

[0031] The three-phase traction inverter modulates the intermediate DC voltage and converts it into a three-phase AC power supply with variable voltage and frequency, enabling control of the traction motor's characteristics. An isolation contactor is designed between the inverter and the permanent magnet motor to isolate the converter and motor under fault conditions. The isolation contactor is installed below the traction converter and connects the traction inverter and permanent magnet synchronous motor via copper busbars. In the event of a fault, the connection between the traction converter and the permanent magnet synchronous motor is physically disconnected, ensuring fault protection. A protective switch is added to the rear end of the isolation contactor, configured to short-circuit the motor's three phases in the event of a two-phase or three-phase short-circuit at the inverter output within the converter. The protective switch is located outside the converter, and its use exacerbates the fault conditions of the converter protection equipment.

[0032] Permanent magnet direct drive technology is the future development direction of converters. The successful development of this project has laid a good foundation for occupying the converter market in the future.

[0033] Technical features of this disclosure:

[0034] 1. Main circuit topology of protection switch for high-power permanent magnet traction system;

[0035] 2. Control method of permanent magnetic protection switch;

[0036] 3. Equipment design method for adding protection switches in permanent magnet circuits.

Claims

1. A permanent magnet traction system protection circuit, comprising a permanent magnet motor and a traction converter system connected to the permanent magnet motor, wherein a three-pole isolation contactor is connected between the permanent magnet motor and the traction converter system; wherein: A short-circuit protection switch is added between the three-pole isolation contactor and the permanent magnet motor; the three-pole switches of the three-pole isolation contactor all lead out independent feedback contacts to be connected to the control unit.

2. A permanent magnet traction system protection circuit as claimed in claim 1, wherein: A current sensor is respectively provided between the three poles of the three-pole isolation contactor and the traction converter system as a feedback contact.

3. A permanent magnet traction system protection circuit as claimed in claim 1 or 2, wherein: The protection switch is a manually controlled switch.

4. A permanent magnet traction system protection circuit as claimed in claim 1 or 2, wherein: The traction converter system includes a pre-charging circuit, a four-quadrant power module, a set of intermediate DC circuits and a three-phase inverter; the three-phase inverter is connected to the permanent magnet motor through a three-pole isolation contactor.

5. A permanent magnet traction system protection circuit as claimed in claim 4, wherein: The pre-charging circuit includes a main contactor and an input current sensor; the four-quadrant power module is composed of four groups of IGBT half-bridge modules, two of the parallel half-bridge circuits in the four-quadrant power module are connected to one end of the main contactor in the pre-charging circuit through a copper bus, and the other two parallel half-bridge circuits in the four-quadrant power module are connected to the input current sensor CT (IN) 1, and the other end of the input current sensor CT (IN) 1 is connected to the secondary winding of the transformer, and the secondary winding of the transformer connected to the pre-charging circuit is the two ends of the same winding.

6. A permanent magnet traction system protection circuit as claimed in claim 4, wherein: The intermediate DC circuit includes a storage circuit, a measurement and protection circuit; the storage circuit is composed of a supporting capacitor.

7. A permanent magnet traction system protection circuit as claimed in claim 6, wherein: The intermediate DC circuit includes a voltage transformer PT11 connected between the two ends of the four-quadrant power module, a resistor HR1 and an indicator light HD1 connected in series with the voltage transformer PT11 in parallel, resistors RGe11 and RGe12 connected in series with the voltage transformer PT11 in parallel, a capacitor GC1 connected between the midpoint of the resistors RGe11 and RGe12 and the other end of RGe12, and the midpoint of the resistors RGe11 and RGe12 is grounded; a voltage transformer PT12 is also connected between the two ends of the capacitor GC1; and also includes a parallel resistor DR11 and a supporting capacitor FC11.

8. A permanent magnet traction system protection circuit as claimed in claim 4, wherein: The three-phase inverter includes four groups of IGBT half-bridge modules. The midpoint of the first group of IGBT half-bridge modules is connected to the other end of RGe12 through resistor OVR1 and current transformer OVCT1, and the midpoints of the remaining three groups of IGBT half-bridge modules are connected to the permanent magnet motor through a three-pole isolation contactor, and current sensors are respectively connected between the midpoints of the three groups of IGBT half-bridge modules and the three-pole isolation contactors.

9. A permanent magnet traction system protection circuit as claimed in claim 4, wherein: The three-phase isolation contactor is installed below the traction inverter and is connected to the traction inverter and the permanent magnet synchronous motor through a copper busbar.

10. A permanent magnet traction system protection method, wherein: The three-pole switches in the three-level isolation contactor all lead out independent feedback contacts to the control unit. The control unit determines the working state of the contactor by detecting the state of the feedback contact of each pole of the three-level isolation contactor and combining it with the working current. The specific detection method is:

1. Under normal working conditions, there is no need to operate the protection switch; 2. When a single-phase engagement occurs, the permanent magnet motor does not form a closed current loop when a single-phase engagement occurs. In this case, the protection switch does not operate.

3. When two-phase and three-phase are engaged, the current sensor detects the current between the inverter and the traction motor. When the current exceeds a certain limit, the protection switch is activated; 4. When the protection switch is closed, the permanent magnet motor can maintain operation under three-phase short-circuit conditions.

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