Electronic field suppression switch of synchronous motor excitation system and control method of electronic field suppression switch

Abstract

The invention discloses a synchronous motor excitation system electronic field suppression switch and a control method thereof, the synchronous motor excitation system electronic field suppression switch comprises an excitation transformer, the excitation transformer is electrically connected with a rectifier bridge, one end of the rectifier bridge is electrically connected with an electronic field suppression switch, and the electronic field suppression switch is electrically connected with a motor excitation winding. The synchronous motor is arranged at one end of the motor excitation winding, the silicon controlled rectifier bridge and the electronic field suppression switch are both controlled by the control device, an electronic circuit is adopted for control, the on-off time is controlled to be millisecond level, the control precision is high, the reliability is high, a tedious relay control loop and a mechanical operation loop of the field suppression switch are omitted, and the cost is reduced. Due to the fact that the electronic field suppression switch directly achieves work and disconnection of the excitation loop through the electronic circuit, when the excitation loop is disconnected, no contact of a traditional field suppression switch exists, high-voltage direct-current arcs are generated when the loop is disconnected, and accidents that the field suppression switch is damaged due to improper treatment of the high-voltage direct-current arcs are avoided.

Description

Technical Field

[0001] The present invention relates to the field of synchronous generators, and particularly to an electronic field discharge switch for a synchronous motor excitation system and a control method thereof. Background Art

[0002] During the operation of a synchronous generator or motor, when a fault occurs in the equipment or an emergency shutdown is required, the excitation current must be quickly cut off to avoid equipment damage. Traditional field discharge switches mostly adopt mechanical structures, which have problems such as slow response speed, easy generation of electric arcs, short service life, and easy jamming of mechanical mechanisms.

[0003] When the traditional mechanical field discharge switch circuit is working normally, the excitation transformer steps down the high voltage to supply the thyristor rectifier bridge. The thyristor rectifier bridge rectifies the AC voltage into a DC voltage. After the field discharge switch is closed, the DC voltage is applied to the generator excitation winding, generating a DC current to form a magnetic field. The generator rotates under the drive of the prime mover, cutting the magnetic field to generate three-phase alternating current and delivering it to the power grid. When a fault occurs in the power grid, the generator needs to be cut off in time, and at the same time, the excitation circuit is disconnected through the field discharge switch. Since the generator excitation winding is a large inductive load, equivalent to an energy storage source, at the moment when the field discharge switch is disconnected, due to the physical property that the inductive current cannot change suddenly, a large electric arc will be generated at both ends of the field discharge switch. This electric arc will burn the mechanical contacts. After the field discharge switch is opened and closed multiple times, the switch contacts will have poor contact due to multiple burns, thus affecting normal operation.

[0004] Some field discharge switches have accidents of being burned out due to improper arc handling.

[0005] The opening and closing of the field discharge switch require a complex operation circuit, increasing the fault points and prone to mis-tripping and mis-closing. The thyristor control circuit is an electronic circuit with a control time in milliseconds, and the control circuit of the field discharge switch FMK is a relay operation circuit with a control time in seconds. It is easy to have a control time deviation when the two cooperate. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is: there are problems such as slow response speed, easy generation of electric arcs, short service life, and easy jamming of mechanical mechanisms.

[0007] The above technical problem is solved by the following technical solution: The present invention provides an electronic field discharge switch for a synchronous motor excitation system, which includes

[0008] An excitation transformer, the outgoing end of the excitation transformer is connected to the incoming end of the rectifier bridge, the outgoing end of the rectifier bridge is connected to the incoming end of the electronic field discharge switch, the outgoing end of the electronic field discharge switch is connected to the incoming end of the motor excitation winding, and the motor excitation winding is arranged on the rotor side of the synchronous motor.

[0009] In a preferred embodiment of the electronic field discharge switch of the synchronous motor excitation system according to the present invention: The rectifier bridge includes thyristors VT1, VT2, VT3, VT4, VT5, and VT6.

[0010] In a preferred embodiment of the electronic field discharge switch of the synchronous motor excitation system according to the present invention: The thyristors VT1 and VT4 are connected in series with each other to form the first bridge arm, the thyristors VT3 and VT6 are connected in series with each other to form the second bridge arm, the thyristors VT5 and VT2 are connected in series with each other to form the third bridge arm, and the excitation transformer is connected to the midpoint of each bridge arm.

[0011] In a preferred embodiment of the electronic field discharge switch of the synchronous motor excitation system according to the present invention: A protection circuit composed of an absorption capacitor and a resistor is provided in parallel at both ends of the electronic field discharge switch.

[0012] In a preferred embodiment of the electronic field discharge switch of the synchronous motor excitation system according to the present invention: It includes a control unit, and the control unit is electrically connected to the primary side of the excitation transformer, the gate electrodes of the thyristors of the rectifier bridge, and the control terminal of the electronic field discharge switch respectively.

[0013] A control method includes,

[0014] The control unit sends trigger pulses to the rectifier bridge;

[0015] The electronic field discharge switch sends a working pulse and starts to conduct, and the loop is in a working state;

[0016] The flow direction of the excitation current is from the rectifier bridge to the electronic field discharge switch to the motor excitation winding.

[0017] In a preferred embodiment of the control method according to the present invention: The control method includes loop self-check and control program self-verification.

[0018] In a preferred embodiment of the control method according to the present invention: The control unit sends an on or off pulse to the electronic field discharge switch in the loop, and the excitation current loop can be controlled.

[0019] In a preferred embodiment of the control method according to the present invention: The control of both the electronic field discharge switch and the rectifier bridge is controlled by the control unit, and digital control is adopted.

[0020] In a preferred embodiment of the control method according to the present invention: A protection circuit is provided in parallel at both ends of the electronic field discharge switch to absorb the overvoltage generated during the turn-off process and prevent equipment damage.

[0021] The beneficial effects of the present invention are as follows: In the electronic field discharge switch, both the thyristor rectifier bridge and the electronic field discharge switch are controlled by a control device. Using electronic circuit control, the control of the turn-on and turn-off times is in the millisecond level, with high control precision and high reliability. The cumbersome relay control circuit and the mechanical operation circuit of the field discharge switch are eliminated. Since the electronic field discharge switch directly realizes the operation and disconnection of the excitation circuit through an electronic circuit, when the excitation circuit is disconnected, there is no contact of the traditional field discharge switch, so there is no high-voltage DC arc generated when the circuit is disconnected, nor is there an accident of damage to the field discharge switch caused by improper handling of the high-voltage DC arc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present invention and do not limit the present invention. Among them:

[0023] Figure 1 shows the circuit schematic diagram of the present invention;

[0024] Figure 2 shows the schematic diagram of the control principle of the present invention;

[0025] Figure 3 shows the on-off pulse schematic diagram of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] In order to enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below in conjunction with the specific embodiments and the drawings.

[0027] The terms used in the present invention are those general terms that are currently widely used in the art in consideration of the functions of the present invention, but these terms can change according to the intentions of those of ordinary skill in the art, precedents, or new technologies in the art. In addition, specific terms can be selected by the applicant, and in this case, their detailed meanings will be described in the detailed description of the present invention. Therefore, the terms used in the specification should not be understood as simple names, but based on the meanings of the terms and the overall description of the present invention.

[0028] Referring to Figure 1 , this embodiment provides an electronic field discharge switch for a synchronous motor excitation system, including

[0029] An excitation transformer 1, the outgoing line end of the excitation transformer 1 is connected to the incoming line end of the rectifier bridge 2, the outgoing line end of the rectifier bridge 2 is connected to the incoming line end of the electronic field discharge switch 3, the outgoing line end of the electronic field discharge switch 3 is connected to the incoming line end of the motor excitation winding 4, and the motor excitation winding 4 is arranged on the rotor side of the synchronous motor 5.

[0030] In this embodiment, the excitation transformer 1 steps down the high voltage and supplies it to the thyristor rectifier bridge 2 composed of VT1 - VT6. The thyristor rectifier bridge 2 rectifies the AC voltage into a DC voltage. After the electronic excitation switch 3 is closed, the DC voltage is applied to the motor excitation winding 4, generating a DC current to form a magnetic field. The generator rotates under the drive of the prime mover, cuts the magnetic field, and generates three - phase alternating current to be transmitted to the power grid. The electronic excitation switch 3 is composed of an IGBT and a protection circuit 31. The IGBT, also known as an insulated gate bipolar transistor, is the most mature and widely used power device among current high - power switching components. It has a small drive power and a low saturation voltage drop and is the core device for energy conversion and transmission.

[0031] As an alternative embodiment, referring to Figure 2 , this embodiment provides a control method, including,

[0032] The control unit 6 sends trigger pulses to the rectifier bridge 2;

[0033] The electronic excitation switch 3 sends out working pulses and starts to conduct, and the circuit is in the working state;

[0034] The flow direction of the excitation current is from the rectifier bridge 2 to the electronic excitation switch 3 to the motor excitation winding 4.

[0035] The control method includes loop self - inspection and control program self - verification. In the loop, the control unit 6 sends out on - or off - pulse to the electronic excitation switch 3, which can control the excitation current loop. The controls of both the electronic excitation switch 3 and the rectifier bridge 2 are controlled by the control unit 6. The control adopts digital control. A protection circuit 31 is connected in parallel at both ends of the electronic excitation switch 3 to absorb the over - voltage generated during the turn - off process and prevent equipment damage.

[0036] As an alternative embodiment, referring to Figures 1 to 3 , this embodiment provides a synchronous motor excitation system electronic excitation switch and its control method, including,

[0037] An excitation transformer 1, the excitation transformer 1 is electrically connected to a rectifier bridge 2 at the upper part. One end of the rectifier bridge 2 is electrically connected to an electronic excitation switch 3. The electronic excitation switch 3 is electrically connected to a motor excitation winding 4. One end of the motor excitation winding 4 is provided with a synchronous motor 5;

[0038] The control unit 6 sends trigger pulses to the rectifier bridge 2;

[0039] The electronic excitation switch 3 sends out working pulses and starts to conduct, and the circuit is in the working state;

[0040] The flow direction of the excitation current is from the rectifier bridge 2 to the electronic excitation switch 3 to the motor excitation winding 4;

[0041] Preferably, the rectifier bridge 2 includes thyristors VT121, VT222, VT323, VT424, VT525, and VT626. The thyristors VT121 and VT424 are connected in series with each other to form the first arm, the thyristors VT323 and VT626 are connected in series with each other to form the second arm, and the thyristors VT525 and VT222 are connected in series with each other to form the third arm. The exciting transformer 1 is connected to the midpoint of each arm. A protection circuit 31 composed of an absorption capacitor and a resistor is provided in parallel at both ends of the electronic excitation breaker 3. It includes a control unit 6, and the control unit 6 is electrically connected to the primary side of the exciting transformer 1, the gate electrodes of the thyristors of the rectifier bridge 2, and the control terminal of the electronic excitation breaker 3 respectively.

[0042] The working principle of the present invention is as follows: When the excitation system is working, while the control device sends trigger pulses to the thyristor rectifier bridge 2 of VT1-VT6, it sends a working pulse (a high level is sufficient) to the electronic excitation breaker 3. When the control electrode side of the electronic excitation breaker 3 receives the working pulse (at high level), the IGBT starts to conduct, and the entire circuit is in the working state. The flow direction of the exciting current is from the rectifier bridge 2 to the electronic excitation breaker 3 to the motor exciting winding 4;

[0043] When a power grid fault occurs and it is necessary to cut off the generator in time and at the same time disconnect the excitation circuit, the control device turns off the trigger pulses of the thyristor rectifier bridge 2 of VT1-VT6, and at the same time turns off the working pulse of the electronic excitation breaker 3 (a low level is sufficient). When the control electrode side of the electronic excitation breaker 3 receives the turn-off pulse (at low level), the IGBT starts to turn off, and the entire circuit is in the disconnected state, and the exciting current cannot flow to the motor exciting winding 4;

[0044] In this kind of electronic excitation breaker device, both the thyristor rectifier bridge 2 of VT1-VT6 and the electronic excitation breaker 3 are controlled by the control unit 6, and are controlled by an electronic circuit. The control of the turn-on and turn-off time is in the millisecond level, with high control precision and high reliability, eliminating the cumbersome relay control circuit and the mechanical operation circuit of the FMK excitation breaker;

[0045] Since the electronic excitation breaker 3 directly realizes the working and disconnection of the excitation circuit through an electronic circuit, when the excitation circuit is disconnected, there is no contact of the traditional excitation breaker, so there is no high-voltage DC arc generated when the circuit is disconnected, nor is there an accident of damage to the excitation breaker caused by improper handling of the high-voltage DC arc. The turn-on and turn-off of the electronic excitation breaker 3 are as Figure 3 shown. The time period from T0 to T1 is the preparation time of the excitation system, which includes time such as loop self-check and control program self-verification. T1 is the working time. While the control unit 6 sends trigger pulses to the thyristor rectifier bridge 2 of VT1-VT6, it sends a high-level working pulse to the electronic excitation breaker 3, and the exciting current loop is connected, and the excitation system starts to work;

[0046] The moment T2 is the stop moment. The control unit 6 turns off the trigger pulses of the thyristor rectifier bridge 2 of VT1-VT6. At the same time, the working pulse low level of the electronic excitation breaker 3 is turned off, the excitation current loop is disconnected, and the excitation system stops working;

[0047] In the above loop, only the control unit 6 needs to send on / off pulses to the electronic excitation breaker 3 to control the excitation current loop;

[0048] The control of both the electronic excitation breaker 3 and the thyristor rectifier bridge 2 of VT1-VT6 is controlled by the control unit 6. The control adopts digital control, the control time can be controlled at the millisecond level, the on / off time constant is at the millisecond level, and the control accuracy is high;

[0049] A protection loop 31 is connected in parallel at both ends of the electronic excitation breaker 3. It is a protection device for the electronic excitation breaker 3, which absorbs the overvoltage generated during the turn-off process, prevents equipment damage, and ensures safety and reliability during on / off within the millisecond level.

[0050] Finally, it should be pointed out that the methods and devices described in detail above are only examples, and those skilled in the art can modify these examples in different ways as long as they do not depart from the scope of the present invention.

Claims

1. An electronic demagnetization switch for a synchronous motor excitation system, characterized in that: include, An excitation transformer (1), wherein an output terminal of the excitation transformer (1) is connected to an input terminal of a rectifier bridge (2), wherein an output terminal of the rectifier bridge (2) is connected to an input terminal of an electronic demagnetization switch (3), wherein an output terminal of the electronic demagnetization switch (3) is connected to an input terminal of a motor excitation winding (4), wherein the motor excitation winding (4) is arranged on the rotor side of a synchronous motor (5).

2. The electronic demagnetization switch of the synchronous motor excitation system according to claim 1 is characterized in that: The rectifier bridge (2) comprises a thyristor VT1 (21), a thyristor VT2 (22), a thyristor VT3 (23), a thyristor VT4 (24), a thyristor VT5 (25) and a thyristor VT6 (26).

3. The electronic demagnetization switch of the synchronous motor excitation system according to claim 2 is characterized in that: The thyristor VT1 (21) and the thyristor VT4 (24) are connected in series to form a first bridge arm, the thyristor VT3 (23) and the thyristor VT6 (26) are connected in series to form a second bridge arm, the thyristor VT5 (25) and the thyristor VT2 (22) are connected in series to form a third bridge arm, and the excitation transformer (1) is connected to the midpoint of each bridge arm.

4. The electronic demagnetization switch of the synchronous motor excitation system according to claim 1, characterized in that: A protection circuit (31) consisting of an absorption capacitor and a resistor is connected in parallel at both ends of the electronic demagnetization switch (3).

5. The electronic demagnetization switch of the synchronous motor excitation system according to claim 1 is characterized in that: It comprises a control unit (6), wherein the control unit (6) is electrically connected to the primary side of the excitation transformer (1), each thyristor gate of the rectifier bridge (2), and the control end of the electronic demagnetization switch (3).

6. A control method, comprising the electronic demagnetization switch of a synchronous motor excitation system according to any one of claims 1 to 5, characterized in that: include, The control unit (6) sends a trigger pulse to the rectifier bridge (2); The electronic demagnetization switch (3) sends out a working pulse and starts to conduct, and the circuit is in a working state; The direction of the excitation current is from the rectifier bridge (2) to the electronic demagnetization switch (3) to the motor excitation winding (4).

7. The control method according to claim 6, characterized in that: The control method includes loop self-check and control program self-check.

8. The control method according to claim 7, characterized in that: The control unit (6) in the loop sends an on or off pulse to the electronic demagnetization switch (3), thereby controlling the excitation current loop.

9. The control method according to claim 8, characterized in that: The electronic demagnetization switch (3) and the rectifier bridge (2) are both controlled by a control unit (6), and the control adopts digital control.

10. The control method according to claim 9, characterized in that: The two ends of the electronic demagnetization switch (3) are connected in parallel with a protection circuit (31) to absorb overvoltage generated during the shutdown process to prevent equipment damage.

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