System suitable for starting phase modifier and control method

Abstract

The invention belongs to the technical field of phase modifier control, and particularly relates to a system suitable for starting a phase modifier and a control method.The system comprises a brushless doubly-fed motor or a doubly-fed motor coaxially connected with a high-capacity phase modifier, and the motor comprises a set of high-voltage windings and a set of low-voltage windings; the high-voltage winding and the low-voltage winding are respectively connected with a high-voltage power grid and a low-voltage power grid through contactors; the contactor connected with the low-voltage winding is connected with an inversion unit of a low-voltage four-quadrant frequency converter, and the inversion unit of the low-voltage four-quadrant frequency converter is connected with a step-down transformer. The method aims to assist in solving a series of problems existing in the turning, starting and synchronous grid connection processes of the current high-capacity phase modifier, and meanwhile, corresponding control strategies are formulated according to working conditions such as restarting at any rotating speed in the turning, static state starting and stopping processes of the phase modifier, so that the reliability of a phase modifier system is improved.

Description

Technical Field

[0001] This invention belongs to the field of synchronous condenser control technology, specifically relating to a system and control method suitable for starting a synchronous condenser. Background Technology

[0002] Currently, the startup of large-capacity 300Mvar synchronous condensers is mostly achieved through frequency conversion startup controlled by SFC (Starting Controller), as shown in the attached diagram. Figure 8 As shown, however, on the one hand, the harmonic current is relatively large during startup, requiring an isolation transformer to reduce the impact of harmonics on the system; on the other hand, an additional startup excitation device is needed to provide excitation for the synchronous condenser. Furthermore, the SFC can only control the synchronous condenser to operate stably at around 300 r / min; extremely low-speed turning of the synchronous condenser requires a dedicated turning device. The turning device is suitable for extremely low-speed operation; the normal operating speed of the synchronous condenser is around 3000 r / min. Some synchronous condensers cannot be disconnected from the turning device during operation, and high-speed operation will affect the gearbox life of the turning device. In summary, the existing technology has the following problems:

[0003] The SFC device has a high harmonic current content during startup, requires an additional startup excitation device, and lacks the ability to rotate at extremely low speeds.

[0004] Some low-speed turning gears cannot be disconnected from the unit during normal operation of the synchronous condenser, and excessive speed and temperature affect the service life of the gearbox;

[0005] The combination of high-voltage frequency converter and asynchronous motor has a large footprint, high harmonic content during startup, and cannot stably drive the unit to operate in the extremely low speed range.

[0006] Patent CN207705809U can effectively solve the above problems by configuring a coaxial device to drive the synchronous condenser. However, the coaxial device currently generally adopts the mode of high-voltage frequency converter plus asynchronous motor. In use, on the one hand, the high-voltage frequency converter occupies a large area and needs to be installed indoors, which affects the construction of the synchronous condenser factory. On the other hand, the rectifier side of the frequency converter will generate a large harmonic current, and the harmonic content increases with the increase of the load. In addition, the high-voltage frequency converter has difficulty controlling the asynchronous motor to operate stably in the extremely low speed range, and cannot completely replace the turning gear. Summary of the Invention

[0007] The purpose of this invention is to provide a novel large-capacity synchronous condenser start-up system and control method to address the problems existing in the prior art. It aims to help solve a series of problems existing in the current process of large-capacity synchronous condenser turning, starting and synchronizing with the grid. At the same time, it formulates corresponding control strategies for operating conditions such as synchronous condenser turning, starting from a stationary state and restarting at any speed during shutdown, thereby improving the reliability of the synchronous condenser system.

[0008] The technical solution of this invention is:

[0009] A system suitable for starting a synchronous condenser includes a brushless doubly-fed motor or a doubly-fed motor coaxially connected to a large-capacity synchronous condenser. The motor includes a high-voltage winding and a low-voltage winding, which are respectively connected to a high-voltage power grid and a low-voltage power grid via contactors. The contactor connected to the low-voltage winding is connected to an inverter unit of a low-voltage four-quadrant frequency converter, and the inverter unit of the low-voltage four-quadrant frequency converter is connected to a step-down transformer.

[0010] A control method for starting a camera, using the system described above, includes the following steps:

[0011] S1. Select the current operating mode based on the received external instructions and the unit's operating status, and control the startup system to execute the corresponding operation;

[0012] S2. In the barring operation state, the barring operation is logically controlled, and the brushless doubly fed motor or the doubly fed motor can drive the synchronous condenser to achieve extremely low-speed barring operation.

[0013] S3. Drag to control the phase shifter while stationary or at any rotation speed;

[0014] S4. Braking and stopping mode, switching camera braking and stopping control.

[0015] Specifically, step S2 performs logical control on the operation of the turning gear, as follows:

[0016] (1) First close the contactor connected to the brushless doubly fed motor or the high voltage winding of the doubly fed motor, and then close the contactor connected to the low voltage winding of the brushless doubly fed motor or the doubly fed motor.

[0017] (2) The converter in the rectifier unit of the four-quadrant frequency converter is in the rectification state. The upper bridge arm of the converter in the inverter unit of the low-voltage four-quadrant frequency converter is kept in the open state, and the lower bridge arm is in the on state by default. When the off signal is detected, it is adjusted to the off state. After the off signal is reset, it is restored to the on state.

[0018] (3) Given a rotational speed n r * As a set value, the actual rotational speed n of the synchronous condenser is collected. r As feedback, the required current amplitude i is calculated using a PI controller. 1amp * Used for wave-by-wave current limiting control;

[0019] (4) Collect the three-phase current i of the low-voltage winding of the brushless doubly-fed motor or the doubly-fed motor. abc1 The magnitude of the current vector i is calculated using Clark transform. 1amp i1amp with i 1amp * The turn-off signal of the lower bridge arm of the converter in the rectifier unit of the four-quadrant frequency converter is obtained by the hysteresis comparator with wave-by-wave current limiting.

[0020] Specifically, the steps for dragging and controlling the camera in step S3, whether in a stationary state or at any rotation speed, are as follows:

[0021] (1) Close the contactor connected to the brushless doubly-fed motor or the high-voltage winding of the doubly-fed motor, and detect the three-phase voltage u of the brushless doubly-fed motor or the low-voltage winding of the doubly-fed motor. abc1 The three-phase voltage u of the high-voltage winding abc2 u is obtained using a phase-locked loop. abc1 The electric angular velocity Ω1, vector magnitude and phase, u abc2 The electric angular velocity Ω2;

[0022] (2) Calculate the control mode selection coefficient k using the following formula (1), where n r To adjust the camera rotation speed, n e =60f g / p e For brushless doubly fed motors or the synchronous speed of doubly fed motors,

[0023]

[0024] (3) The converter in the rectifier unit of the four-quadrant frequency converter operates in rectification mode, and then the contactor connected to the brushless doubly fed motor or the low-voltage winding of the doubly fed motor is closed. The converter output in the inverter unit of the low-voltage four-quadrant frequency converter is connected to u abc1 With the same voltage vector, the control enters the doubly-fed operation mode;

[0025] (4) Calculate the reactive power feedback value Q using the following formula (2), based on the detected n r Select the control loop corresponding to k, and drag the synchronous condenser's rotation speed to the synchronous speed, preparing for synchronous grid connection.

[0026]

[0027] Specifically, in step S4, the braking and stopping mode, the specific steps for controlling the braking and stopping of the synchronous condenser are as follows:

[0028] (1) After detecting that the synchronous condenser disconnects the stator and rotor power supply, repeat steps (1) to (4) in step S2;

[0029] (2) The synchronous condenser speed was detected to have dropped to n. e =60f g / p eThen, first disconnect the contactor connected to the brushless doubly fed motor or the low-voltage winding of the doubly fed motor, and then disconnect the contactor connected to the high-voltage winding in the low-voltage winding of the brushless doubly fed motor or the low-voltage winding of the doubly fed motor.

[0030] (3) Repeat steps (1) to (3) in S3, control the synchronous condenser speed to drop to 5 r / min, disconnect the contactor connected to the brushless doubly fed motor or the low voltage winding of the doubly fed motor, and then disconnect the contactor connected to the high voltage winding in the low voltage winding of the brushless doubly fed motor or the doubly fed motor, and stop the synchronous condenser.

[0031] The beneficial effects of this invention are: the system provided by this invention aims to help solve a series of problems existing in the current process of large-capacity synchronous condenser turning, starting and synchronizing with the grid. At the same time, it formulates corresponding control strategies for operating conditions such as synchronous condenser turning, starting from a stationary state and restarting at any speed during shutdown, thereby improving the reliability of the synchronous condenser system. Attached Figure Description

[0032] Figure 1 This is a topology diagram of the coaxial doubly fed motor driven large-capacity synchronous condenser starting system of the present invention;

[0033] Figure 2 This is a schematic diagram of the overall control logic;

[0034] Figure 3 This is a schematic diagram of the control logic for the turning gear operation;

[0035] Figure 4 This is a schematic diagram illustrating the calculation of the lower bridge arm turn-off signal of the inverter unit in the low-voltage four-quadrant frequency converter operating in rotary locomotive mode.

[0036] Figure 5 This is a schematic diagram of the control process for adjusting the camera to a stationary state or to drag at any rotation speed.

[0037] Figure 6 This is a schematic diagram of the doubly fed drive control mode;

[0038] Figure 7 This is a schematic diagram of the braking and stopping control process of the synchronous condenser;

[0039] Figure 8 This is a topology diagram of a large-capacity synchronous condenser startup system in existing technology. Detailed Implementation

[0040] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] like Figure 1 The diagram shows the topology of the coaxial doubly fed motor-driven large-capacity synchronous condenser starting system provided by this invention. Figure 1As shown, module 1 is a brushless doubly-fed motor or doubly-fed motor coaxially connected to a large-capacity synchronous condenser. This motor has a set of high-voltage windings and a set of low-voltage windings, which are respectively connected to the high-voltage grid (6-10kV) and the low-voltage grid (380-690V); module 2 is a contactor connected to the low-voltage winding in module 1, and module 6 is a contactor connected to the high-voltage winding in module 1; module 3 is the inverter unit of a low-voltage (rated voltage below 690V) four-quadrant frequency converter, and module 4 is the rectifier unit of the four-quadrant frequency converter; module 5 is a step-down transformer used to supply power to modules 3 and 4.

[0042] A control method for starting a camera, using the system described above, includes the following steps:

[0043] S1. Select the current operating mode based on the received external instructions and the unit's operating status, and control the startup system to execute the corresponding operation. The specific control process is as follows: Figure 2 As shown;

[0044] S2. In the barring operation state, the barring operation is logically controlled, and the brushless doubly fed motor or the doubly fed motor can drive the synchronous condenser to achieve extremely low-speed barring operation.

[0045] S3. Drag to control the phase shifter while stationary or at any rotation speed;

[0046] S4. Braking and stopping mode, switching camera braking and stopping control.

[0047] Example 1

[0048] This embodiment provides a method for logic control of the turning gear operation during turning gear operation. A brushless doubly-fed motor or a doubly-fed motor that can drive a synchronous condenser can achieve extremely low-speed turning gear operation. Figure 1 The startup system control process is as follows: Figure 3 As shown, using this method, module 1 can drag the synchronous condenser to achieve extremely low-speed rotary operation. The specific steps are as follows:

[0049] (1) First close the contactor corresponding to module 6, then close the contactor corresponding to module 1;

[0050] (2) The converter in the control module 4 is in the rectification state. The upper bridge arm of the converter in the module 3 is kept in the disconnected state, and the lower bridge arm is in the on state by default. When the turn-off signal is detected, it is adjusted to the turn-off state. After the turn-off signal is reset, it is restored to the on state.

[0051] (3) The calculation method for the turn-off signal is as follows: Figure 4 As shown, given the rotational speed n r * As a set value, the actual rotational speed n of the synchronous condenser is collected. r As feedback, the required current amplitude i is calculated using a PI controller.1amp * Used for wave-by-wave current limiting control;

[0052] (4) Acquisition module 1 three-phase current i of the low-voltage winding abc1 The magnitude of the current vector i is calculated using Clark transform. 1amp i 1amp with i 1amp * The turn-off signal of the lower bridge arm of the converter in module 3 is obtained by the hysteresis comparator with wave-by-wave current limiting.

[0053] Example 2

[0054] This embodiment provides a method for dragging the camera in a stationary state or at any rotational speed. The control flow is as follows: Figure 5 As shown, the specific steps are as follows:

[0055] (1) Close the contactor corresponding to module 6 and detect the three-phase voltage u of the low-voltage winding of module 1. abc1 The three-phase voltage u of the high-voltage winding abc2 u is obtained using a phase-locked loop. abc1 The electric angular velocity Ω1 (positive in positive order and negative in negative order), vector magnitude and phase, u abc2 The electric angular velocity Ω2 (this value is positive in positive order and negative in negative order);

[0056] (2) Calculate the system control mode selection coefficient k using formula (1), where n r To adjust the camera rotation speed, n e =60f g / p e Synchronous speed for module 1;

[0057]

[0058] (3) The converter in control module 4 operates in rectification mode, and then the contactor corresponding to module 2 is closed. The converter output in control module 3 is connected to u. abc1 With the same voltage vector, the control system enters doubly-fed operation mode;

[0059] (4) Calculate the reactive power feedback value Q using formula (2), and then... Figure 6 As shown, based on the detected n r Select the control loop corresponding to k, and drag the synchronous condenser's rotation speed to the synchronous speed, preparing for synchronous grid connection.

[0060]

[0061] Example 3

[0062] This embodiment provides braking and stopping control for the synchronous condenser in braking and stopping mode. The control flow is as follows: Figure 7 As shown.

[0063] (1) After detecting that the synchronous condenser disconnects the stator and rotor power supply, repeat steps (1) to (4) in Example 1;

[0064] (2) The synchronous condenser speed was detected to have dropped to n. e =60f g / p e Then, first disconnect the contactor corresponding to module 2, and then disconnect the contactor corresponding to module 6.

[0065] (3) Repeat steps (1) to (3) in Example 2, control the rotation speed of the camera to drop to 5 r / min, disconnect the contactor corresponding to module 2, then disconnect the contactor corresponding to module 6, and stop the camera.

[0066] As can be seen from the above embodiments, the present invention provides a novel large-capacity synchronous condenser starting system and control method, which aims to help solve a series of problems existing in the current process of large-capacity synchronous condenser turning, starting, and synchronous grid connection. At the same time, corresponding control strategies are formulated for operating conditions such as synchronous condenser turning, starting from a stationary state, and restarting at any speed during shutdown, thereby improving the reliability of the synchronous condenser system.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A system suitable for starting a camera, characterized in that, The system includes a brushless doubly fed motor or a doubly fed motor coaxially connected to a large-capacity synchronous condenser. The motor includes a high-voltage winding and a low-voltage winding. The high-voltage winding and the low-voltage winding are respectively connected to the high-voltage power grid and the low-voltage power grid through contactors. The contactor connected to the low-voltage winding is connected to the inverter unit of a low-voltage four-quadrant frequency converter, and the inverter unit of the low-voltage four-quadrant frequency converter is connected to a step-down transformer.

2. A control method suitable for starting a synchronous condenser, using the system described in claim 1, characterized in that, Includes the following steps: S1. Select the current operating mode based on the received external instructions and the unit's operating status, and control the startup system to execute the corresponding operation; S2. In the barring operation state, the barring operation is logically controlled, and the brushless doubly fed motor or the doubly fed motor can drive the synchronous condenser to achieve extremely low-speed barring operation. S3. Drag to control the phase shifter while stationary or at any rotation speed; S4. Braking and stopping mode, switching camera braking and stopping control.

3. The control method for starting a camera according to claim 2, characterized in that, Step S2 involves logical control of the turning gear operation, as detailed below: (1) First close the contactor connected to the brushless doubly fed motor or the high voltage winding of the doubly fed motor, and then close the contactor connected to the low voltage winding of the brushless doubly fed motor or the doubly fed motor. (2) The converter in the rectifier unit of the four-quadrant frequency converter is in the rectification state. The upper bridge arm of the converter in the inverter unit of the low-voltage four-quadrant frequency converter is kept in the open state, and the lower bridge arm is in the on state by default. When the off signal is detected, it is adjusted to the off state. After the off signal is reset, it is restored to the on state. (3) Given a rotational speed n r * As a set value, the actual rotational speed n of the synchronous condenser is collected. r As feedback, the required current amplitude i is calculated using a PI controller. 1amp * Used for wave-by-wave current limiting control; (4) Collect the three-phase current i of the low-voltage winding of the brushless doubly-fed motor or the doubly-fed motor. abc1 The magnitude of the current vector i is calculated using Clark transform. 1amp i 1amp with i 1amp * The turn-off signal of the lower bridge arm of the converter in the rectifier unit of the four-quadrant frequency converter is obtained by the hysteresis comparator with wave-by-wave current limiting.

4. The control method for starting a synchronous condenser according to claim 1, characterized in that, The specific steps for controlling the phase shifter by dragging in step S3, whether in a stationary state or at any rotation speed, are as follows: (1) Close the contactor connected to the brushless doubly-fed motor or the high-voltage winding of the doubly-fed motor, and detect the three-phase voltage u of the brushless doubly-fed motor or the low-voltage winding of the doubly-fed motor. abc1 The three-phase voltage u of the high-voltage winding abc2 u is obtained using a phase-locked loop. abc1 The electric angular velocity Ω1, vector magnitude and phase, u abc2 The electric angular velocity Ω2; (2) Calculate the control mode selection coefficient k using the following formula (1), where n r To adjust the camera rotation speed, n e =60f g / p e For brushless doubly fed motors or the synchronous speed of doubly fed motors, (3) The converter in the rectifier unit of the four-quadrant frequency converter operates in rectification mode, and then the contactor connected to the brushless doubly fed motor or the low-voltage winding of the doubly fed motor is closed. The converter output in the inverter unit of the low-voltage four-quadrant frequency converter is connected to u abc1 With the same voltage vector, the control enters the doubly-fed operation mode; (4) Calculate the reactive power feedback value Q using the following formula (2), based on the detected n r Select the control loop corresponding to k, and drag the synchronous condenser's rotation speed to the synchronous speed, preparing for synchronous grid connection.

5. The control method for starting a camera according to claim 3 or 4, characterized in that, In step S4, the braking and stopping mode, the specific steps for controlling the braking and stopping of the synchronous condenser are as follows: (1) After detecting that the synchronous condenser disconnects the stator and rotor power supply, repeat steps (1) to (4) in step S2; (2) The synchronous condenser speed was detected to have dropped to n. e =60f g / p e Then, first disconnect the contactor connected to the brushless doubly fed motor or the low-voltage winding of the doubly fed motor, and then disconnect the contactor connected to the high-voltage winding in the low-voltage winding of the brushless doubly fed motor or the low-voltage winding of the doubly fed motor. (3) Repeat steps (1) to (3) in S3, control the synchronous condenser speed to drop to 5 r / min, disconnect the contactor connected to the brushless doubly fed motor or the low voltage winding of the doubly fed motor, and then disconnect the contactor connected to the high voltage winding in the low voltage winding of the brushless doubly fed motor or the doubly fed motor, and stop the synchronous condenser.

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