Synchronous phase modifier system and method of controlling the same

Abstract

This invention relates to the field of synchronous condenser technology, and more particularly to a synchronous condenser system and its control method. A synchronous condenser system includes a control module, a synchronous condenser, a motor, a shaft, a flywheel, and a brake. A control method for the synchronous condenser system enables the system to start and connect to the external power grid, absorb or output active and reactive power based on external signals, and shut down the system. The synchronous condenser and motor of this invention adopt a coaxial dual-rotor structure, making the overall system structure more compact. The control module controls the synchronous condenser system to absorb or output active and reactive power based on the primary frequency regulation parameters and reactive power demand information of the external power grid, participating in primary frequency regulation and power grid reactive power regulation. The control module also helps to smooth high-frequency power fluctuations in wind or photovoltaic power generation by adjusting the duration and period of active and reactive power absorption or output.

Description

Technical Field

[0001] This invention relates to the field of synchronous condenser technology, and more particularly to synchronous condenser systems and their control methods. Background Technology

[0002] With the continuous increase in installed capacity of new energy power generation, mainly wind and solar power, and the proportion of new energy consumption in the power system becoming increasingly higher, the fluctuating, intermittent, and uncertain characteristics of wind and solar power generation have led to prominent issues of voltage fluctuation and frequency stability in power system operation. The integration of distributed new energy power generation on the load side renders the traditional "source follows load" control rule for stable power system operation inapplicable.

[0003] Wind and solar power generation achieves grid-connected operation through power electronic devices. New power systems with a high proportion of new energy sources face challenges such as voltage stability and reactive power control during operation, significant voltage drops and rises during faults, and frequency stability and active power control, with frequent frequency over-limit adjustments due to insufficient inertia. Despite the application and improvement of technologies such as SVC, SVG, and virtual synchronous machines, the problems of gradually decreasing short-circuit ratios and insufficient inertia in high-proportion new energy power systems have not been solved and will become increasingly prominent. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a synchronous condenser system with energy storage function and high rotational inertia and its control method.

[0005] This invention is achieved through the following technical solution:

[0006] A synchronous condenser system, comprising:

[0007] The control module controls the synchronous condenser through the excitation unit and drives the motor through the bidirectional converter. The bidirectional converter can be disconnected from the external power grid. The control module controls the brake to brake or release the flywheel.

[0008] The synchronous condenser has a first stator and a first rotor, and the first stator is disconnectably connected to the external power grid.

[0009] The motor has an inner rotor and an outer rotor, which can rotate independently.

[0010] The rotating shaft connects the inner rotor and the first rotor.

[0011] Flywheel, fixedly connected to the outer rotor;

[0012] Brakes are used to brake the flywheel.

[0013] According to the above technical solution, preferably, the first stator is mounted on the frame and fixed, the first stator covers the outside of the first rotor, the first stator is provided with a first stator winding, the first rotor is provided with an excitation winding, and the first rotor is mounted on a rotating shaft.

[0014] According to the above technical solution, preferably, the excitation unit is connected to the excitation winding on the rotating shaft through two carbon brush slip rings.

[0015] According to the above technical solution, preferably, the outer rotor is equipped with a squirrel-cage winding, and the bidirectional converter is connected to the inner rotor on the shaft through three carbon brush slip rings.

[0016] According to the above technical solution, preferably, the inner rotor is fixedly connected to the rotating shaft, the outer rotor is fixedly connected to the flywheel, the rotating shaft is rotatably connected to the frame, and end covers are connected to both sides of the flywheel and the outer rotor, with the end covers rotatably connected to the rotating shaft.

[0017] According to the above technical solution, preferably, the rotating shaft is connected to the frame via bearings on the outside of the flywheel, between the flywheel and the synchronous condenser, and on the outside of the synchronous condenser, and the two ends of the rotating shaft are connected to the excitation unit and the bidirectional converter via carbon brushes and slip rings, respectively.

[0018] According to the above technical solution, preferably, the flywheel is annular, with a cylindrical space inside the flywheel, and the outer rotor is installed in the cylinder, and the outer rotor is concentric with the flywheel, so as to drive the flywheel to rotate.

[0019] A control method for a synchronous condenser system includes the following steps: starting the synchronous condenser system and connecting it to an external power grid; absorbing active power from the external power grid or outputting active power to the external power grid according to an external signal; and stopping the synchronous condenser system.

[0020] According to the above technical solution, preferably, starting the synchronous condenser system includes the following steps: the brake brakes the flywheel, the control module drives the inner rotor to rotate through the bidirectional converter, the inner rotor drives the first rotor to rotate through the shaft, when the motor speed and the first rotor reach the synchronous speed, the control module connects the bidirectional converter and the first stator to the external power grid, and the control module excites the excitation unit to control the first rotor to maintain synchronous speed rotation.

[0021] According to the above technical solution, preferably, the synchronous condenser system absorbs active power from the external power grid by the following steps: the control module causes the brake to release the flywheel, the control module causes the bidirectional converter to drive the outer rotor to accelerate rotation, the inner rotor, the shaft, the first rotor and the first stator magnetic field maintain synchronous speed, so that the first stator absorbs active power from the external power grid, and the first stator absorbs reactive power from the external power grid under the control of the excitation unit.

[0022] According to the above technical solution, preferably, the synchronous condenser system outputs active power to the external power grid by the following steps: the control unit controls the bidirectional converter to reduce the power supply frequency of the inner rotor, the electromagnetic field speed of the inner rotor is lower than the mechanical speed of the outer rotor, the outer rotor releases its rotational inertia, so that the motor and the synchronous condenser enter the power generation state, and outputs active power to the external power grid through the bidirectional converter and the first stator, and outputs reactive power to the external power grid under the control of the excitation unit.

[0023] According to the above technical solution, preferably, the shutdown of the synchronous condenser system includes the following steps: the control module demagnetizes the first rotor through the excitation unit, the control module reduces the power supply frequency of the inner rotor through the bidirectional converter, and outputs electrical energy to the external power grid through the bidirectional converter and the first stator until the speed of the inner rotor, the shaft and the first rotor are close to zero, the system shuts down and the power is cut off, and when the speed of the outer rotor is zero, the brake brakes the flywheel.

[0024] The beneficial effects of this invention are: the synchronous condenser and the motor adopt a coaxial dual-rotor structure, making the overall system structure more compact. The control module controls the synchronous condenser system to absorb or output active and reactive power based on the primary frequency regulation parameters and reactive power demand of the external power grid, participating in primary frequency regulation and reactive power regulation. The control module also helps to smooth high-frequency power fluctuations in wind or photovoltaic power generation by adjusting the duration and period of active and reactive power absorption or output. Attached Figure Description

[0025] Figure 1 A schematic diagram of the front view structure of an embodiment of the present invention is shown.

[0026] Figure 2 A block diagram illustrating the operation control process of an embodiment of the present invention is shown.

[0027] In the diagram: 1. Control module; 2. Shaft; 3. Flywheel; 4. Brake; 5. Bidirectional converter; 6. Excitation unit; 7. First stator; 8. First rotor; 9. Frame; 10. Carbon brush slip ring; 11. Inner rotor; 12. Outer rotor; 13. Speed ​​sensor; 14. Motor lead wire; 15. Power supply; 16. Stator lead wire. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0029] Example 1: As Figure 1 As shown, a synchronous condenser system includes: a control module 1, a synchronous condenser, a motor, a rotating shaft 2, a flywheel 3, and a brake 4.

[0030] Specifically, control module 1 is used to drive and control the synchronous condenser and the motor respectively, including controlling the start, stop, and speed regulation of the synchronous condenser and the motor. Control module 1 drives and controls the motor through bidirectional converter 5, and controls the synchronous condenser through excitation unit 6. The bidirectional converter 5 is disconnectably connected to the external power grid. When the motor enters the generating state, active and reactive power are input to the external power grid from the bidirectional converter 5. When the motor enters the state of absorbing active and reactive power, active and reactive power are input from the bidirectional converter 5. The excitation unit 6 can be an excitation cabinet, specifically a DC excitation cabinet. Both the excitation unit 6 and the bidirectional converter 5 have bidirectional information channels with control module 1, facilitating control of the system by control module 1. The bidirectional converter 5 and the excitation unit 6 are respectively connected to power supply line 15.

[0031] Specifically, the synchronous condenser has a first stator 7 and a first rotor 8. The first stator 7 is fixedly connected to the frame 9. The excitation unit 6 can drive the first rotor 8 to rotate relative to the first stator 7. The first rotor 8 is connected to the rotating shaft 2, and torque can be transmitted between the first rotor 8 and the rotating shaft 2. That is, the first rotor 8 can drive the rotating shaft 2 to rotate, and vice versa. The first stator 7 is disconnectably connected to the external power grid. When the synchronous condenser enters the power generation state, active power and reactive power are input to the external power grid from the first stator 7. When the synchronous condenser enters the active power and reactive power absorption state, active power and reactive power are input from the first stator 7. The first stator 7 is connected to the external power grid through stator leads 16.

[0032] In one specific embodiment, the first stator 7 is mounted on the frame 9 and fixedly covers the outside of the first rotor 8. The first stator 7 is provided with a first stator winding, the first rotor 8 is provided with an excitation winding, and the first rotor 8 is mounted on the rotating shaft 2.

[0033] In one specific embodiment, the excitation unit 6 is connected to the excitation winding on the rotating shaft 2 through two carbon brush slip rings 10, and inputs DC power to the excitation winding.

[0034] Specifically, the motor has an inner rotor 11 and an outer rotor 12. The inner rotor 11 includes an iron core winding, and the outer rotor 12 includes an outer iron core and a squirrel-cage winding. Both the inner rotor 11 and the outer rotor 12 can rotate independently. The inner rotor 11 is connected to a rotating shaft 2, and torque can be transmitted between the rotating shaft 2 and the inner rotor 11. That is, the rotating shaft 2 can drive the inner rotor 11 to rotate, and the inner rotor 11 can also drive the rotating shaft 2 to rotate. The outer rotor 12 is connected to a flywheel 3, and the outer rotor 12 can drive the flywheel 3 to rotate, and the flywheel 3 can also drive the outer rotor 12 to rotate. The motor can be an asynchronous motor, a synchronous motor, or a brushless doubly-fed motor. The capacity of the motor and the bidirectional converter 5 is generally 5%-20% of the capacity of the synchronous condenser, and can be adjusted according to the actual working conditions. The motor is connected to the bidirectional converter 5 through carbon brushes, slip rings 10, and motor leads 14.

[0035] In one specific embodiment, the inner rotor 11 is fixedly connected to the rotating shaft 2, the outer rotor 12 is fixedly connected to the flywheel 3, the rotating shaft 2 is rotatably connected to the frame 9, and the flywheel 3 is rotatably connected to the rotating shaft 2.

[0036] In one specific embodiment, the outer rotor 12 is provided with a squirrel-cage winding, and the bidirectional converter 5 is connected to the inner rotor 11 on the rotating shaft 2 through three carbon brush slip rings 10, thereby providing three-phase AC power to the inner rotor 11.

[0037] Specifically, the first rotor 8 and the inner rotor 11 are connected to the same shaft 2. Torque can be transmitted between the first rotor 8, the inner rotor 11 and the shaft 2.

[0038] Specifically, flywheel 3 is a large-radius ring with a large moment of inertia, allowing it to dynamically store and release energy. The outer rotor 12 drives flywheel 3 to rotate.

[0039] Specifically, brake 4 is used to brake flywheel 3. When it is necessary for flywheel 3 to stop rotating, brake 4 can be activated to brake flywheel 3.

[0040] Specifically, the speed sensor 13 is used to measure the rotational speed of the flywheel 3. The rotational speed of the flywheel 3 can be used as a reference or control quantity to regulate the synchronous condenser system. The kinetic energy stored in the flywheel 3 can be calculated from its rotational speed.

[0041] In one specific embodiment, the rotating shaft 2 is connected to the frame 9 via bearings on the outside of the flywheel 3, between the flywheel 3 and the synchronous condenser, and on the outside of the synchronous condenser. The two ends of the rotating shaft 2 are connected to the excitation unit 6 and the bidirectional converter 5 via carbon brush slip rings 10.

[0042] In one specific embodiment, the flywheel 3 is annular and has a cylindrical central hole. The outer rotor 12 is installed in the cylindrical central hole, thereby driving the flywheel 3 to rotate.

[0043] In one specific embodiment, the brake 4 is an electromagnetic brake 4. The control module 1 can control the opening or closing of the brake 4.

[0044] In one specific embodiment, the signal output by the speed sensor 13 can be received by the control module 1.

[0045] Example 2: Figure 2 As shown, the control method of the synchronous condenser system in Embodiment 1 includes the following steps: starting the synchronous condenser system and connecting it to the external power grid; according to the external signal, causing the synchronous condenser system to absorb active power and reactive power from the external power grid or to output active power and reactive power to the external power grid; and stopping the synchronous condenser system.

[0046] Specifically, control module 1 uses the primary frequency regulation parameters and reactive power demand information from the external power grid to control the synchronous condenser system to absorb or output active and reactive power, participating in primary frequency regulation and power grid reactive power regulation. Control module 1 also helps to smooth out high-frequency power fluctuations from wind or solar power generation by adjusting the duration and period of active and reactive power absorption or output.

[0047] Specifically, starting the synchronous condenser system includes the following steps: Control module 1 sends a braking signal to brake 4, brake 4 brakes flywheel 3, control module 1 sends a command signal to bidirectional converter 5, bidirectional converter 5 performs frequency conversion vector control on the motor, driving inner rotor 11 to rotate, inner rotor 11 drives first rotor 8 to rotate through shaft 2, when the motor speed is the same as the first rotor 8 speed, control module 1 connects bidirectional converter 5 and first stator 7 to the external power grid, and control module 1 excites excitation unit 6 to control first rotor 8 to maintain synchronous speed rotation. Under the control of excitation unit, first stator absorbs reactive power from external power grid.

[0048] Specifically, the synchronous condenser system absorbs active power from the external power grid through the following steps: The brake 4 in control module 1 sends a release signal, causing the brake 4 to release the flywheel 3. Control module 1 then sends a command to the bidirectional converter 5, causing the bidirectional converter 5 to increase the power supply frequency to the inner rotor 11, thus accelerating the rotation of the outer rotor 12. The outer rotor 12 drives the flywheel 3 to rotate together, and the rotation direction of the outer rotor 12 is the same as the rotation direction of the shaft. The inertia of the outer rotor 12 generates a resistance-type reverse torque on the inner rotor 11, causing the inner rotor 11, shaft 2, and first rotor 8 to accelerate with the outer rotor 12, enabling the first stator 7 to absorb active power from the external power grid. Furthermore, as long as the flywheel 3 and the outer rotor 12 are in an accelerated rotation state, they will absorb active power from the external power grid. By adjusting the magnitude of the acceleration of the flywheel 3 and the outer rotor 12, the rate of active power absorption can be adjusted. Under the control of the excitation unit, the first stator outputs reactive power to the external power grid.

[0049] Specifically, the synchronous condenser system outputs active power to the external power grid through the following steps: The control unit controls the bidirectional converter 5 to reduce the power supply frequency of the inner rotor 11. The electromagnetic field speed of the inner rotor 11 is lower than that of the outer rotor 12. The outer rotor 12 generates slip power, which is balanced by the active power generated by the inner rotor 11. This allows the inner rotor 11 to supply power to the external power grid through the bidirectional converter 5, i.e., the supersynchronous power generation state. The synchronous condenser also enters the power generation state, outputting active power to the external power grid through the first stator 7. As long as the speeds of the flywheel 3 and the outer rotor 12 decrease, active power can be output to the external power grid.

[0050] Specifically, the shutdown of the synchronous condenser system includes the following steps: the control module 1 decelerates the motor through the excitation unit 6, the control module 1 reduces the power supply frequency of the inner rotor 11 through the bidirectional converter 5, the flywheel 3 and the outer rotor 12 decelerate, the inertial energy of the flywheel 3 is converted into active power and output to the external power grid, and the power is output to the external power grid through the bidirectional converter 5 and the first stator 7 until the speed of the inner rotor 11, the shaft 2 and the first rotor 8 are zero, the system shuts down and the power is cut off, and when the speed of the outer rotor 12 is zero or close to zero, the brake 4 brakes the flywheel 3.

[0051] A power system consists of generators, transformers, transmission lines, and loads. When a power system is operating, the generator output voltage must be balanced with the voltage requirements of all points, including transformers, transmission lines, and loads. Transformers, lines, and some inductive loads consume reactive power; that is, inductive loads lower the system voltage, while capacitive loads raise the system voltage.

[0052] When the load on the external power grid changes or the voltage fluctuates on the generating side of new energy sources such as wind power and photovoltaics, the system voltage needs to be kept stable. The synchronous condenser system regulates the reactive power absorbed or output through the excitation unit to maintain system voltage stability. Furthermore, the motor can also achieve reactive power regulation through decoupling control of the bidirectional converter.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A synchronous condenser system, characterized by include: The control module is connected to the synchronous condenser through the excitation unit and to the motor through the bidirectional converter. The bidirectional converter is connected to the external power grid in a disconnectable manner. The control module controls the brake to brake or release the flywheel. The synchronous condenser has a first stator and a first rotor, the first stator covers the first rotor, and the first stator is disconnected from the external power grid. The motor has an inner rotor and an outer rotor, and the inner rotor and the outer rotor rotate independently. A rotating shaft is connected to both the inner rotor and the first rotor. The flywheel is fixedly connected to the outer rotor; The brake is used to brake the flywheel; The first stator is mounted on the frame and has a first stator winding. The first rotor has an excitation winding. The excitation unit is connected to the excitation winding on the first rotor through two carbon brush slip rings. The outer rotor is equipped with a squirrel-cage winding, and the bidirectional converter is connected to the inner rotor through three carbon brush slip rings; The inner rotor is fixedly connected to the rotating shaft, the outer rotor is fixedly connected to the flywheel, the rotating shaft is rotatably connected to the frame, and end caps are respectively connected to both sides of the flywheel and the outer rotor, with the end caps rotatably connected to the rotating shaft. The rotating shaft is connected to the frame via bearings on the outside of the flywheel, between the flywheel and the synchronous condenser, and on the outside of the synchronous condenser. The two ends of the rotating shaft are connected to the excitation unit and the bidirectional converter via carbon brushes and slip rings, respectively.

2. A control method for a synchronous condenser system according to any one of claims 1, characterized in that, Includes the following steps: The synchronous condenser system is started and connected to the external power grid. Based on external signals, the synchronous condenser system absorbs active and reactive power from the external power grid, or outputs active and reactive power to the external power grid based on external signals, and then the synchronous condenser system is shut down.

3. A control method of a synchronous phase modifier system according to claim 2, characterized by, Starting the synchronous condenser system includes the following steps: the brake brakes the flywheel; the control module drives the inner rotor to rotate through the bidirectional converter; the inner rotor drives the first rotor to rotate through the shaft; when the speed of the motor and the speed of the first rotor reach the synchronous speed of the first stator magnetic field, the control module connects the bidirectional converter, the first stator, and the external power grid; and the control module excites and controls the first rotor to maintain synchronous speed rotation through the excitation unit.

4. A control method of a synchronous phase modifier system according to claim 3, characterized by, The synchronous condenser system absorbs active power from the external power grid by the following steps: the control module causes the brake to release the flywheel, the control module drives the outer rotor to accelerate rotation through the bidirectional converter, the inner rotor, the shaft and the first rotor accelerate rotation with the outer rotor or maintain synchronous speed, so that the first stator and the inner rotor absorb active power from the external power grid, and the first stator absorbs reactive power from the external power grid under the control of the excitation unit.

5. A control method of a synchronous phase modifier system according to claim 4, characterized by, The synchronous condenser system outputs active power to the external power grid through the following steps: the control unit reduces the power supply frequency of the inner rotor through the bidirectional converter, so that the electromagnetic speed of the inner rotor is lower than the mechanical speed of the outer rotor, so that the motor and the synchronous condenser are in a power generation state, and outputs active power to the external power grid through the bidirectional converter and the first stator, and outputs reactive power to the external power grid under the control of the excitation unit.

6. A control method of a synchronous phase modifier system according to claim 5, characterized by, The shutdown of the synchronous condenser system includes the following steps: the control module reduces the excitation current of the synchronous condenser through the excitation unit; the control module reduces the power supply frequency of the inner rotor through the bidirectional converter; and outputs electrical energy to the external power grid through the bidirectional converter and the first stator until the speed of the inner rotor, the shaft, and the first rotor approaches zero. The system then shuts down and the power is cut off. When the speed of the outer rotor is zero, the brake applies braking force to the flywheel.

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