Wind turbine generator system suitable for AVC system and its reactive power control method

Abstract

The present invention relates to a wind turbine generator set suitable for an AVC system and a reactive power control method thereof. The wind turbine generator set includes a wind turbine converter, a primary turbine main controller, and an external AVC control device. The external AVC control device includes an external AVC controller and a sensor. The sensor is hard-wired to the external AVC controller and the wind turbine converter. The external AVC controller is connected to the wind turbine converter via a fieldbus. The wind turbine converter is connected to the primary turbine main controller via a fieldbus. The present invention can fully utilize the capacity of a doubly-fed converter, improve the reactive power output capability of the doubly-fed converter, and improve the reactive power response speed during fault ride-through by dynamically optimizing the reactive power distribution between the grid side and the generator side under quasi-fault conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power converter control, and in particular to a wind turbine generator set applicable to an AVC system and a reactive power control method thereof. Background Art

[0002] Traditional doubly-fed wind turbines typically operate in unity power factor (UPF) mode, where the reactive power command issued by the wind turbine control system is set to zero, and the generator only generates active power. With the large-scale integration of wind turbines into the grid, there is an increasing demand for wind turbines to utilize Automatic Voltage Control (AVC) to improve the safety and economic efficiency of grid operation. This places new demands on the reactive power regulation capabilities of wind turbines.

[0003] Reactive power regulation of doubly-fed wind turbines is mainly achieved through the unit control system and wind power converters. Existing doubly-fed wind power converters generally receive active power instructions from the control system. The few converters that issue reactive power generally use the method of issuing reactive power separately on the generator side. Existing technologies do not have a method for dynamically allocating reactive power for converters supporting AVC systems. Summary of the Invention

[0004] In order to address the deficiencies in the existing technology, the present invention provides a wind turbine set suitable for an AVC system, comprising a wind turbine converter, an original turbine main controller, and an external AVC control device, wherein the external AVC control device comprises an external AVC controller and a sensor, the sensor being connected to the external AVC controller and the wind turbine converter through hard wiring, the external AVC controller being connected to the wind turbine converter through a field bus, and the wind turbine converter being connected to the original turbine main controller through a field bus.

[0005] Wherein, the sensors include a voltage sensor and a current sensor.

[0006] The external AVC controller is connected to the wind power converter via a CANopen or Profibus field bus.

[0007] The external AVC controller and the sensor are both connected to the converter controller in the wind power converter.

[0008] The doubly-fed converter implements reactive power control of the AVC system by the following method:

[0009] Step S1: Select several typical working conditions and calculate the power curve of the unit Calculate the reactive capacity limit of the grid-side converter corresponding to each typical operating condition, and set the grid-side reactive capacity limit curve within the converter through curve fitting;

[0010] Among them, in the unit power curve, QDFIG_n is the reactive power of the grid-side converter, S DFIG_n is the apparent power of the grid-side converter, Q DFIG_s is the active power of the grid-side converter;

[0011] Step S2: Select several typical working conditions and calculate the equivalent circuit of the doubly fed generator. Calculate the reactive capacity limit of the generator-side converter under each typical operating condition, and derive the generator-side reactive capacity limit curve through fitting.

[0012] Among them, in the doubly fed machine equivalent circuit, P s is the stator active power of the doubly fed generator, Q s is the stator reactive power of the doubly-fed generator, X m is the magnetizing reactance, U n is the stator phase voltage, I′ r is the rotor current referred to the stator side;

[0013] Step S3: Introduce the reactive power distribution coefficient K and determine the reactive power distribution on the grid side and the generator side using the following formula:

[0014]

[0015] -1≤K≤1

[0016] Among them, Q DFIG is the total reactive power of the doubly fed system, Q DFIG_n is the reactive power of the grid-side converter of the doubly fed system, Q DFIG_s The stator-side reactive power controlled by the generator-side converter;

[0017] Step S4: Acquire the real-time operating conditions and obtain the reactive capacity limits of the generator-side and grid-side converters under the current operating conditions based on the real-time operating conditions and the curves fitted in steps S1 and S2; obtain the reactive power of the generator-side and grid-side converters using the formula in step S3, wherein the K value is dynamically adjusted when the grid voltage approaches the fault ride-through threshold; and K=1 when the grid voltage is not close to the fault ride-through threshold.

[0018] Step S5: The generator side outputs the smaller of the generator side reactive capacity limit and the generator side converter reactive power in step S4; the grid side outputs the smaller of the grid side reactive capacity limit and the residual reactive power in step S4, where the residual reactive power is the difference between the total reactive power of the doubly fed system and the reactive power output by the generator side.

[0019] The present invention further provides a reactive power control method for a doubly-fed wind power converter applicable to an AVC system, comprising the following steps:

[0020] Step S1: Select several typical working conditions and calculate the power curve of the unit Calculate the reactive capacity limit of the grid-side converter corresponding to each typical operating condition, and set the grid-side reactive capacity limit curve within the converter through curve fitting;

[0021] Among them, in the unit power curve, Q DFIG_n is the reactive power of the grid-side converter, S DFIG_n is the apparent power of the grid-side converter, Q DFIG_s is the active power of the grid-side converter;

[0022] Step S2: Select several typical working conditions and calculate the equivalent circuit of the doubly fed generator. Calculate the reactive capacity limit of the generator-side converter under each typical operating condition, and derive the generator-side reactive capacity limit curve through fitting.

[0023] Among them, in the doubly fed machine equivalent circuit, P s is the stator active power of the doubly fed generator, Q s is the stator reactive power of the doubly-fed generator, X m is the magnetizing reactance, U n is the stator phase voltage, I′ r is the rotor current referred to the stator side;

[0024] Step S3: Introduce the reactive power distribution coefficient K and determine the reactive power distribution on the grid side and the generator side using the following formula:

[0025]

[0026] -1≤K≤1

[0027] Among them, Q DFIG is the total reactive power of the doubly fed system, Q DFIG_n is the reactive power of the grid-side converter of the doubly fed system, Q DFIG_s The stator-side reactive power controlled by the generator-side converter;

[0028] Step S4: Acquire the real-time operating conditions and obtain the reactive capacity limits of the generator-side and grid-side converters under the current operating conditions based on the real-time operating conditions and the curves fitted in steps S1 and S2; obtain the reactive power of the generator-side and grid-side converters using the formula in step S3, wherein the K value is dynamically adjusted when the grid voltage approaches the fault ride-through threshold; and K=1 when the grid voltage is not close to the fault ride-through threshold.

[0029] Step S5: The generator side outputs the smaller of the generator side reactive capacity limit and the generator side converter reactive power in step S4; the grid side outputs the smaller of the grid side reactive capacity limit and the residual reactive power in step S4, where the residual reactive power is the difference between the total reactive power of the doubly fed system and the reactive power output by the generator side.

[0030] Wherein, in the step S4, whether the grid voltage is close to the fault ride-through threshold is determined by detecting the voltage change and duration.

[0031] Wherein, in step S1, the fitted grid-side reactive capacity limit curve includes an inductive reactive capacity limit curve and a capacitive reactive capacity limit curve.

[0032] Wherein, in step S2, the fitted generator-side reactive capacity limit curve includes an inductive reactive capacity limit curve and a capacitive reactive capacity limit curve.

[0033] The wind turbine generator set and reactive power control method thereof applicable to the AVC system provided by the present invention can fully utilize the capacity of the doubly-fed converter, improve the reactive power output capability of the doubly-fed converter, and improve the reactive power response speed during fault ride-through by dynamically optimizing the reactive power distribution on the grid side and the generator side under quasi-fault conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 : The communication topology diagram of the wind turbine generator set applicable to the AVC system of the present invention.

[0035] Figure 2 : Workflow diagram of the reactive power control method of the doubly-fed wind power converter applicable to the AVC system of the present invention. DETAILED DESCRIPTION

[0036] In order to have a further understanding of the technical solution and beneficial effects of the present invention, the technical solution and beneficial effects of the present invention are described in detail below with reference to the accompanying drawings.

[0037] The reactive power capacity of a doubly-fed wind turbine converter is directly related to the operating conditions of the wind turbine. Therefore, when the AVC function of a wind turbine is in effect, it is necessary to adjust the reactive power distribution method and the corresponding reactive power control system according to the operating conditions of the wind turbine. For details, please refer to Figure 1 Figure 1 shows the communication topology of a wind turbine suitable for an AVC system according to the present invention. The dashed box and the connected parts represent the newly added hardware compared to existing wind turbines. The external control device consists of a new PLC controller and high-precision current and voltage sensors. The new PLC controller communicates with the wind turbine converter via a fieldbus such as CANopen or Profibus. The wind turbine converter establishes communication connections with both the original and new controllers. Active power commands come from the original controller, while reactive power commands come from the new controller.

[0038] The new controller can integrate the AVC algorithm to determine the reactive power instructions required for the current AVC function based on the data status fed back by the converter through communication and the grid voltage and current collected by high-precision sensors.

[0039] The wind turbine converter simultaneously receives the active power instructions sent by the original master controller and the reactive power instructions sent by the new controller, adds a reactive power control algorithm inside the converter, and responds to the reactive power instructions sent by the new controller in real time according to the unit's operating conditions to cooperate with the new controller to implement the AVC function.

[0040] Therefore, the present invention installs an AVC control device external to the wind turbine set, and there is no need to replace or modify the original wind turbine set main control. By adding an external AVC controller and a high-precision sensor to cooperate with the program upgrade of the wind power converter, the AVC function of the wind turbine set can be realized. It has strong adaptability, good versatility, low cost, and is easy to implement, and has great practical value.

[0041] In the present invention, the new controller sends reactive power control instructions in the following manner:

[0042] 1. Select several typical working conditions and calculate the power curve of the unit. Calculate the grid-side converter capacity limit corresponding to each typical operating condition, and derive the grid-side reactive capacity limit curve (including the inductive reactive capacity limit curve and the capacitive reactive capacity limit curve) by fitting.

[0043] Among them, in the unit power curve, Q DFIG_n is the reactive power of the grid-side converter, S DFIG_n is the apparent power of the grid-side converter (input into the doubly fed converter in advance in the form of parameters), Q DFIG_s is the active power of the grid-side converter (obtained in real time).

[0044] 2. Select several typical working conditions and calculate the equivalent circuit of the doubly fed generator. Calculate the corresponding generator-side converter capacity limit under each typical operating condition, and derive the generator-side reactive capacity limit curve (including the inductive reactive capacity limit curve and the capacitive reactive capacity limit curve) through fitting.

[0045] Among them, in the doubly fed machine equivalent circuit, P s is the stator active power of the doubly fed generator, Q s is the stator reactive power of the doubly-fed generator, X m is the magnetizing reactance, U n is the stator phase voltage, I′ r is the rotor current referred to the stator side.

[0046] 3. Introduce the reactive power distribution coefficient K and determine the reactive power distribution on the grid side and the generator side using the following formula (Formula 3):

[0047]

[0048] -1≤K≤1

[0049] Among them, Q DFIG is the total reactive power of the doubly fed system, Q DFIG_n is the reactive power of the grid-side converter of the doubly fed system, Q DFIG_s It is the stator side reactive power controlled by the generator side converter.

[0050] 5. Considering the large capacity of the generator side, reactive power is preferentially sent from the generator side under normal conditions (K value is 1 in this case). In the fault ride-through state, the generator-side converter may need to block pulses. In this case, it is easier and more reliable to send reactive power from the grid side. Therefore, when the converter detects that the grid voltage is approaching the fault ride-through threshold (determining whether it is close to the fault state by detecting voltage changes and duration), the K value is dynamically adjusted to transfer part of the reactive power originally sent from the generator side to the grid side in advance.

[0051] 6. Determine whether the reactive power command has reached the limit based on the reactive power capacity curves of the grid-side and generator-side converters.

[0052] 7. If the generator-side reactive power command reaches the generator-side limit, the reactive power distribution relationship no longer satisfies Formula 3. The generator-side generates reactive power according to the limit, and the remaining reactive power is supplemented by the grid-side.

[0053] 8. If the grid side also reaches the limit, both the generator side and the grid side will generate reactive power according to the maximum limit.

[0054] Therefore, when approaching the fault threshold, the present invention dynamically optimizes the reactive power distribution on the grid side and the machine side under the quasi-fault state, and transfers part of the reactive power originally sent by the machine side to the grid side in advance. This can fully utilize the capacity of the doubly fed converter, improve the reactive power output capability of the doubly fed converter, and improve the reactive power response speed during fault crossing.

[0055] In actual operation, when the wind turbine set is put into the AVC function, the AVC reactive control flag in the converter is set to 1 through communication or hard wiring, and the original reactive control mode is switched to the control mode provided by the present invention. When the wind turbine set exits the AVC function, the AVC reactive control flag in the converter is cleared to zero through communication or hard wiring, and the reactive control mode is switched to the original reactive control mode.

[0056] Although the present invention has been described using the above preferred embodiments, they are not intended to limit the scope of protection of the present invention. Any person skilled in the art may make various changes and modifications to the above embodiments without departing from the spirit and scope of the present invention. These changes and modifications are still within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the definition of the claims.

Claims

1. A wind turbine generator system suitable for an AVC system, characterized in that: The system includes a wind turbine converter, an original unit main controller, and an external AVC control device. The external AVC control device includes an external AVC controller and a sensor. The sensor is connected to the external AVC controller and the wind turbine converter through hard wiring. The external AVC controller is connected to the wind turbine converter through a field bus. The wind turbine converter is connected to the original unit main controller through a field bus. The doubly-fed converter realizes reactive power control of the AVC system through the following method: Step S1: Select several typical working conditions and calculate the power curve of the unit Calculate the reactive capacity limit of the grid-side converter corresponding to each typical operating condition, and set the grid-side reactive capacity limit curve within the converter through curve fitting; Among them, in the unit power curve, Q DFIG_n is the reactive power of the grid-side converter, S DFIG_n is the apparent power of the grid-side converter, Q DFIG_s is the active power of the grid-side converter; Step S2: Select several typical working conditions and calculate the equivalent circuit of the doubly fed generator. Calculate the reactive capacity limit of the generator-side converter under each typical operating condition, and derive the generator-side reactive capacity limit curve through fitting. Among them, in the doubly fed machine equivalent circuit, P s is the stator active power of the doubly fed generator, Q s is the stator reactive power of the doubly-fed generator, X m is the magnetizing reactance, U n is the stator phase voltage, I r ' is the rotor current referred to the stator side; Step S3: Introduce the reactive power distribution coefficient K and determine the reactive power distribution on the grid side and the generator side using the following formula: -1≤K≤1 Among them, Q DFIG is the total reactive power of the doubly fed system, Q DFIG_n is the reactive power of the grid-side converter of the doubly fed system, Q DFIG_s The stator-side reactive power controlled by the generator-side converter; Step S4: Acquire the real-time operating conditions and obtain the reactive capacity limits of the generator-side and grid-side converters under the current operating conditions based on the real-time operating conditions and the curves fitted in steps S1 and S2; obtain the reactive power of the generator-side and grid-side converters using the formula in step S3, wherein the K value is dynamically adjusted when the grid voltage approaches the fault ride-through threshold; and K=1 when the grid voltage is not close to the fault ride-through threshold. Step S5: The generator side outputs the smaller of the generator side reactive capacity limit and the generator side converter reactive power in step S4; the grid side outputs the smaller of the grid side reactive capacity limit and the residual reactive power in step S4, where the residual reactive power is the difference between the total reactive power of the doubly fed system and the reactive power output by the generator side.

2. The wind turbine generator system suitable for the AVC system according to claim 1, characterized in that: The sensors include a voltage sensor and a current sensor.

3. The wind turbine generator system suitable for an AVC system according to claim 1, characterized in that: The external AVC controller is connected to the wind power converter via a CANopen or Profibus field bus.

4. The wind turbine generator system suitable for an AVC system according to claim 1, wherein: The external AVC controller and the sensor are both connected to the converter controller in the wind power converter.

5. A reactive power control method for a doubly-fed wind power converter suitable for an AVC system, characterized in that: The steps include: Step S1: Select several typical working conditions and calculate the power curve of the unit Calculate the reactive capacity limit of the grid-side converter corresponding to each typical operating condition, and set the grid-side reactive capacity limit curve within the converter through curve fitting; Among them, in the unit power curve, Q DFIG_n is the reactive power of the grid-side converter, S DFIG_n is the apparent power of the grid-side converter, Q DFIG_s is the active power of the grid-side converter; Step S2: Select several typical working conditions and calculate the equivalent circuit of the doubly fed generator. Calculate the reactive capacity limit of the generator-side converter under each typical operating condition, and derive the generator-side reactive capacity limit curve through fitting. Among them, in the doubly fed machine equivalent circuit, P s is the stator active power of the doubly fed generator, Q s is the stator reactive power of the doubly-fed generator, X m is the magnetizing reactance, U n is the stator phase voltage, I r ' is the rotor current referred to the stator side; Step S3: Introduce the reactive power distribution coefficient K and determine the reactive power distribution on the grid side and the generator side using the following formula: -1≤K≤1 Among them, Q DFIG is the total reactive power of the doubly fed system, Q DFIG_n is the reactive power of the grid-side converter of the doubly fed system, Q DFIG_s Stator-side reactive power controlled by the generator-side converter; Step S4: Acquire the real-time operating conditions and obtain the reactive capacity limits of the generator-side and grid-side converters under the current operating conditions based on the real-time operating conditions and the curves fitted in steps S1 and S2; obtain the reactive power of the generator-side and grid-side converters using the formula in step S3, wherein the K value is dynamically adjusted when the grid voltage approaches the fault ride-through threshold; and K=1 when the grid voltage is not close to the fault ride-through threshold. Step S5: The generator side outputs the smaller of the generator side reactive capacity limit and the generator side converter reactive power in step S4; the grid side outputs the smaller of the grid side reactive capacity limit and the residual reactive power in step S4, where the residual reactive power is the difference between the total reactive power of the doubly fed system and the reactive power output by the generator side.

6. The reactive power control method for a doubly-fed wind power converter applicable to an AVC system according to claim 5, characterized in that: In step S4, whether the grid voltage is close to the fault ride-through threshold is determined by detecting the voltage change and duration.

7. The reactive power control method for a doubly-fed wind power converter applicable to an AVC system according to claim 5, characterized in that: In step S1, the fitted grid-side reactive capacity limit curve includes an inductive reactive capacity limit curve and a capacitive reactive capacity limit curve.

8. The reactive power control method for a doubly-fed wind power converter applicable to an AVC system according to claim 5, characterized in that: In step S2, the fitted generator-side reactive capacity limit curve includes an inductive reactive capacity limit curve and a capacitive reactive capacity limit curve.

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