Control device and control method of variable-speed, variable-voltage and variable-frequency wind turbine generator

Abstract

The invention relates to a control device and a control method of a variable-speed, variable-voltage and variable-frequency wind turbine generator. The control device comprises an electrical main loop and an electrical auxiliary loop. Compared with the prior art, the wind turbine generator electrical topological structure suitable for the centralized variable-frequency wind power plant disclosed by the invention utilizes the three-phase uncontrolled rectifying unit, the DC / DC converter and the DC / AC power frequency inverter to convert alternating current on the low-voltage side of a generator set box transformer into direct current or power frequency alternating current suitable for different load requirements; the power supply requirements of different loads of the wind turbine generator are met, when the generator is started, the soft starter is used for controlling the stator voltage amplitude of the three-phase squirrel-cage induction generator to be slowly increased from 0, smooth starting of the generator is achieved, impact of starting current on a power grid is reduced, and equipment damage or energy waste caused by improper control is avoided.

Description

Technical Field

[0001] The present invention relates to the field of wind power generation, and in particular to a control device and a control method for a variable speed, variable voltage and variable frequency wind turbine generator set. Background Art

[0002] Centralized variable frequency wind farm technology uses a large converter station to perform centralized frequency conversion on multiple wind turbines, thereby eliminating the need for dispersed converters in the wind farm and greatly improving the reliability of each wind turbine. The typical application scenario of centralized variable frequency wind farm technology is the flexible dynamic low-frequency wind power system, which is a medium- and long-distance offshore wind power system solution with outstanding potential advantages. It uses low-frequency AC power transmission with variable voltage and frequency conversion, without the need to set up high-voltage and large-capacity converter stations at sea. It has the advantages of low cost and high reliability, and has advantages in active support of grid frequency.

[0003] Different from the current mainstream variable speed constant frequency wind turbines, the frequency and amplitude of the grid connection point voltage are constant. The frequency and amplitude of the grid connection point voltage of the wind turbines in the centralized variable frequency wind farm will change dynamically, so the electrical main circuit and auxiliary circuit of each wind turbine in it need to be redesigned. Although the existing technology has disclosed the overall topological structure of the dynamic low-frequency wind power system and the control strategy of the centralized variable frequency converter station under normal operation, due to the lack of actual centralized variable frequency wind farm projects, the electrical topology inside the variable voltage variable frequency wind turbines of the related technology has not yet been disclosed.

[0004] The electrical main circuit of a wind turbine refers to the main transmission path for the power generated by the generator. In fact, the normal operation of a wind turbine is inseparable from the electrical auxiliary circuit. The electrical auxiliary circuit mainly solves the power supply problems of the yaw system, pitch system, cooling / auxiliary heating system, and secondary control and protection power supply system of the wind turbine. Among them, the drivers of the yaw system and pitch system belong to variable frequency loads, which are mostly power loads and have relatively large power; the secondary control and protection power supply system is used to power the central control system and monitoring system of the wind turbine, and mostly uses industrial frequency power supply. Therefore, the secondary control and protection power supply system belongs to the industrial frequency load, which has relatively small power but high requirements for power supply quality; the cooling / auxiliary heating system can be either a variable frequency load or an industrial frequency load. Although the total capacity of the electrical auxiliary circuit accounts for a small proportion of the rated capacity of the wind turbine, its capacity is also increasing with the continuous increase in the capacity of the single unit.

[0005] The particularity of a centralized variable frequency wind farm is that the voltage at the public connection point of the wind farm is AC power with a wide voltage and frequency conversion range. This means that the voltage at the wind turbine grid connection point is also AC power with a wide voltage and frequency conversion range. The wind turbine's electrical auxiliary circuit needs to draw power from the voltage and frequency conversion grid connection point to supply multiple different types of loads, including constant voltage and frequency industrial frequency loads, as well as multiple variable frequency loads.

[0006] Chinese patent application CN117578581A discloses "an electrical auxiliary circuit device, a wind turbine set and a starting method thereof". This invention overcomes the defects of the prior art such as high power loss, low circuit reliability, low energy utilization efficiency and low economy and provides an electrical auxiliary circuit device, a wind turbine set and a starting method thereof. However, this method is not aimed at centralized variable frequency wind farms, and does not disclose a variable speed, variable voltage and variable frequency control method. Summary of the invention

[0007] The purpose of the present invention is to provide a control device and a control method for a variable speed, variable voltage and variable frequency wind turbine set, disclose an electrical topology structure of a wind turbine set suitable for a centralized variable frequency wind farm, propose an electrical main circuit and auxiliary circuit topology structure scheme that takes economic efficiency into consideration, convert the AC power on the low voltage side of the unit box transformer into DC power or industrial frequency AC power suitable for different load requirements, and meet the power supply requirements of different loads of the wind turbine set.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] A control device for a variable speed, variable voltage and variable frequency wind turbine set, used in a centralized variable frequency wind farm, the control device comprising an electrical main circuit and an electrical auxiliary circuit;

[0010] The electrical main circuit includes a soft starter and a transformer substation. The electrical main circuit is connected to the wind turbine to generate electricity. The soft starter limits the starting current generated by the rotation of the wind turbine when the wind turbine is started, reducing the impact of the starting current on the power grid. The high-voltage side AC port of the transformer substation is directly connected or connected to the common connection point of the voltage and frequency conversion through the power collection network, converts the voltage of the current generated by the wind turbine, and inputs the current into the power grid or other systems.

[0011] The electrical auxiliary circuit includes a three-phase uncontrolled rectifier unit, a DC / DC converter and a DC / AC industrial frequency inverter. The first DC port of the DC / DC converter and the DC port of the three-phase uncontrolled rectifier unit are connected to a common DC bus, the second DC port of the DC / DC converter is connected to the DC port of the DC / AC industrial frequency inverter, the DC / AC industrial frequency inverter is connected to the industrial frequency load, the AC port of the three-phase uncontrolled rectifier unit is connected to the low-voltage side of the unit box transformer of the electrical main circuit, so that the electrical main circuit and the electrical auxiliary circuit are connected, the three-phase uncontrolled rectifier unit converts the AC power input from the unit box transformer into DC power, the DC / DC converter transforms the converted DC power and inputs the DC power into the DC / AC industrial frequency inverter, and the DC / AC industrial frequency inverter inverts the DC power into industrial frequency AC power.

[0012] Furthermore, the electrical main circuit also includes a three-phase squirrel cage induction generator, a three-phase capacitor group and an AC switch, wherein the three-phase capacitor group is connected in parallel with the stator winding of the three-phase squirrel cage induction generator, the soft starter and the AC switch are connected in parallel to form two AC ports, the first AC port of the soft starter and the AC switch is connected in series with the stator winding of the three-phase squirrel cage induction generator, and the second AC port of the soft starter and the AC switch is connected in series with the low-voltage side AC port of the unit box transformer.

[0013] Furthermore, the soft starter is composed of three groups of anti-parallel thyristors and their control systems. When the wind turbine is started, the soft starter starts and controls the stator voltage amplitude of the three-phase squirrel cage induction generator to slowly increase from 0 until the amplitude and phase of the voltages at the two AC ports of the soft starter are the same, and the soft starter is turned off.

[0014] Furthermore, the DC / AC industrial frequency inverter converts direct current into industrial frequency alternating current to supply power to industrial frequency loads, which include a main controller, a converter controller and a unit monitoring system of a wind turbine set.

[0015] Furthermore, the electrical auxiliary circuit also includes a DC / AC variable frequency drive for a pitch system and a DC / AC variable frequency drive for a yaw system, wherein the DC port of the DC / AC variable frequency drive for the pitch system and the DC port of the DC / AC variable frequency drive for the yaw system are connected to a common DC bus with the first DC port of the DC / DC converter and the DC port of the three-phase uncontrolled rectifier unit, so as to invert the DC power output by the three-phase uncontrolled rectifier unit into AC power.

[0016] Furthermore, the pitch system DC / AC variable frequency drive is used to control the pitch motor of the pitch actuator, and the pitch motor drives the wind turbine to perform pitch operation. When the wind turbine adopts unified pitch control, a set of pitch system DC / AC variable frequency drive is used. When the wind turbines adopt independent pitch control, the number of sets of pitch system DC / AC variable frequency drives is equal to the number of blades.

[0017] Furthermore, the yaw system DC / AC variable frequency driver is used to control the yaw motor of the yaw actuator to perform yaw to wind.

[0018] Furthermore, the three-phase uncontrolled rectification unit includes an uncontrolled diode and a capacitor, and the connection method of the uncontrolled diode and the capacitor includes a three-phase bridge connection.

[0019] Furthermore, the formula for the DC voltage value of the second DC port of the DC / DC converter includes:

[0020]

[0021] Among them, U acN50is the rated value of the AC port voltage of the DC / AC power frequency inverter, k dc is the DC voltage utilization rate of the DC / AC power frequency inverter, k margin is the margin factor.

[0022] A control method for a variable speed, variable voltage and variable frequency wind turbine control device, the method comprising:

[0023] When the soft starter is not started and the AC switch is disconnected in the main electrical circuit, the power required for starting is provided to the wind turbine through the common connection point of the voltage and frequency conversion, and the fluctuation of the DC power is smoothed by the three-phase uncontrolled rectifier unit;

[0024] The converted DC power is transformed by using a DC / DC converter;

[0025] Use a DC / AC power frequency inverter to convert the transformed DC power into power frequency AC power, and transmit the power frequency AC power to power frequency loads;

[0026] Use direct current to start the DC / AC variable frequency drive of the yaw system to drive the yaw motor to yaw the wind turbine to the wind;

[0027] After the wind turbine has completed the yaw alignment, the DC / AC variable frequency drive of the variable pitch system is started by direct current to drive the variable pitch motor of the wind turbine to start the wind turbine mechanically, so that the wind turbine speed reaches the lower speed limit of grid-connected operation and stabilizes at this speed;

[0028] Start the soft starter and control the stator voltage amplitude of the three-phase squirrel cage induction generator to slowly increase from 0 until the amplitude and phase of the voltage at the two AC ports of the soft starter are the same. At this time, close the AC switch and turn off the soft starter, stop supplying power to the common connection point of the transformer and frequency converter, and switch the wind turbine to the closed-loop control of the generator active power. The generated electric energy is converted by the voltage of the unit box transformer and output from the common connection point of the transformer and frequency converter.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The present invention proposes a topological structure scheme of an electrical main circuit and an auxiliary circuit for a variable voltage and variable frequency wind turbine set suitable for a centralized variable frequency wind farm, wherein the electrical auxiliary circuit utilizes a three-phase uncontrolled rectifier unit, a DC / DC converter and a DC / AC industrial frequency inverter to convert the alternating current on the low voltage side of the unit box transformer into industrial frequency alternating current suitable for different load requirements, thereby meeting the power supply requirements of different loads of the wind turbine set. When starting the generator, a soft starter is utilized to control the stator voltage amplitude of the three-phase squirrel cage induction generator to increase slowly from 0, thereby realizing smooth starting of the generator, reducing the impact of the starting current on the power grid, and avoiding equipment damage or energy waste due to improper control.

[0031] 2. The three-phase capacitor group is used in the main electrical circuit of the present invention to compensate for the inductive reactive power of the generator, thereby improving the power factor of the system;

[0032] 3. In the electrical auxiliary circuit of the present invention, the yaw system DC / AC variable frequency drive and the pitch system DC / AC variable frequency drive control the wind turbine, ensuring that the wind turbine can accurately adjust the blade angle and orientation to maximize the capture of wind energy and stably output electricity, thereby improving the power generation efficiency and reliability of the wind turbine and reducing operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a structural schematic diagram of the present invention;

[0034] Figure 2 is a flow chart of the method of the present invention;

[0035] Reference numerals:

[0036] 1-main electrical circuit, 2-auxiliary electrical circuit, 11-three-phase squirrel cage induction generator, 12-three-phase capacitor bank, 13-soft starter, 14-AC switch, 15-unit box transformer, 21-three-phase uncontrolled rectifier unit, 22-DC / DC converter, 23-DC / AC industrial frequency inverter, 24-pitch system DC / AC variable frequency drive, 25-yaw system DC / AC variable frequency drive. DETAILED DESCRIPTION

[0037] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0038] Example 1

[0039] The present invention discloses a control device for a variable speed variable voltage variable frequency wind turbine set, which is used for a centralized variable frequency wind farm. Figure 1 As shown, it includes two parts: the main electrical circuit 1 and the auxiliary electrical circuit 2.

[0040] The electrical main circuit 1 includes a three-phase squirrel cage induction generator 11, a three-phase capacitor bank 12, a soft starter 13, an AC switch 14, and a unit transformer 15. The three-phase capacitor bank 12 is connected in parallel with the stator winding of the three-phase squirrel cage induction generator 11. The soft starter 13 and the AC switch 14 are connected in parallel to form two AC ports, the first AC port of the soft starter 13 and the AC switch 14 is connected in series with the stator winding of the three-phase squirrel cage induction generator 11, and the second AC port of the soft starter 13 and the AC switch 14 is connected in series with the low-voltage side AC port of the unit transformer 15. The high-voltage side AC port of the unit transformer 15 is directly connected or connected to the common connection point of the voltage and frequency conversion through the collector network.

[0041] The function of the three-phase capacitor bank 12 is to compensate for the inductive reactive power of the three-phase squirrel cage induction generator 11. The capacitance of the capacitor bank is designed according to the principle of minimizing the dynamic reactive power required by the generator under all wind speed ranges. The dynamic reactive power refers to the absolute value of the difference between the current reactive power of the three-phase squirrel cage induction generator 11 and the current reactive power of the three-phase capacitor bank 12.

[0042] The soft starter 13 is composed of three groups of anti-parallel thyristors and their control systems. The technology is relatively mature and there are mature products to choose from. The rated voltage of the soft starter 13 is designed according to the lower limit voltage value of the common connection point of the transformer and frequency converter, the rated frequency of the soft starter 13 is designed according to the lower limit frequency value of the common connection point of the transformer and frequency converter, and the rated capacity of the soft starter 13 is configured to meet the starting requirements of the three-phase squirrel cage induction generator 11, which is usually a small capacity.

[0043] The AC switch 14 includes a contactor and a circuit breaker switch, and the AC switch 14 is selected according to the rated voltage and rated current of the wind turbine.

[0044] The unit box transformer 15 is a three-phase transformer, which is selected according to the rated voltage and rated current of the wind turbine unit.

[0045] Figure 1 In the embodiment, the high voltage side AC port of the unit box transformer 15 is directly connected to the conductor of the common connection point of the transformer and frequency converter or is connected through the collector network. A switch is provided. The switch receives external instructions, such as instructions from the wind farm control station, to open and close.

[0046] The electrical auxiliary circuit 2 includes a three-phase uncontrolled rectifier unit 21, a DC / DC converter 22, a DC / AC industrial frequency inverter 23, a pitch system DC / AC variable frequency driver 24 and a yaw system DC / AC variable frequency driver 25. The first DC port of the DC / DC converter 22, the DC port of the three-phase uncontrolled rectifier unit 21, the DC port of the pitch system DC / AC variable frequency driver 24 and the DC port of the yaw system DC / AC variable frequency driver 25 are connected to a common DC bus. The second DC port of the DC / DC converter 22 is connected to the DC port of the DC / AC industrial frequency inverter 23. The DC / AC industrial frequency inverter 23 is connected to the industrial frequency load. The AC port of the three-phase uncontrolled rectifier unit 21 is connected to the low-voltage side of the unit box transformer 15 of the electrical main circuit 1. The electrical auxiliary circuit 2 converts AC power into DC power or industrial frequency AC power suitable for different load requirements.

[0047] The three-phase uncontrolled rectifier unit 21 uses an uncontrolled diode as a power semiconductor device, and can use a 6-pulse uncontrolled rectifier technology or a 12-pulse uncontrolled rectifier technology. The three-phase uncontrolled rectifier unit 21 also includes a capacitor for smoothing DC voltage fluctuations. The connection method of the uncontrolled diode and the capacitor includes a three-phase bridge connection.

[0048] The formula for the DC voltage value of the second DC port of the DC / DC converter includes:

[0049]

[0050] Among them, U acN50 is the rated value of the AC port voltage of the DC / AC power frequency inverter 23, that is, the rated voltage of the power frequency load; k dc is the DC voltage utilization rate of the DC / AC power frequency inverter 23, k dc It depends on the pulse width modulation mode of the DC / AC power frequency inverter 23 and is defined as the ratio of the maximum phase voltage effective value that can be generated by the AC port of the DC / AC power frequency inverter 23 to the DC port voltage of the DC / AC power frequency inverter 23. margin is the margin coefficient, which is a constant slightly greater than 1, for example, k margin =1.05.

[0051] The DC / AC power frequency inverter 23 can be a three-phase inverter or a single-phase inverter, and uses a fixed AC port frequency and voltage control, and there are mature control schemes available. The DC / AC power frequency inverter 23 is used to power the secondary loads of the wind turbine, and its power supply objects include but are not limited to the main controller, the converter controller and the unit monitoring system. The DC / AC power frequency inverter 23 is a DC / AC converter that uses voltage amplitude and phase control to achieve inversion from direct current to power frequency alternating current, and is used to provide power frequency alternating current with constant voltage and frequency to the secondary loads of the wind turbine.

[0052] The pitch system DC / AC variable frequency drive 24 receives the pitch control command from the main controller and is used to control the pitch motor of the pitch actuator. When the wind turbine adopts unified pitch, one set of pitch system DC / AC variable frequency drive is used; when the wind turbine adopts independent pitch, the number of sets of pitch system DC / AC variable frequency drive is equal to the number of blades.

[0053] The yaw system DC / AC variable frequency driver 25 receives the yaw control instruction from the main controller and is used to control the yaw motor of the yaw actuator.

[0054] The electrical auxiliary circuit 2 can also be equipped with a centralized energy storage configuration, where a set of energy storage units is connected in parallel to the second DC port of the DC / DC converter 22, and the energy storage unit includes an energy storage battery and an energy storage converter.

[0055] The purpose of configuring energy storage is to provide emergency power supply for wind turbines to ensure the safety of the units and to achieve black start of the units.

[0056] Example 2

[0057] The present invention discloses a control method for a variable speed variable voltage variable frequency wind turbine control device for controlling the control device of embodiment 1, the method steps are as follows: Figure 2 Shown, incl.

[0058] S1, when the soft starter 13 in the electrical main circuit 1 is not started and the AC switch 14 is disconnected, the power required for starting is provided to the wind turbine through the common connection point of the voltage and frequency conversion, and the fluctuation of the DC power is smoothed by the three-phase uncontrolled rectifier unit 21;

[0059] S2, transforming the converted direct current using a DC / DC converter;

[0060] S3, using the DC / AC power frequency inverter 23 to convert the direct current into power frequency alternating current, and transmit it to the power frequency load, where the power frequency load includes but is not limited to the main controller, the converter controller and the unit monitoring system;

[0061] S4, using the yaw system DC / AC variable frequency driver 25 to drive the yaw motor to yaw the wind turbine set to the wind, so that the wind turbine is consistent with the wind direction, thereby improving the power generation efficiency;

[0062] S5, after the wind turbine is yawed to the wind, the DC / AC frequency converter 24 of the pitch system is used to drive the pitch motor of the wind turbine to start the wind turbine mechanically, so that the speed of the wind turbine reaches the lower speed limit of the grid-connected operation and stabilizes at the speed;

[0063] S6, start the soft starter 13, control the stator voltage amplitude of the three-phase squirrel cage induction generator 11 to slowly increase from 0, until the amplitude and phase of the voltage at the two AC ports of the soft starter 13 are the same, then close the AC switch 14, and turn off the soft starter 13, so that the wind turbine set switches to the generator active power closed-loop control, and the generated electric energy is output from the transformer and frequency conversion common connection point after voltage conversion through the unit box transformer 15.

[0064] When a wind turbine is needed to generate electricity, it is necessary to first apply a starting power supply to the wind turbine to start the rotation of the wind turbine. Therefore, it is necessary to pass the voltage and frequency conversion common connection point from the outside to the inside of the wind turbine.

[0065] After closing the AC switch 14 and turning off the soft starter 13, the pitch system switches from the mechanical starting control mode to the generator active power closed-loop control, wherein the generator active power reference value in the unit maximum power tracking mode is the unit rated power, and the generator active power reference value in the unit active scheduling mode is the active power command received by the unit.

[0066] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A control device for a variable speed, variable voltage and variable frequency wind turbine generator set, used in a centralized variable frequency wind farm, characterized in that: The control device comprises an electrical main circuit and an electrical auxiliary circuit; The electrical main circuit includes a soft starter and a transformer substation. The electrical main circuit is connected to the wind turbine to generate electricity. The soft starter limits the starting current generated by the rotation of the wind turbine when the wind turbine is started, reducing the impact of the starting current on the power grid. The high-voltage side AC port of the transformer substation is directly connected or connected to the common connection point of the voltage and frequency conversion through the power collection network, converts the voltage of the current generated by the wind turbine, and inputs the current into the power grid or other systems. The electrical auxiliary circuit includes a three-phase uncontrolled rectifier unit, a DC / DC converter and a DC / AC industrial frequency inverter. The first DC port of the DC / DC converter and the DC port of the three-phase uncontrolled rectifier unit are connected to a common DC bus, the second DC port of the DC / DC converter is connected to the DC port of the DC / AC industrial frequency inverter, the DC / AC industrial frequency inverter is connected to the industrial frequency load, the AC port of the three-phase uncontrolled rectifier unit is connected to the low-voltage side of the unit box transformer of the electrical main circuit, so that the electrical main circuit and the electrical auxiliary circuit are connected, the three-phase uncontrolled rectifier unit converts the AC power input from the unit box transformer into DC power, the DC / DC converter transforms the converted DC power and inputs the DC power into the DC / AC industrial frequency inverter, and the DC / AC industrial frequency inverter inverts the DC power into industrial frequency AC power.

2. The control device for a variable speed, variable voltage and variable frequency wind turbine generator set according to claim 1, characterized in that: The electrical main circuit also includes a three-phase squirrel cage induction generator, a three-phase capacitor bank and an AC switch, wherein the three-phase capacitor bank is connected in parallel with the stator winding of the three-phase squirrel cage induction generator, the soft starter is connected in parallel with the AC switch to form two AC ports, the first AC port of the soft starter and the AC switch is connected in series with the stator winding of the three-phase squirrel cage induction generator, and the second AC port of the soft starter and the AC switch is connected in series with the low-voltage side AC port of the unit box transformer.

3. The control device for a variable speed, variable voltage and variable frequency wind turbine generator set according to claim 1, characterized in that: The soft starter is composed of three groups of anti-parallel thyristors and their control system. When the wind turbine is started, the soft starter starts and controls the stator voltage amplitude of the three-phase squirrel cage induction generator to slowly increase from 0 until the amplitude and phase of the voltage at the two AC ports of the soft starter are the same, and the soft starter is turned off.

4. The control device for a variable speed, variable voltage and variable frequency wind turbine generator set according to claim 1, characterized in that: The DC / AC industrial frequency inverter converts direct current into industrial frequency alternating current to supply power to industrial frequency loads, which include the main controller, converter controller and unit monitoring system of the wind turbine set.

5. The control device for a variable speed, variable voltage and variable frequency wind turbine generator set according to claim 1, characterized in that: The electrical auxiliary circuit also includes a DC / AC variable frequency drive for a pitch system and a DC / AC variable frequency drive for a yaw system, wherein the DC port of the DC / AC variable frequency drive for the pitch system and the DC port of the DC / AC variable frequency drive for the yaw system are connected to a common DC bus with the first DC port of the DC / DC converter and the DC port of the three-phase uncontrolled rectifier unit, so as to invert the DC power output by the three-phase uncontrolled rectifier unit into AC power.

6. The control device for a variable speed, variable voltage and variable frequency wind turbine generator set according to claim 5, characterized in that: The pitch system DC / AC variable frequency drive is used to control the pitch motor of the pitch actuator, and the pitch motor drives the wind turbine to perform pitch operation. When the wind turbine adopts unified pitch change, a set of pitch system DC / AC variable frequency drive is used. When the wind turbines adopt independent pitch change, the number of sets of pitch system DC / AC variable frequency drive is equal to the number of blades.

7. The control device for a variable speed, variable voltage and variable frequency wind turbine generator set according to claim 5, characterized in that: The yaw system DC / AC variable frequency driver is used to control the yaw motor of the yaw actuator to perform yaw to wind.

8. The control device for a variable speed, variable voltage and variable frequency wind turbine generator set according to claim 1, characterized in that: The three-phase uncontrolled rectifier unit includes an uncontrolled diode and a capacitor, and the connection method of the uncontrolled diode and the capacitor includes a three-phase bridge connection.

9. The control device for a variable speed, variable voltage and variable frequency wind turbine generator set according to claim 1, characterized in that: The formula for the DC voltage value of the second DC port of the DC / DC converter includes: Among them, U acN50 is the rated value of the AC port voltage of the DC / AC power frequency inverter, k dc is the DC voltage utilization rate of the DC / AC power frequency inverter, k margin is the margin factor.

10. A control method for a variable speed, variable voltage and variable frequency wind turbine control device using the control device according to any one of claims 1 to 9, characterized in that the method comprises: When the soft starter is not started and the AC switch is disconnected in the main electrical circuit, the power required for starting is provided to the wind turbine through the common connection point of the voltage and frequency conversion, and the fluctuation of the DC power is smoothed by the three-phase uncontrolled rectifier unit; The converted DC power is transformed by using a DC / DC converter; Use a DC / AC power frequency inverter to convert the transformed DC power into power frequency AC power, and transmit the power frequency AC power to power frequency loads; Use direct current to start the DC / AC variable frequency drive of the yaw system to drive the yaw motor to yaw the wind turbine to the wind; After the wind turbine has completed the yaw alignment, the DC / AC variable frequency drive of the variable pitch system is started by direct current to drive the variable pitch motor of the wind turbine to start the wind turbine mechanically, so that the wind turbine speed reaches the lower speed limit of grid-connected operation and stabilizes at this speed; Start the soft starter and control the stator voltage amplitude of the three-phase squirrel cage induction generator to slowly increase from 0 until the amplitude and phase of the voltage at the two AC ports of the soft starter are the same. At this time, close the AC switch and turn off the soft starter, stop supplying power to the common connection point of the transformer and frequency converter, and switch the wind turbine to the closed-loop control of the generator active power. The generated electric energy is converted by the voltage of the unit box transformer and output from the common connection point of the transformer and frequency converter.

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