Variable pitch control system and control method for wind turbine generator

Abstract

The invention relates to the technical field of wind power equipment, in particular to a wind turbine generator variable pitch control system and method.The wind turbine generator variable pitch control system comprises a half-control rectification loop, a driver direct-current bus, an inversion alternating-current loop and a super-capacitor module, and the half-control rectification loop is connected with a three-phase alternating-current power grid; the driver direct-current bus is connected with the half-control rectification loop, the inversion alternating-current loop is connected with the driver direct-current bus, and the inversion alternating-current loop controls the pitch angle of the paddle through the motor; the super capacitor module is connected with the half-control rectification loop and the positive electrode end of the driver direct-current bus. The super capacitor module is connected with the driver direct-current bus in parallel through a circuit with a relay. According to the variable-pitch control system, loop switching of connection of the super-capacitor module is carried out through on-off of the relay, the function of a traditional independent charger is replaced through loop switching of the super-capacitor module, a brake resistor and a bleeder circuit are not needed, and therefore the cost, the fault rate and the design and installation difficulty of the variable-pitch control system are reduced, and the size of the system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power equipment, and in particular to a wind turbine pitch control system and a control method. Background Art

[0002] The variable pitch control system is an important component of a wind turbine generator set. It is responsible for adjusting the pitch angle of the wind turbine blades to capture maximum wind energy at low wind speeds, and adjusting the blade pitch angle to keep the wind turbine load stable at high wind speeds.

[0003] Existing variable pitch control systems mainly use independent charger solutions, such as Figure 1 As shown. The three-phase AC power supply of the grid power supply L1, L2, and L3 is connected to the AC / DC charger, and the DC output of the charger charges the supercapacitor module. Since the supercapacitor module is directly connected to the driver DC bus UC, the two maintain the same potential. The DC bus voltage is inverted into the AC circuit U, V, and W through the three-phase inverter circuit composed of VT1~VT6 to drive the variable pitch motor to rotate, thereby controlling the blade pitch angle. If the variable pitch motor is in the power generation state, the generated electricity can be directly absorbed by the supercapacitor module to ensure that the DC bus UC will not be over-voltage.

[0004] The variable pitch control system with independent charger has some disadvantages, mainly because the AC / DC charger is expensive, which increases the cost of the variable pitch system; the AC / DC charger is large in size, and it is a power component, so it generates a lot of heat, which increases the difficulty of the variable pitch control cabinet design. In addition, the AC / DC charger contains a large number of power electronic devices, which has a certain failure rate, which increases the failure rate of the variable pitch control system. Summary of the invention

[0005] The present invention provides a wind turbine pitch control system and control method, which are used to solve the defects of high cost and high failure rate of existing pitch control systems, thereby reducing the cost, failure rate and design and installation difficulty of the pitch control system and reducing the volume of the pitch control system.

[0006] The present invention provides a wind turbine variable pitch control system, comprising a semi-controlled rectifier circuit, a driver DC bus, an inverter AC circuit and a supercapacitor module, wherein the input end of the semi-controlled rectifier circuit is connected to a power grid; the driver DC bus is connected to the output end of the semi-controlled rectifier circuit; the input end of the inverter AC circuit is connected to the driver DC bus, and the output end of the inverter AC circuit controls the pitch angle of the blades through an electric motor; the input end of the supercapacitor module is connected to the output end of the semi-controlled rectifier circuit, and the output end of the supercapacitor module is connected to the positive terminal of the driver DC bus, and the supercapacitor module is connected in parallel with the driver DC bus through a circuit with a first relay to form the same potential.

[0007] According to a wind turbine pitch control system provided by the present invention, the wind turbine pitch control system also includes a pre-charging circuit, which is connected to the positive terminal of the driver DC bus and is used to pre-charge the capacitor UC of the driver DC bus.

[0008] According to a wind turbine pitch control system provided by the present invention, a diode D3, a current limiting resistor R1 and a second relay are sequentially arranged on the pre-charging circuit.

[0009] According to a wind turbine pitch control system provided by the present invention, the input end of the supercapacitor module is serially connected with a fuse F1, an insulated gate bipolar transistor VT7 and a diode D1.

[0010] According to a wind turbine pitch control system provided by the present invention, the semi-controlled rectifier circuit is a three-phase rectifier circuit, and each phase of the three-phase rectifier circuit has a thyristor and a diode connected in series; the inverter AC circuit is a three-phase inverter circuit, and each phase of the three-phase inverter circuit has two insulated gate bipolar transistors connected in series.

[0011] The present invention also provides a wind turbine pitch control method, comprising steps S1 to S3.

[0012] S1. Pre-charge the capacitor UC of the driver DC bus through the pre-charging circuit. After the capacitor UC is fully charged, start the half-controlled rectification circuit and disconnect the pre-charging circuit.

[0013] S2, charging the supercapacitor module. After the supercapacitor module is fully charged, the first relay is closed to connect the supercapacitor module and the driver DC bus in parallel to have the same potential.

[0014] S3. Power is supplied to the inverter AC circuit through the half-controlled rectifier circuit and the driver DC bus. The output end of the inverter AC circuit controls the pitch angle of the blades through the motor to achieve variable pitch. When the motor that controls the pitch angle of the blades is in the power generation state, the supercapacitor module is used to absorb the energy generated by the motor. When the driver DC bus voltage exceeds the preset upper limit value, the half-controlled rectifier circuit is closed until the driver DC bus voltage recovers to below the preset upper limit value, and the half-controlled rectifier circuit is reconnected for power supply.

[0015] According to a wind turbine pitch control method provided by the present invention, when the power grid fails, the first relay is disconnected, so that the supercapacitor module serves as a backup power supply to supply power to the driver DC bus until the output end of the inverter AC circuit controls the blades to be aligned in place through the motor; when the power grid is restored, steps S1, S2 and S3 are re-executed, and then the wind turbine pitch control system works normally.

[0016] According to a wind turbine pitch control method provided by the present invention, the wind turbine pitch control system is provided with a first preset upper limit and an over-limit preset time. When the grid voltage exceeds the first preset upper limit and lasts for a period of time within the over-limit preset time, the half-controlled rectifier circuit is closed, and when the grid voltage recovers to below the first preset upper limit, the power supply of the half-controlled rectifier circuit is restored; when the grid voltage exceeds the first preset upper limit and lasts for a period of time exceeding the over-limit preset time, the half-controlled rectifier circuit is closed and a capacitor fault alarm is issued at the same time.

[0017] According to a wind turbine pitch control method provided by the present invention, the wind turbine pitch control system is also provided with a second preset high limit value, and the second preset high limit value is higher than the first preset high limit value. When the grid voltage exceeds the second preset high limit value, the half-controlled rectifier circuit is closed and a grid overvoltage fault alarm is performed at the same time.

[0018] According to a wind turbine pitch control method provided by the present invention, in step S2, during the process of charging the supercapacitor module to full, the total charge is obtained by integrating the charging current and time, and the capacitance of the supercapacitor module is calculated based on the ratio of the total charge and the supercapacitor module voltage to determine the health status of the supercapacitor module.

[0019] The wind turbine variable pitch control system and control method provided by the present invention start the semi-controlled rectifier circuit to charge the supercapacitor module. After the supercapacitor module is fully charged, the first relay is closed so that the supercapacitor module and the driver DC bus are connected in parallel to the same potential. The inverter AC circuit is powered by the semi-controlled rectifier circuit and the driver DC bus. The output end of the inverter AC circuit controls the pitch angle of the blade through the motor to achieve variable pitch. When the motor that controls the pitch angle of the blade is in the power generation state, the supercapacitor module is used to absorb the energy emitted by the motor; when the driver DC bus voltage exceeds the preset upper limit value, the semi-controlled rectifier circuit is closed until the driver DC bus voltage recovers to below the preset upper limit value, and the semi-controlled rectifier circuit is reconnected for power supply. The present invention switches the circuit connected to the supercapacitor module by turning on and off the first relay. By switching the circuit of the supercapacitor module, the function of the traditional independent charger is replaced, and the braking resistor and the discharge circuit are not required, thereby reducing the cost, failure rate and design and installation difficulty of the variable pitch control system and reducing the volume of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a schematic diagram of a traditional pitch control system.

[0022] Figure 2 This is one of the schematic diagrams of the wind turbine pitch control system provided by the present invention.

[0023] Figure 3 This is the second schematic diagram of the wind turbine pitch control system provided by the present invention.

[0024] Figure 4 It is a flow chart of the variable pitch control method of a wind turbine set provided by the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present invention.

[0027] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0028] In the embodiments of the present invention, unless otherwise clearly specified and limited, the first feature being "above" or "below" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "above" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0029] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0030] Combine the following Figure 2~Figure 4 The invention describes a wind turbine pitch control system and a control method.

[0031] An embodiment of the present invention provides a wind turbine pitch control system, see Figure 2 As shown, it includes a half-controlled rectifier circuit, a driver DC bus, an inverter AC circuit and a supercapacitor module, the input end of the half-controlled rectifier circuit is connected to the three-phase AC power grid; the driver DC bus is connected to the output end of the half-controlled rectifier circuit; the input end of the inverter AC circuit is connected to the driver DC bus, and the output end of the inverter AC circuit controls the pitch angle of the blade through an electric motor; the input end of the supercapacitor module is connected to the output end of the half-controlled rectifier circuit, the output end of the supercapacitor module is connected to the positive end of the driver DC bus through a circuit with a diode D2, and the supercapacitor module is connected in parallel with the driver DC bus through a circuit with a first relay to form the same potential.

[0032] It can be understood that the wind turbine pitch control system of this embodiment does not include an independent charger, and the circuit connection of the supercapacitor module is switched by turning on and off the first relay. The circuit switching of the supercapacitor module replaces the function of the traditional independent charger, and does not require a brake resistor and a discharge circuit, thereby reducing the cost, failure rate and design and installation difficulty of the pitch control system, and reducing the volume of the system. Specifically, the semi-controlled rectifier circuit is started to charge the supercapacitor module. After the supercapacitor module is fully charged, the first relay is closed so that the supercapacitor module and the driver DC bus are connected in parallel to the same potential. The inverter AC circuit is powered by the semi-controlled rectifier circuit and the driver DC bus. The output end of the inverter AC circuit controls the pitch angle of the blade through the motor to achieve pitch change. When the motor that controls the pitch angle of the blade is in the power generation state, the supercapacitor module is used to absorb the energy emitted by the motor; when the driver DC bus voltage exceeds the preset upper limit value, the semi-controlled rectifier circuit is closed until the driver DC bus voltage recovers to below the preset upper limit value, and the semi-controlled rectifier circuit is reconnected for power supply.

[0033] In some embodiments of the wind turbine pitch control system of the present invention, the wind turbine pitch control system also includes a pre-charging circuit, which is connected to the positive end of the driver DC bus and is used to pre-charge the capacitor UC of the driver DC bus.

[0034] It is understandable that if the three-phase AC grid is used for power supply directly, the three-phase AC grid may generate a short-term large current impact on the power switch devices, DC bus capacitors, super capacitor modules and other devices in the wind turbine pitch control system, which may cause damage to the related devices. In this embodiment, before the three-phase AC grid is used for power supply, the capacitor UC of the driver DC bus is pre-charged by the pre-charging circuit. After the capacitor UC of the driver DC bus is charged, it is connected to the three-phase AC grid for power supply. At this time, the voltage difference is very small, and the related devices will not be impacted by instantaneous current, thereby protecting the normal operation of the wind turbine pitch control system.

[0035] Specifically, in some examples, a diode D3, a current limiting resistor R1 and a second relay are sequentially arranged on the pre-charging circuit. Figure 2 As shown, the output current of the live wire end of the three-phase AC power grid is rectified by the diode D3 and output to the driver DC bus for charging, wherein the current limiting resistor R1 can effectively share the voltage to prevent damage to the capacitor UC of the driver DC bus caused by overvoltage and overcurrent, thereby achieving a safe charging process; the second relay is used to control the charging process of the pre-charging circuit. After the second relay is closed, the pre-charging circuit can charge the capacitor UC of the driver DC bus. After charging is completed, the second relay is disconnected.

[0036] In some embodiments of the wind turbine pitch control system of the present invention, the input end of the supercapacitor module is connected in series with a fuse F1, an insulated gate bipolar transistor VT7 and a diode D1 in sequence, wherein the fuse F1 plays a charging protection role to prevent overcurrent from causing damage to the power devices in the charging circuit, and the insulated gate bipolar transistor VT7 can be used as a power switching device, and PWM control of the current is performed through the power switching device VT7 to charge the supercapacitor module.

[0037] In some other embodiments of the wind turbine pitch control system of the present invention, the half-controlled rectifier circuit is a three-phase rectifier circuit, and each phase of the three-phase rectifier circuit has a thyristor and a diode connected in series to form a three-phase half-controlled rectifier, see Figure 2 As shown, L1, L2 and L3 of the three-phase AC power grid form three phases, the first bridge arm is connected in series with thyristor V1 and diode D4, the second bridge arm is connected in series with thyristor V2 and diode D5, and the third bridge arm is connected in series with thyristor V3 and diode D6. The half-controlled rectifier circuit is used to convert the AC signal of the three-phase AC power grid into a DC signal to charge the ultra-super capacitor module and power the driver DC bus. The inverter AC circuit is a three-phase inverter circuit. Each phase of the three-phase inverter circuit has two insulated gate bipolar transistors connected in series. See again Figure 2 As shown, U, V, and W represent the three-phase power output by the driver to the variable pitch motor. The first bridge arm is connected in series with insulated gate bipolar transistors VT1 and VT4, the second bridge arm is connected in series with insulated gate bipolar transistors VT2 and VT5, and the third bridge arm is connected in series with insulated gate bipolar transistors VT3 and VT6. The insulated gate bipolar transistors include thyristors and diodes of reverse parallel thyristors, which are used to invert control current to control the three-phase motor.

[0038] In other embodiments of the wind turbine pitch control system of the present invention, see Figure 3 As shown, a braking resistor R2 can also be connected in parallel to the drive DC bus, and the supercapacitor module is no longer used to absorb the power generated by the pitch motor. For details, see Figure 3 As shown, when the system is powered on, the L1 pre-charging circuit (composed of a diode D3, a current-limiting resistor R1, and a second relay) is used to charge the DC bus UC. After it is fully charged, the pre-charging circuit is disconnected by the second relay. After that, the grid power supplies L1, L2, and L3 are rectified into DC by a semi-controlled rectifier circuit composed of thyristors V1~V3 and diodes D4~D6 to maintain the DC bus UC voltage. This embodiment eliminates the need for a traditional independent AC / DC charger, directly draws power from the DC bus UC of the variable pitch drive, and uses the power switch device VT7 to perform PWM control of the current to charge the supercapacitor module. When the variable pitch motor is in the power generation state and the DC bus UC voltage rises to the limit value, the power switch device VT8 is turned on, and the energy of the DC bus UC is discharged to the braking resistor R2 to ensure that the DC bus UC will not be over-voltage.

[0039] The wind turbine pitch control method provided by the present invention is described below. The wind turbine pitch control method described below and the wind turbine pitch control system described above can be referenced to each other.

[0040] A specific embodiment of the present invention provides a wind turbine pitch control method, see Figure 4 As shown, it includes steps S1 to S3.

[0041] S1, the wind turbine pitch control system is powered on, and the capacitor UC of the driver DC bus is pre-charged through the pre-charging circuit. After the capacitor UC is fully charged, the thyristors V1~V3 and diodes D4~D6 of the half-controlled rectification circuit are started to rectify and output the three-phase AC power grid, and the pre-charging circuit is disconnected through the second relay.

[0042] S2, after starting the half-controlled rectifier circuit, PWM control current is performed through the power switch device VT7 to charge the supercapacitor module. After the supercapacitor module is fully charged, the power switch device VT7 is stopped and the first relay is closed to connect the supercapacitor module and the driver DC bus in parallel to the same potential.

[0043] S3. Power is supplied to the inverter AC circuit through the half-controlled rectifier circuit and the driver DC bus. The inverter AC circuit VT1~VT6 inverts the AC circuits U, V, and W. The variable pitch motor is driven from the output end to control the pitch angle of the blades to achieve variable pitch. When the variable pitch motor that controls the pitch angle of the blades is in the power generation state, the supercapacitor module is used to absorb the energy emitted. The energy emitted by the variable pitch motor will be absorbed by the supercapacitor module. When the driver DC bus voltage exceeds the preset upper limit value (generally set to be slightly lower than the voltage value that damages the driver DC bus capacitor), the half-controlled rectifier circuit is temporarily closed until the driver DC bus voltage recovers to below the preset upper limit value, and then the half-controlled rectifier circuit is reconnected for power supply.

[0044] In some embodiments of the wind turbine pitch control method of the present invention, when the three-phase AC power grid loses power, the semi-controlled rectifier circuit stops working. At this time, the second relay is closed and the first relay is disconnected, so that the supercapacitor module serves as a backup power supply to supply power to the driver DC bus through the diode D2, so that the driver DC bus is always kept within the operating voltage range until the output end of the inverter AC circuit controls the blades to be aligned in place through the motor; when the three-phase AC power grid is restored to power, steps S1, S2 and S3 need to be re-executed in sequence, and then the wind turbine pitch control system works normally. Re-executing steps S1, S2 and S3 can avoid short-term large current shocks caused by the power grid to the power switching devices, DC bus UC and supercapacitor modules.

[0045] In some other embodiments of the wind turbine pitch control method of the present invention, the wind turbine pitch control system is provided with a first preset high limit and an over-limit preset time. When the three-phase AC power grid voltage exceeds the first preset high limit and the duration is within the over-limit preset time, the half-controlled rectifier circuit is closed. When the three-phase AC power grid voltage recovers to below the first preset high limit, the half-controlled rectifier circuit is restored to power supply again. When the three-phase AC power grid voltage exceeds the first preset high limit and the duration exceeds the over-limit preset time, the half-controlled rectifier circuit is closed and a capacitor fault alarm is issued at the same time. The wind turbine pitch control system is also provided with a second preset high limit, which is higher than the first preset high limit. When the three-phase AC power grid voltage exceeds the second preset high limit, the half-controlled rectifier circuit is closed and a power grid overvoltage fault alarm is issued at the same time.

[0046] It can be understood that the first preset high limit, the second preset high limit and the over-limit preset time in this embodiment are all for protecting the components of the wind turbine pitch control system, wherein the first preset high limit is a voltage value that may cause damage to the components, and the second preset high limit is a voltage value that will inevitably cause damage to the components. If the voltage of the three-phase AC power grid rises temporarily and exceeds the first preset high limit, the thyristors V1~V3 of the half-controlled rectifier circuit are turned off, and V1~V3 are restored to conduction when the voltage of the three-phase AC power grid is restored to complete the self-consumption of feedback energy. If the voltage of the three-phase AC power grid rises and exceeds the first preset high limit and the duration also exceeds the over-limit preset time, or the voltage of the three-phase AC power grid exceeds the second preset high limit, it is necessary to turn off the thyristors V1~V3 of the half-controlled rectifier circuit to protect the internal components of the pitch control system from the influence of high voltage, and at the same time, a fault alarm is issued.

[0047] Based on the above-mentioned several embodiments of the wind turbine pitch control method provided by the present invention, in step S2, in the process of charging the supercapacitor module to full, the total charge is obtained by integrating the charging current and time, and the capacitance of the supercapacitor module is calculated based on the ratio of the total charge and the voltage of the supercapacitor module to determine the health status of the supercapacitor module. It can be understood that the supercapacitor module needs to be charged during each use of the pitch control system. This embodiment can detect the health status of the supercapacitor module during each charging process of the supercapacitor module to ensure that the supercapacitor module is in good working condition and to ensure the normal operation of the pitch control system.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wind turbine pitch control system, characterized in that: include: A half-controlled rectifier circuit, wherein an input end of the half-controlled rectifier circuit is connected to a power grid; A driver DC bus, wherein the driver DC bus is connected to an output end of the half-controlled rectifier circuit; An inverter AC circuit, wherein the input end of the inverter AC circuit is connected to the driver DC bus, and the output end of the inverter AC circuit controls the pitch angle of the blades through the motor; A supercapacitor module, wherein the input end of the supercapacitor module is connected to the output end of the half-controlled rectifier circuit, the output end of the supercapacitor module is connected to the positive terminal of the driver DC bus, and the supercapacitor module is connected in parallel with the driver DC bus through a circuit with a first relay to form the same potential.

2. The wind turbine pitch control system according to claim 1, characterized in that: It also includes a pre-charging circuit, which is connected to the positive terminal of the driver DC bus and is used to pre-charge the capacitor UC of the driver DC bus.

3. The wind turbine pitch control system according to claim 2, characterized in that: The pre-charging circuit is provided with a diode D3, a current limiting resistor R1 and a second relay in sequence.

4. The wind turbine pitch control system according to claim 1, characterized in that: The input end of the super capacitor module is connected in series with a fuse F1, an insulated gate bipolar transistor VT7 and a diode D1.

5. The wind turbine pitch control system according to any one of claims 1 to 4, characterized in that: The half-controlled rectifier circuit is a three-phase rectifier circuit, each phase of which has a thyristor and a diode connected in series; the inverter AC circuit is a three-phase inverter circuit, each phase of which has two insulated gate bipolar transistors connected in series.

6. A wind turbine pitch control method, characterized in that: include: S1, pre-charge the capacitor UC of the driver DC bus through the pre-charging circuit, start the half-controlled rectification circuit after the capacitor UC is fully charged, and disconnect the pre-charging circuit; S2, charging the supercapacitor module. After the supercapacitor module is fully charged, the first relay is closed to connect the supercapacitor module and the driver DC bus in parallel to the same potential. S3. Power is supplied to the inverter AC circuit through the half-controlled rectifier circuit and the driver DC bus. The output end of the inverter AC circuit controls the pitch angle of the blades through the motor to achieve variable pitch. When the motor that controls the pitch angle of the blades is in the power generation state, the supercapacitor module is used to absorb the energy generated by the motor. When the driver DC bus voltage exceeds the preset upper limit value, the half-controlled rectifier circuit is closed until the driver DC bus voltage recovers to below the preset upper limit value, and the half-controlled rectifier circuit is reconnected for power supply.

7. The wind turbine pitch control method according to claim 6, characterized in that: When the grid loses power, the first relay is disconnected, allowing the supercapacitor module to serve as a backup power source to supply power to the driver DC bus until the output end of the inverter AC circuit controls the blades to be aligned through the motor; when the grid is restored, steps S1, S2 and S3 are re-executed, and then the wind turbine variable pitch control system works normally.

8. The wind turbine pitch control method according to claim 6, characterized in that: The wind turbine pitch control system is provided with a first preset high limit and an over-limit preset time. When the grid voltage exceeds the first preset high limit and lasts for a period of time within the over-limit preset time, the half-controlled rectifier circuit is closed. When the grid voltage recovers to below the first preset high limit, the power supply of the half-controlled rectifier circuit is restored. When the grid voltage exceeds the first preset high limit and lasts for a period of time exceeding the over-limit preset time, the half-controlled rectifier circuit is closed and a capacitor fault alarm is issued at the same time.

9. The wind turbine pitch control method according to claim 8, characterized in that: The wind turbine pitch control system is also provided with a second preset high limit value, which is higher than the first preset high limit value. When the grid voltage exceeds the second preset high limit value, the half-controlled rectifier circuit is closed and a grid overvoltage fault alarm is issued at the same time.

10. The wind turbine pitch control method according to any one of claims 6 to 9, characterized in that: In step S2, when the supercapacitor module is charged to full, the total charge is obtained by integrating the charging current and time, and the capacitance of the supercapacitor module is calculated based on the ratio of the total charge and the supercapacitor module voltage to determine the health status of the supercapacitor module.

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