A wind turbine pitch control system and control method

Abstract

The present invention relates to the technical field of wind power equipment, and in particular to a wind turbine pitch control system and control method. The wind turbine pitch control system includes a semi-controlled rectifier circuit, a driver DC bus, an inverter AC circuit, and a supercapacitor module. The semi-controlled rectifier circuit is connected to a three-phase AC power grid, the driver DC bus is connected to the semi-controlled rectifier circuit, the inverter AC circuit is connected to the driver DC bus, and the inverter AC circuit controls the pitch angle of the blades through an electric motor. The supercapacitor module is connected to the positive terminal of the semi-controlled rectifier circuit and the driver DC bus, and the supercapacitor module is connected in parallel with the driver DC bus through a circuit with a relay. The present invention switches the circuit connected to the supercapacitor module by switching the relay on and off. By switching the supercapacitor module circuit, the function of a traditional independent charger is replaced, and no braking resistor and discharge circuit are required, thereby reducing the cost, failure rate, and design and installation difficulty of the pitch control system and reducing the volume of the system.

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 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 pitch control systems mainly use independent charger solutions, such as Figure 1 As shown in the figure, the three-phase AC power grid L1, L2, and L3 is connected to an AC / DC charger. The charger's DC output charges the supercapacitor module. Because the supercapacitor module is directly connected to the driver's DC bus UC, both maintain the same potential. The DC bus voltage is inverted into AC circuits U, V, and W through the three-phase inverter circuit composed of VT1 to VT6, driving the pitch motor to rotate and control the blade pitch angle. When the pitch motor is generating electricity, the generated electricity is directly absorbed by the supercapacitor module, ensuring that the DC bus UC does not overvoltage.

[0004] The pitch control system with a separate charger has several drawbacks. These include the high cost of the AC / DC charger, which increases the cost of the pitch control system. The AC / DC charger is bulky and, as a power component, generates significant heat, complicating the design of the pitch control cabinet. Furthermore, the AC / DC charger contains numerous power electronic components, which can lead to a certain degree of failure, increasing the failure rate of the 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 size of the pitch control system.

[0006] The present invention provides a wind turbine 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. 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 end 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, the pre-charging circuit is provided with a diode D3, a current-limiting resistor R1 and a second relay in sequence.

[0009] According to a wind turbine pitch control system provided by the present invention, the input end of the supercapacitor module is sequentially connected in series 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. Precharge the capacitor UC of the driver's DC bus through the pre-charging circuit. After the capacitor UC is fully charged, start the half-controlled rectifier circuit and disconnect the pre-charging circuit.

[0013] S2. Charge the supercapacitor module. After the supercapacitor module is fully charged, close the first relay so that the supercapacitor module and the driver DC bus are connected 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 blade through the motor to achieve pitch control. 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 generated by the motor. When the driver DC bus voltage exceeds the preset upper limit, the half-controlled rectifier circuit is turned off until the driver DC bus voltage returns to below the preset upper limit, 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 source to supply power to the driver DC bus until the output end of the inverter AC circuit controls the blades to be 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 operates 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 high limit and an over-limit preset time. When the 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 grid voltage recovers to below the first preset high limit, the power supply of the half-controlled rectifier circuit is restored again; when the 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.

[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, 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.

[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 charge, 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 pitch control system and control method provided by the present invention starts a half-controlled rectifier circuit to charge a 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 half-controlled rectifier circuit and the driver DC bus are used to power the inverter AC circuit. The output end of the inverter AC circuit controls the pitch angle of the blades through the motor to achieve pitch control. When the motor that controls the blade pitch angle is in a generating state, the supercapacitor module is used to absorb the energy generated by the motor. When the driver DC bus voltage exceeds a preset upper limit, the half-controlled rectifier circuit is closed until the driver DC bus voltage returns to below the preset upper limit, at which point the half-controlled rectifier circuit is reconnected to supply power. The present invention switches the circuit connected to the supercapacitor module by turning the first relay on and off. The circuit switching of the supercapacitor module replaces the function of a traditional independent charger and eliminates the need for 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 size 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, a brief introduction is given below to 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 any 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 wind turbine pitch control method provided by the present invention. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall 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" indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They 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 device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limiting the embodiments of the present invention.

[0027] In describing the embodiments of the present invention, it should be noted that, unless otherwise specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of the present invention based on the specific circumstances.

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

[0029] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean 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 can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0030] The following combination Figures 2 to 4 The wind turbine pitch control system and control method of the present invention are described.

[0031] One 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 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, and 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. 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 is understandable that the wind turbine pitch control system of this embodiment does not include an independent charger. 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 braking resistor and a discharge circuit, thereby reducing the cost, failure rate and design and installation difficulty of the pitch control system and reducing the size 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 blades through the motor to achieve pitch control. 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, the semi-controlled rectifier circuit is turned off until the driver DC bus voltage recovers below the preset upper limit, 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 directly using a three-phase AC grid for power supply may cause a short-term high-current shock to components such as power switching devices, DC bus capacitors, and supercapacitor modules in the wind turbine pitch control system, potentially causing damage to related components. In this embodiment, before the three-phase AC grid is used for power supply, the capacitor UC of the driver's DC bus is pre-charged through a pre-charging circuit. After the capacitor UC of the driver's DC bus is fully charged, it is then connected to the three-phase AC grid for power supply. At this time, the voltage difference is very small, and the related components will not be shocked 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 provided 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. Among them, the current limiting resistor R1 can effectively share the voltage, prevent the capacitor UC of the driver DC bus from being damaged by overvoltage and overcurrent, and realize 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, 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 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. Figure 2 As shown, L1, L2, and L3 of the three-phase AC grid form three phases. The first bridge arm is connected in series with a thyristor V1 and a diode D4, the second bridge arm is connected in series with a thyristor V2 and a diode D5, and the third bridge arm is connected in series with a thyristor V3 and a diode D6. The half-controlled rectifier circuit is used to convert the AC power signal of the three-phase AC grid into a DC power signal to charge the ultra-supercapacitor 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 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 anti-parallel thyristors, which are used to invert the 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 driver DC bus, eliminating the need for a supercapacitor module 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 L1, L2, and L3 are rectified into DC through a half-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, draws power directly from the DC bus UC of the pitch drive, and uses the power switch device VT7 to perform PWM control of the current to charge the supercapacitor module. When the 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 rectifier circuit are started to start rectifying the three-phase AC grid and output the power. At the same time, the pre-charging circuit is disconnected through the second relay.

[0042] S2. After starting the half-controlled rectifier circuit, the power switch device VT7 is used to control the current through PWM 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 circuits VT1~VT6 invert the AC circuits U, V, and W, and drive the variable pitch motor 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, and 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 returns 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 half-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 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 the grid power supply from generating short-term large current shocks to the power switching devices, DC bus UC and supercapacitor modules.

[0045] In 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 a preset over-limit time. When the three-phase AC grid voltage exceeds the first preset high limit and the duration is within the preset over-limit time, the half-controlled rectifier circuit is shut down. When the three-phase AC grid voltage recovers to below the first preset high limit, the half-controlled rectifier circuit is restored to power supply. When the three-phase AC grid voltage exceeds the first preset high limit and the duration exceeds the preset over-limit time, the half-controlled rectifier circuit is shut down and a capacitor fault alarm is issued. 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 grid voltage exceeds the second preset high limit, the half-controlled rectifier circuit is shut down and a grid overvoltage fault alarm is issued.

[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 intended to protect 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 three-phase AC grid voltage temporarily rises and exceeds the first preset high limit, the thyristors V1~V3 of the half-controlled rectifier circuit are turned off, and when the three-phase AC grid voltage recovers, V1~V3 are restored to conduction to complete the self-consumption of feedback energy. If the three-phase AC grid voltage rises and exceeds the first preset high limit and the duration also exceeds the over-limit preset time, or the three-phase AC grid voltage 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, issue a fault alarm.

[0047] Based on the above-mentioned several embodiments of the 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. It is understandable that the supercapacitor module needs to be charged each time the pitch control system is used. This embodiment can detect the health status of the supercapacitor module during each supercapacitor module charging process 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 various 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 an input end of the inverter AC circuit is connected to the driver DC bus, and an output end of the inverter AC circuit controls the pitch angle of the blades through the motor; A supercapacitor module, wherein the positive electrode of the output end of the half-controlled rectifier circuit is connected to the positive electrode of the supercapacitor module through a circuit having a fuse F1, an insulated gate bipolar transistor VT7, and a diode D1, so as to charge the supercapacitor module through the half-controlled rectifier circuit; the positive electrode of the supercapacitor module is connected to the positive electrode of the driver DC bus through a circuit having a diode D2, so that the supercapacitor module serves as a backup power supply to supply power to the driver DC bus; the positive electrode of the supercapacitor module is also connected to the positive electrode of the driver DC bus through a circuit having a first relay, so that when the first relay is closed, the supercapacitor module is connected in parallel with the driver DC bus to form the same potential; A pre-charging circuit, wherein a diode D3, a current-limiting resistor R1, and a second relay are sequentially provided on the pre-charging circuit, and the pre-charging circuit 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; The supercapacitor module is connected in parallel with the driver DC bus through a circuit with a first relay to form the same potential, and is suitable for switching the circuit connected to the supercapacitor module by turning the first relay on and off. When the power grid is normal, the first relay is closed, and the inverter AC circuit is powered by the half-controlled rectifier circuit and the driver DC bus. When the power grid fails, the first relay is disconnected, allowing the supercapacitor module to serve as a backup power supply to power the driver DC bus.

2. The wind turbine pitch control system according to claim 1, 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.

3. A wind turbine pitch control method, characterized in that: The wind turbine pitch control system according to claim 1 or 2 comprises: S1, pre-charge the capacitor UC of the driver's DC bus through the pre-charging circuit. After the capacitor UC is fully charged, the half-controlled rectifier circuit is started and the pre-charging circuit is disconnected; S2. Charge the supercapacitor module. After the supercapacitor module is fully charged, close the first relay so that the supercapacitor module and the driver DC bus are connected in parallel to have 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 blade through the motor to achieve pitch control. 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 generated by the motor. When the driver DC bus voltage exceeds the preset upper limit, the half-controlled rectifier circuit is turned off until the driver DC bus voltage returns to below the preset upper limit, and the half-controlled rectifier circuit is reconnected for power supply.

4. The wind turbine pitch control method according to claim 3, 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 in place through the motor; when the grid is restored, steps S1, S2 and S3 are re-executed, and then the wind turbine pitch control system operates normally.

5. The wind turbine pitch control method according to claim 3, 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 the duration is 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 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.

6. The wind turbine pitch control method according to claim 5, 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.

7. The wind turbine pitch control method according to any one of claims 3 to 6, characterized in that: In step S2, when the supercapacitor module is fully charged, 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.

Images