Variable-pitch motor electromagnetic brake loop and wind generating set variable-pitch system

Abstract

The utility model relates to a variable-pitch motor electromagnetic brake loop and a wind generating set variable-pitch system. The variable-pitch motor electromagnetic brake loop comprises a first relay, a second relay, a third relay, a variable-pitch motor electromagnetic brake and a first limiting switch, and the variable-pitch motor electromagnetic brake and the first limiting switch are connected to different terminal rows of a variable-pitch frequency converter respectively; the second relay is connected in series with the first limit switch, the third relay is connected in parallel with the second relay, and the second relay and the third relay are configured to be synchronously controlled by the first limit switch; the first relay comprises two sets of auxiliary contacts, and the two sets of auxiliary contacts of the first relay are connected with the variable-pitch motor electromagnetic brake in series and connected with the variable-pitch motor electromagnetic brake in parallel. Therefore, the variable pitch failure rate caused by the first relay can be reduced, meanwhile, a safety loop is added, and the risk that the tooth-shaped belt is snapped is eradicated.

Description

Technical Field

[0001] This disclosure relates to the field of wind power generation technology, and in particular to an electromagnetic braking circuit for a pitch motor and a pitch system for a wind turbine generator set. Background Technology

[0002] In the Goldwind 1.5MW unit, the electromagnetic brake device of the pitch motor plays a crucial role in controlling the blades during pitch control, ensuring they operate in the required position. Damage to the electromagnetic brake device will cause the turbine to report faults such as "large pitch position deviation," "low pitch capacitor voltage," and "high pitch motor temperature." In severe cases, it can lead to the blades failing to retract in time, and even breakage of the pitch belt due to excessive pitch control, resulting in safety accidents. Therefore, the proper functioning of the electromagnetic brake device of the wind turbine pitch motor is of paramount importance to the safe operation of the wind turbine unit.

[0003] Therefore, how to design an electromagnetic braking circuit for a pitch motor that can reduce the frequency of pitch failures and improve braking reliability has become a technical problem that urgently needs to be solved by those skilled in the art. Utility Model Content

[0004] To address the aforementioned technical issues, this disclosure provides an electromagnetic braking circuit for a pitch motor and a pitch system for a wind turbine generator set, which reduces the frequency of pitch failures and improves braking reliability.

[0005] In a first aspect, this disclosure provides an electromagnetic brake circuit for a pitch motor, comprising: a first relay, a second relay, a third relay, an electromagnetic brake for the pitch motor, and a first limit switch, wherein the electromagnetic brake for the pitch motor and the first limit switch are respectively connected to different terminal blocks of the pitch inverter.

[0006] The second relay is connected in series with the first limit switch, and the third relay is connected in parallel with the second relay. The second relay and the third relay are configured to be synchronously controlled by the first limit switch.

[0007] The first relay includes two sets of auxiliary contacts. The two sets of auxiliary contacts of the first relay are connected in series with the electromagnetic brake of the pitch motor, and the two sets of auxiliary contacts are connected in parallel.

[0008] Optionally, the coil of the third relay is connected in parallel with the second relay, and the normally open contact of the third relay is located between the auxiliary contact of the first relay and the electromagnetic brake of the pitch motor.

[0009] Optionally, the circuit further includes a first diode, which is connected in parallel with the coil of the third relay. The negative terminal of the first diode is electrically connected to port A1 of the coil of the third relay, and the positive terminal of the first diode is electrically connected to port A2 of the coil of the third relay.

[0010] Optionally, the first limit switch is a 92° limit switch.

[0011] Optionally, the first limit switch includes a manual forward pitch knob, and the circuit further includes a fourth relay, the A1 port of the coil of the fourth relay being electrically connected to the manual forward pitch knob.

[0012] Optionally, the circuit further includes a second diode, which is connected in parallel with the coil of the fourth relay. The negative terminal of the second diode is connected to port A1 of the coil of the fourth relay, and the positive terminal of the second diode is electrically connected to port A2 of the coil of the fourth relay.

[0013] Optionally, the normally closed contact of the fourth relay is located between the second relay and the negative terminal of the first diode, and one end of the normally open contact of the fourth relay is electrically connected to the A1 port of the coil of the third relay, and the other end is connected to the input terminal of the 24V DC power supply.

[0014] Optionally, the A2 port of the fourth relay coil and the positive terminal of the second diode are connected to the A2 port of the third relay coil.

[0015] Optionally, the pitch motor electromagnetic brake includes an electromagnetic brake and a diode, wherein the electromagnetic brake and the diode are connected in parallel.

[0016] Secondly, based on the same inventive concept, this disclosure provides a wind turbine pitch system, including the pitch motor electromagnetic brake circuit as described in the first aspect.

[0017] Compared with the prior art, the technical solution provided in this disclosure has the following advantages: This disclosure provides a pitch motor electromagnetic brake circuit, including: a pitch inverter, a first relay, a second relay, a third relay, a pitch motor electromagnetic brake, and a first limit switch. The pitch motor electromagnetic brake and the first limit switch are respectively connected to different terminal blocks of the pitch inverter. The second relay is connected in series with the first limit switch, and the third relay is connected in parallel with the second relay. The second and third relays are configured to be synchronously controlled by the first limit switch. The first relay includes two sets of auxiliary contacts, which are connected in series with the pitch motor electromagnetic brake and in parallel. Thus, by connecting the two sets of auxiliary contacts of the first relay in parallel, the operational reliability of the first relay can be improved, and the frequency of pitch failures can be reduced. By connecting the third relay in parallel with the second relay, the reliability of the brake circuit of the pitch system can be greatly improved, and the possibility of the pitch belt being pulled off due to exceeding the limit can be reduced. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0019] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The diagram shown is a schematic diagram of an electromagnetic brake circuit connection for a pitch motor according to an embodiment of this disclosure. Detailed Implementation

[0021] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0022] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0023] Figure 1 The diagram shown is a schematic diagram of an electromagnetic brake circuit connection for a pitch motor according to an embodiment of this disclosure. Please refer to it. Figure 1This disclosure provides a pitch motor electromagnetic brake circuit 100, including: a first relay K2, a second relay K3, a third relay K11, a pitch motor electromagnetic brake C1, and a first limit switch X1. The pitch motor electromagnetic brake C1 and the first limit switch X1 are respectively connected to different terminal blocks of the pitch inverter. The second relay K3 is connected in series with the first limit switch X1, and the third relay K11 is connected in parallel with the second relay K3. The second relay K3 and the third relay K11 are configured to be synchronously controlled by the first limit switch X1. The first relay K2 includes two sets of auxiliary contacts D1. The two sets of auxiliary contacts D1 of the first relay K2 are connected in series with the pitch motor electromagnetic brake C1, and the two sets of auxiliary contacts D1 are connected in parallel.

[0024] Specifically, in one optional embodiment provided in this disclosure, one end of the pitch motor electromagnetic brake C1 is connected to terminal block X2.6 of the pitch inverter, and the other end is grounded; one end of the first limit switch X1 is connected to terminal block X2.7 of the pitch inverter, and the other end is grounded through a grounding terminal. The pitch inverter is the core component of the wind turbine generator's pitch system, mainly composed of a rectifier, inverter, and controller. Its main function is to convert industrial frequency AC power into variable frequency AC power, thereby precisely controlling the motor's speed and direction, and adjusting the blade angle to maximize wind energy conversion efficiency. The terminal block is an important component for the electrical connection between the pitch inverter and external circuits. Through the terminal block, the pitch inverter can reliably connect to the power supply, motor, and other control equipment, ensuring stable power transmission and accurate transmission of control signals.

[0025] It should be noted that the term "connection" mentioned in the embodiments of this disclosure can refer to both direct and indirect connections, and this disclosure does not impose a specific limitation on it. The term "electrical connection" mentioned in the embodiments of this disclosure can refer to both direct electrical connections achieved through wires or communication interfaces, and indirect electrical connections achieved through other intermediate media, and this disclosure does not impose a specific limitation on it.

[0026] The second relay K3 is connected in series with the first limit switch X1, and the third relay K11 is connected in parallel with the second relay K3. The second relay K3 and the third relay K11 are configured to be synchronously controlled by the first limit switch X1. In wind turbine pitch control systems, two levels of limit protection are commonly used: the first level is a proximity switch, and the second level is a limit switch. That is, when the proximity switch fails and the wind turbine cannot brake, the limit switch activates to brake. If the coil of the first relay K2 becomes stuck, both sets of auxiliary contacts D1 must be de-energized, resulting in the pitch motor's electromagnetic brake C1 continuously releasing and failing to brake. If the first limit switch X1 is forcibly crossed, the toothed belt may break, posing a risk of runaway. The second relay K3 is connected in series with the first limit switch X1 to assist the first limit switch X1 in operation. The third relay K11 is connected in parallel with the second relay K3 as a protection relay. After the first limit switch X1 is triggered, the second relay K3 is de-energized, and the third relay K11 connected in parallel with the second relay K3 is de-energized and disconnected, causing the pitch motor electromagnetic brake C1 to be de-energized, thereby braking and stopping the machine.

[0027] Both sets of auxiliary contacts D1 of the first relay K2 are open when the pitch is constant and closed when the pitch is variable. Under normal circumstances, the states of the two sets of auxiliary contacts D1 move together with the coil. Sometimes, when the first relay K2 malfunctions, one set of auxiliary contacts D1 may activate while the other does not. Connecting the two sets of auxiliary contacts D1 in parallel can prevent this from happening. Failure of only one set of auxiliary contacts D1 will not cause turbine failure. The first relay K2 controls the operation of the pitch motor electromagnetic brake C1 system and the operation of the pitch motor fan. Therefore, by connecting the two sets of auxiliary contacts D1 in parallel in the control circuit 100 of the first relay K2 and the pitch motor electromagnetic brake C1, the pitch motor electromagnetic brake C1 can still operate normally even if any one set of auxiliary contacts D1 in the first relay K2 fails. Turbine failure will only occur when both sets of auxiliary contacts D1 fail simultaneously.

[0028] Please continue to refer to this. Figure 1 This disclosure provides an electromagnetic brake circuit 100 for a pitch motor. The coil 10 of the third relay K11 is connected in parallel with the second relay K3. Specifically, the coil 10 of the third relay K11 is connected in parallel with the second relay K3 through the normally closed contact 40 of the fourth relay K12. The normally open contact 20 of the third relay K11 is located between the auxiliary contact D1 of the first relay K2 and the electromagnetic brake C1 of the pitch motor.

[0029] Specifically, since the first limit switch X1 uses a normally closed contact, the second relay K3 is normally energized. When the first limit switch X1 is triggered, the second relay K3 is de-energized. Similarly, when the second relay K3 is de-energized, the third relay K11 is de-energized. The normally open contact 20 of the third relay K11, located between the first relay K2 and the pitch motor electromagnetic brake C1, is de-energized and opens, causing the pitch motor electromagnetic brake C1 to de-energize and thus stop the machine, ensuring the blades stop at a safe position. By connecting the coil 10 of the third relay K11 in parallel with the coil of the second relay K3, and placing the normally open contact 20 of the third relay K11 between the two sets of auxiliary contacts D1 of the first relay K2 and the pitch motor electromagnetic brake C1, the safety protection of the third relay K11 can be triggered in the event of failure of the first relay K2, causing the pitch motor electromagnetic brake C1 to de-energize and stop the machine. Thus, the third relay K11 serves as a safety emergency relay. In the event of the failure of the first relay K2, the third relay K11 is triggered for safety protection, ensuring that the blades stop in a safe position, that the toothed belt is not broken, and that the unit operates safely.

[0030] Please continue to refer to this. Figure 1 This disclosure provides an electromagnetic brake circuit 100 for a pitch motor. The circuit 100 further includes a first diode R1, which is connected in parallel with the coil 10 of a third relay K11. The negative terminal of the first diode R1 is electrically connected to port A1 of the coil 10 of the third relay K11, and the positive terminal of the first diode R1 is electrically connected to port A2 of the coil 10 of the third relay K11.

[0031] Specifically, a relay coil is essentially an inductive element. When the coil is energized, it generates a magnetic field and stores energy; when the coil is de-energized, the magnetic field collapses rapidly, and according to the law of electromagnetic induction, a back electromotive force (EMF) is generated in the coil in the same direction as the original current. The peak voltage of this back EMF can be several times the supply voltage, and its duration varies from a few microseconds to a few milliseconds, depending on the inductance and resistance of the coil. This back EMF can cause serious damage to other components in the circuit, especially threatening the switching devices that drive the relay coil. High-voltage spikes can break down the insulation of these components, leading to circuit failure or component damage. In this embodiment, the first diode R1 provides a freewheeling path. When the coil 10 of the third relay K11 is de-energized, the reverse electromotive force causes the first diode R1 to conduct in the forward direction, providing a low-impedance freewheeling path for the current in the coil 10 of the third relay K11. The current forms a loop through the first diode R1, allowing the energy in the coil 10 of the third relay K11 to be released gradually instead of generating a high-voltage spike. Voltage clamping: the first diode R1 clamps the voltage across the coil 10 of the third relay K11 at its forward conduction voltage drop, preventing high voltage from damaging the driving element. Energy absorption: the first diode R1 absorbs the energy released when the coil 10 of the third relay K11 is de-energized, preventing the energy from being released in the form of sparks or electromagnetic radiation, thereby reducing interference to the circuit. Thus, by connecting the first diode R1 in parallel with the coil 10 of the third relay K11, the protection of the third relay K11 can be achieved simply and effectively without complex circuitry.

[0032] Please continue to refer to this. Figure 1 This disclosure provides an electromagnetic brake circuit 100 for a pitch motor, wherein the first limit switch X1 is a 92° limit switch.

[0033] Specifically, a 92° limit switch is a device triggered at a specific angle for limiting mechanical movement. Through its internal mechanical structure, it switches circuit states when an object reaches a preset angle (e.g., 92 degrees) to achieve equipment protection or motion control. In this embodiment, the triggering conditions for the 92° limit switch include: 1. In automatic control mode, the first-stage 87° proximity switch fails, triggering the 92° limit switch; 2. In manual or forced manual mode, manually shifting the pitch backward triggers the 92° limit switch. After the 92° limit switch is triggered, the second relay K3 and the third relay K11 are de-energized, causing the pitch motor's electromagnetic brake C1 to de-energize, thereby stopping the machine.

[0034] Please continue to refer to this. Figure 1 This disclosure provides an electromagnetic brake circuit 100 for a pitch motor. The first limit switch X1 includes a manual forward pitch knob. The circuit 100 also includes a fourth relay K12. The A1 port of the coil 30 of the fourth relay K12 is electrically connected to the manual forward pitch knob.

[0035] Specifically, after the 92° limit switch is triggered, backward pitching is not allowed; only forward pitching is permitted. Otherwise, there is a risk of breaking the toothed belt. In this embodiment, the A1 port of the coil 30 of the fourth relay K12 is electrically connected to the manual forward pitching knob. The fourth relay K12 is controlled by the manual forward pitching signal. When the 92° limit switch is triggered, the pitch motor electromagnetic brake C1 engages. At this time, manual forward pitching can energize the fourth relay K12. Thus, by connecting the coil 30 of the fourth relay K12 to the manual forward pitching knob, the fourth relay K12 can be energized during manual forward pitching, thereby energizing the third relay K11. When the third relay K11 is energized, the normally open contact 20 of the third relay K11, located between the auxiliary contact D1 of the first relay K2 and the pitch motor electromagnetic brake C1, closes, releasing the pitch motor electromagnetic brake C1.

[0036] It should be noted that KL1104 in the diagram is a digital input module. Manual forward and backward pitch signals can be input to the digital input module. In the Goldwind 1.5MW wind turbine generator set, the digital input module transmits the manual forward and backward pitch signals to the PLC (Programmable Logic Controller). The PLC sends control commands (such as start, stop, and speed adjustment) to the pitch inverter through digital output terminals or communication interfaces based on the input signals and preset logic. The inverter adjusts the output frequency according to the PLC's commands to drive the pitch motor and feeds back the operating status (such as fault codes and actual frequency) to the PLC through digital output terminals or communication interfaces.

[0037] Please continue to refer to this. Figure 1 The present disclosure provides an electromagnetic brake circuit 100 for a pitch motor. The circuit 100 further includes a second diode R2, which is connected in parallel with the coil 30 of a fourth relay K12. The negative terminal of the second diode R2 is connected to port A1 of the coil 30 of the fourth relay K12, and the positive terminal of the second diode R2 is electrically connected to port A2 of the coil 30 of the fourth relay K12.

[0038] Specifically, the second diode R2 is connected in parallel with the coil 30 of the fourth relay K12. When the coil 30 of the fourth relay K12 is de-energized, the reverse electromotive force causes the second diode R2 to conduct in the forward direction, providing a low-impedance freewheeling path for the current in the coil 30 of the fourth relay K12. The current forms a loop through the second diode R2, allowing the energy in the coil 30 of the fourth relay K12 to be released gradually instead of generating a high-voltage spike. The second diode R2 can also absorb the energy released when the coil 30 of the fourth relay K12 is de-energized, preventing the energy from being released in the form of sparks or electromagnetic radiation, thereby reducing interference to the circuit. In addition, the second diode R2 clamps the voltage across the coil 30 of the fourth relay K12 at its forward voltage drop, preventing high voltage from breaking down the driving element. Thus, by connecting the second diode R2 in parallel with the coil 30 of the fourth relay K12, the protection of the fourth relay K12 can be achieved simply and effectively without complex circuitry.

[0039] Please continue to refer to this. Figure 1 This disclosure provides an electromagnetic brake circuit 100 for a pitch motor. The normally closed contact 40 of the fourth relay K12 is located between the negative terminal of the second relay K3 and the first diode R1. One end of the normally open contact 50 of the fourth relay K12 is electrically connected to the A1 port of the coil 10 of the third relay K11, and the other end is connected to the input terminal of a 24V DC power supply.

[0040] Specifically, in one optional embodiment provided in this disclosure, the normally closed contact 40 of the fourth relay K12 is located between the negative terminal of the second relay K3 and the first diode R1, and is used to energize the coil 10 of the third relay K11 under normal conditions; one end of the normally open contact 50 of the fourth relay K12 is electrically connected to the A1 port of the coil 10 of the third relay K11, and the other end is connected to the input terminal of the 24V DC power supply, and is used to energize the coil 10 of the third relay K11 again when the 92° limit switch is triggered, the coil 10 of the third relay K11 is de-energized, and the third relay K11 is re-energized when manually shifting the paddle forward.

[0041] Please continue to refer to this. Figure 1 This disclosure provides an electromagnetic brake circuit 100 for a pitch motor, wherein the A2 port of the coil 30 of the fourth relay K12 and the positive terminal of the second diode R2 are connected to the A2 port of the coil 10 of the third relay K11.

[0042] Specifically, when the 92° limit switch is triggered, the wind turbine will shut down due to a malfunction, requiring personnel to climb the tower for maintenance. At this time, the third relay K11 will be de-energized, and the pitch motor electromagnetic brake C1 will be in a holding state, preventing pitch control. By electrically connecting the fourth relay K12 to the third relay K11, the fourth relay K12 can be energized during manual forward pitch control, which in turn energizes the third relay K11. At this point, the wind turbine can pitch forward, disengaging the 92° limit switch. Once the 92° limit switch is disengaged, the third relay K11 will engage, allowing normal pitch control again.

[0043] Please continue to refer to this. Figure 1 This disclosure provides an electromagnetic brake circuit 100 for a pitch motor. The electromagnetic brake C1 of the pitch motor includes an electromagnetic brake Y1 and a diode V1, with the electromagnetic brake Y1 and the diode V1 connected in parallel.

[0044] Specifically, the core mechanism of electromagnetic brake Y1 is based on electromagnetic effects, and its structure includes components such as an electromagnetic coil, brake disc, friction pads, and springs. When the electromagnetic coil is energized, it generates a magnetic field that attracts the friction pads on the brake disc to contact the electromagnet, achieving a braking effect through friction. Diode V1 primarily serves as a freewheeling protection function in the electromagnetic brake circuit, preventing damage to circuit components from back electromotive force generated when the coil is de-energized. Electromagnetic brake Y1 and diode V1 together constitute the core control unit of the pitch motor electromagnetic brake C1, achieving dual functions of braking and protection: electromagnetic brake Y1 uses electromagnetic effects to quickly stop or release the drive shaft, meeting the pitch system's requirements for blade angle adjustment. Diode V1 eliminates back electromotive force through its freewheeling function, ensuring the reliability of electromagnetic brake Y1 and its control circuit, and extending equipment life. The de-energized braking characteristic of electromagnetic brake Y1 and the overvoltage protection of diode V1 form a dual safety mechanism, preventing equipment damage or accidents caused by malfunctions.

[0045] Please continue to refer to this. Figure 1 This disclosure provides a pitch control system for a wind turbine generator set, including the pitch motor electromagnetic brake circuit 100 as described above.

[0046] Specifically, this disclosure is a design modification based on the Goldwind 1.5MW pitch system, aimed at reducing the pitch failure rate caused by the first relay K2, while adding a safety circuit 100 to eliminate the risk of toothed belt breakage.

[0047] In summary, this disclosure provides a pitch motor electromagnetic brake circuit and a wind turbine pitch system, comprising: a first relay, a second relay, a third relay, a pitch motor electromagnetic brake, and a first limit switch. The pitch motor electromagnetic brake and the first limit switch are respectively connected to different terminal blocks of the pitch inverter. The second relay is connected in series with the first limit switch, and the third relay is connected in parallel with the second relay. The second and third relays are configured to be synchronously controlled by the first limit switch. The first relay includes two sets of auxiliary contacts, which are connected in series with the pitch motor electromagnetic brake and in parallel. Thus, by connecting the two sets of auxiliary contacts of the first relay in parallel, the operational reliability of the first relay can be improved, and the frequency of pitch failures can be reduced. By connecting the third relay in parallel with the second relay, the reliability of the brake circuit of the pitch system can be greatly improved, and the possibility of the pitch belt being pulled apart due to exceeding the limit can be reduced.

[0048] The above are merely specific embodiments of this disclosure, enabling those skilled in the art to understand or implement this disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to these embodiments, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A variable pitch motor electromagnetic brake circuit, characterized in that, include: The system includes a first relay, a second relay, a third relay, a pitch motor electromagnetic brake, and a first limit switch. The pitch motor electromagnetic brake and the first limit switch are respectively connected to different terminal blocks of the pitch inverter. The second relay is connected in series with the first limit switch, and the third relay is connected in parallel with the second relay. The second relay and the third relay are configured to be synchronously controlled by the first limit switch. The first relay includes two sets of auxiliary contacts. The two sets of auxiliary contacts of the first relay are connected in series with the electromagnetic brake of the pitch motor, and the two sets of auxiliary contacts are connected in parallel.

2. The variable pitch motor electromagnetic brake circuit of claim 1, wherein, The coil of the third relay is connected in parallel with the second relay, and the normally open contact of the third relay is located between the auxiliary contact of the first relay and the electromagnetic brake of the pitch motor.

3. The variable pitch motor electromagnetic brake circuit of claim 2, wherein, The circuit also includes a first diode, which is connected in parallel with the coil of the third relay. The negative terminal of the first diode is electrically connected to port A1 of the coil of the third relay, and the positive terminal of the first diode is electrically connected to port A2 of the coil of the third relay.

4. The variable pitch motor electromagnetic brake circuit of claim 1, wherein, The first limit switch is a 92° limit switch.

5. The variable pitch motor electromagnetic brake circuit of claim 3, wherein, The first limit switch includes a manual forward pitch knob, and the circuit also includes a fourth relay, the A1 port of the coil of the fourth relay being electrically connected to the manual forward pitch knob.

6. The variable pitch motor electromagnetic brake circuit of claim 5, wherein, The circuit also includes a second diode, which is connected in parallel with the coil of the fourth relay. The negative terminal of the second diode is electrically connected to port A1 of the coil of the fourth relay, and the positive terminal of the second diode is electrically connected to port A2 of the coil of the fourth relay.

7. The variable pitch motor electromagnetic brake circuit of claim 5, wherein, The normally closed contact of the fourth relay is located between the second relay and the negative terminal of the first diode. One end of the normally open contact of the fourth relay is electrically connected to port A1 of the coil of the third relay, and the other end is connected to the input terminal of the 24V DC power supply.

8. The variable pitch motor electromagnetic brake circuit of claim 6, wherein, The A2 port of the fourth relay coil and the positive terminal of the second diode are connected to the A2 port of the third relay coil.

9. The variable pitch motor electromagnetic brake circuit of claim 1, wherein, The electromagnetic brake of the pitch motor includes an electromagnetic brake and a diode, with the electromagnetic brake and the diode connected in parallel.

10. A wind turbine generator system, characterized by, Includes the pitch motor electromagnetic brake circuit as described in any one of claims 1-9.

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