Hydraulic pitch control system and wind turbine generator set

Abstract

This disclosure provides a hydraulic pitch control system and a wind turbine generator set. The hydraulic pitch control system includes: a pitch cylinder; a motor-pump assembly connected to the pitch cylinder, including a motor and a pump connected to the motor, and controlling the extension and retraction speed of the pitch cylinder by controlling the speed of the motor; and an accumulator assembly connected to the motor-pump assembly to provide hydraulic oil required by the wind turbine generator set in emergency feathering conditions, wherein the motor-pump assembly controls the normal pitch opening and retraction of the wind turbine generator set and provides initial oil supply to the accumulator assembly.

Description

Technical Field

[0001] This disclosure pertains to the field of wind power, and more specifically, relates to a hydraulic pitch system and a wind turbine generator set. Background Technology

[0002] Conventional hydraulic pitch control systems employ valve-controlled cylinder technology. The motor-pump unit provides power to pressurize the accumulator group. The accumulator group serves as both the main and emergency power source for the hydraulic pitch control system. As it acts as an emergency power source, the pressure of the accumulator group must be maintained at a high pressure (e.g., within the range of 260 bar to 285 bar). When the accumulator group pressure drops below 260 bar, the motor-pump unit starts to pressurize the accumulator group. When the accumulator group pressure reaches 285 bar, the motor-pump unit stops, and the entire pitch control system executes pitch control actions by receiving power oil from the accumulator group.

[0003] However, under normal conditions, the hydraulic pitch control system has a relatively small pitch driving force. Depending on the pitch load, the required pressure for the pitch cylinder is approximately 150-180 bar (average is approximately 170 bar), and it operates within this pressure range for about 95% of the time. The minimum pressure of the accumulator is between 260-285 bar, and the average is approximately 270 bar. Therefore, the hydraulic system experiences a pressure loss of 100 bar (270 bar - 170 bar), resulting in an energy consumption of approximately 35%. In addition, factors such as the proportional valve pressure difference, pump volumetric efficiency, and pipeline pressure loss also affect the overall efficiency of conventional hydraulic pitch control, which is below 50%. The energy loss is relatively high, and the energy utilization rate is very low. The lost energy is converted into heat and needs to be cooled by a cooling system, which also has a relatively large power consumption. This increases the valve failure rate and raises maintenance costs.

[0004] In addition, hydraulic pitch systems that use a combination of valve control and pump control may experience conflicts between the accumulator's pressurization and the pitch pump control when a hydraulic power source is required, resulting in low control efficiency and affecting system safety. Summary of the Invention

[0005] One of the purposes of this disclosure is to provide a hydraulic pitch system that can improve control efficiency.

[0006] According to a first aspect of this disclosure, a hydraulic pitch system for a wind turbine generator set is provided, the hydraulic pitch system comprising: a pitch cylinder; a motor-pump assembly connected to the pitch cylinder, including a motor and a pump connected to the motor, and controlling the extension and retraction speed of the pitch cylinder by controlling the rotational speed of the motor; and an accumulator assembly connected to the motor-pump assembly to provide hydraulic oil required by the wind turbine generator set in emergency feathering conditions, wherein the motor-pump assembly controls the normal pitch opening and retraction of the wind turbine generator set and provides initial oil supply to the accumulator assembly.

[0007] According to embodiments of this disclosure, the hydraulic pitch system may further include: an auxiliary motor pump connected to an accumulator group and used for internal pressure relief of the accumulator group; the hydraulic pitch system may further include an accumulator safety valve group, the accumulator safety valve group including: a first electrically controlled switching valve connected in series between the accumulator group and the motor pump group; and a first check valve connected in series between the accumulator group and the auxiliary motor pump, wherein the inlet of the first check valve is connected to the auxiliary motor pump, the outlet of the first check valve is connected to the accumulator group and the first working port of the first electrically controlled switching valve, and the second working port of the first electrically controlled switching valve is connected to the motor pump group.

[0008] According to embodiments of this disclosure, the accumulator safety valve assembly may further include a first relief valve, which is connected in parallel with a first electrically controlled switch valve and is connected between the accumulator assembly and the hydraulic oil tank.

[0009] According to embodiments of this disclosure, the motor pump unit may further include: a second electrically controlled switch valve, the first working port of which is connected to an accumulator group, and the second working port of which is connected to the large chamber of the pitch cylinder; and a third electrically controlled switch valve, the first working port of which is connected to the small chamber of the pitch cylinder, and the second working port of which is connected to a hydraulic oil tank. The hydraulic pitch system forms an emergency feathering oil supply path sequentially through the accumulator group, the third electrically controlled switch valve, and the large chamber of the pitch cylinder, and also forms an emergency feathering oil return path sequentially through the small chamber of the pitch cylinder, the third electrically controlled switch valve, and the hydraulic oil tank.

[0010] According to embodiments of this disclosure, the motor pump assembly may further include: a fourth electrically controlled switching valve, the first working port of which is connected to the small chamber of the pitch cylinder, the second working port of which is connected to the first working port of the pump; a fifth electrically controlled switching valve, the first working port of which is connected to the large chamber of the pitch cylinder, the second working port of which is connected to the second working port of the pump; and a first bridging valve assembly module, including a first valve and a second valve connected in series and bridging the second working ports of the fourth and fifth electrically controlled switching valves, a first node between the first and second valves connected to a hydraulic oil tank, and the second valve being an electrically controlled valve. The hydraulic pitch system forms a pitch-starting oil supply path sequentially through the first working port of the pump, the fourth electrically controlled switching valve, and the small chamber of the pitch cylinder, and also forms a pitch-starting oil return path sequentially through the large chamber of the pitch cylinder and the fifth electrically controlled switching valve. The pitch-starting oil return path further includes a first pitch-starting oil return path from the second valve to the hydraulic oil tank and a second pitch-starting oil return path from the second working port of the fifth electrically controlled switching valve to the second working port of the pump.

[0011] According to embodiments of this disclosure, the motor pump unit may further include: a second bridging valve module, including a sixth electrically controlled switch valve bridging the first working port of the fourth electrically controlled switch valve and the first working port of the fifth electrically controlled switch valve; a second check valve, the inlet of which is connected to the hydraulic oil tank, and the outlet of which is connected to the first working port of the pump, wherein the hydraulic pitch system forms a differential pitch recovery oil supply path that sequentially passes through the second working port of the pump and the fifth electrically controlled switch valve, and sequentially forms a differential pitch recovery circulation oil circuit that sequentially passes through the small chamber of the pitch cylinder, the sixth electrically controlled switch valve, and the large chamber of the pitch cylinder, and forms a replenishment oil path from the hydraulic oil tank, the second check valve, and the first working port of the pump.

[0012] According to embodiments of this disclosure, the motor pump unit may further include a third bridging valve module. The third bridging valve module includes a third relief valve and a fourth relief valve connected in series and bridging the first working port of the fourth solenoid valve and the first working port of the fifth solenoid valve. A second node between the third relief valve and the fourth relief valve is connected to the first node. The hydraulic pitch system forms a normal pitch supply path that sequentially passes through the second working port of the pump, the fifth solenoid valve, and the large chamber of the pitch cylinder; a normal pitch return path that sequentially passes through the small chamber of the pitch cylinder, the fourth solenoid valve, and the first working port of the pump; and a replenishment path that sequentially passes through the hydraulic oil tank, the second check valve, and the first working port of the pump.

[0013] According to embodiments of this disclosure, the motor pump unit may further include: a fifth relief valve, with a first node connected to a first working port of the fifth relief valve, and a second working port of the fifth electrically controlled switch valve connected to a second working port of the fifth relief valve; a sixth relief valve, connected in parallel with the first valve, with the first working port of the sixth relief valve connected to the second node and the first node, and the second working port of the sixth relief valve connected to the first working port of the pump.

[0014] According to embodiments of this disclosure, the hydraulic tank can be a pressurized tank.

[0015] According to a second aspect of this disclosure, a hydraulic pitch control system for a wind turbine generator set is provided, characterized in that it comprises: a pitch cylinder; a motor-pump assembly connected to the pitch cylinder and controlling the normal pitch opening and retraction of the wind turbine generator set, and including a motor and a pump connected to the motor, and controlling the extension and retraction speed of the pitch cylinder by controlling the rotational speed of the motor; an accumulator assembly connected to the motor-pump assembly to provide hydraulic oil required by the wind turbine generator set in an emergency feathering condition; and a second electrically controlled switching valve, the first working port of the second electrically controlled switching valve being connected to the accumulator assembly, and the second working port of the second electrically controlled switching valve being connected to the large chamber of the pitch cylinder; wherein the second electrically controlled switching valve is disconnected in the emergency feathering condition of the wind turbine generator set's pitch opening condition, emergency feathering condition, and normal retraction condition.

[0016] According to embodiments of this disclosure, the hydraulic pitch system further includes: an auxiliary motor pump connected to an accumulator group and used for internal pressure relief of the accumulator group; the hydraulic pitch system may also include: a third electrically controlled switch valve, the first working port of the third electrically controlled switch valve being connected to the small chamber of the pitch cylinder, and the second working port of the third electrically controlled switch valve being connected to the hydraulic oil tank; wherein, in an emergency feathering condition, the hydraulic pitch system forms an emergency feathering oil supply path sequentially through the accumulator group, the second electrically controlled switch valve, and the large chamber of the pitch cylinder, and forms an emergency feathering oil return path through the small chamber of the pitch cylinder, the third electrically controlled switch valve, and the hydraulic oil tank.

[0017] According to embodiments of this disclosure, the motor-pump assembly may further include: a fourth electrically controlled switching valve, the first working port of which is connected to the small chamber of the pitch cylinder, the second working port of which is connected to the first working port of the pump; a fifth electrically controlled switching valve, the first working port of which is connected to the large chamber of the pitch cylinder, the second working port of which is connected to the second working port of the pump; and a first bridging valve assembly module, including a first valve and a second valve connected in series and bridging the second working ports of the fourth and fifth electrically controlled switching valves, a first node between the first and second valves connected to a hydraulic oil tank, and the second valve being an electrically controlled valve. In the pitch-opening condition, the hydraulic pitch system forms a pitch-opening oil supply path sequentially through the first working port of the pump, the fourth electrically controlled switching valve, and the small chamber of the pitch cylinder, and forms a pitch-opening oil return path sequentially through the large chamber of the pitch cylinder and the fifth electrically controlled switching valve. The pitch-opening oil return path also includes a first pitch-opening oil return path from the second valve to the hydraulic oil tank and a second pitch-opening oil return path from the second working port of the fifth electrically controlled switching valve to the second working port of the pump.

[0018] According to embodiments of this disclosure, the motor pump unit may further include: a second bridging valve module, including a sixth electrically controlled switch valve bridging the first working port of the fourth electrically controlled switch valve and the first working port of the fifth electrically controlled switch valve; a second check valve, the inlet of which is connected to the hydraulic oil tank, and the outlet of which is connected to the first working port of the pump, wherein the hydraulic pitch system forms a differential pitch recovery oil supply path that sequentially passes through the second working port of the pump and the fifth electrically controlled switch valve, and sequentially forms a differential pitch recovery circulation oil circuit that sequentially passes through the small chamber of the pitch cylinder, the sixth electrically controlled switch valve, and the large chamber of the pitch cylinder, and forms a differential pitch recovery oil replenishment path from the hydraulic oil tank, the second check valve, and the first working port of the pump.

[0019] According to embodiments of this disclosure, the motor pump unit may further include a third bridging valve module. The third bridging valve module includes a third relief valve and a fourth relief valve connected in series and bridging the first working port of the fourth solenoid valve and the first working port of the fifth solenoid valve. The second node between the third relief valve and the fourth relief valve is connected to the first node. Under normal pitch control conditions, the hydraulic pitch system forms a normal pitch control oil supply path that passes sequentially through the second working port of the pump, the fifth solenoid valve, and the large chamber of the pitch cylinder; a normal pitch control oil return path that passes sequentially through the small chamber of the pitch cylinder, the fourth solenoid valve, and the first working port of the pump; and a normal pitch control oil replenishment path that passes sequentially through the hydraulic oil tank, the second check valve, and the first working port of the pump.

[0020] According to embodiments of this disclosure, the motor pump unit may further include: a fifth relief valve, with a first node connected to a first working port of the fifth relief valve, and a second working port of the fifth electrically controlled switch valve connected to a second working port of the fifth relief valve; a sixth relief valve, connected in parallel with the first valve, with the first working port of the sixth relief valve connected to the second node and the first node, and the second working port of the sixth relief valve connected to the first working port of the pump.

[0021] According to a second aspect of this disclosure, a wind turbine generator set is provided, comprising: a hub; a hydraulic pitch system, as described above and installed within the hub; a pitch controller for controlling the hydraulic pitch system to achieve pitch control; and blades, the blade roots of which are connected to the hub, wherein the telescopic rod of the pitch cylinder of the hydraulic pitch system is movably connected to the blade roots, and the cylinder body end of the pitch cylinder of the hydraulic pitch system is connected to the hub.

[0022] The hydraulic pitch system according to embodiments of this disclosure can improve control efficiency and enhance system reliability and safety.

[0023] The hydraulic pitch system according to embodiments of this disclosure can reduce energy loss of the accumulator. Attached Figure Description

[0024] These and / or other aspects and advantages of this disclosure will become clearer and more readily understood from the following description of embodiments, taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a schematic diagram of a hydraulic pitch system according to an embodiment of the present disclosure; Figure 2 The direction of hydraulic oil flow under emergency feathering conditions according to embodiments of the present disclosure is shown. Figure 3 The direction of hydraulic oil flow under the open-pipe condition according to an embodiment of the present disclosure is shown; Figure 4 The direction of hydraulic oil flow is shown in the differential propeller recovery condition according to an embodiment of the present disclosure; Figure 5 The direction of hydraulic oil flow under normal tillage conditions according to an embodiment of the present disclosure is shown. Detailed Implementation

[0025] The following detailed description is provided to aid in obtaining a full understanding of the methods, apparatus, and / or systems described herein. However, the order of operations described herein is merely illustrative and is not limited to those orders set forth herein; equivalent substitutions or changes may be made, except for operations that must occur or be performed in a specific order. Furthermore, for clarity and conciseness, descriptions of content well-known in the art will be omitted or simplified.

[0026] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains upon understanding this disclosure. Unless expressly defined herein, terms (such as those defined in a general dictionary) shall be interpreted as having a meaning consistent with their meaning in the context of the relevant field and in this disclosure, and shall not be interpreted in an idealized or overly formalistic manner.

[0027] Unless otherwise specified, the same reference numerals generally refer to the same elements (e.g., components, steps, and methods). Reference numerals described in previous embodiments that reappear in later embodiments may be omitted. Furthermore, technical features described in different or the same embodiments can be combined in any way, as long as the combined embodiment or technical solution is complete and can solve the technical problems of this application or achieve the technical effects described or not described in this disclosure but which can be determined based on the complete technical solution described above.

[0028] In this disclosure, "connection" or "connection" encompasses not only physical, direct, rigid connections but also extends to the connectivity between fluid pathways. For example, it refers not only to the physical connection between two components via rigid pipes, hoses, or integrated blocks but also to the state where the fluid medium can flow freely. When referring to "connection," it includes not only the physical connections mentioned above but also logical connections. This means that even if components are not physically directly connected, as long as they can indirectly form a fluid pathway through control elements (such as valves) or other functional components (such as filters, accumulators, etc.), they can be considered to be in a "connected" state. For example, a solenoid directional valve can be used to switch the fluid flow direction under different operating conditions, thereby changing the operating mode of the actuator. Therefore, expressions similar to "connection" or "connection" between A and B can include cases where A and B are directly connected or directly linked, as well as cases where A and B are connected or connected through at least one other intermediate component. The connection or connection of one port or end of multiple ports or ends of the same component to another component typically refers to the hydraulic oil flowing through that port or end flowing through that other component.

[0029] In addition to the pump control achieved by the electric motor pump set, the hydraulic pitch system disclosed herein also utilizes an auxiliary electric motor pump to improve control efficiency and prevent conflicts arising from the need for a single electric motor pump to replenish oil to the accumulator while simultaneously achieving pump-controlled pitch, thereby improving control efficiency.

[0030] The hydraulic pitch system disclosed herein utilizes an auxiliary electric motor pump for internal pressure replenishment of the accumulator group, eliminating the need for the motor in the electric motor pump group to frequently participate in the pressure charging of the accumulator group.

[0031] Furthermore, the hydraulic pitch control system of this disclosure does not require the accumulator group to participate in pitch control except in emergency feathering conditions. This avoids the underutilization of the accumulator group's high voltage, reduces the accumulator group's energy consumption, and improves the system's energy efficiency. A detailed description of embodiments of this disclosure follows.

[0032] Figure 1 This is a schematic diagram of a hydraulic pitch system according to an embodiment of the present disclosure. Figure 2 The hydraulic oil flow direction under emergency feathering conditions according to embodiments of the present disclosure is shown. Figure 3 The direction of hydraulic oil flow under the open-pipe condition according to an embodiment of the present disclosure is shown. Figure 4 The hydraulic oil flow direction under differential propeller recovery conditions according to embodiments of the present disclosure is shown. Figure 5 The direction of hydraulic oil flow under normal tillage conditions according to an embodiment of the present disclosure is shown.

[0033] Reference Figure 1 The hydraulic pitch system disclosed herein includes a pitch cylinder, a motor-pump assembly, an accumulator assembly, and an auxiliary motor-pump. Furthermore, the hydraulic pitch system of this disclosure may also include an accumulator safety valve assembly.

[0034] An electric motor pump unit (EMP) integrates a motor and a pump, and may also include valve assemblies. It is a pitch control power source and control system integration used to achieve closed-loop pump-controlled pitch. The valve assemblies in an EMP primarily control and regulate the direction and pressure of the fluid for precise pitch control. Valve assemblies typically include various valves such as directional control valves, pressure control valves, and flow control valves. Directional control valves primarily control the direction of hydraulic oil flow, thus determining the direction of movement of actuators (such as hydraulic cylinders), and may include solenoids, check valves, etc. Pressure control valves regulate the pressure level within the system, ensuring the system is not damaged by overpressure. For example, a pressure control valve can be a relief valve, which opens when the system pressure reaches a set value, allowing excess hydraulic oil to flow back to the tank, thus protecting the system. The valve assemblies in an EMP can be flexibly combined according to specific needs. For example, multiple functional valves can be centrally installed in an integrated block, saving space and facilitating management.

[0035] The electric motor pump assembly may include a servo motor and a fixed displacement pump (e.g., a bidirectional hydraulic pump), or it may include an asynchronous motor and a servo-controlled closed-loop pump. However, the electric motor pump assembly disclosed herein is not limited to these and may have other configurations capable of achieving closed-loop pump-controlled pitch control. Furthermore, in the case of a bidirectional pump, the motor's speed and rotation direction can control the pump's oil delivery direction, thereby controlling the direction and flow rate of the oil circuit.

[0036] The auxiliary motor pump includes a motor and a pump. The pump in the auxiliary motor is used for internal oil replenishment or internal pressure replenishment of the accumulator group. The pump in the auxiliary motor pump can be a common fixed displacement pump; however, this disclosure is not limited thereto. The displacement of the pump in the auxiliary motor pump can be less than the displacement of the pump in the motor pump group. As an example, the displacement of the pump in the auxiliary motor pump can be less than one-tenth of the displacement of the pump in the motor pump group. Specifically, the displacement of the pump in the auxiliary motor pump can be 2cc to 3cc (e.g., 2.5cc), and the displacement of the pump in the motor pump group can be 30cc to 50cc (e.g., 40cc). Furthermore, the type of pump in the auxiliary motor pump can be different from the type of pump in the motor pump group; the pump in the motor pump group can be a bidirectional pump, while the pump in the auxiliary motor pump can be a unidirectional pump.

[0037] The accumulator assembly comprises accumulators and accumulator supports. The accumulators are mounted on the supports, which can be mounted on the wheel hub. The accumulator assembly is an auxiliary power source for the hydraulic pitch system and can be used solely as a power source for emergency feathering. Specifically, each accumulator in the assembly can store sufficient hydraulic energy and absorb pressure pulsations. In emergencies, the accumulator assembly can rapidly release the stored energy to provide power support to the hydraulic circuits, ensuring the emergency response capability of the pitch system.

[0038] Accumulator safety valve assemblies are used to protect the accumulator group from maximum pressure and to ensure the accumulator release function. Accumulator safety valve assemblies typically include check valves, relief valves, etc. Furthermore, the configuration of the accumulator safety valve assembly is not specifically limited and can be determined based on the configuration of the accumulator group.

[0039] The pitch cylinder is the actuator for pitch control. Each blade can contain two cylinders. There are no specific restrictions on the type of pitch cylinder, nor are there any specific restrictions on the installation method of the pitch cylinder in the wind turbine generator set.

[0040] Reference Figures 1 to 5 The motor-pump unit can be connected to the pitch cylinder. The motor-pump unit includes a motor 1 and a pump 2 connected to the motor 1. The motor-pump unit can control the extension and retraction speed of the pitch cylinder by controlling the speed of the motor 1. The motor 1 can be a servo motor, and the pump 2 can be a bidirectional pump.

[0041] Accumulator 16 is connected to the motor pump set to provide the hydraulic oil required by the wind turbine generator set in the emergency feathering condition. In other pitch conditions besides the emergency feathering condition, accumulator 16 may not supply hydraulic oil to the hydraulic system to avoid frequent pressurization of accumulator 16.

[0042] The initial oil supply or replenishment of the accumulator group 16 under specific conditions can be achieved by the motor pump set. For example, the motor pump set can provide initial oil supply to the accumulator group 16 or replenish oil to the accumulator group 16 after an emergency feathering operation. When the pressure of the accumulator group 16 is lower than the first minimum threshold due to internal leakage, internal leakage replenishment can be performed by the auxiliary motor pump.

[0043] Reference Figures 1 to 5 An auxiliary electric motor pump can be connected to the accumulator group 16 and used for internal leakage pressure replenishment or oil replenishment of the accumulator group 16. Oil replenishment of the accumulator group 16 can be performed via the auxiliary electric motor pump when internal leakage occurs, without the need for oil replenishment via the electric motor pump group, thus avoiding conflicts between the closed-loop pump control of the electric motor pump group and the oil replenishment of the accumulator group.

[0044] In addition, the accumulator group 16 does not need to provide a power source in pitch conditions other than emergency feathering conditions. Therefore, the high voltage and low utilization of the accumulator group 16 can be avoided, the energy consumption of the accumulator group 16 can be reduced, and the system safety can be improved.

[0045] The following is combined with Figures 2 to 5 This disclosure describes the specific hydraulic circuit and the hydraulic oil flow patterns under different pitch control conditions.

[0046] Emergency descent When a wind turbine reports a fault, requires emergency feathering, or experiences a power outage or electrical system problem, the hydraulic pitch system uses the accumulator as a power source to fully extend the pitch cylinder, enabling the turbine blades to retract.

[0047] Specific reference Figure 1 and Figure 2 The hydraulic pitch system disclosed herein also includes an accumulator safety valve assembly, which may include a first electrically controlled switching valve 13 and a first check valve 20.

[0048] The first electrically controlled switching valve 13 can be connected in series between the accumulator group 16 and the motor pump group. The first electrically controlled switching valve 13 can be of different types. For example, the first electrically controlled switching valve 13 can be a solenoid valve. For example, the first electrically controlled switching valve 13 can be a two-position two-way solenoid valve.

[0049] The first check valve 20 can be connected in series between the accumulator group 16 and the auxiliary motor pump. The inlet of the first check valve 20 is connected to the auxiliary motor pump, the outlet of the first check valve 20 is connected to the accumulator group 16 and the first working port of the first electrically controlled switch valve 13, and the second working port of the first electrically controlled switch valve 13 is connected to the motor pump group.

[0050] The accumulator safety valve assembly may also include a first relief valve 12, which may be connected in parallel with the first electrically controlled switch valve 13, and the first relief valve 12 is connected between the accumulator assembly 16 and the hydraulic oil tank. The hydraulic oil tank here may be a regular oil tank or a pressurized oil tank (the pressurized oil tank can pressurize the system and prevent the hydraulic pump from sucking in air).

[0051] Although not shown, the accumulator safety valve assembly of this disclosure may also include other components in addition to the first electrically controlled switching valve 13, the first check valve 20 and the first relief valve 12.

[0052] As an example, the accumulator safety valve assembly may also include a first pressure sensor 14.3, which can be used to measure the oil supply pressure of the accumulator assembly 16. Additionally, although not shown, the accumulator assembly 16 may have a pressure sensor. The pressure information detected by the first pressure sensor 14.3 and the pressure sensors in the accumulator assembly 16 can be provided to a controller (not shown). Based on the received pressure information and the system-set upper and lower pressure thresholds, the controller determines the current operating status of the hydraulic system and accordingly controls the start / stop of the auxiliary motor pump and the relevant valves. Specifically, when the pressure sensor in the accumulator assembly 16 detects that the pressure of the accumulator assembly 16 is lower than the set lower limit, it indicates that the pressure of the accumulator assembly 16 is insufficient. The controller will issue a command to energize and start the auxiliary motor pump to replenish the pressure in the accumulator assembly 16 to the normal operating range (e.g., 260 bar to 285 bar). Conversely, when the pressure reaches or exceeds the set upper limit, the controller will de-energize and stop the auxiliary motor pump to prevent overpressure operation of the accumulator assembly, thereby protecting the equipment. Furthermore, the controller can also change the direction of hydraulic oil flow by controlling the energization and de-energization of components such as solenoid valves in the hydraulic pitch system. For example, in the pitch system, the controller can precisely control the energization state of the valve group based on wind speed and position feedback signals to achieve precise adjustment of the pitch angle and ensure the safe and efficient operation of the wind turbine generator set.

[0053] Reference Figure 2 The electric motor pump unit disclosed herein may also include a second electrically controlled switch valve 8 and a third electrically controlled switch valve 5. The second electrically controlled switch valve 8 and the third electrically controlled switch valve 5 may have the same configuration as the first electrically controlled switch valve 13, which will not be described in detail here.

[0054] The first working port of the second electrically controlled switch valve 8 can be connected to the accumulator group 16, and the second working port of the second electrically controlled switch valve 8 can be connected to the large chamber of the pitch cylinder. The first working port of the third electrically controlled switch valve 5 can be connected to the small chamber of the pitch cylinder, and the second working port of the third electrically controlled switch valve 5 can be connected to the hydraulic oil tank.

[0055] Reference Figure 2 The hydraulic pitch system forms an emergency feathering oil supply path that passes sequentially through the accumulator group 16, the second electronically controlled switch valve 8, and the large chamber of the pitch cylinder, and also forms an emergency feathering oil return path that passes through the small chamber of the pitch cylinder, the third electronically controlled switch valve 5, and the hydraulic oil tank.

[0056] Additionally, the hydraulic pitch system of this disclosure may also include a filter 17, which may be located on the emergency feathering return path. For example, the filter 17 may be located between the third electrically controlled switching valve 5 and the booster tank. The filter 17 keeps the hydraulic oil in the pipeline and the oil in the tank clean at all times, protecting the pump and thereby improving the reliability of the hydraulic pitch system. Although not shown, the hydraulic pitch system of this disclosure may also include a cooling module. As an example, the cooling module may include a motor, a pump, a cooling fan, and cooling fins. The motor and pump can draw hydraulic oil from the booster tank, cool it through the cooling fins, and then the cooled hydraulic oil can flow back to the booster tank. The cooling fan can blow air onto the cooling fins. Since the accumulator group 16 of this disclosure supplies oil under emergency feathering conditions (e.g., only under emergency feathering conditions), the system generates relatively little heat. Therefore, the cooling module may be omitted, or a cooling module with relatively low heat dissipation capacity may be selected to reduce the heat dissipation power of the cooling module.

[0057] Although not shown, various other components may be installed on the emergency feathering supply and return paths of the hydraulic pitch system disclosed herein, such as pressure sensors, filters, relief valves, check valves, etc.

[0058] Additionally, it should be noted that the electrically controlled switching valve of this disclosure can also be implemented by having different valve assemblies, as long as the valve assembly can perform the switching function.

[0059] Sail start condition In a motor-pump controlled closed-loop hydraulic pitch system, the motor rotates counterclockwise during pitch engagement. Adjusting the motor's speed changes the hydraulic pump's output flow, thus regulating the pitch cylinder's speed. The only power source for pitch engagement is the motor-pump unit, which provides hydraulic pressure based on the cylinder's load, resulting in no energy loss. During pitch engagement, the pitch cylinder retracts. The flow rate of hydraulic fluid supplied to the rod chamber of the cylinder by the motor-pump is less than the flow rate into the pump from the rodless chamber, therefore, some hydraulic oil usually needs to be recovered. Hydraulic oil can be recovered via a booster tank as needed.

[0060] Reference Figure 1 and Figure 3 The electric pump assembly disclosed herein may further include a fourth electrically controlled switching valve 9, a fifth electrically controlled switching valve 6.1, and first bridging valve assembly modules 3.1 and 3.2.

[0061] The first working port of the fourth electrically controlled switching valve 9 is connected to the small chamber (i.e., the rod chamber) of the pitch cylinder, and the second working port of the fourth electrically controlled switching valve 9 is connected to the first working port of the pump 2. The fourth electrically controlled switching valve 9 may have the same configuration as the first electrically controlled switching valve 13, which will not be described in detail here.

[0062] The first working port of the fifth electrically controlled switching valve 6.1 can be connected to the large chamber (i.e., the rodless chamber) of the pitch cylinder, and the second working port of the fifth electrically controlled switching valve 6.1 can be connected to the second working port of the pump 2. The fifth electrically controlled switching valve 6.1 can have the same configuration as the first electrically controlled switching valve 13, which will not be described in detail here.

[0063] The first bridging valve group modules 3.1 and 3.2 may include a first valve 3.1 and a second valve 3.2 connected in series and bridging the second working port of the fourth solenoid valve 9 and the second working port of the fifth solenoid valve 6.1. A first node between the first valve 3.1 and the second valve 3.2 is connected to a hydraulic oil tank (e.g., a booster tank). The second valve 3.2 may be a solenoid valve. The hydraulic oil tank used in the closed-loop pump control and the hydraulic oil tank used when replenishing the accumulator may be the same hydraulic oil tank, and both may be booster tanks.

[0064] Under the propeller opening condition, the hydraulic pitch system forms a propeller opening oil supply path that passes sequentially through the first working port of pump 2, the fourth electrically controlled switch valve 9, and the small chamber of the pitch cylinder, and forms a propeller opening oil return path that passes sequentially through the large chamber of the pitch cylinder and the fifth electrically controlled switch valve 6.1.

[0065] In addition, the propeller return path may also include a first propeller return path from the second valve 3.2 to the hydraulic oil tank and a second propeller return path from the second working port of the fifth electronically controlled switch valve 6.1 to the second working port of the pump 2.

[0066] The first bridging valve assembly modules 3.1 and 3.2 can have different configurations. (Refer to...) Figures 1 to 5 Each of the first valve 3.1 and the second valve 3.2 can be a check valve, specifically a hydraulically controlled check valve. (See reference...) Figure 3 In the pitching operation, the hydraulic pitch system forms a pitching oil supply path sequentially through the first working port of pump 2, the fourth electrically controlled switch valve 9, and the small chamber of the pitch cylinder. At this time, the high-pressure oil at the inlet of the fourth electrically controlled switch valve 9 flows to the control port of the second valve 3.2, causing the second valve 3.2 to open. This forms a pitching return oil path sequentially through the large chamber of the pitch cylinder, the fifth electrically controlled switch valve 6.1, and the second valve 3.2, as well as a pitching return oil path sequentially through the large chamber of the pitch cylinder, the fifth electrically controlled switch valve 6.1, and pump 2. However, this disclosure is not limited to this; each of the first valve 3.1 and the second valve 3.2 can be a solenoid valve. Alternatively, the first valve 3.1 and the second valve 3.2 can also be implemented as a valve assembly, as long as the first valve 3.1 and the second valve 3.2 can perform switching functions. As an example, the second valve 3.2 can be an electrically controlled check valve, which can open the hydraulic path when needed.

[0067] Reference Figure 3 Under the propeller-opening condition, excess hydraulic oil in the large chamber of the pitch cylinder can be recovered to the booster tank through the second valve 3.2.

[0068] Differential propeller recovery During operation, wind turbine generators constantly adjust the blade angle, frequently performing pitch opening and retraction actions. When the load is less than the preset load (for example, when the blades are retracted at 1-10°), differential pitch retraction can be used to save energy. Differential pitch retraction involves extending the pitch cylinder, allowing hydraulic fluid from the rod chamber to flow into the rodless chamber. This achieves a small flow rate and fast action. The speed of the pitch cylinder is adjusted by controlling the flow rate of the hydraulic pump through the rotational speed of the motor in the motor-pump unit. During the entire pitch retraction process, the accumulator does not participate in the operation, thus solving the problem of energy loss caused by high voltage and low utilization of the accumulator.

[0069] Reference Figure 1 , Figure 3 and Figure 4 The electric pump assembly of this disclosure may further include a second bridging valve assembly module, which may include a sixth electrically controlled switching valve 6.2 bridging the first working port of the fourth electrically controlled switching valve 9 and the first working port of the fifth electrically controlled switching valve 6.1. However, the construction of the second bridging valve assembly module is not limited thereto, and any valve or valve assembly capable of switching may be applicable. As an example, the sixth electrically controlled switching valve 6.2 may have the same configuration as the first electrically controlled switching valve 13.

[0070] Reference Figure 1 and Figure 3 The hydraulic pitch system disclosed herein may further include a second check valve 7.1, the inlet of which may be connected to a hydraulic oil tank, and the outlet of which may be connected to the first working port of pump 2.

[0071] Reference Figure 4 The hydraulic pitch system forms a differential pitch recovery oil supply path that sequentially passes through the second working port of pump 2 and the fifth electrically controlled switch valve 6.1, and sequentially forms a differential pitch recovery circulation oil circuit that passes through the small chamber of the pitch cylinder, the sixth electrically controlled switch valve 6.2, and the large chamber of the pitch cylinder. It also forms a replenishment oil path from the hydraulic oil tank, the second check valve 7.1, and the first working port of pump 2. This allows the differential return oil, sequentially passing through the second working port of pump 2 and the fifth electrically controlled switch valve 6.1, to directly replenish the large chamber of the differential pitch recovery circulation oil circuit.

[0072] Additionally, refer to Figure 3 , Figure 4 and Figure 5The motor pump unit may also include a third bridging valve module. This third bridging valve module may include a third relief valve 4.1 and a fourth relief valve 4.2 connected in series and bridging the first working port of the fourth electrically controlled switch valve 9 and the first working port of the fifth electrically controlled switch valve 6.1. A second node between the third relief valve 4.1 and the fourth relief valve 4.2 is connected to the first node. The specific configuration of the third bridging valve module is not limited to this.

[0073] Normal stroke In some operating conditions, differential pitch recovery is not required, such as under heavy loads. In such cases, the differential pitch recovery torque may not meet the turbine root load torque requirements, necessitating non-differential pitch recovery. In this situation, the cylinder extends, and the oil flowing from the rod chamber is less than the oil required by the rodless chamber. Therefore, in addition to the closed-loop pump control drive of pump 2, additional oil needs to be supplied to the hydraulic circuit via a booster tank to achieve system oil balance. The system can switch between differential and normal pitch recovery based on the pitch angle or the load magnitude. In other words, the controller can control the energization and de-energization of various valves by detecting the pitch position or the magnitude of the blade root load, thereby achieving different control modes.

[0074] Reference Figure 5 The hydraulic pitch system forms a normal pitch supply path that passes through the second working port of pump 2, the fifth electronically controlled switch valve 6.1, and the large chamber of the pitch cylinder in sequence; a normal pitch return path that passes through the small chamber of the pitch cylinder, the fourth electronically controlled switch valve 9, and the first working port of pump 2 in sequence; and a replenishment path that passes through the hydraulic oil tank, the second check valve 7.1, and the first working port of pump 2 in sequence.

[0075] The first, second, and third bridging valve group modules of this disclosure are connected across the oil supply and return paths of the pitch cylinder. The specific configuration of the first, second, and third bridging valve group modules of this disclosure is not limited to the configuration described above. Those skilled in the art can select different configurations according to their needs; for example, more complex bridging valve group modules can be selected. In addition to the components shown in the accompanying drawings, each bridging valve group module may also include other components such as auxiliary components.

[0076] Reference Figures 2 to 5 The electric pump assembly disclosed herein may further include a fifth relief valve 4.4 and a sixth relief valve 4.3. A first node may be connected to the first working port of the fifth relief valve 4.4, and a second working port of the fifth electrically controlled switch valve 6.1 may be connected to the second working port of the fifth relief valve 4.4. The sixth relief valve 4.3 may be connected in parallel with the first valve 3.1, and the first working port of the sixth relief valve 4.3 is connected to both the second node and the first node, while the second working port of the sixth relief valve 4.3 may be connected to the first working port of the pump 2.

[0077] The third relief valve 4.1, the fourth relief valve 4.2, the fifth relief valve 4.3, and the sixth relief valve 4.4 are safety valves in the system oil circuit. They can ensure that the pressure in the oil circuit where the relevant relief valve is located does not exceed the predetermined pressure (e.g., 315 bar), thus protecting both the system valves and the hydraulic pump and preventing damage to the valves and the pump.

[0078] Furthermore, the electric pump assembly disclosed herein may also include other auxiliary components. For example, see reference... Figure 5 The electric motor pump assembly disclosed herein may further include a second pressure sensor 14.1 and a third pressure sensor 14.2. The second pressure sensor 14.1 may be connected to the node between the third relief valve 4.1 and the third electrically controlled switching valve 5, and the third pressure sensor 14.2 may be connected to the node between the fifth electrically controlled switching valve 6.1 and the fourth relief valve 4.2. The second pressure sensor 14.1 can be used to measure the oil pressure in the oil circuit connected to the small chamber of the pitch cylinder, and the third pressure sensor 14.2 can be used to measure the oil pressure in the oil circuit connected to the large chamber of the pitch cylinder. The oil pressure detected by the second pressure sensor 14.1 and the third pressure sensor 14.2 can be transmitted to the pitch controller in the main controller, and the pitch controller can control the relevant valves or pumps according to the detected oil pressure. In addition, although not shown, hydraulic oil on the high-pressure side can be supplied to the control port of the first valve 3.1, so that the first valve 3.1 can be opened or closed when the inlet oil pressure reaches the conduction oil pressure.

[0079] The hydraulic pitch control system disclosed herein can be integrated into a wind turbine generator set to drive the blades of the wind turbine generator set to adjust their pitch. The hydraulic pitch control system is housed within the hub of the wind turbine generator set. The telescopic rod of the pitch cylinder of the hydraulic pitch control system is movably connected (e.g., hinged) to the root of the wind turbine generator set blades, and the cylinder body end of the pitch cylinder is connected to the hub. Additionally, the wind turbine generator set can also control a pitch controller to achieve pitch adjustment using the hydraulic pitch control system.

[0080] The hydraulic pitch system disclosed herein may include multiple hydraulic cylinders, for example, two hydraulic cylinders (a first hydraulic cylinder and a second hydraulic cylinder). For example, the first hydraulic cylinder may push the inner wall of the blade root and the second hydraulic cylinder may pull the inner wall of the blade root, or the first hydraulic cylinder may pull the inner wall of the blade root and the second hydraulic cylinder may push the inner wall of the blade root to generate a rotational torque at the hub center point, causing the blade to rotate.

[0081] The hydraulic pitch system according to embodiments of this disclosure can reduce energy loss of the accumulator and improve energy utilization.

[0082] The hydraulic pitch system according to the embodiments of this disclosure can avoid conflicts between accumulator charging and pitch pump control, thereby improving system control efficiency.

[0083] The hydraulic pitch system according to embodiments of this disclosure can improve system safety.

[0084] The above description is merely a preferred embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any changes or substitutions that are easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A hydraulic variable pitch system for a wind turbine generator system, characterized by, include: Pitch cylinder; An electric pump unit, connected to the pitch cylinder, includes a motor and a pump connected to the motor, and controls the extension and retraction speed of the pitch cylinder by controlling the rotational speed of the motor. An accumulator group is connected to the motor pump group to provide the hydraulic oil required by the wind turbine generator set in emergency feathering conditions. The motor pump unit controls the normal opening and closing of the wind turbine generator set and provides initial fuel supply to the accumulator group.

2. The hydraulic pitch system of the wind turbine generator set according to claim 1, characterized in that, The hydraulic pitch system further includes an auxiliary motor pump, connected to the accumulator group and used for internal pressure replenishment of the accumulator group. The hydraulic pitch system also includes an accumulator safety valve assembly, which comprises: The first electrically controlled switching valve is connected in series between the accumulator group and the motor pump group; A first check valve is connected in series between the accumulator group and the auxiliary motor pump. The inlet of the first check valve is connected to the auxiliary motor pump, the outlet of the first check valve is connected to the accumulator group and the first working port of the first electrically controlled switch valve, and the second working port of the first electrically controlled switch valve is connected to the motor pump group.

3. The hydraulic pitch system of the wind turbine generator set according to claim 2, characterized in that, The accumulator safety valve group also includes a first relief valve, which is connected in parallel with the first electrically controlled switch valve, and the first relief valve is connected between the accumulator group and the hydraulic oil tank.

4. The hydraulic pitch system of the wind turbine generator set according to claim 1, characterized in that, The motor pump set also includes: The second electrically controlled switch valve has its first working port connected to the accumulator group and its second working port connected to the large chamber of the pitch cylinder. The third electrically controlled switch valve has its first working port connected to the small chamber of the pitch cylinder and its second working port connected to the hydraulic oil tank. The hydraulic pitch system forms an emergency feathering oil supply path that passes sequentially through the accumulator group, the second electrically controlled switch valve, and the large chamber of the pitch cylinder, and also forms an emergency feathering oil return path that passes through the small chamber of the pitch cylinder, the third electrically controlled switch valve, and the hydraulic oil tank.

5. The hydraulic pitch system of the wind turbine generator set according to claim 1, characterized in that, The motor pump set also includes: A fourth electrically controlled switching valve, wherein the first working port of the fourth electrically controlled switching valve is connected to the small chamber of the pitch cylinder, and the second working port of the fourth electrically controlled switching valve is connected to the first working port of the pump. The fifth electrically controlled switch valve has its first working port connected to the large chamber of the pitch cylinder, and its second working port connected to the second working port of the pump. The first bridging valve assembly module includes a first valve and a second valve connected in series and bridging the second working port of the fourth electrically controlled switching valve and the second working port of the fifth electrically controlled switching valve. A first node between the first valve and the second valve is connected to a hydraulic oil tank. The second valve is an electrically controlled valve. The hydraulic pitch system forms a pitch-starting oil supply path that sequentially passes through the first working port of the pump, the fourth electrically controlled switch valve, and the small chamber of the pitch cylinder, and forms a pitch-starting oil return path that sequentially passes through the large chamber of the pitch cylinder and the fifth electrically controlled switch valve. The pitch-starting oil return path also includes a first pitch-starting oil return path from the second valve to the hydraulic oil tank and a second pitch-starting oil return path from the second working port of the fifth electrically controlled switch valve to the second working port of the pump.

6. The hydraulic pitch system of the wind turbine generator set according to claim 5, characterized in that, The motor pump set also includes: The second bridging valve module includes a sixth electrically controlled switch valve bridging the first working port of the fourth electrically controlled switch valve and the first working port of the fifth electrically controlled switch valve. A second check valve, the inlet of which is connected to the hydraulic oil tank, and the outlet of which is connected to the first working port of the pump. The hydraulic pitch system forms a differential pitch recovery oil supply path that sequentially passes through the second working port of the pump and the fifth electrically controlled switch valve, and sequentially forms a differential pitch recovery circulation oil circuit that passes through the small chamber of the pitch cylinder, the sixth electrically controlled switch valve, and the large chamber of the pitch cylinder, and also forms a replenishment oil path from the hydraulic oil tank, the second check valve, and the first working port of the pump.

7. The hydraulic pitch system of the wind turbine generator set according to claim 6, characterized in that, The motor pump unit also includes a third bridging valve module, which includes a third relief valve and a fourth relief valve connected in series and bridging the first working port of the fourth solenoid valve and the first working port of the fifth solenoid valve. A second node between the third relief valve and the fourth relief valve is connected to the first node. The hydraulic pitch system forms a normal pitch supply path that passes sequentially through the second working port of the pump, the fifth solenoid valve, and the large chamber of the pitch cylinder; a normal pitch return path that passes sequentially through the small chamber of the pitch cylinder, the fourth solenoid valve, and the first working port of the pump; and a replenishment path that passes sequentially through the hydraulic oil tank, the second check valve, and the first working port of the pump.

8. The hydraulic pitch system of the wind turbine generator set according to claim 7, characterized in that, The motor pump set also includes: The fifth relief valve, the first node is connected to the first working port of the fifth relief valve, and the second working port of the fifth electrically controlled switch valve is connected to the second working port of the fifth relief valve; A sixth relief valve is connected in parallel with the first valve, and the first working port of the sixth relief valve is connected to the second node and the first node, and the second working port of the sixth relief valve is connected to the first working port of the pump.

9. The hydraulic pitch system of the wind turbine generator set according to claim 3, characterized in that, The hydraulic oil tank is a pressurized oil tank.

10. A hydraulic pitch control system for a wind turbine generator set, characterized in that, include: Pitch cylinder; The motor-pump assembly is connected to the pitch cylinder and controls the normal opening and closing of the wind turbine generator set. It includes a motor and a pump connected to the motor, and controls the extension and retraction speed of the pitch cylinder by controlling the speed of the motor. An accumulator group is connected to the motor pump group to provide the hydraulic oil required by the wind turbine generator set in emergency feathering conditions. The second electrically controlled switch valve has its first working port connected to the accumulator group and its second working port connected to the large chamber of the pitch cylinder. The second electrically controlled switch valve is disconnected during the emergency feathering condition of the wind turbine generator set's pitching operation, emergency feathering condition, and the emergency feathering condition within the normal pitching operation.

11. The hydraulic pitch system of the wind turbine generator set according to claim 10, characterized in that, The hydraulic pitch system further includes an auxiliary motor pump, connected to the accumulator group and used for internal pressure replenishment of the accumulator group. The hydraulic pitch system further includes a third electrically controlled switch valve, the first working port of which is connected to the small chamber of the pitch cylinder, and the second working port of which is connected to the hydraulic oil tank. In the emergency feathering condition, the hydraulic pitch system forms an emergency feathering oil supply path that passes sequentially through the accumulator group, the second electrically controlled switch valve, and the large chamber of the pitch cylinder, and forms an emergency feathering oil return path that passes through the small chamber of the pitch cylinder, the third electrically controlled switch valve, and the hydraulic oil tank.

12. The hydraulic pitch system of the wind turbine generator set according to claim 10, characterized in that, The motor pump set also includes: A fourth electrically controlled switching valve, wherein the first working port of the fourth electrically controlled switching valve is connected to the small chamber of the pitch cylinder, and the second working port of the fourth electrically controlled switching valve is connected to the first working port of the pump. The fifth electrically controlled switch valve has its first working port connected to the large chamber of the pitch cylinder, and its second working port connected to the second working port of the pump. The first bridging valve assembly module includes a first valve and a second valve connected in series and bridging the second working port of the fourth electrically controlled switching valve and the second working port of the fifth electrically controlled switching valve. A first node between the first valve and the second valve is connected to a hydraulic oil tank. The second valve is an electrically controlled valve. In the aforementioned pitch-starting condition, the hydraulic pitch system forms a pitch-starting oil supply path that sequentially passes through the first working port of the pump, the fourth electrically controlled switch valve, and the small chamber of the pitch cylinder, and forms a pitch-starting oil return path that sequentially passes through the large chamber of the pitch cylinder and the fifth electrically controlled switch valve. The pitch-starting oil return path also includes a first pitch-starting oil return path from the second valve to the hydraulic oil tank and a second pitch-starting oil return path from the second working port of the fifth electrically controlled switch valve to the second working port of the pump.

13. The hydraulic pitch system of the wind turbine generator set according to claim 12, characterized in that, The motor pump set also includes: The second bridging valve module includes a sixth electrically controlled switch valve bridging the first working port of the fourth electrically controlled switch valve and the first working port of the fifth electrically controlled switch valve. A second check valve, the inlet of which is connected to the hydraulic oil tank, and the outlet of which is connected to the first working port of the pump. The hydraulic pitch system forms a differential pitch recovery oil supply path that sequentially passes through the second working port of the pump and the fifth electrically controlled switch valve, and sequentially forms a differential pitch recovery circulation oil circuit that passes through the small chamber of the pitch cylinder, the sixth electrically controlled switch valve, and the large chamber of the pitch cylinder, and also forms a differential pitch recovery oil replenishment path that passes through the hydraulic oil tank, the second check valve, and the first working port of the pump.

14. The hydraulic pitch system of the wind turbine generator set according to claim 13, characterized in that, The motor pump unit also includes a third bridging valve module, which includes a third relief valve and a fourth relief valve connected in series and bridging the first working port of the fourth solenoid valve and the first working port of the fifth solenoid valve. The second node between the third relief valve and the fourth relief valve is connected to the first node. Under normal pitch control conditions, the hydraulic pitch system forms a normal pitch control oil supply path that passes sequentially through the second working port of the pump, the fifth solenoid valve, and the large chamber of the pitch cylinder; a normal pitch control oil return path that passes sequentially through the small chamber of the pitch cylinder, the fourth solenoid valve, and the first working port of the pump; and a normal pitch control oil replenishment path that passes sequentially through the hydraulic oil tank, the second check valve, and the first working port of the pump.

15. The hydraulic pitch system of the wind turbine generator set according to claim 14, characterized in that, The motor pump set also includes: The fifth relief valve, the first node is connected to the first working port of the fifth relief valve, and the second working port of the fifth electrically controlled switch valve is connected to the second working port of the fifth relief valve; A sixth relief valve is connected in parallel with the first valve, and the first working port of the sixth relief valve is connected to the second node and the first node, and the second working port of the sixth relief valve is connected to the first working port of the pump.

16. A wind turbine generator set, characterized in that, include: Wheel hub; A hydraulic pitch system, the hydraulic pitch system according to any one of claims 1-15, and installed in the hub; A pitch controller controls the hydraulic pitch system to achieve pitch control. A blade, the root of which is connected to the hub; The telescopic rod of the pitch cylinder of the hydraulic pitch system is movably connected to the root of the blade, and the cylinder body of the pitch cylinder of the hydraulic pitch system is connected to the hub.

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