Variable pitch system and wind turbine generator system

Abstract

This invention provides a pitch control system and a wind turbine generator set. The pitch control system includes a pitch drive unit, which comprises a first hydraulic cylinder, a second hydraulic cylinder, and a main oil circuit. One of the first and second hydraulic cylinders is a digital hydraulic cylinder, and the digital hydraulic cylinder includes a digital directional valve. The other of the first and second hydraulic cylinders is connected to the digital directional valve. The main oil circuit supplies oil to both the first and second hydraulic cylinders, thereby simultaneously controlling their extension and retraction movements via the digital directional valve. The pitch control system provided according to this invention, while ensuring the basic functions of pitch control, achieves improved control efficiency due to its fast response speed and high control precision.

Description

Technical Field

[0001] This utility model relates to the field of wind power generation technology, and in particular to a pitch control system and a wind turbine generator set. Background Technology

[0002] Hydraulic pitch control refers to the use of a hydraulic transmission system to drive changes in the pitch angle of a wind turbine generator, thereby maximizing power generation efficiency under different wind speed conditions while ensuring the safe and stable operation of the wind turbine generator.

[0003] In existing technologies, hydraulic pitch control systems with proportional directional valves, high-speed switching valves, or servo valves are typically used to control hydraulic cylinders to drive blade pitch. While this achieves the basic purpose of pitch control, it suffers from the following problems:

[0004] Proportional directional valves, high-speed switching valves, or servo valves all have high requirements for the cleanliness of hydraulic oil. Long-term operation can easily lead to control deviations, hydraulic oil leakage, high operating energy consumption, and low control efficiency. Utility Model Content

[0005] The purpose of this invention is to provide a pitch control system and a wind turbine generator set to solve the problems of low control efficiency caused by the operation of existing hydraulic pitch control systems, which are prone to control deviations and have high energy consumption.

[0006] According to a first aspect of the present invention, the present invention provides a pitch control system, wherein the pitch control system includes a pitch drive unit, the pitch drive unit includes a first hydraulic cylinder, a second hydraulic cylinder and a main oil circuit, one of the first hydraulic cylinder and the second hydraulic cylinder is a digital hydraulic cylinder, the digital hydraulic cylinder includes a digital directional valve, the other of the first hydraulic cylinder and the second hydraulic cylinder is connected to the digital directional valve, and the main oil circuit is used to supply oil to the first hydraulic cylinder and the second hydraulic cylinder so as to simultaneously control the extension and retraction movements of the first hydraulic cylinder and the second hydraulic cylinder via the digital directional valve.

[0007] In some embodiments, the first hydraulic cylinder includes a first rod chamber and a first rodless chamber, the second hydraulic cylinder includes a second rod chamber and a second rodless chamber, and the digital directional valve includes a first working port, a second working port, a third working port, and a fourth working port; wherein the first rodless chamber and the second rod chamber are both connected to the third working port of the digital directional valve, and the first rod chamber and the second rodless chamber are both connected to the fourth working port of the digital directional valve, so that the main oil circuit can simultaneously control one of the first hydraulic cylinder and the second hydraulic cylinder to extend and the other to retract via the digital directional valve.

[0008] In some embodiments, the first working port is connected to the third working port, and the second working port is connected to the fourth working port, thereby forming a first passage between the digital directional valve, the first hydraulic cylinder, and the second hydraulic cylinder; or, the first working port is connected to the fourth working port, and the second working port is connected to the third working port, thereby forming a second passage between the digital directional valve, the first hydraulic cylinder, and the second hydraulic cylinder; wherein, the first working port is connected to the oil inlet to form an oil inlet path, the second working port is connected to the oil outlet to form a return path, the oil inlet path, the first passage, and the return path form the first oil passage of the pitch drive unit, the oil inlet path, the second passage, and the return path form the second oil passage of the pitch drive unit, and the first oil passage and the second oil passage form the main oil passage.

[0009] In some embodiments, the oil inlet circuit is provided with a plurality of first control valves for controlling the on / off state of the oil circuit, and the first passage and the second passage are provided with a plurality of second control valves and a plurality of third control valves for controlling the on / off state of the oil circuit.

[0010] In some embodiments, the pitch system further includes an emergency oil circuit and an accumulator group. One of the first rodless chamber and the second rod chamber, or the first rod chamber and the second rodless chamber, is controllably connected to the accumulator group to form an oil inlet channel for the emergency oil circuit. The other of the first rodless chamber and the second rod chamber, or the first rod chamber and the second rodless chamber, is controllably connected to the oil outlet to form an oil outlet channel for the emergency oil circuit. The oil inlet channel and the oil outlet channel form the emergency oil circuit, which operates separately from the main oil circuit.

[0011] In some embodiments, the pitch system further includes: a first control valve group and a second control valve group, wherein the first rodless chamber and the second rod chamber are connected to the accumulator group via the first control valve group, and the first rod chamber and the second rodless chamber are connected to the oil outlet via the second control valve group, wherein the first control valve group is capable of controlling the connection and disconnection between the first rodless chamber and the second rod chamber and the accumulator group, respectively, and the second control valve group is capable of controlling the connection and disconnection between the first rod chamber and the second rodless chamber and the oil outlet, respectively.

[0012] In some embodiments, the first rod chamber and the second rodless chamber are connected by a pipeline, and the fourth working port and the oil outlet channel are both connected to the pipeline.

[0013] In some embodiments, the accumulator group has an accumulator group port, and the inlet is connected to the accumulator group port so that hydraulic oil can be supplied to the accumulator group through the inlet and the accumulator group port.

[0014] In some embodiments, the pitch system further includes a differential oil passage connecting the oil outlet passage and the oil inlet passage, and is provided with a one-way control valve that allows hydraulic oil to flow between the oil outlet passage and the oil inlet passage.

[0015] In some embodiments, the pitch system further includes: an oil tank and a pump unit, for recovering hydraulic oil from the oil outlet, and the pump unit delivering hydraulic oil from the oil tank toward the oil inlet.

[0016] In some embodiments, the pitch system includes a pitch bearing for connecting the hub and the blade, a first hydraulic cylinder and a second hydraulic cylinder are respectively mounted on one of the inner ring and the outer ring of the pitch bearing, and the telescopic rods of the first hydraulic cylinder and the second hydraulic cylinder are both connected to the other of the inner ring and the outer ring of the pitch bearing, and the blade is connected to the pitch bearing with the telescopic rods.

[0017] In some embodiments, the first hydraulic cylinder and the second hydraulic cylinder are respectively disposed on the outer ring of the pitch bearing, and the telescopic rods of the first hydraulic cylinder and the second hydraulic cylinder are both connected to the inner ring of the pitch bearing. The first hydraulic cylinder pushes the inner ring of the bearing and the second hydraulic cylinder pulls the inner ring of the bearing, or the first hydraulic cylinder pulls the inner ring of the bearing and the second hydraulic cylinder pushes the inner ring of the bearing, so as to drive the blade to pitch.

[0018] In some embodiments, a support plate is provided on the outer ring of the bearing, and the first hydraulic cylinder and the second hydraulic cylinder are rotatably mounted on the support plate.

[0019] In some embodiments, the support plate is provided with a rotating support shaft, and the first hydraulic cylinder and the second hydraulic cylinder are respectively disposed on the rotating support shaft.

[0020] According to a second aspect of the present invention, a wind turbine generator set includes a hub, blades, a pitch controller, and a pitch drive unit according to the pitch system described above. The pitch controller can control the first and second hydraulic cylinders of the pitch drive unit to extend and retract under the condition of oil supply from the main oil circuit, thereby enabling the blades to rotate relative to the hub.

[0021] According to the pitch control system and wind turbine generator provided in this embodiment, by simultaneously controlling the extension and retraction of the first and second hydraulic cylinders via a digital directional valve, the pitch drive unit can be used to adjust the blade angle of the wind turbine generator. Thus, while ensuring the basic functions of pitch control, it achieves improved control efficiency due to its fast response speed and high control precision. Furthermore, the pitch control system of this invention is simple, reliable, less sensitive to the cleanliness of the hydraulic oil, and has a low cost, meeting the long-term operation requirements of wind turbine generators. Attached Figure Description

[0022] The above and other aspects, features, and other advantages of the present invention will become clearer and more readily understood from the following detailed description of exemplary embodiments taken in conjunction with the accompanying drawings, in which:

[0023] Figure 1 This is a schematic diagram of the pitch system provided according to the first embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the pitch system in the open pitch state according to the first embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of the pitch control system in the pitch-retarded state according to the first embodiment of the present invention;

[0026] Figure 4 This is a schematic diagram of the pitch control system in emergency pitch recovery state according to the first embodiment of the present invention;

[0027] Figure 5 This is a structural schematic diagram of a pitch system and pitch bearing in a mating state according to the first embodiment of the present invention;

[0028] Figure 6 This is a structural schematic diagram of another matching state of the pitch system and pitch bearing provided according to the first embodiment of the present utility model.

[0029] Symbol Explanation

[0030] 10. Pitch drive unit; 11. First hydraulic cylinder; 111. First rod chamber; 112. First rodless chamber; 12. Second hydraulic cylinder; 121. Second rod chamber; 122. Second rodless chamber; 20. First passage; 21. First interface; 30. Second passage; 31. Second interface; 41. First control valve; 42. Second control valve; 43. Third control valve; 50. Oil inlet; 60. Oil outlet; P. First working port; T. Second working port; A. Third working port; B. Fourth working port; 70. Accumulator group oil port; 80. Oil inlet circuit; 90. Oil return circuit; 100. Differential oil circuit; 130. Oil inlet channel; 131. Third interface; 132. First control valve group; 140. Oil outlet channel; 141. Fourth interface; 142. Second control valve group; 150. Digital directional valve;

[0031] 200, Pitch bearing; 201, Inner ring of bearing; 202, Outer ring of bearing; 2021, Support plate; 2022, Rotary support shaft. Detailed Implementation

[0032] The following detailed descriptions are provided to aid the reader in gaining a comprehensive understanding of the methods, apparatus, and / or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatus, and / or systems described herein will become apparent upon understanding this disclosure. For example, the order of operations described herein is merely illustrative and is not limited to those orders set forth herein, but may be altered as will become clear upon understanding this disclosure, except for operations that must occur in a specific order. Furthermore, for clarity and conciseness, descriptions of features known in the art may be omitted.

[0033] The features described herein may be implemented in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein are provided only to illustrate some of the many possible ways of implementing the methods, apparatus and / or systems described herein, many of which will become clear upon understanding the disclosure of this utility model.

[0034] As used herein, the term “and / or” includes any one of the associated listed items and any combination of any two or more.

[0035] Although terms such as “first,” “second,” and “third” may be used herein to describe various components, assemblies, regions, layers, or parts, these components, assemblies, regions, layers, or parts should not be limited by these terms. Rather, these terms are used only to distinguish one component, assembly, region, layer, or part from another. Thus, without departing from the teaching of the examples described herein, the first component, first assembly, first region, first layer, or first part referred to as the first component, first assembly, first region, first layer, or first part may also be referred to as the second component, second assembly, second region, second layer, or second part.

[0036] In the specification, when an element such as a layer, region, or substrate is described as being "on" another element, "connected to," or "mounted to" another element, the element may be directly "on" another element, directly "connected to," or "mounted to" the other element, or one or more other elements may be present in between. Conversely, when an element is described as being "directly on" another element, "directly connected to," or "directly mounted to" another element, no other elements may be present in between.

[0037] The terminology used herein is for describing various examples only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. The terms “comprising,” “including,” and “having” indicate the presence of the described features, quantities, operations, components, elements, and / or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, operations, components, elements, and / or combinations thereof. The term “a plurality” represents any quantity of two or more.

[0038] The directional terms "upper," "lower," "inner," and "outer" used in this invention are all based on the reference orientation of the pitch system under normal operating conditions. This definition method will help ensure that readers or users can clearly understand the relative positional relationships of the various components and functions, and should not be construed as a limitation of this invention.

[0039] 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 invention pertains after understanding the invention. 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 invention, and shall not be interpreted in an idealized or overly formalistic manner.

[0040] Furthermore, in the description of the examples, detailed descriptions of well-known related components or functions will be omitted when it is believed that such detailed descriptions would lead to a vague interpretation of the present invention.

[0041] The inventive concept of this utility model is to apply digital hydraulic cylinders to the pitch system, and to design the oil circuit of the pitch system in combination with the requirements of various hydraulic pitch conditions. This can reduce costs, reduce the sensitivity of the pitch system to the cleanliness of hydraulic oil, and improve the control efficiency of the pitch system while meeting the basic requirements of pitch.

[0042] The following will combine Figures 1 to 6 The present invention will now be described in the form of a pitch system provided by an embodiment of the present invention.

[0043] Figure 1 This is a schematic diagram of the pitch system provided according to the first embodiment of the present invention. Figure 2 This is a schematic diagram of the pitch system in the open pitch state according to the first embodiment of this utility model. Figure 3 This is a schematic diagram of the pitch control system in the pitch-retarded state according to the first embodiment of this utility model. Figure 4 This is a schematic diagram of the pitch control system in emergency pitch retraction state according to the first embodiment of this utility model. Figure 5 This is a structural schematic diagram of a pitch system and pitch bearing in a mating state according to the first embodiment of the present invention; Figure 6 This is a structural schematic diagram of another matching state of the pitch system and pitch bearing provided according to the first embodiment of the present utility model.

[0044] According to a first aspect of the present invention, a pitch control system is provided, wherein, as Figure 1 , Figure 5 and Figure 6 As shown, the pitch system is used to adjust the blade angle of a wind turbine generator. The pitch system includes a pitch drive unit 10, which comprises a first hydraulic cylinder 11, a second hydraulic cylinder 12, and a main oil circuit. One of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 is a digital hydraulic cylinder, which includes a digital directional valve 150. The other of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 is connected to the digital directional valve 150. The main oil circuit supplies oil to the first hydraulic cylinder 11 and the second hydraulic cylinder 12, so as to simultaneously control the extension and retraction movements of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 via the digital directional valve 150.

[0045] According to the pitch system provided in this embodiment, one of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 is a digital hydraulic cylinder, and the other of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 is connected to a digital directional valve 150 of the digital hydraulic cylinder. Thus, by simultaneously controlling the extension and retraction movements of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 via the digital directional valve 150, the pitch drive unit 10 can be used to adjust the blade angle of the wind turbine generator set. This ensures the basic function of pitch control while providing fast response and high control precision, thereby improving the control efficiency of the pitch system. Furthermore, the pitch system of this invention is simple, reliable, less sensitive to the cleanliness of the hydraulic oil, and has a low cost, meeting the long-term operation requirements of wind turbine generator sets.

[0046] In this utility model, the digital directional valve 150 can be a three-position four-way valve, which adjusts the valve core opening by electromagnetic force or motor torque to achieve continuous flow regulation, and can switch between two extreme positions of the valve core to realize the oil circuit opening and closing. It has high control precision and can respond quickly, thereby improving the control efficiency of the pitch system.

[0047] According to this utility model, the extension and retraction movements of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are not specifically limited. Specifically, at the same time, the extension rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 can operate synchronously or asynchronously.

[0048] In the first embodiment of this utility model, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are arranged facing the same side and the telescopic rods do not operate synchronously. In this case, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 can push the blade to rotate relative to the hub by means of push-pull action, so as to realize the adjustment of the blade angle.

[0049] In the second embodiment of this utility model, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are arranged facing the same side and the telescopic rods can operate synchronously. In this case, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 can jointly drive the blade to rotate relative to the hub due to synchronous movement, so as to realize the adjustment of the blade angle.

[0050] In the third embodiment of this utility model, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are arranged facing different sides and the telescopic rods can operate synchronously. In this case, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 can push the blade to rotate relative to the hub by means of push-pull action, so as to realize the adjustment of the blade angle.

[0051] In the fourth embodiment of this utility model, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are arranged facing different sides and the telescopic rods do not move synchronously. In this case, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 move synchronously so as to jointly drive the blade to rotate relative to the hub, thereby realizing the adjustment of the blade angle.

[0052] In this invention, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are arranged facing the same side. As a specific example, see [reference needed]. Figure 5 and Figure 6 The telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 both face the same side.

[0053] In some embodiments of this invention, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 operate asynchronously. As a specific example, the first hydraulic cylinder 11 pushes the inner wall of the bearing inner ring 201 while the second hydraulic cylinder 12 pulls the inner wall of the bearing inner ring 201, or the first hydraulic cylinder 11 pulls the inner wall while the second hydraulic cylinder 12 pushes the inner wall. In other embodiments of this invention, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 operate synchronously. As a specific example, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 extend or retract simultaneously.

[0054] It should be noted that, for the sake of simplicity, the configuration of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 in the third and fourth embodiments is not shown in the figures. Although the configuration of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 in the third and fourth embodiments is not shown, those skilled in the art can clearly understand the third and fourth embodiments by referring to the configuration of the first and second embodiments.

[0055] In the following embodiments, the inventive concept of this utility model will be specifically described with the case that the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 operate asynchronously, while other embodiments will not be described in detail.

[0056] In some embodiments, the first hydraulic cylinder 11 includes a first rod chamber 111 and a first rodless chamber 112, the second hydraulic cylinder 12 includes a second rod chamber 121 and a second rodless chamber 122, and the digital directional valve 150 includes a first working port P, a second working port T, a third working port A, and a fourth working port B. The first rodless chamber 112 and the second rod chamber 121 are both connected to the third working port A of the digital directional valve 150, and the first rod chamber 111 and the second rodless chamber 122 are both connected to the fourth working port B of the digital directional valve 150. This allows the main hydraulic circuit to simultaneously control the extension of one of the first hydraulic cylinder 11 and the retraction of the other via the digital directional valve 150.

[0057] In these embodiments, by controlling one of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 to extend and the other to retract simultaneously via the main oil circuit through the digital directional valve 150, it is possible to facilitate asynchronous operation of the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12.

[0058] Specifically, the first working port P is connected to the third working port A, and the second working port T is connected to the fourth working port B, forming a first passage 20 together with the first hydraulic cylinder 11 and the second hydraulic cylinder 12; or, the first working port P is connected to the fourth working port B, and the second working port T is connected to the third working port A, forming a second passage 30 together with the first hydraulic cylinder 11 and the second hydraulic cylinder 12. The first working port P is connected to the oil inlet 50 to form an oil inlet path 80, and the second working port T is connected to the oil outlet 60 to form a return path 90. The oil inlet path 80, the first passage 20, and the return path 90 form the first oil passage of the pitch drive unit 10, and the oil inlet path 80, the second passage 30, and the return path 90 form the second oil passage of the pitch drive unit 10. The first and second oil passages form the main oil passage. Here, the oil inlet 50 is a high-pressure oil inlet.

[0059] In these embodiments, the main oil circuit is formed by the independently operating first and second oil circuits, which can meet the basic requirements of the wind turbine blades when opening and closing the pitch.

[0060] In some embodiments, the oil inlet circuit 80 is provided with a first control valve 41 for controlling the on / off state of the oil circuit, and the first passage 20 and the second passage 30 are provided with multiple second control valves 42 and multiple third control valves 43 for controlling the on / off state of the oil circuit. The first control valve 41, the second control valve 42, and the third control valve 43 are all valve groups with both a passage and a disconnection. As a specific example, the first control valve 41, the second control valve 42, and the third control valve 43 can all be single valves or combinations of multiple valve bodies. As a specific example, the first control valve 41, the second control valve 42, and the third control valve 43 are all solenoid directional valves or solenoid ball valves. It should be noted that this utility model does not limit the specific types of the first control valve 41, the second control valve 42, and the third control valve 43; any valve body that allows one passage and the other disconnection is acceptable. Those skilled in the art can select other types of valve bodies under the guidance of this utility model. Furthermore, it should be noted that the first and second oil circuits of the main oil circuit operate independently; one is used to open the propeller blades, and the other is used to retract the propeller blades. Taking the first oil circuit for retracting the pitch and the second oil circuit for opening the pitch as an example, during the pitch opening or retracting process, the pitch controller of the wind turbine generator can control the first control valve 41, the second control valve 42 and the third control valve 43 of the second oil circuit to open, while the other valves are closed.

[0061] As a specific example, the first control valve 41 is located between the oil inlet 50 and the digital directional valve 150, the second control valve 42 is located between the first interface 21 and the third working port A, and the third control valve 43 is located between the fourth working port B and the second interface 31.

[0062] In these embodiments, by setting a first control valve 41, a second control valve 42, and a third control valve 43 to control the on / off of the oil circuit, the pitch controller can easily switch to the required oil circuit based on actual needs during use, so that the blade angle can be adjusted based on wind direction, maintenance, and other requirements.

[0063] In some embodiments, the pitch system further includes an emergency oil circuit and an accumulator group, wherein the emergency oil circuit is an oil circuit that operates separately from the main oil circuit. Specifically, one of the first rodless chamber 112 and the second rod chamber 121, the first rod chamber 111 and the second rodless chamber 122 is controllably connected to the accumulator group, forming the oil inlet channel 130 of the emergency oil circuit; the other of the first rodless chamber 112 and the second rod chamber 121, the first rod chamber 111 and the second rodless chamber 122 is controllably connected to the oil outlet 60, forming the oil outlet channel 140 of the emergency oil circuit. The oil inlet channel 130 and the oil outlet channel 140 together form the emergency oil circuit.

[0064] In these embodiments, the pitch system incorporates an emergency hydraulic circuit. This circuit ensures the proper retraction of the blades in emergencies such as main hydraulic circuit maintenance or power outages, preventing damage from external factors. Furthermore, the emergency hydraulic circuit is internally connected via a controllable switching mechanism, thus avoiding interference with the operation of the main hydraulic circuit. Moreover, operating the emergency and main hydraulic circuits separately creates a dual-safety mechanism. Even if the main hydraulic circuit completely fails, the emergency hydraulic circuit can still operate independently via a one-way connection, ensuring that the unit's basic safety functions remain unaffected.

[0065] In some embodiments, the first hydraulic cylinder 11 is a digital hydraulic cylinder, and the second hydraulic cylinder 12 is a conventional hydraulic cylinder. The pitch system also includes: a first control valve group 132 and a second control valve group 142. The first rodless chamber 112 and the second rod chamber 121 are connected to the accumulator group through the first control valve group 132 to form an oil inlet channel 130 of the emergency oil circuit. The first rod chamber 111 and the second rodless chamber 122 are connected to the oil outlet 60 through the second control valve group 142 to form an oil outlet channel 140 of the emergency oil circuit. The oil inlet channel 130 and the oil outlet channel 140 form the emergency oil circuit.

[0066] More specifically, the first rod chamber 111 and the second rodless chamber 122 are connected by a pipeline, and the fourth working port B and the oil outlet channel 140 are both connected to the pipeline. In this way, during use, the oil path of the hydraulic oil flowing from the first rod chamber 111 and the second rodless chamber 122 can be selected according to actual needs, and it is a redundant design to cope with various emergencies.

[0067] In some embodiments, the accumulator group has an accumulator group port 70 and an inlet port 50 connected to the accumulator group port 70, so that hydraulic oil can be supplied to the accumulator group through the inlet port 50 and the accumulator group port 70.

[0068] In these embodiments, by connecting the accumulator group port 70 to the inlet port 50, hydraulic oil is supplied to the accumulator group through the inlet port 50 and the accumulator group port 70, thereby ensuring that the accumulator group can store sufficient hydraulic energy and absorb pressure pulsations. In an emergency, the accumulator group can quickly release the stored energy to provide power support for the emergency hydraulic circuit, ensuring the timely operation of the emergency hydraulic circuit and guaranteeing the emergency response capability of the pitch system.

[0069] According to this application, the pitch system also includes a pressure relief oil circuit for protecting the first hydraulic cylinder 11 and the second hydraulic cylinder 12. The pressure relief oil circuit connects the oil outlet passage 140 and the accumulator group port 70, and is equipped with a relief valve. When the maximum pressure of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 does not exceed the relief pressure (the maximum load capacity of the cylinder), the relief valve closes. In this case, the oil flows from the oil outlet passage 140 to the oil outlet port 60 through the corresponding second control valve group 142. When the maximum pressure of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 exceeds the relief pressure (the maximum load capacity of the cylinder), the relief valve opens, allowing a portion of the hydraulic oil in the oil outlet passage 140 to flow to the accumulator and another portion to flow to the oil outlet port 60, achieving the effect of pressure relief.

[0070] The connection position of the pressure relief oil circuit on the oil outlet channel 140 can be set at any position on the oil outlet channel 140, for example, but not limited to, between the fourth interface 141 and the second control valve group 142, or between the valves of the second control valve group 142.

[0071] In some embodiments, the pitch system further includes a differential oil passage 100, which connects an oil outlet passage 140 and an oil inlet passage 80, and is provided with a one-way control valve that allows hydraulic oil to flow between the oil inlet passage 80 and the oil outlet passage 80.

[0072] In these embodiments, by setting up a differential oil circuit 100 and using the differential oil circuit 100 to connect the oil outlet channel 140 of the emergency oil circuit unidirectionally to the oil inlet channel of the main oil circuit, hydraulic oil can be quickly replenished. Specifically, when the main oil circuit loses pressure or has insufficient flow, the emergency oil circuit can quickly replenish hydraulic oil to the main oil circuit through a unidirectional connection to maintain system pressure and ensure that the blades can complete critical operations such as emergency feathering, avoiding safety accidents such as turbine stall and runaway. In addition, the unidirectional connection ensures that the emergency oil circuit prioritizes emergency needs. Even if the main oil circuit fails partially, the emergency oil circuit can still provide power to critical actuators through a unidirectional connection, ensuring the safe shutdown of the unit. Furthermore, in emergency situations, the differential oil circuit can work in conjunction with the emergency oil circuit to further improve the blade adjustment speed, shorten the response time, and further improve the control efficiency of the pitch system.

[0073] In some embodiments, the pitch system further includes an oil tank and a pump unit, wherein the oil tank recovers hydraulic oil from the oil outlet 60, and the pump unit delivers hydraulic oil from the oil tank toward the oil inlet 50 as a source of hydraulic oil in each oil circuit.

[0074] The pitch system according to this utility model will now be described in detail with reference to the accompanying drawings.

[0075] In existing technologies, the required direction of blade rotation varies depending on the specific pitch control condition. Specifically, during pitch control, the pitch controller controls the hydraulic pitch system to drive the blades to rotate relative to the hub, increasing the blade's frontal area and improving wind power generation efficiency. During pitch retraction / feeding, the pitch controller controls the hydraulic pitch system to drive the blades to rotate in the opposite direction relative to the hub, retracting the blades to reduce the frontal area, maintain a stable blade rotation speed, or reduce the impact of high wind loads on the wind turbine generator.

[0076] According to this invention, a dual-cylinder push-pull structure is used to simultaneously provide driving force for the pitch system. During the pitch opening process, oil is introduced into the rod chamber of one hydraulic cylinder and returned to the rodless chamber, realizing the pull-joint point action; oil is introduced into the rodless chamber of the other hydraulic cylinder and returned to the rod chamber, realizing the push-joint point action. This push-pull motion achieves the pitch opening. The pitch retraction process is the reverse of the pitch opening process; specifically, by controlling the oil inlet and return directions of the hydraulic cylinders to be opposite to the pitch opening direction, the blades rotate relative to the hub to retract the pitch.

[0077] In addition, the pitch system also has an emergency pitch retraction function. In an emergency, all solenoid valves lose power, the digital directional valve 150 cannot switch, and the pump motor cannot supply high-pressure oil. At this time, the accumulator group supplies the stored high-pressure hydraulic oil to the valve group and hydraulic cylinder through the accumulator group oil port 70, driving the hydraulic cylinder piston rod to retract, realizing emergency pitch retraction and ensuring the safety of the wind turbine generator.

[0078] In this invention, by utilizing the digital directional valve of the digital hydraulic cylinder, the oil circuit of the pitch system is optimized based on the digital directional valve. This can reduce hydraulic oil leakage, lower the requirements for the cleanliness of the hydraulic oil, reduce the impact of the viscosity change of the hydraulic oil at low temperature on the transmission efficiency of the pitch system, and improve the reliability, stability and control efficiency of the pitch system.

[0079] Before starting the wind turbine, the pitch system performs self-checks and initialization to ensure all components are in normal working order. The main hydraulic circuit begins supplying oil, providing the necessary hydraulic power to the first and second hydraulic cylinders. Based on changes in wind speed and direction, the wind turbine's pitch controller sends commands to the pitch system, requesting adjustments to the blade angle. The pitch system precisely controls the flow of high-pressure oil into the rod-side or rodless-side chambers of the first and second hydraulic cylinders via electromagnetic and digital directional valves in the digital hydraulic pitch circuit. By controlling the extension or retraction of the hydraulic cylinder piston rods, the pitch system rotates the blades, thereby adjusting the blade angle to optimize wind energy capture. During normal pitch opening and retraction, the pump unit supplies high-pressure oil to the main hydraulic circuit through inlet 50. At this time, a portion of the hydraulic oil is used to fill the accumulator group and absorb pressure pulsations through accumulator group inlet 70.

[0080] In this exemplary embodiment, the first hydraulic cylinder 11 is a digital hydraulic cylinder, and the second hydraulic cylinder 12 is a conventional hydraulic cylinder. The telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are arranged on the same side of the pitch bearing 200.

[0081] Reference Figure 2 The first hydraulic cylinder 11 includes a first rod chamber 111 and a first rodless chamber 112, and the second hydraulic cylinder 12 includes a second rod chamber 121 and a second rodless chamber 122. The digital directional valve 150 includes a first working port P, a second working port T, a third working port A, and a fourth working port B. The first rodless chamber 112 and the second rod chamber 121 are both connected to the third working port A of the digital directional valve 150. The pitch system includes a first oil pipe, with its two ends connected to the first rodless chamber 112 and the second rod chamber 121, respectively, and a first interface 21 formed between the two ends. The first rod chamber 111 and the second rodless chamber 122 are both connected to the fourth working port B of the digital directional valve 150. The pitch system also includes a second oil pipe, with its two ends connected to the first rod chamber 111 and the second rodless chamber 122, respectively, and a second interface 31 formed between the two ends. (Refer to...) Figure 2When the digital directional valve 150 is energized, the first working port P connects to the fourth working port B, and the second working port T connects to the third working port A. The first interface 21 connects to the third working port A, and the second interface 31 connects to the fourth working port B. Thus, the digital directional valve 150, together with the internal passages of the first hydraulic cylinder 11 and the second hydraulic cylinder 12, constitutes the second passage 30. In this configuration, the oil inlet passage 80, the second passage 30, and the oil return passage 90 form the second oil passage of the pitch drive unit 10. The second oil passage simultaneously controls the extension of one of the first hydraulic cylinder 11 and the retraction of the other.

[0082] The hydraulic circuit is designed with the second oil circuit as the propeller start-up circuit. During normal propeller start-up, hydraulic oil flows from the inlet 50 through the inlet circuit 80 equipped with the first control valve 41 to the first working port P of the digital directional valve 150. Then, the hydraulic oil sequentially passes through the fourth working port B and the third control valve 43, and enters the first rod chamber 111 of the first hydraulic cylinder 11 and the second rodless chamber 122 of the second hydraulic cylinder 12, respectively. It then flows out from the first rodless chamber 112 of the first hydraulic cylinder and the second rod chamber 121 of the second hydraulic cylinder, respectively. At this time, the hydraulic oil then flows through the first interface 21 to the second working port T, and then flows to the outlet 60.

[0083] Reference Figure 3 When the digital directional valve 150 is energized, the first working port P connects to the third working port A, and the second working port T connects to the fourth working port B. The first interface 21 connects to the third working port A, and the second interface 31 connects to the fourth working port B, thus forming the first passage 20. This passage is formed jointly by the digital directional valve 150 and the interiors of the first hydraulic cylinder 11 and the second hydraulic cylinder 12. In this configuration, the oil inlet passage 80, the first passage 20, and the oil return passage 90 form the first oil passage of the pitch drive unit 10. The first oil passage simultaneously controls the extension of one of the first hydraulic cylinder 11 and the second hydraulic cylinder 12, while the other retracts. This extension and retraction is the reverse of the corresponding pitch opening process.

[0084] Continuing with the example above, using the first oil circuit as the oil circuit design for propeller retraction, during normal propeller retraction, hydraulic oil flows through the inlet port 50 and the inlet circuit 80 equipped with the first control valve 41 to the first working port P of the digital directional valve 150. Then, the hydraulic oil sequentially passes through the third working port A and the second control valve 42, and enters the first rodless chamber 112 of the first hydraulic cylinder and the second rod chamber 121 of the second hydraulic cylinder, respectively, before flowing out from the first rod chamber 111 of the first hydraulic cylinder and the second rodless chamber 122 of the second hydraulic cylinder. At this point, the hydraulic oil then flows through the second interface 31, the third control valve 43, the fourth working port B, and the second working port T to the outlet port 60. Here, to reduce back pressure, during propeller retraction, the hydraulic oil flowing out of the first rod chamber 111 of the first hydraulic cylinder and the second rodless chamber 122 of the second hydraulic cylinder can also flow to the outlet port 60 through the fourth interface 141 and the second control valve group 142. The return oil path can be selected based on actual needs, and this utility model does not impose excessive limitations on it.

[0085] In these embodiments, the hydraulic circuit settings in the two states described above can meet the basic requirements of blade pitch control, enabling the blades to adjust their angle of attack based on actual needs. During wind turbine operation, the pitch system continuously monitors parameters such as blade angle, wind speed, and wind direction. Based on the real-time monitored data, the pitch system dynamically adjusts the blade angle to ensure the wind turbine always operates in optimal condition. For example, at low wind speeds, increasing the blade angle of attack can improve power generation efficiency; at high wind speeds, decreasing the blade angle of attack can protect the wind turbine. It should be noted that during this process, the blade rotation angle in both processes does not exceed 90°. Thus, it can also be understood that the angle of rotation of the blades relative to the hub driven by the pitch drive unit does not exceed 90°.

[0086] In the event of extreme wind conditions, grid failures, or other emergencies, the wind turbine's pitch controller will trigger an emergency pitch retraction command. Continuing with the example above, the emergency pitch retraction process activates the emergency oil circuit, which operates separately from the main oil circuit. At this time, all solenoid valves lose power, the digital directional valve 150 cannot switch, and the pump motor cannot supply high-pressure oil.

[0087] Reference Figure 4The pitch system also includes a first control valve group 132 and a second control valve group 142. The first rodless chamber 112 and the second rod chamber 121 are connected to the accumulator group through the first control valve group 132, forming the inlet channel 130 of the emergency oil circuit. The first rod chamber 111 and the second rodless chamber 122 are connected to the outlet 60 through the second control valve group 142, forming the outlet channel 140 of the emergency oil circuit. The inlet channel 130 and the outlet channel 140 form the emergency oil circuit. The first control valve group 132 can control the connection and disconnection of the first rodless chamber 112 and the second rod chamber 121 with the accumulator group, respectively. The second control valve group 142 can control the connection and disconnection of the first rod chamber 111 and the second rodless chamber 122 with the outlet 60, respectively.

[0088] Continuing with the example above, in an emergency, the accumulator group will respond quickly, releasing the high-pressure hydraulic oil stored inside through the accumulator group port 70. This oil flows through the first control valve group 132 and the third interface 131 to the first rodless chamber 112 of the first hydraulic cylinder 11 and the second rod chamber 121 of the second hydraulic cylinder 12. The oil then flows out from the first rod chamber 111 of the first hydraulic cylinder 11 and the second rodless chamber 122 of the second hydraulic cylinder, and flows through the fourth interface 141 and the second control valve group 142 to the oil outlet 60. The high-pressure hydraulic oil drives the first and second hydraulic cylinders to actuate, causing the blades to rotate rapidly to a safe position, thus achieving emergency blade retraction. The emergency blade retraction function ensures the safety of the wind turbine generator set in an emergency, avoiding damage to the unit or safety accidents caused by blade loss of control.

[0089] Through the above specific examples, this utility model applies the digital directional valve of a digital hydraulic cylinder to the hydraulic circuit design of a pitch system. The dual hydraulic cylinder push-pull structure arrangement enables normal pitch opening / retraction and emergency pitch retraction functions, allowing the pitch system to accurately control the angle of the wind turbine blades, optimize wind energy capture, and ensure the safety of the unit in emergencies. Furthermore, it is reliable in operation and has low cost.

[0090] It should be noted that the above description has specifically exemplified the solution of this application by using the second oil circuit as the propeller-starting oil circuit and the first oil circuit as the propeller-retracting oil circuit. For another solution using the first oil circuit as the propeller-starting oil circuit and the second oil circuit as the propeller-retracting oil circuit, the only difference is the direction of hydraulic oil flow. Other aspects can be understood by referring to the exemplary description, and will not be repeated here.

[0091] According to this utility model, the pitch drive unit 10 is installed in the hub and directly or indirectly connected to the root of the blade to drive the blade to rotate relative to the hub, thereby meeting the wind turbine's requirements for adjusting the blade angle under different operating conditions.

[0092] In a preferred embodiment, the pitch system further includes a pitch bearing 200, which is mounted between the hub and the blade, serving as a connection hub between the two, allowing the blade to rotate relative to the hub, thereby facilitating pitch operation. In an exemplary embodiment, one of the hub and the blade is connected to the inner ring 201 of the pitch bearing 200, and the other is connected to the outer ring 202 of the pitch bearing 200. Thus, by rotating the inner ring 201 of the pitch bearing 200 relative to the outer ring 202, the blade can rotate relative to the hub.

[0093] In these embodiments, the pitch bearing 200 can greatly improve the flexibility of the blade rotation relative to the hub, so that the blade can rotate smoothly and steadily under the action of the pitch drive unit 10, reducing friction and resistance during rotation, and improving the efficiency and accuracy of pitch control.

[0094] In some embodiments, the first hydraulic cylinder 11 and the second hydraulic cylinder 12 can form a pitch drive unit 10 through a push-pull action, enabling the inner ring 201 of the bearing to rotate relative to the outer ring 202 of the bearing, thereby adjusting the blade angle. The first hydraulic cylinder 11 and the second hydraulic cylinder 12 can also work together to form the pitch drive unit 10, jointly applying a driving force to enable the inner ring 201 of the bearing to rotate relative to the outer ring 202 of the bearing, thereby adjusting the blade angle. The push-pull drive method offers faster response speeds or better system stability. As an example, push-pull drive can more flexibly adapt to different wind conditions and power generation needs, and can save hydraulic oil, reducing the requirement for oil tank volume in the pitch system. The cooperative working mode can achieve higher load capacity.

[0095] In this invention, the push-pull drive is suitable for scenarios requiring rapid and accurate adjustment of the blade angle, while the combined drive is suitable for situations requiring high torque or high load operation. This invention does not limit the specific drive mode; those skilled in the art can choose based on actual needs.

[0096] According to this utility model, the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are both installed on one of the inner ring 201 and the outer ring 202 of the pitch bearing 200, and the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are both connected to the other of the inner ring 201 and the outer ring 202 of the pitch bearing 200. The blade is connected to the pitch bearing 200 with the telescopic rods.

[0097] According to this utility model, the outer ring of the bearing is fixedly connected to the hub, and the inner ring of the bearing is fixedly connected to the blade. Thus, the pitch bearing 200 connects the hub and the blade. Specifically, the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are both mounted on the outer ring 202 of the bearing, and the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are both connected to the inner wall of the inner ring 201 of the pitch bearing 200. The telescopic movement of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 causes the blade to rotate relative to the hub.

[0098] More specifically, the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are rotatably mounted on the outer ring 202 of the pitch bearing 200, and the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are connected to the inner ring 201 of the pitch bearing 200. The first hydraulic cylinder 11 pushes the inner ring 201 and the second hydraulic cylinder 12 pulls the inner ring 201, or the first hydraulic cylinder 11 pulls the inner ring 201 and the second hydraulic cylinder 12 pushes the inner ring 201, so as to drive the blade to pitch.

[0099] like Figure 2 , Figure 3 , Figure 5 and Figure 6 As shown, the pitch control system utilizes the simultaneous output of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 to provide the driving force for pitch control. During the pitch opening process, oil enters the rod chamber of the first hydraulic cylinder 11 and returns oil to the rodless chamber, causing the telescopic rod to pull the inner ring 201 of the bearing. Similarly, oil enters the rodless chamber of the second hydraulic cylinder 12 and returns oil to the rod chamber, causing the telescopic rod to push the inner ring 201 of the bearing, thus generating a rotational torque around the hub center point and enabling the blades to open. During the pitch retraction process, the output directions of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are opposite to those during the pitch opening process, thereby enabling the blades to retract.

[0100] In these embodiments, a first hydraulic cylinder 11 and a second hydraulic cylinder 12 are used together to form the pitch drive unit 10. This allows the first hydraulic cylinder 11 and the second hydraulic cylinder 12 to meet the driving requirements of the blades. Furthermore, in this case, based on the driving requirements, the volume of the hydraulic cylinders can be reduced compared to the volume of a single hydraulic cylinder. This allows for more efficient use of the space within the wind turbine hub, avoiding the space occupancy reduction caused by excessively large individual cylinders. Additionally, driving the pitch drive unit 10 through a push-pull action allows for quick and accurate adjustment of the blade angle, suitable for the needs of wind turbine generators.

[0101] As a specific example, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are both connected to the inner ring 201 of the pitch bearing 200. The telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are on the same side and are respectively set on both sides of the central axis of the pitch bearing 200, and their extension lines intersect each other.

[0102] In these embodiments, based on this configuration and in conjunction with the hydraulic circuit design, the first hydraulic cylinder 11 and the second hydraulic cylinder 12 can drive the pitch drive unit 10 based on the push-pull action.

[0103] As a specific example, the inner wall of the bearing inner ring 201 is provided with a connecting plate, which protrudes radially relative to the inner wall of the bearing inner ring 201.

[0104] In some embodiments, the telescopic rod of the first hydraulic cylinder 11 and the telescopic rod of the second hydraulic cylinder 12 are respectively hinged to two regions on one surface of the connecting plate. These two regions may be in contact or may be spaced apart; the present invention does not impose further limitations on this.

[0105] In other embodiments, the telescopic rod of the first hydraulic cylinder 11 is hinged to the first surface of the connecting plate, and the telescopic rod of the second hydraulic cylinder 12 is hinged to the second surface of the connecting plate, wherein the first and second surfaces are opposite to each other. As an example, the telescopic rods of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are respectively hinged to two surfaces of the connecting plate in the thickness direction. Here, the hinge points of the two telescopic rods can be aligned along the thickness direction or have a certain deviation.

[0106] In some embodiments, a support plate 2021 is provided in the inner cavity of the bearing outer ring 202, and the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are rotatably mounted on the support plate 2021.

[0107] In these embodiments, by rotatably mounting the first hydraulic cylinder 11 and the second hydraulic cylinder 12 on the support plate 2021, the rotation of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 is more flexible, which facilitates the adjustment of the blade angle based on the actual wind conditions.

[0108] As an example, a rotating support shaft 2022 is provided on the support plate 2021, and the first hydraulic cylinder 11 and the second hydraulic cylinder 12 are respectively mounted on the rotating support shaft 2022. The rotating support shaft 2022 enables the first hydraulic cylinder 11 and the second hydraulic cylinder 12 to be rotatably mounted, resulting in a simple structure.

[0109] The pitch control system and wind turbine generator set provided in this embodiment of the invention enable the pitch drive unit to adjust the blade angle of the wind turbine generator set by simultaneously controlling the extension and retraction movements of the first hydraulic cylinder and the second hydraulic cylinder via a digital directional valve. In this way, while ensuring the basic function of pitch control, the control efficiency of the pitch control system can be improved due to its fast response speed and high control accuracy.

[0110] According to a second aspect of this utility model, a wind turbine generator set is disclosed. The wind turbine generator set includes a hub, blades, a pitch controller, and a pitch system as described above. The pitch controller controls the first hydraulic cylinder 11 and the second hydraulic cylinder 12 of the pitch drive unit 10 of the pitch system to extend and retract under oil supply from the main oil circuit, causing the blades to rotate relative to the hub, thereby driving the blades to pitch.

[0111] In an exemplary embodiment, the pitch system further includes a pitch bearing 200, which connects the hub and the blades, allowing the blades to rotate relative to the hub, thereby facilitating pitch control. In an exemplary embodiment, one of the hub and the blades is connected to the inner ring 201 of the pitch bearing 200, and the other is connected to the outer ring 202 of the pitch bearing 200. Thus, by rotating the inner ring 201 of the pitch bearing 200 relative to the outer ring 202, the blades can rotate relative to the hub.

[0112] According to the wind turbine generator set provided in this embodiment, one of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 of the pitch drive unit 10 is a digital hydraulic cylinder, and the other of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 is connected to the digital directional valve 150 of the digital hydraulic cylinder. Thus, by simultaneously controlling the extension and retraction movements of the first hydraulic cylinder 11 and the second hydraulic cylinder 12 via the digital directional valve 150, the pitch drive unit 10 can be used to adjust the blade angle of the wind turbine generator set. This ensures the basic function of pitch control while providing fast response and high control precision, thereby improving the control efficiency of the pitch system. Furthermore, the pitch system of this invention is simple, reliable, less sensitive to the cleanliness of the hydraulic oil, and has a low cost, meeting the long-term operation requirements of the wind turbine generator set.

Claims

1. A variable pitch system, characterized by The pitch system includes: The pitch drive unit (10) includes a first hydraulic cylinder (11), a second hydraulic cylinder (12), and a main oil circuit. One of the first hydraulic cylinder (11) and the second hydraulic cylinder (12) is a digital hydraulic cylinder. The digital hydraulic cylinder includes a digital directional valve (150). The other of the first hydraulic cylinder (11) and the second hydraulic cylinder (12) is connected to the digital directional valve (150). The main oil circuit is used to supply oil to the first hydraulic cylinder (11) and the second hydraulic cylinder (12) so as to simultaneously control the extension and retraction movements of the first hydraulic cylinder (11) and the second hydraulic cylinder (12) via the digital directional valve (150).

2. The variable pitch system of claim 1, wherein, The first hydraulic cylinder (11) includes a first rod chamber (111) and a first rodless chamber (112), the second hydraulic cylinder (12) includes a second rod chamber (121) and a second rodless chamber (122), and the digital directional valve (150) includes a first working port (P), a second working port (T), a third working port (A) and a fourth working port (B). The first rodless chamber (112) and the second rod chamber (121) are both connected to the third working port (A) of the digital directional valve (150), and the first rod chamber (111) and the second rodless chamber (122) are both connected to the fourth working port (B) of the digital directional valve (150), so that the main oil circuit can simultaneously control one of the first hydraulic cylinder (11) and the second hydraulic cylinder (12) to extend and the other to retract via the digital directional valve (150).

3. The variable pitch system of claim 2, wherein, The first working port (P) is connected to the third working port (A), and the second working port (T) is connected to the fourth working port (B), so that a first passage (20) is formed between the digital directional valve (150), the first hydraulic cylinder (11), and the second hydraulic cylinder (12); or, the first working port (P) is connected to the fourth working port (B), and the second working port (T) is connected to the third working port (A), so that a second passage (30) is formed between the digital directional valve (150), the first hydraulic cylinder (11), and the second hydraulic cylinder (12). Wherein, the first working port (P) is connected to the oil inlet (50) to form an oil inlet path (80), the second working port (T) is connected to the oil outlet (60) to form a return oil path (90), the oil inlet path (80), the first passage (20) and the return oil path (90) form the first oil passage of the pitch drive unit (10), the oil inlet path (80), the second passage (30) and the return oil path (90) form the second oil passage of the pitch drive unit (10), and the first oil passage and the second oil passage form the main oil passage.

4. The variable pitch system of claim 3, wherein, The oil inlet passage (80) is provided with a plurality of first control valves (41) for controlling the opening and closing of the oil passage, and the first passage (20) and the second passage (30) are provided with a plurality of second control valves (42) and a plurality of third control valves (43) for controlling the opening and closing of the oil passage.

5. The variable pitch system of claim 3, wherein, The pitch system also includes: Emergency fuel line; The accumulator group has one of the first rodless chamber (112) and the second rod chamber (121), the first rod chamber (111) and the second rodless chamber (122) connected to the accumulator group in an on / off controllable manner to form an oil inlet channel (130) of the emergency oil circuit. The other of the first rodless chamber (112) and the second rod chamber (121), the first rod chamber (111) and the second rodless chamber (122) is connected to the oil outlet (60) in an on / off controllable manner to form an oil outlet channel (140) of the emergency oil circuit. The oil inlet channel (130) and the oil outlet channel (140) form the emergency oil circuit, and the emergency oil circuit and the main oil circuit operate separately.

6. The variable pitch system of claim 5, wherein, The pitch system further includes a first control valve group (132) and a second control valve group (142). The first rodless chamber (112) and the second rod chamber (121) are connected to the accumulator group through the first control valve group (132). The first rod chamber (111) and the second rodless chamber (122) are connected to the oil outlet (60) through the second control valve group (142). The first control valve group (132) can control the connection and disconnection of the first rodless chamber (112) and the second rod chamber (121) with the accumulator group, respectively. The second control valve group (142) can control the connection and disconnection of the first rod chamber (111) and the second rodless chamber (122) with the oil outlet (60), respectively.

7. The variable pitch system of claim 6, wherein, The first rod chamber (111) and the second rodless chamber (122) are connected by a pipeline, and the fourth working port (B) and the oil outlet channel (140) are both connected to the pipeline.

8. The variable pitch system of claim 5, wherein, The accumulator group has an accumulator group port (70), and the inlet (50) is connected to the accumulator group port (70) so that hydraulic oil can be supplied to the accumulator group through the inlet (50) and the accumulator group port (70).

9. The variable pitch system of claim 5, wherein, The pitch system also includes a differential oil passage (100) that connects the oil outlet passage (140) and the oil inlet passage (80), and is provided with a one-way control valve that allows hydraulic oil to flow toward the oil inlet passage (80).

10. The variable pitch system of claim 3, wherein, The pitch system also includes: The oil tank recovers the hydraulic oil from the outlet (60); The pump unit delivers hydraulic oil from the tank toward the oil inlet (50).

11. The variable pitch system of any one of claims 1 to 10, wherein, The pitch system includes a pitch bearing for connecting the hub and the blades. The first hydraulic cylinder (11) and the second hydraulic cylinder (12) are both mounted on one of the inner ring (201) and the outer ring (202) of the pitch bearing (200). The telescopic rods of the first hydraulic cylinder (11) and the second hydraulic cylinder (12) are both connected to the other of the inner ring (201) and the outer ring (202) of the pitch bearing (200). The blades are connected to the pitch bearing (200) with the telescopic rods attached.

12. The variable pitch system of claim 11, wherein, The first hydraulic cylinder (11) and the second hydraulic cylinder (12) are respectively mounted on the outer ring (202) of the pitch bearing (200). The telescopic rods of the first hydraulic cylinder (11) and the second hydraulic cylinder (12) are both connected to the inner ring (201) of the pitch bearing (200). The first hydraulic cylinder (11) pushes the inner ring (201) and the second hydraulic cylinder (12) pulls the inner ring (201), or the first hydraulic cylinder (11) pulls the inner ring (201) and the second hydraulic cylinder (12) pushes the inner ring (201) to drive the blade to pitch.

13. The variable pitch system of claim 11, wherein, A support plate (2021) is provided on the outer ring (202) of the bearing. The first hydraulic cylinder (11) and the second hydraulic cylinder (12) are rotatably mounted on the support plate (2021). A rotating support shaft (2022) is provided on the support plate (2021). The first hydraulic cylinder (11) and the second hydraulic cylinder (12) are respectively mounted on the rotating support shaft (2022).

14. A wind power unit, characterized in that The wind turbine generator set includes a hub, blades, a pitch controller, and a pitch system according to any one of claims 1 to 13, wherein the pitch controller is capable of controlling the first hydraulic cylinder (11) and the second hydraulic cylinder (12) of the pitch drive unit (10) of the pitch system to extend and retract under the condition of oil supply from the main oil circuit, so that the blades rotate relative to the hub.

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