Composition of hydraulic system of wind turbine generator set

A wind turbine has many moving parts. The nacelle rotates in the horizontal plane, always following the wind. The rotor rotates along the horizontal axis to generate power. In a variable pitch wind turbine, the blades that make up the rotor rotate around the central axis at the root to adapt to different wind conditions. When shutting down, the blade tips are thrown out to form damping. The hydraulic system is used to adjust the blade pitch, damping, shutdown, braking, etc.

1. Drive systems

Wind turbines use two drive systems, namely the braking system (deflector and main shaft a high-speed shaft slewing system) and the blade angle control and nacelle deflector slewing control system. The braking system is hydraulically controlled, while the blade and deflector controls are either hydraulically or electrically driven. The debate over which drive to use is no exception in wind turbine design. Whether hydraulic or electrical is used to control the blade angle output power, speed, or frequency response generally depends on the experience of the manufacturer.

2、Pitch control system

Blade angle (pitch) control system design should be considered when the wind generator encounters strong winds like typhoons, the unit can immediately stop running to interrupt the power supply, and at this time the blade needs to be controlled in parallel with the wind direction to ensure that the blade no longer rotates, after the power interruption, the unit’s energy storage system began to work, such as hydraulic accumulators or batteries. Hydraulic linear actuators (hydraulic cylinders) are used when controlled hydraulically, and electrical rotary actuators are used when controlled electrically. A hydraulic linear actuator is installed in the spindle, and the accumulator applied when stopping is also installed in the shaft.

The foreign hydraulic linear drive is the hydraulic, electronic, and electrical advantages of the hydraulic linear drive together (Electro-hydraulic system), referred to as a Hybrid system, this system is worth promoting energy-saving.

This integrated electric-hydraulic servo drive system consisting of hydraulic cylinders, hydraulic pumps, AC motors, accumulators, solenoid valves, sensors and power sources has the advantages of good dynamic performance, high output power, electrical install ability and maintainability. It can reduce the shortcomings of the hydraulic system, such as oil leakage and the effect of oil contamination, so that the reliability has been significantly improved, and when the power is interrupted, and can fully show the advantages of the hydraulic drive, that is, and hydraulic cylinders in series with the hydraulic cylinder, from the accumulator to obtain the supply of oil, so that the blades windward surface and the wind direction parallel to the impeller to stop the rotation. The hydraulic system is supplied directly by the hydraulic cylinder with position sensor and the gear pump with bidirectional oil supply, there is no valve in the middle, which reduces the pressure loss and oil leakage point, and this kind of system saves more than 40% energy than the servo control system.

In addition to the above Hybrid system, in foreign countries, blade angle control and deflector rotary also use linear electro-hydraulic servo-proportional hydraulic cylinders and return to the hydraulic proportional servo-driven motor. These systems have good dynamic and static performance, long life and other advantages, but in terms of saving energy and oil pollution is worse than the Hybrid system.

At present, the world’s major companies provide wind power hydraulic systems, widely used proportional servo closed-loop control systems. American Parker Company for wind power generation to provide a variety of hydraulic components and complete sets of wind power systems (including braking, deflector, and blade angle, etc. control system). The angle control system consists of specially designed hydraulic cylinders mounted in the hub of the wind turbine, the hydraulic cylinders are equipped with position sensors, and the cylinders are also integrated with the required hydraulic valves, each wind turbine is equipped with two or three sets of independent angle control systems (one for each blade). The system has the advantages of high reliability and safety, good dynamic and static performance, easy maintenance, and less leakage. The system uses high-performance proportional servo control which can be controlled by analog or digital signals. valve assemblies supplied by Parke have been rigorously tested in advance, which reduces installation and commissioning time, lowers costs, and saves on operation and maintenance costs. The hydraulic supply is provided by a separate hydraulic station with good filtration. The deflector slewing system has a good ability to keep the blades correctly centered in the wind direction, resulting in good performance for wind power generation.

parker offers both electric and hydraulic control systems. the hydraulic system allows for a more compact direct drive, with good overload protection to avoid component damage, and the system utilizes a closed-loop proportional servo control for good dynamic and static performance. parker also offers stand-alone systems to go along with the three systems mentioned above. Parker offers a separate, well-filtered, accumulator-supplied hydraulic power source to ensure safe stopping and unit safety in the event of power failure, in conjunction with all three systems.

Eaton company in the United States the wind power generation hydraulic control system has done a lot of research work, provided by the wind turbine blade angle closed-loop proportional control system can withstand high and low-temperature working conditions, and the system’s dynamic and static performance is good, the position of high precision.

Eaton company in the United States the wind power generation hydraulic control system has done a lot of research work, provided by the wind turbine blade angle closed-loop proportional control system can withstand high and low-temperature working conditions, and the system’s dynamic and static performance is good, the position of high precision.

Pitch Control System Example:

American Zond company’s Z- 40 hydraulic pitch control mechanism

The hydraulic pitch control mechanism belongs to the electro-hydraulic servo system, a typical pitch hydraulic actuator principle shown in the figure above. The paddle is connected to the hydraulic cylinder through a mechanical linkage mechanism, and the change in pitch angle is basically proportional to the displacement of the hydraulic cylinder. When the hydraulic cylinder piston rod to the left moves to the maximum position, the pitch angle of 88 °, while the piston to the right moves to the maximum position, the pitch angle of – 5 °. In the normal operation of the system, two three-way solenoid valves a, b, and c are energized, the hydraulic check valve is open, and the displacement of the hydraulic cylinder by the electro-hydraulic proportional valve reversing valve for precise control. When the wind speed is lower than the rated wind speed, no matter how the wind speed changes, the electro-hydraulic proportional reversing valve maintains the pitch angle of the paddle as 3 °, taking into account the leakage of the cylinder, the electro-hydraulic proportional reversing valve is fine-tuned to keep the pitch angle unchanged; when the wind speed is higher than the rated wind speed, according to the output power, the electro-hydraulic proportional reversing valve is used to change the output flow rate accurately, thus controlling the pitch angle of the blade, so that the output power is constant.

3、Hydraulic brake system

Nacelle and spindle a high-speed shaft rotary system using a hydraulic disc plate brake spindle high-speed shaft rotary system for the diameter of 60 ~ 100m blade braking. Sharp braking will cause strong vibration of the blade and rotary system and generate a large load. For this reason, it is necessary to provide feedback on the shaft’s rotational speed, and a method of adjusting the braking pressure by changing the amplitude (soft braking) can reduce the load several times.

Parker, Eaton, and Rexroth also produce disk vane brake systems that can withstand harsh conditions with good safety. Low leakage, small size, space-saving, and hydraulic source supplied from a separate hydraulic station.

Example of hydraulic braking system BONUS-150KW wind turbine brake hydraulic system in Denmark

（1）Starting boot:

when the control system issues a start command (can be automatic or manual), the motor starts immediately, the pressure from the “P” port into the valve block, the left half of the valve block for the tip of the pressure part; the right half of the disc brake to provide pressure. Motor starts at the same time, and the solenoid valves 10 #, and 11 # are charged by the connection into a closed state, the pressure oil can only be along the check valve 6 # -2 into the right half when the pressure value reaches 10.3MPa adjusted by the pressure switch 7 #, the valve 10 # open, the pressure began to enter the tip of the part so that the vane damping plate retracted, and at the same time will open the solenoid valve 12 #, close the solenoid valve 13 #, so that the circular brake disk Pressure unloading, ready for starting. When the leaf tip retracts the round brake disk is also released at the same time, and the motor stops rotating when the pressure of the pressure switch 15# reaches 7MPa. 17# and 18# are accumulators, which utilize the compressed gas to store the energy in the pressure oil, replenish the leakage due to the leaf tip resisting plate and the round brake disk in the process of operation, and reduce the frequent starting of the motor.

（2） Brake shutdown:

when the wind control system’s shutdown command is issued, the solenoid valve 10# is immediately energized, 11# is de-energized, closing the 10# solenoid valve and opening the 11# solenoid valve, and then de-energizing the 12# and 13# solenoid valves, i.e., opening the 13#, closing the 12#, as a result of which after the blade tip resistance plate is popped up, the round gate disc also operates the brakes to make the wind machine shutdown smoothly.

（3） Performance characteristics

From the design point of view, the braking torque of this wind turbine comes from two aspects, one is the blade tip damping brake, the other is the disc brake, and the braking torque is on the low-speed shaft, so the impact force on the gearbox during braking is small. In addition, there are the following features:

①smooth braking process, small vibration, due to the braking process first by the uniform distribution of the three blades of the tip of the leaf damping pole action, reduce the speed, and then by the disc brake braking, which makes the braking process becomes more stable.

② Brake mechanism is independent of each other: the brake system of the two sets of brake mechanisms is independent of each other, i.e., not due to a set of brake system failures caused by the other set of loss of working ability, for example, when the hydraulic system failure, pressure cannot be built up, disc brake cannot be normal braking, the tip of the leaf damping plate just because of the loss of pressure and was popped out to play the role of the damping brakes, which enhanced the reliability of the braking system.

③ with stall protection mechanism: the brake system is equipped with a centrifugal pressure cylinder at the root of the blade, when the wind turbine is out of control and the car, under the action of centrifugal force, makes the pressure rise to the adjustable value of the pressure switch 14 #, 14 # action and was opened, fly the car safety valve 16 # is connected, the pressure in the blade tip damping plate is released, the damping plate is popped out, and play a protective role.