The hydraulic system is a mechanical unit which realizes the power transmission and motion control with the pressure liquid as the medium.

The hydraulic system has the advantages of stable transmission, high power density, easy to realize stepless speed regulation, easy to change components and overload protection, and is widely used in large wind turbines.

Control of hydraulic power unit in wind power generation system In the fixed pitch wind turbine, the hydraulic system is mainly used for aerodynamic braking, mechanical braking, yaw drive and braking. In the variable pitch wind turbine, the hydraulic system is mainly used to control the pitch mechanism and mechanical braking, and also for yaw drive and braking.

It is also used for cooling and filtration of lubricating oil of gearbox, generator water cooling, temperature control of converter, switch engine room and driving crane, etc.

Overview of hydraulic system in wind power generation system Pressure shocks should be kept to a minimum, and pressure shocks or large pressure drops cannot lead to danger. Even in the case of power supply failure and recovery, safe working conditions must be ensured. The following external factors shall not affect the operation of the hydraulic system: (1) Salt and other contaminated media, (2) sand and Dust, (3) impurities, (4) external magnetic field, electromagnetic field and electric field, (5) sunlight, (6) vibration.

If the hydraulic system constitutes a part of the protection system, the power grid failure, external limit temperature should not endanger the operation of the system. The synchronous generator operates at constant speed, which is determined by the connected power grid frequency and is independent of the torque acting on it. The speed specified in the power grid frequency is what is commonly called synchronous speed. An asynchronous generator is also a generator that allows for certain deviations, that is, deviation from the speed specified by the power grid frequency. In other words, the rotational speed can vary with the torque applied. It is the most commonly used generator form in wind turbines. Variant of the winding rotor is commonly used. The deviation is defined as the difference between the speed of the generator and the speed determined by the power grid. A slip is sometimes given in the form of a percentage of the latter. If the maximum deviation is not more than 1%, the operating mode of the asynchronous generator is still due to the fixed speed, at this time the transfer is not big. If a larger slip is allowed, within 10%, this can be changed by electronic technology, such as a rotor current controller, then it can be reduced to a variable slip.

The variable pitch or stall control of a wind turbine means that it ensures that the generator does not exceed the allowable slip. The advantage of the variation is mainly reflected in the wind turbine to achieve the rated power. In the case of rated power, the power fluctuation is caused by the change of wind speed. When gust strikes the rotor of a wind turbine, the deviation can increase the speed of the generator to respond to Gust, without causing the increase of power generation.

Such a slip ensures smooth power output while maintaining the load on the blades, the spindle and the gear box. In the hydraulic system, the energy is transmitted and controlled by the liquid in the closed circuit under certain pressure. Use of hydraulic systems in wind turbines, such as hydraulic accumulators for blades to pitch. The hydraulic system must be equipped with protection against exceeding the maximum allowable pressure. Pressure relief valve can be used in this and can prevent the explosion of fatal accidents in fire accidents.

All parts of the hydraulic system must be easily assembled, adjusted and maintained.