Research On Pitch Servo System Of Permanent Magnet Direct-drive Wind Turbine

In response to the strategic goal of global energy sustainable development,the active development and utilization of clean renewable energy has become the main trend of today's society.Wind energy has been widely used in the field of new energy by virtue of its clean,low cost and reproducible advantages.In this paper,the variable pitch system of permanent magnet direct drive wind turbine is analyzed theoretically and studied from two aspects,one is the variable pitch system and the other is servo system.The variable pitch system of the wind turbine is based on the external natural wind velocity to obtain the pitch angle,and then the pitch angle is sent to the pitch servo system,and the pitch servo motor controls the blade angle of the wind turbine to complete the pitch.Firstly,the paper analyses and studies the variable pitch system of wind power generation,when the external wind speed is less than the rated wind speed,the win d turbine starts to work,at this time to maintain the pitch angle ?=0,to achieve maximum wind energy capture;When the external wind speed is larger than the rated wind speed,the pitch servo system starts to work,increases the bl ade pitch angle,reduces the system wind energy utilization to maintain the output power of the wind turbine in the vicinity of the rating.Using PMSM as variable pitch servo motor,the rotor structure and operating principle are studied,and the mathemati c model of PMSM in rotating coordinate system is deduced through the formula of coordinate change,and some common PMSM vector control methods are analyzed and compared.Then,the mathematical models of the main control system are introduced,including the natural wind speed model,the wind turbine model,the transmission system model and the variable pitch actuator model.The simulation model of the main control system of wind turbine variable pitch is set up in Matlab.Secondly,the position feedforward control variable Pitch servo system is studied.Firstly,the PID control variable pitch servo system is studied theoretically,and the simulation model verification is built in MATLAB.The simulation results show that the position response speed of PID control variable pitch servo system is slow and the ability of resisting load disturbance is very poor.Then,the position feedforward control is introduced into the PID control pitch servo system,the simulation results show that the PID control strategy will follow the position following lag;And the servo system can follow the given position quickly after adding position feedforward,without hysteresis,and improve the position response speed and the control precision of the servo system.Finally,the sliding mode variable structure control servo system is studied theoretically,and the simulation model is built in MATLAB,and the simulation results are analyzed: the sliding mode variable structure control system can realize the rapid response of the system,but the speed of the pitch servo motor is much higher than the rated speed.In addition,the amplitude of position and velocity fluctuation is still large when the load mutation occurs in the sliding mode control system.Finally,aiming at the load disturbance of the pitch servo system is large,as well as the traditional sliding mode variable structure used in variable pitch servo system speed uncontrollable problem,the improved sliding mode variable structure control servo system is studied,and a piecewise sliding mode variable structure controller with variable exponential reaching law and a reduced order load torque observer are designed.And the simulation model verification is built in MATLAB.The simulation results show that the improved sliding mo de variable structure control technology successfully solves the problem of speed uncontrollable,and also increases the system's ability of resisting load disturbance while realizing the fast performance of the pitch system.