Rotational Speed Control Strategy Of Direct-driven Pmsm Wind Turbine

Wind power generation technology plays an important role in solving the energy and environment problems.In the context of environmental protection and sustainable development,so much attention has been paid to develop it.Because the direct-driven wind turbine eliminates the gearbox and other vulnerable structures,and high energy density,high low voltage across ability of permanent magnet synchronous motor(PMSM),the direct-drive permanent magnet synchronous wind generator has high efficiency,high reliability,and low maintenance costs,and gradually becomes the main development direction of large-scale variable-speed constant-frequency wind turbine.Due to the non-linear nature of the direct-driven PMSM wind turbine system and unprescribed trajectory of the tracking speed at the time of tracking the maximum wind energy,in order to achieve a better speed tracking performance the adaptive control strategy of this nonlinear system has high practical value.This dissertation mainly studies the speed control problem of direct drive permanent magnet synchronous wind turbine under the condition of unprescribed wind speed.The mathematical model of direct-driven permanent magnet synchronous wind power generation system has been established,and the target of speed control of wind turbine has been analyzed.The simplified model and precise model has been studied respectively,and an adaptive speed tracking controller has been designed.The simplified third-order model is the most commonly used mathematical model in the study of speed control of wind turbines,in which the one-mass drive-train model is used to reduce the order of the system.Based on the assumption of periodic effective average wind speed and the structural characteristics of the system,the ideal current under steady tracking state can be considered as the output of an external system.Then,the adaptive internal model observer has been constructed by using the symmetry of the system,and then the Lyapunov stability theorem is used to determine the structure and parameters of the controller.When considering the disturbance of the voltage,in order to achieve better control effect,the model of the controlled object has been improved,and the speed controller with voltage disturbance rejection has been designed.In order to improve the accuracy of speed tracking,a more accurate two-mass drive-train model has been used in transmission part.As the system with this kind of model has five order,a coordinate transformation which can transforms the system into a low-triangular structure with zero dynamics has been used to reduce the difficulty of controller design.The state feedback controller has been designed by using backstepping method and output feedback controller has been realized by state observer.By using Lyapunov stability theorem,it has been proved that the output feedback controller can track the given speed trajectory.In order to make the system track the unprescribed speed track without steady state error,a controller with adaptive internal model has been designed.In this controller,the control input of the ideal steady state has been set as the output of an external system,and the actual control input was composed of the internal model output and a convergence term,which greatly simplifies the complexity of the controller.The simulation show that the adaptive internal model controller can track the optimal speed trajectory and realize the maximum power point tracking under the periodic wind speed condition.When taking the flexible deformation of the drive shaft into account,the controller based on two-mass drive-train model can achieve tracking project without steady state error.