Research On Sliding Mode Control Algorithm For Maximum Power Point Tracking Of Low Wind Speed Wind Turbine

Among many wind turbine control algorithms,sliding mode control method is widely used in maximum power point tracking(MPPT)stage because of its advantages in solving system parameter uncertainty,wind speed disturbance and other problems.In recent years,with the development of low wind speed wind field,the sliding mode control method combined with MPPT control of wind turbine has shown some shortcomings.On the one hand,the more violent turbulence degree and wind speed fluctuation make the speed tracking effect further weakened.On the other hand,the pursuit of high wind energy capture efficiency causes drastic fluctuations in output electromagnetic torque,which leads to the increase of system load and large mechanical losses of wind turbine system.Therefore,for the above two aspects of the problem.Three improvement strategies are proposed in this paper.The main achievements are listed as follows:To solve the problems of wind speed disturbance and large speed tracking error in the MPPT process of wind turbines,this paper proposes a complementary sliding mode control algorithm to improve the tracking response of the maximum power point of wind turbines.Firstly,a complementary sliding mode controller is constructed by combining the generalized sliding mode surface with complementary sliding mode surface,and it is proved by combining lyapunov stability control theory that the new controller can effectively ensure the convergence of speed tracking error.At the same time,the saturation function is used instead of the traditional symbol function,so as to reduce the chattering phenomenon during the switching control effectively.Secondly,in view of the uncertain disturbance caused by wind speed fluctuation in the control process,the wind speed disturbance term is separated by linearization method,and then the adaptive observer is designed to estimate the disturbance,and it is introduced into the sliding mode controller to implement disturbance compensation,so as to reduce the influence of the disturbance.Finally,the simulation results show that the improved algorithm can effectively deal with the above two problems and improve the efficiency of wind energy capture.In order to improve the wind energy capture efficiency in MPPT process,the problem of generator electromagnetic torque fluctuation is analyzed.In this paper,a sliding mode surface design method using rotational speed error as a variable isabandoned,and the wind electromechanical magnetic power output error is selected as a sliding mode variable.However,in the process of simulation verification,it is found that although the MPPT control method based on this idea can smooth the electromagnetic torque fluctuation of generator,it is at the cost of greater wind energy capture efficiency.Considering the integration effect in sliding mode control rate,the tracking response process can be accelerated.Therefore,this paper combines integral action with power tracking to design an MPPT controller that can achieve higher wind energy capture efficiency and lower load.The stability of the controller is verified by Lyapunov stability theory.The experimental results show that the new integrated sliding mode controller can not only smooth the electromagnetic torque of generator and reduce the system load,but also obtain higher wind energy capture efficiency.In order to reduce the influence of wind speed disturbance on the MPPT stage of wind turbine,the electromagnetic torque fluctuation of generator should be reduced as much as possible in improving wind energy capture.In this paper,an inverse integral sliding mode control strategy is proposed.First of all,based on the single mass model of wind turbine,the integral backward sliding mode controller is constructed by combining the integral control with the backward method.Secondly,because the wind speed disturbance will cause the fluctuation of the aerodynamic torque of the wind turbine,which may affect the output power of the system,the disturbance observer is used to estimate and observe the aerodynamic torque.Combined with Lyapunov theory,it is proved that the controller can meet the stability requirement.Finally,the simulation experiment shows that the integrated backward sliding mode controller can not only improve the wind energy capture efficiency in the maximum power point tracking stage of the wind turbine,but also further reduce the electromagnetic torque fluctuation of the generator and reduce the system load.