Sliding Mode Extremum Seeking Control Without Steady-state Oscillation For The Maximum Power Point Tracking Of Wind Energy Conversion System

With the continuous consumption of fossil fuels,the continuous strengthening of the concept of sustainable development and the constant growth of energy demand,renewable energy development and utilization has become an inevitable trend.Wind energy has become one of the most potential renewable energy sources because of its advantages of no pollution and easy access.In this paper,the optimal output tracking of small permanent magnet wind power generation system is studied.The research is mainly carried out in the partial load region of wind turbine.The relationship between the optimal speed of permanent magnet generator,optimal output voltage and the maximum output power of the DC-side is deduced,and then combines it with the sliding mode extreme seeking control(SMESC)to achieve the best reference power tracking of wind power system.The main advantage of this method is that only voltage and current sensors are required and mechanical sensors for measuring speed or wind speed in conventional small permanent magnet wind power systems are omitted,resulting in cost savings and increased reliability of the wind power system.In addition,in order to improve the tracking accuracy of SMESC algorithm,the relationship between the steady-state amplitude of SMESC and its control parameters is deduced in this paper,and then the without steady-state oscillation SMESC algorithm is proposed.The proposed method uses the arc tangent function with adjustable slope instead of the binary sign function in the traditional SMESC algorithm.And the slope of the arctangent function is reduced in steady-state by adjusting the parameters in order to reduce the integral gain of SMESC algorithm.This can reduce or even eliminate the steady-state oscillation of the SMESC algorithm.The main advantage of the improved algorithm is that it can avoid the tradeoff between the tracking speed and the control accuracy of the traditional SMESC algorithm.Under the premise of not affecting the tracking speed,the actual output power and the oscillation amplitude of the rotational speed are reduced and thus to some extent reduce the mechanical fatigue of wind turbine.At the same time,the convergence of the improved algorithm is proved in detail by Lyapunov theorem.In order to convert the optimal reference power tracked by the SMESC algorithm into the switching control signal of the boost chopper,a power sliding mode controller is designed to replace the dual-loop PI controller in traditional WECS.Its main feature is the direct generation of switching signals,no carrier signal,with better tracking performance and simpler control structure,omitting the PI parameter adjustment process.This paper builds the simulation platform based on PSCAD / EMTDC software.The performance of improved SMESC and the power sliding mode controller are verified.The traditional SMESC algorithm,perturbation observation method and perturbation extreme seeking control algorithm are used as the contrast algorithm.Simulated analysis is carried out under the conditions of abrupt wind speed,random wind speed and load mutation.The results show that the method proposed in this paper has better performance and can improve the energy efficiency of wind power system.