Research On MPPT Method Of Directly-driven Permanent Magnet Synchronous Generator Based On Improved Sliding Mode Controller

With the increasingly serious global energy shortage,the status of clean energy has become more and more important.As a clean and pollution-free renewable energy,wind energy has attracted much attention because of its unique advantages,and the development prospect of the global wind power industry is broad.Direct driven permanent magnet synchronous generator(D-PMSG)has become the first choice in the wind power industry because of its small volume,low cost,high power generation efficiency,simple structure and strong reliability.How to scientifically improve the utilization efficiency of wind energy and optimize the maximum power point tracking(MPPT)process of D-PMSG system has also become a research hotspot in the wind power field.Based on the detailed analysis of the structure and principle of D-PMSG system,this paper deeply studies the maximum power tracking optimal control strategy of DPMSG system.The current maximum power tracking methods of D-PMSG system mainly include blade tip speed ratio method,optimal power curve method and mountain climbing search method.Based on these methods,the corresponding controller can be designed to optimize the MPPT process.As a common control method,sliding mode control(SMC)is widely used in nonlinear systems.Although the D-PMSG system based on traditional PI or traditional SMC controller can also track the maximum power point without static error in the steady state,there are some problems,such as slow response,too much chattering and too large overshoot.Therefore,based on the traditional exponential approach law,the speed regulation function is introduced,and a new approach law is designed to reduce the chattering in the sliding mode approach process and accelerate the convergence speed.The new approach law is applied to design the sliding mode speed controller for D-PMSG system and verify its stability.The D-PMSG system using the above controller still has load disturbance,which affects the motor speed and then the quality of MPPT.Therefore,this paper improves the sliding mode load torque observer(LTO)to observe the torque change in real time,and designs the MPPT strategy of wind power system based on SMC+LTO.In the design of torque observer,the smooth immune function),(xgδ function is used to adjust the variable gain.Compared with the traditional constant gain LTO,it reduces the demand for gain setting,accelerates the convergence speed,further weakens the fluctuation of observed torque,and converts it into reference current for feedforward compensation,which effectively suppresses the influence of load disturbance.Through the comparative experiment with traditional SMC on Matlab/Simulink,it is verified that the proposed strategy can realize the optimization of MPPT control of D-PMSG at rated wind speed.There are many external disturbances in D-PMSG system.In addition to the fluctuation of load torque,there are also the disturbances caused by the random change of wind speed,the influence of large inertia of fan,motor cogging torque and electromagnetic fluctuation torque,which lead to the problems of speed chattering and inaccurate power tracking process.Therefore,the disturbance torque observer(DTO)is designed in this paper.The external disturbances are regarded as load disturbances.At the same time,the first-order low-pass filter is introduced to improve the structure of the observer to reduce the error influence of speed differential link and high-frequency noise in the observer.At the same time,the MPPT strategy of wind power system based on SMC+DTO is designed.Through the comparative simulation with traditional PI and SMC controller on Matlab/Simulink under different wind speed conditions,it is verified that the designed control strategy has the good effect of fast tracking the maximum power and improving the utilization efficiency of wind energy.