Simulation Research On Grid-connected Control System Of Small Direct-drive Permanent Magnet Synchronous Generator

With the promulgation of the national policy for vigorously developing clean and renewable energy,the renewable energy represented by wind power generation has attracted wide attention.However,the large-scale wind power generation systems are basically established in remote areas where the mean annual wind speed is above 6m/s at the moment.It is further suitable for most areas where the mean annual wind speed cannot meet the requirements of large-scale wind power generation to develop the small-scale wind power generation systems.At present,the development of off-grid operation technology is relatively mature,but the cost and maintain cost of this method is too high to implement widely.The Small-sized wind power generator units with high efficiency,energy saving and low cost have received more and more attention.Due to the characteristics of high efficiency and reliability,the Direct-drive permanent magnet synchronous generators are the mainstream models of small-scale grid-connected wind power generation.First,this thesis introduces the basic structure of a small direct-drive permanent magnet synchronous wind power grid-connected system,expounds the working models of the direct-drive permanent magnet synchronous generator and the PWM rectifier,and establishes their mathematical models respectively.According to the operating characteristics of the PWM rectifier,the principles of field-oriented control and the improved model prediction direct power control are introduced respectively,the delay compensation and duty cycle optimization calculation are added on the basis of the traditional model predictive direct power control.And they are severally applied to the controllable power generation system composed of a direct-drive permanent magnet synchronous generator and a PWM rectifier.A simulation experiment was conducted in MATLAB/Simulink,and the simulation results verified by the feasibility and effectiveness of the improved predictive direct power control.Secondly,this thesis researches the control system of the single-phase grid-connected inverter,and introduces the design of proportional resonance control and phase-locked loop technology in detail which are applied to the single-phase grid-connected inverter.A simulation experiment carried out in MATLAB/Simulink proves its control effect.Finally,this thesis proposes a two-stage full-control control strategy for a small direct-drive permanent magnet synchronous wind power grid-connected system.The former stage adopts full-control rectification,and the control method adopts modified model prediction direct power control.The latter stage adopts single-phase Grid-connected inverter,the outer loop uses proportional resonance control.The simulation results show that the proposed two-level full-control control strategy not only can realize the stable and efficient operation of the small direct-drive permanent magnet synchronous power generation grid-connected system,but can output the grid-connected current that is in phase with the grid voltage and has good sinusoidality.And it can output the same sinusoidal grid-connection current as the grid voltage.