Research On Flux-Weakening Control Strategy For Direct-Drive Permanent Magnet Wind Power Generation System With Fixed Pitch

At present,the grid-connected direct-drive permanent-magnetic wind turbine is mainly composed of variable-pitch wind turbine and fixed-pitch wind turbine.Variable pitch wind turbine requires a set of pitch adjustment structures to operate at constant power range above the rated wind speed,which increasing the complexity of the control system and the servo system.Fixed pitch wind turbine eliminates the complexity of the pitch adjustment system,so the unit structure is simple,high reliability,and is still widely used.However,when the wind turbine is running from the rated wind speed to the cut-out wind speed range,it is usually necessary to reduce the wind power utilization factor by reducing the wind power utilization factor to maintain the power constant,which requires the generator and the converter to have sufficient power quantity to meet the needs of low-speed large torque.In view of this,this paper designs a new control strategy,which reduces the wind power utilization factor in the high wind speed area by increasing the wind speed of the wind turbine to keep its power constant,and introduces the voltage closed-loop current leading angle flux-weakening control strategy to achieve the rated wind speed above the interval generator power constant control,thereby effectively reducing the converter power margin.The structure of this paper is as follows:Firstly,the power control technology of wind turbine and the research status of direct drive permanent magnet wind power generation system are introduced.At the same time,the present situation of the theory of flux-weakening is also introduced.Based on the full power converter technology,the mathematical model of the wind turbine,the mathematical model of PMSM and the mathematical model of the grid side PWM converter are established respectively.This paper focuses on the new power control strategy of the wind turbine and detailed description of the control strategy of the new type direct drive permanent magnet synchronous wind power generation system.Then,this paper introduces the principle of flux-weakening control and analyzes the influence of the motor parameters on the flux-weakening properties.In the realization of the weak magnetic strategy,this paper uses the voltage closed-loop current leading angle flux-weakening control strategy,which can realize the smooth transition from constant torque state to constant power state.On this basis,the weak magnetic control process of the machine side and the grid side converter is analyzed and simulated by Matlab/Simulink toolbox.At the same time,through the experimental platform,the application of the voltage closed-loop current leading angle flux-weakening control strategy in the off-grid permanent magnet synchronous generator has been verified.Finally,in order to expand the constant power operation range of the permanent magnet synchronous generator,the wind speed of the wind turbine is increased to reduce the air volume of the system in the high wind speed area,so as to improve the power generation of the system,a new method based on space vector pulse width modulation and a new over modulation algorithm is designed.The algorithm is much simpler and quicker than the traditional overmodulation algorithm,and it does not require additional hardware input.It only needs to add a time processing module on the basis of conventional SVPWM.The over modulation algorithm,combined with the voltage closed-loop current leading angle flux-weakening control algorithm,which is embedded into the fixed pitch direct drive permanent magnet wind power generation system,simulation and analysis using Matlab/Simulink toolbox.