Research Of The Control Strategy Of Back To Back Converter For Direct-driven Wind Power System

Wind energy source is an energy of green、clean、non-Polluting, andis one of the fastest growing renewable energy which hasgained a high profile on international range. Wind power generationsystem is an important device which is able to achieve the wind energyinto the electric energy, full-power converter is an important part of thewind power generation system to realize the energy fed into the grid,research on full-power converter control technology receives the attentionof scholars from various countries. The direct drive wind power systemeliminates the gearbox, which will not only improve system efficiency,but also reduce the cost of investment and maintenance; it is the trend ofwind power technology and the current research. This paper mainlystudies the full power converter control strategy of direct drive windpower system.This paper established the mathematical model of each part of directdrive permanent magnet wind turbine generator system, it focuses on thestructure of back-to-back PWM converter topological, and the PIcontroller is used as current controller. The double close loop controlstrategy based on rotor flux oriented is chosen in the generator side, andthe double close loop control strategy based on the grid voltage orientedis chosen in the grid side. Then the simulation results show that thegenerator can follow the wind speed, capture the maximum wind energy;the gird-side can maintain the DC bus voltage stability, achieve the activepower and the reactive power decoupling.The conventional PI controller can only achieve to track DC signalwith no error, so coordinate transform are need, which is lead to increasethe complexity of system structure and the difficulty of the controlalgorithm; in order to improve the dynamic performance of the system,the cross-coupling term and former feed-forward compensation term inassociation with temperature and the circuit parameters are increased, thatwill reduce the stability of the system. Because of the limitation oftraditional PI controller, a proportional integral resonant (PR) controller was proposed. The PR controller can realize no static error adjustmenttracking when the input signal is AC signal in the stationary coordinatesystem. Based on analyzing the basic principle and the performancecharacteristics in-depth of PR controller, an improved PR controller isproposed，then that used in direct-drive Permanente magnet wind turbinegenerator system. The vector control strategy used in generator side andgrid side based on PR controller and the simulation model is built byMatlab/simulink. The simulation results comparison of the PI controlmethod show the effectiveness and superiority of vector control strategybased on PR controller.