Study On Operation Control Of Doubly Fed Wind Power Converter Under Grid Fault

According to the operation of doubly fed wind power converter under the grid fault, the simulations are studied and the experiments are verified in this paper through theoretical analyses and improved methods. Some achievements of academic research and engineering application value are obtained.(1)The mathematical model of the doubly fed induction generator(DFIG) system in the three phase stationary coordinate system and the dq synchronous rotating coordinate system are established. The mathematical model of the grid side and the rotor side converter are derived and the common control strategies are made. And the transient responses of DFIG system under the grid fault are analyzed in detail.(2) The double second–order generalized integrator frequency locked loop(DSOGI-FLL) which can quickly separate the grid voltage positive and negative sequence has been designed. Proportional resonant(PR) controller with the harmonic compensation has been designed as well.The control strategies of grid side and rotor side converter have been put forward by combining the frequency locked loop and proportional resonant controller above. The overcurrent of the grid side converter has been induced and the bus voltage fluctuation has been effectively inhibited. The ability to suppress the harmonic current of the rotor side converter is improved, and the peak current of the fault is decreased obviously. The low voltage ride through(LVRT) function is realized. The correctness and effectiveness of the improved control strategies are verified by comparing analyses of simulations.(3)The cooperative control strategies of the grid side converter andthe machine side converter are designed in the case of the LVRT. The gird power is enhanced by increasing the reactive power output of the system.In the severe grid fault, the cooperative control of the crowbar circuit with the dynamic resistances which are connected in parallel is adopted. The protection principle of crowbar circuit is analyzed and the corresponding control strategy is designed. And one effective scheme of resistance selection and the selection of switching time have been provided for the crowbar circuit.(4) The design of hardware circuit and software program are carried out. The experiments have been verified on the experimental platform of the 7.5kW double fed induction generator.