| Following the world trends of development and use in wind power, China wind powerdevelops rapidly. Wind power technology with the no pollution to the environment, becomesthe fastest growing clean energy in the global. Especially, with the wind power technologymatures and mega watt wind power generators introduce, wind power in the proportion ofpower grid also continues to be raised gradually. Low voltage ride-through (LVRT) becomesthe problem that our country necessary faced with some large-scale use of wind power.This paper, focusing on doubly-fed and direct-driven wind power generators LVRT invariable-speed wind power, research the relative control technology that be proved by thesimulation.Firstly, propose the rotor side converter control strategy based on the stator flux vectorcontrol method, achieving generator stator active power and reactive power decouplingcontrol, then discuss the basic characteristics of the wind turbine. According to the workingprinciple and characteristics of doubly-fed induction generator, the synchronizationcoordinates are given, which laid a foundation for following chapters.Secondly, in order to restrain the rotor of the doubly fed induction generator appearingover-voltage and over-current shock under the grid faults, the doubly-fed machine system hadbeen established, after considering the electric network fluctuation. The paper presented theimproved strategy of the stator flux vector to control the generator speed and stator outputreactive power. The numerical simulation in MATLAB shows that the method effectivelyimproved the control for the rotor current under grid fault; enhance the stability of powersystem and the ability of low voltage ride through.Thirdly, static synchronous compensator (STATCOM) based on sliding mode controlstrategy is proposed to improve the wind power system’s low voltage ride through (LVRT)capability on double fed induction generator (DFIG) wind power system, as the power gridvoltage drop depth.The principle of STATCOM and characteristics on sliding mode variablestructure strategy are presented. Also，the simulation model of the whole system includingSTATCOM was established. Simulation results show that STATCOM based on sliding modecontrol strategy, as voltage faulted, effectively restrain such a phenomena that Dc bus voltagepressure, rotor current surge and reactive power fluctuation，which improved grid powerquality and LVRT capability.Fourthly, in order to enhance the performance of direct-drive permanent magnet windpower generation system，a new type of sodium polysulfide-bromide redox flow battery(PSB)energy storage system (ESS) is added at DC-side of the converter．A detailed description ofPMSG and its controller systems were presented. Correspondingly, the ESS is improved andthe control strategy of bi-directional converter is developed．The simulation model isestablished，and the dynamic response process and operation characteristics are analyzed. The simulation results show that PBS ESS can balance the demand for power grid when the windrapidly changes and smooth the fluctuation of generator output power, so that theperformances of grid connected operation and LVRT are effectively improved．... |
