Research On Converter Control Strategy Of Doubly-Fed Wind Generators When Grid Voltage Little Value Dropped

With the wind power capacity increasing, the proportion of the wind power systems are more and more large in the whole power systems; The interaction effect between wind power systems and the grid are also more and more obviously. Because wind power systems are mostly distributed in the complex terrain, climate changeful remote mountainous area, the distance of grid connection is farther, and the route is longer, thus the voltage fluctuation is larger. Especially, when the grid voltage dropped, the electromagnetic power of generators will get smaller. It is distinct from steam turbo generator and hydraulic generator, the active torque of wind generators is determined by wind speed. Due to uncontrollability of the wind speed, thereby, the wind power systems will be easier to oscillate.In order to solve the problem, the grid wind generators must be provided with the ability of low voltage ride through in actual grid wind power systems, the systems ensure that it can uninterrupted operate when the power grid broke down, prevent that the whole power systems unstable run when the wind power grid occur to take off.This paper, with the most widely used type doubly-fed wind generators as the research object, around the related issues of converter control strategy, to carry out further research, in order to improve low voltage ride through ability when the grid voltage little dropped.Based on the analysis of the basic principle and characteristics of Doubly-fed wind generators, this paper build mathematical model in two phase rotation coordinates.Based on the analysis of the influence of rotor side converter and nets side converter when the grid voltage little dropped, obtain the conclusion that rotor over current and fluctuations of DC bus voltage when the grid voltage little dropped. According to the conclusion, specific to the rotor side converter, this paper puts forward the improved control strategy of added compensation quantity of exciter current change on the basis of traditional control strategy, in order to improve control ability of rotor side converter for rotor current, effectively reduce that the rotor happened over current; Specific to the net side converter, this paper puts forward the improved control strategy that the load current and voltage disturbance as a feed-forward simultaneously introduce into the system on the basis of traditional feed-forward control strategy, in order to reduce the peak value of DC bus voltage fluctuations and keep the DC bus voltage stability; Thus up to improve low voltage ride through ability of the wind power systems when the grid voltage little dropped.Combined with the analysis and improvement of control strategy of the rotor converter and nets side converter in this paper, based on the temporary and steady simulation software PSCAD of power system, used simulation module of the wind farms in simulation software, sets up the simulation model of doubly-fed induction wind power system; And specific to the suggested improvement strategy of this paper, puts up simulation analysis and verification. The simulation results show that the above improved control strategy can effectively restrain rotor over current of wind power system, reduce wave amplitude of DC bus voltage, thus improve low voltage ride through ability when the grid voltage little dropped.