Research On Control Strategy For Optimal Operation Of Stand-Alone Wind Turbines Based On Doubly-Fed Induction Generators

The power industry share of global energy consumption is increasing year by year, become the key of the energy structure change. Because of the low carbon energy is popular around the world, wind power is not to be ignored. Relative to the booming grid type wind power, a lonely island type wind power also has considerable development prospects. It is not only save resources and meet people’s need who without electricity, but also become the important supplement of the smart grid. This paper select doubly-fed wind power generator as the research object which is widely used in wind power, study the optimizing control strategy of stand alone, in order to improve the quality of output power and utilization rate of wind power.Firstly, the mechanism and characteristics of the main features of improved system topology is expounded. The model of doubly-fed induction generator(DFIG) and stator convertor in the synchronous reference frame is described, which is the theoretical basis for the research. A simulation experimental platform is developed by Matlab/Simulink, which provides experimental basis for the research.Then, basing on the stator flux linkage force orientation way which is commonly used, the double closed-loop vector control is developed, of which the outer ring is the stator voltage, in order to stabilize the stator output voltage of stand-alone DFIG. Simulation results show that the proposed control scheme effectively achieves the stator voltage precise tracking for a given voltage, the deficiency of the indirect current control is solved, but the voltage fluctuation amplitude is bigger when wind speed changing and load switching, and the parameter robustness is not strong.A sliding-mode-direct-voltage-control of stand-alone DFIG is proposed. Based on the analysis result of mathematical model of stand-alone DFIG by the relative gain array, the relationship for direct control between rotor voltage and stator voltage in synchronous rotating coordinates is derived, and the control structure is simplified. In order to reduce the voltage fluctuation when wind speed changing and load switching and doesn’t depends on the accurately generator parameters, sliding-mode controller is designed. The operational performances of stand-alone DFIG with the corresponding vector control are analyzed and compared by using Matlab/Simulink. The results have shown the effectiveness of suppress the voltage fluctuation when wind speed changing and load switching, and the strong robustness of the control system.Lastly, a capture strategy of maximizing the wind energy for stand-alone DFIG is proposed. A new topological structure of stand-alone DFIG system is used, controlling the the power of stator convertor to make motor speed change with wind speed in order to capture maximal wind energy. The simulation results have shown the correctness and feasibility of the proposed control strategy.