Research On The Optimal Control Of Doubly-Fed Induction Generators Under Asymmetrical Grid Conditions

Wind power is one of the important clean and renewable energy forms. It is very important to the national energy reform and adjustment. Because of the characteristics of DFIG, it has been widely used in the field of wind power. At present, the research of the DFIG under unbalanced voltage condition has many achievements. In a variety of actual environment, the grid voltage and load unbalance is happened occasionally which affects seriously the target parameters of the control system. Therefore, the research of the DFIG under unbalanced voltage condition is the key to the question. This paper has carried on the thorough research from the conventional PI control of the grid voltage balance condition to the unbalanced voltage condition. According to the different control targets under unbalanced voltage condition, the paper studies the optimization control strategy. The theory method is verified by simulation and experiment. The control method has certain theoretical research and practical application value.First of all, the mathematical modeling of the DFIG’s RSC and GSC under balanced voltage condition is established and analyzed. The adopted control method of the RSC and GSC is the PI controller. The RSC and GSC use conventional stator voltage oriented and the grid voltage oriented respectively. The paper builds the matlab/simulink of the RSC and GSC,and carry out the simulation of power control. Under the condition of power grid voltage unbalance, the mathematical modeling of the DFIG’s RSC and GSC under balanced voltage condition is established. By means of analysis of electromagnetic calorimeter (voltage, current or magnetic chain, etc.) that the cause of the double frequency fluctuations, puts forward a new simple compensation control strategy. The compensation control strategy can improve the dynamic performance of the DFIG under unbalanced voltage condition, and restrain effectively volatility of the RSC’s and GSC’s control target. The second-order generalized integrator is also proposed to improve the frequency lock loop, and use a new type of Second Order Generalized Integrator-Quadrature Signal Generator. The new type can eliminate the dc bias of three-phase voltage sampling and improve the performance of the frequency lock loop.Finally, this paper designs a set of doubly-fed induction generator rotor side experimental platform. The platform verifies its regular speed control strategy. The process of the speed is from synchronization, synchronization to the synchronization. Then, the platform carries on active power and reactive power control under balanced voltage condition, the experimental results show that the stability of the rotor side. In the end, the single phase voltage drop is aimed to simulate the grid voltage unbalance condition. With joining compensation control algorithm, the active power and reactive power fluctuation has been effectively suppressed.