Research On Sliding Mode Current Control Strategy For Doubly Fed Induction Generator Based On Internal Model

The converter is an important part of the doubly fed induction generator wind turbines,which is the key to realize the variable frequency constant frequency power generation of the wind turbine. The control strategy affects the stable operation of the unit. In the synchronous rotating coordinate system, the rotor d?q axial current coupling items contain stator parameters such as stator and rotor inductance and resistance, and the motor parameters change with the change of working condition, resulting in the conventional vector control strategy can not completely eliminate the d?q axial current coupling. Therefore, in this paper, based on the internal model control structure and combined with the sliding mode control strategy, the d?q axis current of the wind turbine is decoupled.Firstly, according to the structure and working principle of the doubly-fed induction motor,the equivalent circuit of the motor is obtained, and the mathematical model of the three-phase stationary coordinate system is established. Through the coordinate transformation of the three-phase stationary to the two-phase rotation, the vector model of the stator flux linkage is used to derive the mathematical model of the doubly-fed generator in the two-phase rotating coordinate system.Secondly, according to the principle and characteristics of internal model control and combined with the doubly-fed generator synchronous rotating coordinate system under the mathematical model, the decoupling term is transformed into the transformation function, and the basic transfer function of the internal model structure is obtained. According to the design steps of the internal model controller, the internal model controller structure is given, and the dynamic response performance satisfying the system requirements is obtained by matching the internal model parameters; Using the sliding mode control principle and combining with the mathematical model of the doubly-fed generator, the sliding mode surface of d?q and current slip mode control law are defined. The stability of the system is analyzed by using the Lyapunov stability theory. On the basis of the internal model controller, the sliding mode current control structure based on the internal model is given.Finally, a simulation model of the doubly-fed wind power generation system based on the internal model of the sliding mode current decoupling is designed. The three operating conditions of wind turbines, the sub-synchronous, synchronous and super synchronous are simulated and compared with the conventional control strategy, the results were compared and analyzed. when the wind speed changes, the main output power and reactive power, rotor d?q axis current and other major physical volume overshoot small, fast response time, adjust the time is short; in the motor parameter changes, the physical quantity above is different from the original motor parameters when the deviation is small, can follow the reference value better. It can be seen that the proposed control strategy not only improves the dynamic performance of the wind turbine, but also has more excellent robustness.