Research On Control Strategy Of DFIG Under Voltage Unbalance Conditions

The doubly fed wind generation system has advantages such as the operation range to be broad, the high wind energy utilization efficiency, small capacity of power converters and so on, so it has wide applications. Currently, the researches of control strategy for the doubly fed wind generation system are mostly done based on the balanced grid voltage. However, in the actual system, some abnormal running states, caused of grid asymmetric impendence and system asymmetric fault, would endanger safe and stable operation of generation and power system. The mathematical models and control policies of the doubly fed wind generation system under the grid voltage balance conditions are studied firstly in this paper. On this basis, the operating characteristics of the doubly fed wind generation system under unbalanced grid voltage are analyzed, and existed questions of the doubly fed wind generation system in operation under unbalanced grid voltage are discussed thoroughly. In order to restrain the pulsations that caused by unbalanced grid voltage, an unbalanced control strategy based on resonant regulators of rotor side and the grid-side converters is proposed in this paper. And compared with unbalanced control strategy based on double dq and PI regulators. Simulation results show that both control strategies are able to restrain control aim pulsations in steady condition. However, the unbalanced control strategy based on resonant regulators is better than that based on double dq and PI regulators in dynamic performance. In addition, proceeding from the entire doubly fed wind generation system, a combined control strategy of the rotor side and the grid side converters is studied. Through simulation analysis, the stability of the DC bus voltage can be maintained better and overall system dynamic performance also can be improved when the combined control strategy is used.