Research On Reactive Voltage Coordination Control Strategy Of Large-scale Wind Farms

With continuous improvement of wind power technology, the wind power industry has been rapidly developed. The scale of wind farms connected to the power grid has further expanded and causes many problems as well. The output fluctuation of large-scale wind farms will cause voltage fluctuations, especially at the centralized point of common coupling (PCC). Owing to variable speed constant frequency operation characteristics and reactive power regulation function, doubly fed induction generator(DFIG)is drawing more and more attention. However, few studies have been done about reactive voltage control strategy of large-scale DFIG wind farms. Besides, equivalent model of large DFIG wind farm used for regulation of reactive power also need intensive study.To solve the above problem, this paper firstly establishes the mathematical model of DFIG including its wind speed, wind turbine, generator and control of inverter. On this basis, the dynamic reactive power output characteristics of DFIG, as well as the reactive power range, have been studied. At the same time, the principle and reactive power compensation characteristic of shunt capacitor and static synchronous compensator(STATCOM) have been introduced. And the control model of STATCOM has been established.As for the equivalent model for large DFIG wind farm, this paper analyses the typical topology of wind farms and divides the generators of wind farm by Jensen Model based on Wake Model. And the equivalent model for large DFIG wind farm is established using the method of improved capacity weighted equivalent.Finally, a two-tier and multi-stage reactive voltage coordination control strategy for the PCC voltage of large-scale wind farms is proposed with the consideration of both DFIG, shunt capacitor and STATCOM, based on the reactive power output characteristics of these devices and the equivalent model of DFIG wind farm. This strategy mainly includes the switch of shunt capacitor based on wind speed prediction data, the allocation between wind farms based on the reactive voltage sensitivity and the reallocation between DFIG and STATCOM. Meanwhile, the effectiveness and applicability of this reactive voltage coordination control strategy are verified by using the equivalent model of large DFIG wind farm above.