Transient stability and performance based on nonlinear power flow control design of wind turbines

In this paper,¹ the equations are formulated to model the dynamic behavior of a wind turbine coupled to the electric grid through a Unified Power Flow Controller (UPFC). This concept is demonstrated in order to treat wind plants more as a controllable energy source rather than a negative load, which is the current trend among renewable energy systems. The results of this research include the determination of the required performance of a proposed Flexible AC Transmission System (FACTS)/storage device, such as a UPFC, to enable the maximum power output of a wind turbine while meeting the constraints of the bulk electric system. The UPFC is required to operate as both a generator and load (energy storage) on the power system in this design. An illustrative example demonstrates this concept applied to a UPFC with a 1MW fixed speed wind turbine. The wind turbine is operated with multiple wind profiles for below-rated wind power conditions. The wind turbine is connected in series through a UPFC to the infinite bus. Numerical simulation cases are reviewed that best demonstrate the stability and performance of a UPFC as applied to a renewable energy system.