Wind farm reactive support and voltage control

Wind farms typically contain a variety of voltage control equipment including tap-changing transformers, switched capacitors, SVCs, STATCOMs, and the generators themselves. This paper focuses on the control of this equipment by addressing three major issues. The first is the ability of wind turbines to provide reactive power; voltage saturation in the collector system often limits the reactive power output of individual generators. The second topic is the stability of the system when independent control laws for the various types of equipment interact. Specifically, under some conditions a tap-changing transformer may not behave as expected or become unstable. The third major issue is the high-level control of the substation or wind farm; it is desirable to treat all the equipment as an integrated system rather than independent devices in order to meet cost, maintenance, fault tolerance, or other requirements. This high-level control problem is addressed for several types of available future information including exact future knowledge and stochastic predictions. Deterministic and Stochastic Dynamic Programming are used to develop control algorithms. The results demonstrate that while exact future knowledge is very useful, simple prediction methods yield no benefit.