Online Voltage Collapse Prevention Through Optimal Load Shedding and Dynamic Generation Control

Load recovery dynamics and generator reactive power limitation are two major contributing factors for voltage collapses in electric power systems. Even though impending voltage collapse can often be avoided by appropriate control of loads, the traditional form of load control (shedding) is unpopular due to the resulting consumer disruption. On the other hand, the enforced generators´ reactive power limits in operation are normally quite conservative. Better utilizing the reactive power reserve would provide a cost efficient way to reduce the required load shedding amount. Nowadays, with the development of smart grids, advances in communications and computer systems allow more measurements within a large scale network and more resources to be controlled and coordinated. The paper analyzes the generation reactive power limits in a dynamic control framework and discussed the potential of using field current as a more accurate reactive power limitation indicator. Based on this indicator, a dynamic optimal control algorithm is proposed to incorporate both load and generation controls. It shows that adopting dynamic generation control can effectively reduce the control cost of load shedding. Also, regulating field current provides an effective way of monitoring and guaranteeing the post-control stability.