Automatic Load Shedding Research For Power System

Frequency is one of the most important operational state parameters of power system. Frequency drop even frequency collapse will be caused due to the active power shortage by disturbances. When the active power shortage is serious, the under-frequency load shedding devices may not operate. It is necessary to perform automatic load shedding control to remove some loads quickly. Then the system frequency after disturbances or stepout can be maintained at a certain level. It's helpful to recover the system frequency to the permissible value as soon as possible. So, the automatic load shedding of frequency stability control for power system is a study of great significance in many aspects. The frequency stability can be improved and the load shedding amount can be reduced as far as possible after disturbances. When an extremely serious disturbance is applied to power system, the system can be prevented from frequency collapse and widespread outage by performing automatic load shedding control. Recently, a new view point of wide-area measurements technology is provided to the large-scale interconnected power system frequency stability control.The present status of power system automatic load shedding research is summarized and analyzed, and the key problems are pointed out in this paper. Three methods for frequency stability analysis are also introduced and analyzed, those are the dynamic power flow method, the direct method for frequency stability analysis of power system and the prediction algorithm of frequency emergency control based on wide-area measurements. A WSCC9-bus system and IEEE's 50-generator modified test system are established by using PSS/E. Massive dynamic simulations are performed on the IEEE's 50-generator modified test system. The influences of different load shedding schemes on the frequency and bus voltage are analyzed based on the same total amount of load shedding. And the influences of different load models on system frequency stability are also analyzed. An automatic load shedding algorithm of frequency stability emergency control for power system based on wide-area measurements technology is proposed in this paper, by modifying the direct method for frequency stability analysis of power system. At last, the proposal algorithm has been tested by PSS/E simulation on the WSCC9-bus system and IEEE's 50-generator modified test system. The results of simulation show the proposal algorithm is valid.