Study On Several Problems On Power System Stability Analysis

The power system is facing many new challenges as the development of electrical power industry. Power system voltage stability becomes more severe. High Voltage Direct Current and other flexible transmission technologies can improve transmission capability of electrical power. But, in the mean time, they also bring transient stability and transient voltage stability problems. Large electrical plants were built far from load centers for economical and environment factors. Therefore, long-distance lines are needed to transmit electrical power to meet heavy load demands. These are contributed to voltage unstability. Original rules were changed when electrical power market has been put into practice. These problems must be solved. So this paper mainly studied on several facets to voltage stability.High voltage direct current technology can transmit electrical power for long distance. Also, synchronization problem is not existed. So, it developed quickly and multi-infeed high direct current has been formed in south china power grid. In order to improve calculation precision, detail model of HVDC is needed. But it will bring heavy calculation. So, simple models of HVDC have been used recently. Based on EEAC theory, the calculation precision affectiong about transient stability and taransient voltage stability which used simle model is analyzed in the paper. The simple model of equivalent constant current loads can be used for transient stability in single infeed DC system. It is indicated the precision is good for transient stability and taransient voltage stability simulation when system load is constant impedance load or dynamical load.More and more attention was paid to small disturbance research of coupled multi-infeed DC and AC transient stability. Control strategy for HVDC has been studied for large disturbance. Based on EEAC theory, the influence of different kinds of load models on coupled multi-infeed DC/ AC transient stability and transient voltage stability is analyzed in detail. Both dynamic loads and constant power loads are unfavorable to multi-infeed DC /AC system stability. But constant current loads and constant impedance loads are favorable to multi-infeed DC/ AC system stability. For transient stability, it is better when system loads are constant impedance loads. And compared with constant impedance, transient voltage stability will decrease when system loads are constant current type. It will be worse when system loads are constant power or dynamic type.In order to prevent voltage stability, lager amounts of work has been made in recently time. But only static voltage stability and small disturbance voltage stability are addressed. Based on the sensitivity of transient voltage security margin with respect to reactive power injection, a power system can be divided into control areas for preventive control of transient voltage security. Thus, the optimization problem of transient voltage security of a large power system can be decoupled into those of subareas. The rationality and effectiveness of the proposed method are proved with simulations on both test system and a real system.It has been ignored for a long time that reactive power can be improved transient stability and trasmision limit. It is indicted by the simulation of OMIB system and practical...