Under Frequency And Under Voltage Coordination Load Shedding Strategy Of Power Grid

With the development of HVDC, the size of power system grows up andthe network structure of the power system is becoming more and morecomplicated. But the probability of occurrence and complexity of griddisturbances increase. As “the third defense line” of preventing the system frombreaking out, UFLS and UVLS play a very important role in the futuredevelopment. However, currently, most research are focusing on consideringvoltage and frequency separately. The frequency and the voltage influence eachother in actual operation and they co-exist. Simple control strategy can’t controlthe low frequency and low voltage of the power system simultaneously. It isimportant and urgent to study the coordinate control of them.This paper starts with the static and dynamic characteristics of thefrequency. It studies the under-frequency load shedding strategy in depth. It alsodiscusses the control method and requirements based on voltage stabilityprinciple. Finally, a load shedding strategy which considers transient stabilityand coordination of UFLS and UVLS has been proposed, both frequency andvoltage are considered in constraints,“search and check” method are adopted. GA(Genetic Algorithm) is applied in searching procedure, and the possiblesolutions are estimated by comparing the frequency offset index, a more stablestrategy which performs better has been achieved. Numerical examples onPSASP verify the rationality and feasibility of the strategy.