Simulation Based Under Frequency Load Shedding Scheme Setting And Relative Software Design

Under frequency load shedding (UFLS) is also named as automatic frequency load shedding (AFLS). It is trigged by frequency dropping and to shed some amounts of system loads in order to maintain system stability and keep it from collapse, when a large disturbance causes a great deficiency in active power. With the interchange between nets deepening day by day, the structure and operation environment becoming more and more complicated have create new challenges to maintain stability of power system. Under this condition, how to keep and improve system stability, especially as a system suffering a large disturbance and how to shed loads with less cost are hot problems.The importance and the development of UFLS are reviewed and analyzed in the paper. In order to supply the gap of the traditional method which ignores load characteristics, a new idea based on the consideration of load characteristics has been presented. As important elements of power system, loads'voltage and frequency characteristics affect each other. The power consumption of loads can be quite different under different voltage or frequency level. Therefore, distribution locations for a UFLS scheme may influence the effect under disturbances. What's more, the different importance among loads is an important side to distribute a UFLS in utility. Therefore, considering those characteristics as studying a UFLS scheme can make it more accurate.All of work related to the paper is fulfilled by the use of the power system analysis tool PSASP. In order to apply the calculation module and access databases of PSASP, methods to develop interfaces of PSASP are presented at first after the structure of software and database are described. Then the influence of loads on frequency dynamics is proven in bench mark EPRI-36 applying classic load model. Next, after a UFLS scheme has been distributed according to the different proportions of three types power consumer in each load bus, particle swarm optimization (PSO) method has been used to get an optimal result.In the end, software is developed based on above analysis. With a good user interface, software can work out an optimal scheme or verify a scheme after the disturbance set and modes of operation are provided. Through analysis of a simulation for a real power net, methods and software are proven to be valid and feasible.