Research On Frequency Characteristic And Control Strategy In Independent Regional Power Grid

For large grid failure, the regional grid forms the isolated net after islanding from power main grid. On the other hand, due to historical and economic reasons, there still exist regional power grid independent operation in our country. Such power belongs to the typical "big unit, big load, small network", unit’s capacity and load account for a more proportion, the frequency stability is the most outstanding problem of the network security and stability. Therefore, the study of isolated grid frequency dynamic characteristics and stability control strategy is very meaning to ensure the stability and safe operation of isolitary grid.In this paper, based on the frequency change of isolated power grid, mathematical expressions of a dynamic process of primary frequency regulation without and with frequency modulation limiter are derived. And then mathematical expressions of the maximum frequency deviation, maximum rate of frequency change and static frequency deviation are got. The influence on the primary frequency regulation by governor static difference coefficient, the ratio of generator participating in primary frequency regulation, the generator inertia time constant, and the governor time constant is analyzed. The dynamic process of secondary frequency regulation is analyzed. Optimization method of secondary frequency regulation by adding the differential link is proposed. In this paper, based on electrolysis plant independent operation, for anode effect of aluminum electrolysis, optimization method of primary frequency regulation by adding the acceleration feedforward is put forward; for load shedding when electrolysis plant separates with external grid, the method of modifying the load setting automatically is proposed. Next, this paper discusses the stability control principle of the electrolytic aluminum regional power network. The stability control strategy of system power unbalance,which is controlled in the scope of the primary frequency after the fault, is proposed, and a certain margin is considered. The calculation method of primary frequency regulation capability of regional power network is proposed, and the range of the load shedding or generation shedding is obtained. According to the characteristics of the thyristor rectifier unit, load control strategy is put forward. Finally, the validity of proposed methods is verified by establishing the model of the regional power grid in the power system analysis software package (PSASP7.0).