Coordinated control strategies between unit and grid in islanded power system

Abstract

Isolated power system may be caused by large area blackout in interconnected power system in the case of accident, extreme weather or manual disoperation. Coordinated control strategies between unit and grid have their limitations in islanded power system. The local power plant wouldn't play a big role in these cases, as its stability relies heavily on support of the interconnected power system. No consideration of divisional operation mode, the system stability control are set based on the interconnected power system and there are many challenge and threats to establish or maintain islanded power system. This paper analyzes the factors of grid side and unit side which influence isolated power system. The dynamic models which are suit for isolated power system with generating unit of medium and small capacity are used in the paper to meet the need of the applicable ones to study their dynamic characteristics. For clarification of relation between different load disturbance and units' governing system, stability of the local power system is studied by the simulation in different load disturbance, adjusting the system parameters and control logic. Not only proper control strategy of power plant but their evaluation indexes are suggested to improve performance and achieve stability in islanded power system. With considering the frequency characteristic difference of interconnected and islanded power system, an optimization method of under frequency load shedding is proposed to meet the frequency security requirements in the two cases. To take Guangzhou power gird for an example, islanded power system test were made and analyzed under the real power grid condition, which indicated the effectiveness and credibility of the effort mentioned. The proposed method of coordinated control strategy enhances the performance of both power system and units to deal with accident's threat and the challenge and has active guidance meaning and applied value to guarantee security.