Secondary Voltage Control Of AC Microgrid

Since modern times,human society has entered a period of rapid development and a large amount of fossil energy has been consumed,which causes great damage to the environment.There is a need of finding substitutes for traditional energy to solve the problems of energy shortage and environmental pollution.Subsequently,distributed generation,microgrid and other new generation technologies based on renewable energy emerge and develop greatly.Power balance control is an important part of stable operation of microgrid.When the microgrid runs in parallel with the utility,the energy interaction between the microgrid and the distribution network is realized.The microgrid supplies energy to the utility when the power generated exceeds its own needs;On the contrary,the power shortage of microgrid is supplemented by the utility.However,the islanded microgrid only rely on its own resources for power balance control,voltage control and frequency regulation.The paper focuses on the secondary voltage control of isolated island microgrid.Most proposed secondary voltage control strategies for isolated microgrid are based on single control variable(voltage or reactive power),which can only control reactive power or voltage with high precision.A novel secondary control strategy based on two variables is proposed in this paper.The voltage sensitivity and reactive power distribution coefficient are introduced,and the compensation amount of voltage control and reactive power control is constructed by combining the traditional droop control.The reactive power sharing with higher accuracy is realized and the system PCC bus voltage is controlled within a smaller error range.by the proposed scheme.Secondly,the small signal model of DG unit including filter circuit,voltage and current control loop and power control loop is constructed.The application of Lyapunov first method is expounded to judge the small signal stability of power system.According to the root locus of the dominant eigenvalue of the system,the influence of different parameter on the stability of the system is analyzed.Finally,a microgrid system with a high proportion of photovoltaic power generation in a university is studied.The simulation model is built in PSCAD/EDMC environment,which is used to verify the effectiveness and adaptability of the proposed strategy under the conditions of load fluctuation and power sources failure.The research shows that the reactive power output of DGs can be adjusted in a large range by the scheme and a high precise voltage control for a specified bus is achieved without affecting the reactive power sharing,which enhances the flexibility of microgrids and improves the quality of power.