Research On The Control Strategy For Upfc To Enhance Power System Resilience

Power system resilience is the ability of a power system to resist the impact of extreme events.In the temporal domain,enhancing the power system resilience includes the preparation before the event,the cooperative control during the event,the recovery strategy after the event and finallly the experience summary in the longer time scale.In this dissertation,the technical feasibility and specific strategies of UPFC(Unified Power Flow Controller,UPFC)to enhance the power system resilience are studied and explored on two different time scales: before and during the event,by applying the UPFC's ability to quickly and flexibly adjust the output voltage of series unit and parallel unit.Before the event,based on the dual closed-loop structure of UPFC controller,a novel control strategy by using the series unit of UPFC to adjust the line impedance of the system is proposed.By changing the static operation point of the system and adjusting the short-circuit capacity of some selected system nodes,the protection range that covered by the relay protection unit of the power system and the voltage stability of the nodes can be improved.Finally,the operation flexibility of the power system as well as the integration ability of the power system to the renewable energy sources can be significantly enhanced.During the event,this dissertation proposed to use the capacitor energy of the unified power flow controller to add the virtual inertia control link based on the traditional control strategy of UPFC.In this way UPFC is able to participate in supporting the grid frequency,so as to improve the power system's flexibility.Based on the proposed virtual inertia control strategy of UPFC,the dissertation further analyzed the influence of different parameters of UPFC and virtual inertia controller on the effect of power grid frequency support.Through various simulations with the MATLAB platform,it is verified that the proposed virtual inertia control strategy can effectively boost the power system frequency response support ability,reduce the power system frequency fluctuations caused by serious faults,and enhance the power system operation flexibility.Therefore,this dissertation proved that UPFC has the potential to improve the dynamic performance of a power system,and extends the control and operation mode of UPFC.It is believed that with the development of power electronic device technology and the improvement of energy storage technology,the new flexible power electronic equipment unit represented by UPFC will be able to effectively improve the operation flexibility of the power system and reduce the loss of the power system caused by extreme events.