Piecewise control strategy for electric spring

Electric spring (ES) as a device to solve the voltage fluctuation problem caused by the connection of a large number of renewable energy sources to the power grid has developed quickly. ES which involves a power inverter with a capacitor in DC side (ES-C) with the simple structure and low cost has great potential for application with strict control requirements and some operation details are not been discussed. In this study, based on the analytical solution of ES-C's operating points, the operation region of ES-C is divided into four parts. Also, a piecewise control strategy was proposed to ensure the safe and stable operation of ES-C. With the piecewise control, ES-C can participate in system frequency regulation while maintaining load voltage as rated voltage. Also, the simulations in PSCAD/EMTDC proved that the proposed piecewise control can switch between operation regions and can make full use of the operating points of ES-C.