Accurate output power control of converters for microgrids based on local measurement and unified control

Abstract

The precise output power control and seamless transit of micro-source converters (MSCs) between grid-tied and islanded operation modes are of great significance for the stability of voltage and frequency, and power flow control in a microgrid. The wireless droop control method (WDCM) is one of the effective methods for MSCs to share loads dynamically and automatically and realize the “plug and play” function. But this method strongly rely on the local voltage and current sampling signals of MSC to dynamically control its output power, therefore the voltage drop induced by the line impedance will cause errors in output power control of MSCs and induce the system unstable. To realize the accurate power tracking and sharing, as well as the automatic seamless transition between grid-tied and islanded modes of microgrid, an accurate output power control method based on local measurement and unified control algorithm is proposed. In this method, two virtual impedances and an on-line estimated power compensation conductance are designed to form a unified controller for MSC, which uses the refined droop control method. The controller is valid for all types of line impedance and loads, besides, the sampling points of voltage and current required are located at the local MSC output terminals, thus increasing the modularity, reliability and flexibility of the controller. Finally, the validity of the improved control scheme is verified by simulation and experiment.