Improved master-slave control for Smooth Transition Between Grid-connected and Islanded Operation of DC Microgrid Based on I -ΔV Droop

Abstract

DC microgrids with energy storage units are becoming attractive solutions for absorbing and transmitting renewable energy. The energy storage unit can be charged or discharged as a current source according to system commands when connected to the DC grid, and can act as a voltage source to maintain the power balance of renewable energy and local loads in the island mode. However, during the island detection, the DC bus voltage is uncontrollable, and the transition between modes of operation may cause DC bus voltage fluctuations and even make the system unstable. Therefore, a smooth transition between grid-connected and island mode is necessary. In this paper, combined with the advantages of peer-to-peer control, an improved master-slave control strategy based on I-ΔV droop is proposed to control the smooth transition between grid-connected and island mode. It enables the energy storage unit to operate under current control like conventional master-slave control during grid connection, and adaptive smooth transition to voltage control based on I-ΔV droop during island detection and islanding. Analysis and experimental results show that smooth transition between grid-connected and island mode can be easily achieved, especially in the case of non-intention islanding.