Power-Sharing Method of Multiple Distributed Generators Considering Control Modes and Configurations of a Microgrid

This paper describes the active power and frequency-control principles of multiple distributed generators (DGs) in a microgrid. Microgrids have two operating modes: 1) a grid-connected mode and 2) an islanded mode. During islanded operation, one DG unit should share output generation power with other units in exact accordance with the load. Two different options for controlling the active power of DGs are introduced and analyzed: 1) unit output-power control (UPC) and 2) feeder flow control (FFC). Taking into account the control mode and the configuration of the DGs, we investigate power-sharing principles among multiple DGs under various system conditions: 1) load variation during grid-connected operation, 2) load variation during islanded operation, and 3) loss of mains (disconnected from the main grid). Based on the analysis, the FFC mode is advantageous to the main grid and the microgrid itself under load variation conditions. However, when the microgrid is islanded, the FFC control mode is limited by the existing droop controller. Therefore, we propose an algorithm to modify the droop constant of the FFC-mode DGs to ensure proper power sharing among DGs. The principles and the proposed algorithm are verified by PSCAD simulation.