Distributed Averaging Optimization-based Technique for Microgrid Secondary Control

Abstract

In this paper, we present a distributed averaging optimization-based controller for secondary control of islanded microgrid. In islanded mode, grid-forming units collaborate to maintain the voltage and frequency of the microgrid through droop control. However, traditional droop control suffers from poor reactive power sharing due to voltage drop in the lines. Therefore, secondary control interferes to improve power sharing in addition to restore the voltage and frequency errors produced by droop control. The proposed controller seeks minimum inconsistency of power sharing among units while keeping the frequency at its nominal value and the terminal voltage within allowable tolerance i.e. ±5% of its nominal value. The active and reactive power sharing are communicated through low frequency peer-to-peer communication channel and the average value is calculated locally. A convex optimization function is utilized to minimize the difference of power sharing among grid-forming units. The optimization function is implemented using CVX/CVXGEN and embedded in the control system in real-time on a discrete basis over a time horizon of one second. The controller is validated through simulation using MATLAB/SIMULINK. In addition, plug-and-play capability is tested for the proposed controller.