Unbalance compensation control in microgrids based on the unbalance profile

Abstract

Voltage unbalances are a common issue in microgrids (MGs), especially under islanded operation. In these conditions, distributed generators (DGs) can be used as compensating devices. Currently, the compensation techniques based on DGs focus on a specific point of the grid, usually the Point of Common Coupling (PCC) or a Sensitive Load Bus (SLB). The unbalance conditions in several points of the grid can present tolerable levels, while other points require attention. In such cases, the capacity of compensation may not be efficiently employed. Therefore, this paper brings an adaptive solution that, first, establishes approximate unbalance levels in all buses of the system according to the measurements made in a reduced number of locations and, then, choose between either a SLB or the most unbalanced branch in the grid to be used as the reference for compensation. The method for the estimation of the unbalance values is based on the analysis of the behavior of the negative sequence impedance and on the influence of the current unbalance factor (CUF) in the propagation of the voltage unbalance. Simulations using MatLab/Simulink are performed to validate the performance of the proposed method.