Voltage Support and Selective Harmonic Current Compensation in Advanced AC Microgrids

Abstract

The high penetration of distributed energy resources (DERs) and non-linear loads in low-voltage (LV) grids may cause overvoltage and voltage harmonic distortion. This paper proposes an automatic control strategy to flexibly steer dispatchable DERs in AC microgrids (MGs) while simultaneously mitigating harmonic voltage distortion and over- and undervoltage at the MG nodes. Voltage support is performed through integrated local and coordinated volt-var and volt-watt functionalities, with a well-defined coordinated sequence of actions to avoid active power curtailment. A voltage detection-based decentralized selective harmonic current compensation (HCC) is enabled when the voltage total harmonic distortion exceeds the established threshold at the MG point of common coupling (PCC). The proposed scheme consists of a model-free control that provides power flow controllability at the MG PCC. It does not require computationally intensive algorithms, does not require extra grid-side and/or load-side current measurements, and effectively regulates the internal MG node voltages regardless of the line impedance X/R feature. The strategy is evaluated based on multiple simulations and experimental results, considering a LV MG model with several DERs as well as unbalanced, non-linear loads and non-dispatchable photovoltaic inverters. The simulations and experimental results showed an improved overall voltage profile throughout the MG nodes in terms of magnitude and distortion, which certifies the feasibility of the proposed scheme in real-field applications.