Coordinated Allocation of PV and Capacitors with Var Capability for Voltage Unbalance Mitigation in LV Distribution Grids

Abstract

The increased penetration of photovoltaic systems (PVs) and unbalanced loads in low-voltage (LV) distribution systems can adversely affect the overall performance of the utility grid (UG). These impacts include voltage unbalance, power losses, thermal overloading of lines, and various power quality issues. To mitigate voltage unbalance, reactive power control (RPC) techniques are employed by regulating PV inverters and capacitor banks. This study focuses on coordinating the sizing and placement of PVs with reactive power capability (Var) to reduce voltage unbalance and maintain acceptable limits for other power quality indices, particularly in unbalanced three-phase systems. During full load conditions, there is insufficient excess capacity available for reactive power injection or absorption by PV inverters. Therefore, to improve their reactive power capability, the inverters must be oversized relative to the nominal rating of the installed PV systems, which increases capital costs and harmonic levels within distribution networks. To address this, both PVs and capacitor banks are optimally allocated using a multi-objective grey wolf optimization (MOGWO) algorithm within the IEEE 123-bus unbalanced distribution system, using MATLAB and OpenDSS platforms. As a result of this proposed planning, voltage unbalance, power loss, and voltage deviation are significantly decreased by 19%, 34%, and 14% (under 100% overloading), respectively, along with a 215% increase in PV penetration levels. Furthermore, the proposed planning emphasizes that the combination of PVs and capacitor banks can effectively reduce voltage unbalance, which in turn reduces power losses and thermal line overloading.