Hierarchical control for voltage unbalance mitigation considering load management in stand-alone microgrid

Abstract

Unevenly distributed loads at different phases may lead to stability issues and incur high losses in a low inertial microgrid with a rise in Voltage Unbalance (VU). Thus, a suitable control mechanism is mandatory for stable microgrid operation and mitigating VU under peak and off-peak loading conditions. This paper presents a hierarchical control mechanism that includes a primary Droop-based Positive-Negative Sequence Compensation (PNSC) approach and a secondary controlling technique implemented using Demand Side Management (DSM). Besides mitigating VU, DSM also performs effective energy management by manipulating Thermostatically Controlled Loads (TCLs) and Electric Vehicle Charging stations (EVCs), with specific emphasis on the Thermal Comfort (TC) of customers. The primary controller's stability is also examined to test and validate its potential to mitigate VU during off-peak loading. Furthermore, a comprehensive analysis of the proposed hierarchical controller is performed with several dynamics taken into account. Moreover, the control technique is designed to mitigate generation and demand mismatch while adhering to IEC-61000-3-13. The effectiveness of the proposed control framework is tested using a modified IEEE-13 bus system in a MATLAB/ Simulink and Digsilent PowerFactory environment. Further the Hardware in Loop (HIL) is done in OPAL-RT to validate the real time performance of the system.