Techniques for compensation of unbalanced conditions in LV distribution networks with integrated renewable generation: An overview

An increasing number of single-phase loads and renewable energy resources (RESs), such as single-phase rooftop PV units, are unevenly distributed in low voltage (LV) distribution networks. This exacerbates unbalanced conditions in the network which in turn adversely affects the power quality, stability and reliability. This paper presents a comprehensive review of the state-of-the-art techniques for alleviation of the unbalanced conditions in both three-wire and four-wire LV three-phase distribution networks. Technical issues arising from the unbalanced conditions are highlighted. Several definitions of the unbalance indicators and standards that are widely used for unbalance analysis are also given. Furthermore, recent unbalance compensation techniques based on three devices; namely, power electronic converters, electric vehicles (EVs) and energy storage systems (ESSs) are critically reviewed. It is found that the power electronic converters with suitable control strategies and management of EV chargers and plug-in electric vehicles (PEVs) have been intensively studied so far. However, based on the literature survey, there is currently no work on applying cutting-edge methods, such as the distributed cooperative control strategy and multi-agent deep reinforcement learning (MADRL), to utilize distributed single-phase ESSs to mitigate the unbalanced conditions. Therefore, key challenges, possible unbalance mitigation techniques and future research directions are recommended and discussed.