Abstract
Unbalanced active powers can affect power quality and system reliability due to high penetration and uneven allocation of single-phase photovoltaic (PV) rooftop systems and load demands in a three-phase four-wire microgrid. This paper proposes a distributed control strategy to alleviate the unbalanced active powers using distributed single-phase battery storage systems. In order to balance the unbalanced active powers at the point of common coupling (PCC) in a distributed manner, the agents (households’ single-phase battery storage systems) must have information on the active powers and phases. Inspired by supervised learning, a clustering approach was developed to use labels in order to match the three-phase active powers at the PCC with the agents’ phases. This enables the agent to select the correct active power data from the three-phase active powers. Then, a distributed power balancing control strategy is applied by all agents to compensate the unbalanced active powers. Each agent calculates the average grid power based on information received from its neighbours so that all agents can then cooperatively operate in either charging or discharging modes to achieve the compensation. As an advantage, the proposed distributed control strategy offers the battery owners flexibility to participate in the strategy. Case studies comparing performance of local, centralized, and the proposed distributed strategy on a modified IEEE-13-bus test system with real household PV powers and load demands are provided.
Highlights
In recent years, unbalanced conditions in three-phase four-wire power systems, due to high penetration and uneven allocation of single-phase rooftop PV systems and load demands, have become exacerbated [1]
The performance of the proposed strategy was verified on a modified IEEE-13-bus test system in Figure 1 with real data of rooftop PV units powers and load demands over h, taken from [30]
The power mismatch between the PV unit and the load demand is locally compensated within each household; it might fail to achieve the unbalance compensation at the point of common coupling (PCC) even if the loads are balanced
Summary
In recent years, unbalanced conditions in three-phase four-wire power systems, due to high penetration and uneven allocation of single-phase rooftop PV systems and load demands, have become exacerbated [1]. The unbalanced active powers among phases and between single-phase PV systems and local loads can have a negative effect on power quality and system reliability due to large current flowing through neutral wires. The unbalanced conditions were considered to be static since the penetration and variation of renewable energy sources (RESs) in power systems were low. Owing to high variation in a number of single-phase PV rooftop systems distributed in the three-phase four-wire power systems, balancing between single-phase loads and rooftop PV sources and among the three phases becomes more difficult and, the traditional methods cannot properly manage the unbalanced conditions.
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