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Delta-connected switched capacitors are common in three-wire MV distribution systems as found in Europe and Australia but the majority of past studies focus on star-connected capacitors as applied in North America. This study presents a comprehensive optimization based sequential strategy and a multi-objective optimization based real-time strategy for the optimal placement and control of delta-connected switched capacitors. Considering load variations, a comprehensive optimization for capacitor placement is formulated to maximize the net annual returns from network loss reduction and capacity release. A sequential strategy based on loss sensitivity analysis is presented for efficient capacitor placement on large-scale unbalanced distribution networks. Then a capacitor control strategy is proposed to simultaneously minimize network losses, voltage deviations and voltage unbalance factor (VUF) while a weighted sum method reflects the preferences on the mutually conflicting control objectives. For the mixed integer programming (MIP) problems of capacitor placement and control, an improved backward/forward sweep (BSFS) load flow based particle swarm optimization (PSO) method is used. Finally, the robustness of the proposed capacitor placement and control strategies are verified by comparison against existing popular schemes through detailed simulations over 24 h on a real unbalanced Australian MV network.Index Terms-Capacitor switching, optimization methods, power capacitors, power distribution planning, power quality.

The continuous expansion of consumer-driven installations of residential rooftop photovoltaic (PV) systems causes serious power quality, notable voltage variations and unbalance, which limit the number and capacity of the further connections. The latent reactive power capability of PV inverters can increase the network PV hosting capability. This study proposes both reactive power control and real power curtailment as a comprehensive inverter control strategy to improve the operating performance of unbalanced three-phase four-wire low voltage distribution networks with high penetrations of residential PV systems. A multi-objective optimal power flow (OPF) problem that can simultaneously improve voltage magnitude and balance profiles while minimising network loss and generation costs is defined. The solution is found using the global solver based on Sequential Quadratic Programming algorithm with multiple starting points in Matlab. Detailed simulations are performed and analysed for typical operating scenarios over 24-h period on a real three-phase four-wire unbalanced distribution network in Perth Solar City trial, Australia. Smart meter readings are used to justify the accuracy and validation of the network model and the proposed multi-objective OPF model.

The global acceptance and off-grid charging of plug-in electric vehicles (PEVs) are expected to grow tremendously in the next few years. Uncoordinated PEV charging can cause serious grid issues such as overloading of transformers and unacceptable voltage drops. Single-phase residential charging can also initiate or contribute to voltage unbalance conditions in the distribution networks. A potential solution and key challenge for PEV integration is shifting of the charging activities to off-peak periods. This paper proposes a new PEV coordination approach based on genetic algorithm (GA) optimization to perform online centralized charging and discharging considering transformer loading and node voltage magnitude and unbalance profiles. It allows PEV as source of active and reactive power to participate in energy market based on different prices during a day, without any degradation. Finally, the impacts of uncoordinated and the proposed GA coordinated PEV charging/discharging strategy are simulated for a real unbalanced Western Australian distribution network in the Perth solar city over 24 h.

The worldwide acceptance of plug-in electric vehicles (PEVs) is expected to tremendously grow in the next few years. Uncoordinated PEV charging can cause serious grid issues such as overloading of transformers and unacceptable voltage drops. Single-phase residential charging can also initiate or contribute to voltage unbalance in distribution networks. A potential solution for the PEV integration is shifting the charging activities from peak to valley periods. Therefore, this paper firstly investigates the impacts of uncoordinated single-phase PEV charging at residential houses on three-phase distribution networks. Then, it proposes a novel PEV charging coordination strategy based on heuristic genetic algorithm (GA) to perform online centralized charging considering transformer loading and bus voltage profiles. Based on this, a decentralized PEV reactive power discharging approach is presented where the reactive power is discharged at selected nodes for further reduction of voltage unbalance. The impacts of uncoordinated PEV charging as well as the performance of the proposed centralized PEV charging and decentralized var discharging strategies are tested on a real unbalanced Western Australian distribution network under the Perth Solar City project over 24 hours. INDEX TERMS Centralized PEV charging, decentralized PEV var discharging, voltage unbalance and distribution network.

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