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Any mismatch between load and generation (due to a generator or an interconnection trip) is intended to be balanced and stabilized by contingency reserve, which is also known as contingency Frequency Control Ancillary Services (FCAS) requirement. Load Frequency Relief (LFR), which represents the effect of frequency dependent loads on power system frequency excursion, is crucial for correctly evaluating contingency reserve requirement during generation dispatch to ensure an adequate frequency response. Over estimation of LFR can be accountable for less planned reserve during an economic dispatch that may cause undesirable frequency performance. On the other hand, under estimation of LFR can result in an excessive reserve and hence could unnecessarily increase system operational cost. Conventionally, LFR is considered as a fixed quantity during the evaluation of FCAS requirement. However, recent experience in the Australian power grid suggests that such an assumption may lead to an inaccurate outcome. To explore the above issue, this research investigates the LFR using field measurement data, which were captured at different locations of the southern states of Australia (e.g., Tasmania and Victoria). An approach is developed to identify the predominating factors affecting the LFR and subsequently a technique is proposed to appropriately determine contingency FCAS requirement. [ABSTRACT FROM PUBLISHER]

In distribution power systems line transposition is not a common practice and phase loading levels are always changing. Therefore, perfect balance is never achieved at a distribution level. Non-transposed lines can cause unequal voltage drops between phases and this may be further exacerbated by uneven loads in each phase. Consequently, the voltage magnitude of a certain phase may suffer a severe decrease, breaching the lower voltage limit or unbalanced three-phase voltages at a remote bus may violate the percentage voltage imbalance accepted in the standards. This paper examines the mechanism of causing uneven voltage drops and investigates the impacts of unbalanced line configurations with different phase loading levels on network voltage imbalance. Methodologies are proposed to analyze voltage drops affected by line and load imbalance. Based on these methods, general guidelines are recommended to mitigate the voltage problems, which are useful for network analysis, planning and reconfiguration. [ABSTRACT FROM PUBLISHER]

• The proposed method can solve voltage issues and enable higher PV penetration. • PV imbalance makes traditional methods less effective on overvoltage mitigation. • A joint centralized-decentralized method is developed for unbalanced PV scenarios. • The new approach controls fast PV fluctuations in a coordinated and distributed way. Due to random connection of small-size single-phase rooftop photovoltaic (PV) generators in residential areas, low voltage distribution systems tend to have unbalanced PV integration across phases. In such situations, traditional reactive power compensation methods may cause unintended Voltage-Reactive Power responses across phases due to line coupling, which consequently affects their effectiveness on overvoltage mitigation. Such overvoltage problems significantly hinder the future integration of clean and renewable solar energy resources in power networks. In this paper, the limitations of traditional methods in PV imbalance scenarios are revealed and comprehensively analyzed by a voltage sensitivity method for the first time. On this basis, an innovative joint centralized-decentralized method is developed to overcome the PV imbalance-induced voltage regulation challenge. Specifically, the inverter's reactive power response to PV power variations in different phases is adaptively scheduled in order to avoid adverse effect of inter-phase Voltage-Reactive Power interaction on voltage regulation. The effectiveness of the proposed method is validated by time-series simulations with recorded data and a real-life low voltage distribution system in Australia. With the traditional method (i.e. power factor droop control strategy), 93 minutes' overvoltage can be observed in the case study, which will trigger overvoltage protection and disconnect PV inverters from the grid. While, the proposed method can always control the system voltage within the allowable range, and it consequently avoids PV disconnection. By solving this bottleneck issue, more PV systems can be integrated into distribution networks, which consequently contributes to CO 2 emission reduction in future. [ABSTRACT FROM AUTHOR]

There are more large-scale photovoltaic (PV) plants being established in rural areas due to availability of low-priced land. However, distribution grids in such areas traditionally have feeders with low X/R ratios, which makes the independent reactive power compensation method less effective on voltage regulation. Consequently, upstream step voltage regulator (SVR) may suffer from excessive tap operations with PV-induced fast voltage fluctuations. Although a battery energy storage system (BESS) can successfully smooth PV generation, frequent charge/discharge will substantially affect its cost effectiveness. In this paper, a real-time method is designed to coordinate PV inverters and BESS for voltage regulation. To keep up with fast fluctuations of PV power, this method will be executed in each 5 s control cycle. In addition, charging/discharging power of BESS is adaptively retuned by an active adjustment method in order to avoid BESS premature energy exhaustion in a long run. Finally, through a voltage margin control scheme, the upstream SVR and downstream PV inverters and BESS are coordinated for voltage regulation without any communication. This research is validated via a real-time digital simulator MatLab cosimulation platform, and it will provide valuable insights and applicable strategies to both utilities and PV owners for large-scale PV farm integration into rural networks. [ABSTRACT FROM PUBLISHER]

• Feasibility of a voltage management approach in a distribution feeder is studied. • A double-auction based transactive control is designed for voltage management. • Closed form expression of market clearing var dispatch signal is derived. • Real-time demonstration of the proposed approach is provided for a use-case. • Simulation is performed in both software-in-loop and hardware-in-loop platforms. This article evaluates the feasibility of a double-auction-based Transactive Energy System (TES) for engaging the reactive power (VAR) capability of inverters in a utility-scale photovoltaic (PV) plant for voltage management in distribution feeders. In the proposed approach, a PV plant owner (seller) provides VAR supply curves in terms of price-quantity pairs considering the inverters' P-Q capability, efficiency, opportunity cost for real power curtailment, losses, etc. At the same time, the utility (buyer) proposes VAR demand curves in price-quantity pairs exhibiting the marginal price of VAR. Market clearing points are obtained from the intersection points of supply and demand curves which are then used to create VAR dispatch signals from the PV plant. To conduct a feasibility study of this approach, an Australian distribution network with a utility-scale PV plant (capacity 3.275 MW P) is modeled in RSCAD and simulated in real-time on MATLAB, RSCAD-RTDS co-simulation platform using real historical data. Considering a use case, namely, conservation voltage reduction (CVR), the operational feasibility along with cost-benefit analysis is demonstrated in software-in-the-loop (SIL) and hardware-in-the-loop (HIL) platform. Another use case, exploring the benefit from the tap-change reduction of step-voltage-regulator, is investigated. These two use cases yield net positive benefit when the partially loaded inverter is engaged to sink VAR without curtailing its real power. These studies explore further use cases, e.g., PV hosting capacity, network reconfiguration, etc., to be incorporated in TES for experiencing substantial economic benefits. [ABSTRACT FROM AUTHOR]