Computational analysis of impedance transformations for four-wire power networks with sparse neutral grounding

The rapid increase of distributed energy resources (DERs) installation at residential and commercial levels can pose significant technical issues on the voltage levels and capacity of the network assets in distribution networks. Most of these issues occur in low-voltage distribution networks (LVDNs) or near customer premises. A lack of understanding of the networks and advanced planning approaches by distribution network providers (DNSPs) has led to rough estimations for maximum DERs penetration levels that LVDNs can accommodate. These issues might under- or over-estimate the actual hosting capacity of the LVDNs. Limited available data on LVDNs' capacity to host DERs makes planning, installing, and connecting new DERs problematic and complex. In addition, the lack of transparency in LVDN data and information leads to model simplifications, such as ignoring the phase imbalance. This can lead to grossly inaccurate results. The main aim of this paper is to enable the understanding of the true extent of local voltage excursions to allow more targeted investment, improve the network's reliability, enhance solar performance distribution, and increase photovoltaic (PV) penetration levels in LVDNs. Therefore, this paper reviews the state-of-the-art best practices in modeling unbalanced LVDNs as accurately as possible to avoid under- or over-estimation of the network's hosting capacity. In addition, several PV system modeling variations are reviewed, showing their limitations and merits as a trade-off between accuracy, computational burden, and data availability. Moreover, the unbalanced power flow representations, solving algorithms, and available tools are explained extensively by providing a comparative study between these tools and the ones most commonly used in Australia. This paper also presents an overview of unbalanced optimal power flow representations with their related objectives, solving algorithms, and tools.

This paper presents the results of experiment-based simulation aimed at analyzing the harmonic distortion behavior of nonlinear loads and the background voltage distortion of power supply in building low-voltage (LV) distribution network. The procedure of constructing experiment-based simulation model and harmonic monitoring at various points of common coupling (PCCs) in LV network are introduced for analyzing voltage and current harmonic distortion behavior due to attenuation effect. The model is proposed for future microgrid modeling analysis at different PCCs in LV networks. The simulation model was constructed from captured harmonic data and the corresponding LV network topology. The simulation model has been verified by comparing with field measurement results. The VTHD and ITHD relationship curve and the attenuation effect curve for personal computers (PC) have been proposed by using the simulation model. In particular case study has been conducted to compare the conventional and state-of-art switch mode power supply (SMPS) used in PCs.

The low-voltage distribution networks have some structural features, such as short supply line, more lines branch and influence of transition resistance of the short-circuit current. These characteristics seriously affect the development of fault location technology. The paper, based on the basis of the structural features about the low-voltage distribution networks, create the distribution networks of description matrix by knowledge of mathematical topology and use the distribution network fault location algorithm based on web-based structure matrix. By the algorithm, the area of fault judgment and the actual distribution network fault location are fully consistent. The new theory provides a new way of thinking for fault location in low-voltage distribution networks.

The high proportion of distributed photovoltaics (PVs) connected to distribution substation areas causes complex operation of the medium- and low-voltage distribution network. New power electronic devices represented by soft open point (SOP) can achieve a flexible interconnection between distribution substation areas. In this paper, a cooperative operation optimization method for medium- and low-voltage distribution networks considering flexible interconnected distribution substation areas is proposed. Firstly, interval affine is used to model the resource aggregation and obtain the flexibility region constraints of distribution substation areas. Then, a multi-scale cooperative operation framework for medium- and low-voltage distribution networks is constructed. The medium-voltage distribution network adopts the centralized method to solve and issue operation strategy instructions. The distribution substation area generates a voltage-reactive power adaptive regulation curve and performs intra-day rolling control. Finally, the case studies show that the proposed method has efficient operation strategy of medium- and low-voltage distribution networks and can alleviate the voltage fluctuation caused by high integration of PVs.

A dynamic reference voltage adjustment strategy for Open-UPQC to increase hosting capacity of electrical distribution networks

A large number of distributed photovoltaic grids have exacerbated the problems of voltage limit, three-phase imbalance and power reversal of the low-voltage distribution network, bringing challenges to the stable operation of the distribution network. Aiming at the problem of absorbing a high proportion of distributed photovoltaics, this paper proposes a space-time coordination based on Voltage Source Converter (VSC) and energy storage by exploiting the power regulation potential of low-voltage AC and DC distribution networks and energy storage. Optimization. Firstly, the power transfer characteristics of VSC and energy storage at the spatial and temporal levels are analyzed; secondly, with the goal of minimizing PV cut-off and network loss, and energy storage and VSC power as optimization variables, a low-voltage AC-DC hybrid distribution is established. Finally, taking a typical low-voltage AC-DC hybrid distribution network as an example, the validity of the proposed method is proved by simulation, and the photovoltaic capacity of the low-voltage distribution network is improved.

Local control method and simulation analysis of hybrid AC/DC low-voltage distribution networks with high-proportion photovoltaics

The growing penetrations of rooftop photovoltaics (PVs) into low-voltage (LV) distribution networks are challenging voltage regulation. Developing an effective volt-var (VV) control has been the focus of many researchers with various approaches proposed so far. However, assuming a single voltage level and balanced network model, widely adopted in existing literatures, tends to cause inaccurate and even infeasible control solutions. Besides, existing distribution VV control studies are usually based on the day-ahead predictions of PV generations and loads, introducing inevitable and non-negligible errors. To address the challenges above, this paper proposes a VV co-optimization across unbalanced medium-voltage (MV) and LV networks, by traditional and emerging techniques, to ensure the network operation with the required power quality. Specifically, the operation of MV delta-connected switched capacitors and LV distributed PV inverters is coordinated, under a three-stage strategy that suits integrated and unbalanced radial distribution networks. The proposal aims to simultaneously improve voltage magnitude and balance profiles while reducing network power loss, at the least controlling cost. To effectively solve the proposed VV optimization problem, a joint solver of the modified particle swarm optimization and the improved direct load flow is employed. Finally, the proposal is evaluated by simulations on real Australian distribution networks over 24 h.

In this study, a mechanism is developed to support the distribution system operators (DSOs) with a better grid management scheme regarding congestion management by incorporating a data-driven congestion scheme and thus reducing the congestion. The objective of the work is to avoid/reduce the thermal overloading of the transformer with an affordable approach. A data-driven model is developed, which can help DSOs to solve congestion problems in the low-voltage (LV) distribution network. Demand response is applied for the procurement of flexibility, using available flexibility to mitigate the congestion in the distribution network. Once the congestion occurs, the DSO can refer to the data-driven classification model and mitigate the congestion with the minimised cost. A typical Dutch LV distribution network is considered for analysis. It is observed that the DSO has significant savings and reduction of congestion occurrence in the LV distribution network. The performance and accuracy of the developed data-driven model are also found to be well within satisfactory limits.

The possibility of high Photovoltaic (PV) and Electric Vehicle (EV) penetration in Low-Voltage (LV) Distribution Networks (DN) is examined in this research utilising a typical DN found in Malta as a case study. The European Union (EU) has established goals and directives that make it quite probable that DNs will include a lot of PVs, causing overvoltages, and a lot of EVs, charging erratically, causing undervoltages. A DN may encounter both unfavourable scenarios on the same day since PV generation and EV charging often occurs simultaneously, particularly in residential case studies. Utilising dispersed or centralised storage effectively is one method to address these problems, however, doing so may postpone the need for costly DN expenditures. The paper demonstrates the level of automatic mitigation achieved in Malta residential areas. The information provided is mostly by actual measurements taken at the start of the LV feeder.

The increasing deployment of residential photovoltaic (PV) systems poses a significant operational challenge to low-voltage (LV) distribution networks. Most PV systems in Malta are installed in a uniform south-facing orientation with low tilt angles, to maximize energy yield throughout the year. However, the synchronized generation peaks accentuate reverse power flows through the network, resulting in overvoltage issues and the exceedance of line current ratings. This paper investigates how PV orientation and tilt angles can be used as a passive mitigation measure to reduce technical issues in LV networks. Using a synthetic Maltese residential feeder, four PV deployment scenarios have been investigated. These combined two tilt angles (10° and 35°), and two orientation strategies (uniform south-facing and mixed south-east-west) within a Monte Carlo simulation. Results show that both increasing the tilt angle from 10° to 35° and changing the orientation strategy from uniform south-facing to mixed reduces overvoltage issues and flattens the utilization factor curves. The total energy yields are also quantified for each scenario. This demonstrates that simple design choices can maintain high PV hosting capacity without the need for active control or costly grid reinforcement.

Phase reassignment for load balance in low-voltage distribution networks

Low-voltage (LV) feeder voltage magnitude and unbalance are often the constraining factors on a feeder's capacity to absorb rooftop photovoltaic (PV) generation. This paper presents a new probabilistic method for voltage management in distribution networks through the placement of distribution static compensators (dSTATCOMs) and on-load tap changers (OLTCs) considering the reactive capability of PV inverters in multiple LV and medium-voltage distribution networks. The method uses a modified particle swarm optimization. In this paper, several scenarios for the placements of multiple dSTATCOMs with and without embedded energy storage systems using both reactive and real power compensation are investigated in combination with an OLTC equipped with independent per-phase tap-changing control. The voltage constraints in the proposed method are statistically defined using three duration curves. These are the voltage unbalance, maximum voltage, and minimum voltage duration curves. The method is comprehensively tested for varying load and PV generation based on data from a real Australian distribution network with considerable unbalance and distributed PV generation. The results show that PV hosting capacity increases where the proposed approach is applied.

The next decade is likely to witness considerable growth in the application of plug-in electric vehicles (PEVs). However, uncoordinated PEV charging in low-voltage distribution networks may cause grid issues, such as transformer overload and voltage unbalance (VU). Therefore, it is essential to consider a more suitable methodology of voltage regulation for the consumers placed at the end of the feeder when the network is predominantly resistive. With this background, this article investigates the capability of dynamic PEV load transfer within the three phases of a distribution network to propose a new hybrid PEV coordination approach. In addition to the online centralized battery charging and var discharging, this approach performs local voltage profiles improvement by switching PEV at selected single-phase residential houses such that a PEV can be switched from a heavily loaded phase to a (relatively) lightly loaded phase. This results in better voltage regulations and VU reductions. The impacts of uncoordinated and proposed genetic algorithm (GA) coordinated PEV charging on VU and node voltage profiles and losses are simulated for a real unbalanced Western Australian distribution network in the Perth solar city over 24 h.

Low voltage (LV) distribution networks mainly feed single-phase customers. Even if the end-users of a given LV network may have similar electrical behaviors, unbalances among the three-phase loading are extremely common. This issue is exacerbated by the appearance of new single-phase intensive and often coincident loads, such as the electric vehicles’ residential charging stations. In this work, a methodology is proposed to evaluate the effects of residential charging on the quality of supply voltage of LV grids. Then, a decentralised approach is proposed, based on the multi-agent system technology, which allows the different flexibility resources available on the grid to act together to achieve a global goal. In the scenario analysed, the agents cooperate to regulate the network nodal voltage, taking into account the characteristics of the resources they are controlling and the needs of distributed energy resources’ owners. A case study derived from a real portion of the Italian distribution system demonstrates the validity of the approach in solving the network operation criticalities (i.e., voltage regulation issues, line congestions, voltage unbalances, etc.).