Research on Three-Phase Unbalanced Power Quality Control in Low Voltage Distribution Platform

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.

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.

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

The three-phase imbalance in low-voltage distribution networks (LVDNs) seriously threatens the security and stability of the power system. At present, a standard solution is automatic phase commutation, but this method has limitations because it does not address the branch imbalance and premature convergence or instability of the commutation algorithm. Therefore, this paper proposes a novel refined regulation commutation system, combined with a modified optimized commutation algorithm, and designs a model and simulation for feasibility verification. The refined regulatory model incorporates branch control units into the traditional commutation system. This effectively disperses the main controller’s functions to each branch and collaborates with intelligent fusion terminals for precise adjustment. The commutation algorithm designed in this paper, combined with the above model, adopts strategies such as symbol encoding, cubic chaotic mapping, and adaptive adjustment based on traditional genetic algorithms. In addition, in order to verify the effectiveness of the proposed method, this paper establishes a mathematical model with the minimum three-phase imbalance and commutation frequency as objectives and establishes a simulation model. The results of the simulation demonstrate that this method can successfully lower the three-phase imbalance of the low-voltage distribution network. It leads to a decrease of the main circuit’s three-phase load imbalance rate from 27% to 6% and reduces each branch line’s three-phase imbalance ratio to below 10%. After applying the method proposed in this paper, the main and branches circuit three-phase imbalance are both lower than the limit ratio of the LVDNs, which can improve the quality and safety of electricity consumption. Additionally, the results also prove that the commutation algorithm under this method has faster convergence speed, better application effect, and better stability, which has promotion and application value.

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 increasing photovoltaic (PV) power sources connected to low-voltage (LV) distribution networks generate a new grid environment featuring various types of power generations near consumers and bidirectional active and reactive power flows. However, the large-scale deployment of PVs is hindered by the power quality problems, particularly voltage deviation. To overcome this obstacle, proper mitigation techniques should be developed to eliminate the negative impacts of high-PV penetration in LV networks. This article provides an in-depth review of recently developed technologies that prevent voltage deviation in LV grids with PVs. Following an investigation of the voltage fluctuation phenomena along the distribution feeder due to variable PV output and power demand, the mathematical relationship between power flow and voltage level is revealed. The solutions that mitigate the voltage variation are then investigated and classified. Their effectiveness, advantages, and disadvantages are illustrated. Finally, the current trend in grid integration of PVs and other distributed generators (DGs) under future grid framework is discussed. Voltage Deviation Challenge.

Over the last decade governments in Australia and around the globe have heavily promoted the installation of rooftop solar photovoltaics (PV) in residential low voltage (LV) distribution networks. While distributed solar PV offers a range of benefits, they have not significantly reduced distribution network demand during critical periods due to the incongruity between the residential load profile and the solar PV generation curve. The residential load profile has load demand in the morning, moderate demand during mid-morning, low demand during the middle of the day and peak demand in the evenings. In winter the mid-morning demand is greater than in summer leading to instances where there are two peak demand periods during the day. Solar PV generation is low during the morning and steadily increases until the middle of the day and then decreases until the evening. Peak solar PV generation typically occurs when demand in the network is low. This entails that solar PV resources are poorly utilised and high concentrations of solar PV generation in LV distribution networks can often lead to the degradation of power quality through overvoltage and instances of reverse power flow. Moreover, the addition of solar PV to existing LV networks with unbalanced phases can often exacerbate existing power quality issues in a particular overloaded phase. Corrective measures to address power quality issues may require costly augmentations to the electricity network.

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.

Under the background of the construction of “three types and two networks”, the introduction of a large number of heterogeneous intelligent terminals, ubiquitous open networks, interactive real-time control services and wide area interconnected power systems have transmitted the network security risks to all aspects of the power system. The security defense capability of power system is not only the superposition of security defense equipment, but also the excellent network security team. The continuous improvement of the level of network security is inseparable from the accumulation of network security attack and defense technology and practical experience, as well as practical tools and equipment with the characteristics of the power industry. In order to meet the increasingly severe security protection challenges, actively implement the security protection requirements of the power information system, ensure the safe and stable operation of the power system, build a network shooting range suited to the attributes of the power industry, and continuously improve the ability of network security protection, consolidate the foundation of digital transformation to ensure the safe and stable operation of power system and reliable power supply.The safe and stable operation of the information system needs to carry out comprehensive and in-depth vulnerability troubleshooting. In view of the lack of power business loophole mining and security event verification shooting range environment, this paper studies the power security shooting range construction technology.

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.

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

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.

The paper investigates the power losses for real distribution networks in harmonic polluted state. Actually, the low voltage (LV) distribution networks supply a significant number of nonlinear consumers which causes a distorted and unbalanced state. A negative effect of these states is represented by the increase of power losses in distribution network elements. Even if the symmetrical sinusoidal state is initially considered for the power losses, in reality this often leads to power lines overloading, especially for the neutral. The method for power losses estimation in LV distribution network in harmonic polluted environment is very difficult to use. The aim of this paper is to present a reasonably accurate approach to evaluate the effects of harmonic currents on power losses for LV distribution networks using fuzzy techniques. Moreover, to highlight the proposed methodology, a study case for a real low voltage distribution network in order to compute the additional power losses due to the distorted state is provided.

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.