Efficient and Improved ANN-Based Voltage-Rise Mitigation Strategy in Distribution Network with Distributed Solar Photovoltaic System

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.

Grid-connected photovoltaic system in Malaysia: A review on voltage issues

Clean energy incentives and the continuous fall in the cost of photovoltaic (PV) installations have led to a steady growth in residential PV systems. One of the main consequences of this high PV penetration in low voltage (LV) distribution networks is the overvoltage issue. Active power curtailment of PV inverters has been previously used to curtail the output power of the inverters below its operating point to prevent such overvoltages. This technique, however, uses a constant droop-based approach to curtail the power, based on the difference between the measured voltage and a critical voltage level. In this paper, this technique is implemented in a typical LV distribution network in North America with high PV penetration level. The simulation results show that the system undergoes excessive curtailment resulting in unnecessary energy loss. An adaptive droop-based approach using adaptive dynamic programming (ADP) is proposed as a possible solution to minimize the total energy loss in the system while keeping the system voltage under the critical operating limits. The energy loss due to curtailment has decreased by 25% after implementing the adaptive-droop based approach using ADP.

The present paper aims at assessing the effects produced on the distribution system by dispersed generators directly connected to LV networks. In particular, the introduction of photovoltaic (PV) generation systems has been studied, since such systems are the only ones having a natural inclination to be easily integrated into high density urban LV distribution networks. In the proposed study some aspects of the quality of power supplied to the customers will be dealt with taking into consideration slow voltage variations. In this regard the effect of dispersed generation (DG) on the voltage profile of a LV distribution feeder has been examined. With reference to a different kind of load distribution along the line, analytical expressions have been derived to determine the limit value of the power that can be injected into the distribution network without causing overvoltages. These expressions have been developed under some simplifying hypothesis related both to the DG unit and to the distribution network.

Integration of photovoltaic (PV) systems in low voltage distribution networks (LVDN) creates additional new challenges in terms of power quality and system operation. However, PV systems have technical benefits in addition to their environmental benefits that reduce the energy losses and improve the voltage profile of low voltage (LV) networks. This ultimately reduces the stress on transformer load tap changers, reduces peak load of the utility, and decreases the resistive power loss in high voltage transmission and medium voltage distribution. This paper focuses on the maximum possibility of PV penetration and its effects on the operating condition of Nepalese LVDN. The voltage profile of the feeder, line load, transformer reverse power flow, and line conductor current limit are considered as four main criteria for the investigation. All these criteria are analyzed for three different schemes of PV location: uniformly distributed PV among the customer, aggregation of PV at the start of the feeder, and the end of the feeder. Analysis shows that the penetration level in uniformly distributed PV scheme and end aggregated PV penetration scheme is limited by voltage criteria. However, both conductor current capacity and voltage criteria are dominant in the start aggregated PV penetration scheme.

Optimal sizing methodology for photovoltaic and wind hybrid rooftop generation systems in residential low voltage distribution networks

A paradigm shift is taking place in Low Voltage (LV) distribution networks, motivated by progressive implementation of renewable micro-generation (µG), mainly Photovoltaic (PV), near household consumers. The concept of self-consumption linked to battery storage is emerging as a way to enhance the quality of electrical network. Smart-Grid (SG) environment comes close to this approach and may have a crucial relevance on management of intelligent power distribution networks, in the framework of a Smart Environment. This paper proposes an additional contribution on the subject by investigating the economic profitability of PV battery systems being analyzed with respect to its impact and economic feasibility, taking into consideration their initial investment and operation costs. The purpose is to verify if prosumer’s investment is financially more interesting than purchasing all electricity needed for consumption from the LV grid. The results of the performed economic analysis show that self-consumption with storage is a potential solution.

The rapid growth of rooftop photovoltaic (PV) arrays installed in residential houses leads to serious voltage quality problems in low voltage distribution networks (LVDNs). In this paper, a combined method using the battery energy management of plug-in electric vehicles (PEVs) and the active power curtailment of PV arrays is proposed to regulate voltage in LVDNs with high penetration level of PV resources. A distributed control strategy composed of two consensus algorithms is used to reach an effective utilization of limited storage capacity of PEV battery considering its power/capacity and state of charge. A consensus control algorithm is also developed to fairly share the required power curtailment among PVs during overvoltage periods. The main objective is to mitigate the voltage rise due to the reverse power flow and to compensate the voltage drop resulting from the peak load. Overall, the proposed algorithm contributes to a coordinated charging/discharging control of PEVs battery which provides a maximum utilization of available storage capacity throughout the network. In addition, the coordinated operation minimizes the required active power which is going to be curtailed from PV arrays. The effectiveness of the proposed control scheme is investigated on a typical three-phase four-wire LVDN in presence of PV resources and PEVs.

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.

Due to the economic and environmental benefits, it is envisaged that many residential customers will increasingly utilize rooftop photovoltaic (PV) systems and plug-in electric vehicles (PEVs). However, the intermittent nature of PVs and the additional loads required for the PEV charging can increase the power quality issues in the low voltage distribution networks (LVDN). In particular, the surplus PV produced power during low load and the random connection of PEVs in addition to the asymmetrical loading levels of residential consumers can aggravate the voltage quality in LVDNs. In this paper, different voltage parameters for the LVDNs with installed rooftop PVs and PEVs are assessed. Further, a novel control strategy is proposed for the domestic management of the PEV charging and the efficacious utilization of reactive power for maintaining the voltage variations within the allowable limits. The simulation results demonstrate the impacts of the integration of PVs and PEVs on the voltage quality and confirm the effectiveness of the proposed strategy to mitigate the voltage variations in LVDNs.

The security region (SR) of a distribution network (DN) is typically characterized as a connected set consisting of nodal active and reactive power injections that ensure the operational security of the DN, and is an important security metric. With extensive integration of distributed photovoltaic systems into low-voltage (LV) DNs, recent studies advocate that medium-voltage (MV) DN security assessment should entail LV security constraints. However, assessing the SR for an integrated MV and LV (IMLV) DN is concerned little in prior studies and is a challenging task at both modeling and solution levels. Firstly, to address the issue of inaccuracies in LV DN models, a pre designed outlier-immune two-sided conservative linear approximation method is designed to recover the LV DN model with satisfactory accuracy for the subsequent assessment. Then, an SR assessment model based on two-stage robust optimization is proposed that incorporates the constraints related to network equipment and uncertainties. To reduce computational time, a feasible inexact column-and-constraint generation (FI-C&CG) algorithm is further designed. Case studies on different scales of multi-phase DNs demonstrate the necessity of considering the interaction between the MV and LV DNs when assessing the SR, and showcase the superior computational performance of the FI C&CG algorithm compared to the regular C&CG.

Recently, transformerless (TL) inverters are being extensively used in small-scale photovoltaic (PV) systems due to their compact-size, lighter-weight, lower-cost and higher-efficiency compared to their counterpart with transformer. However, the growing penetration of these small-scale based PV systems and low-inertia induction motor (IM) loads in low-voltage distribution networks (DNs) make the grid more vulnerable to short-term voltage stability (STVS). Hence, this paper thoroughly examines the STVS of DN with high-penetration of TL-PV units, and provides countermeasures by TL-PV systems to mitigate any short-term voltage instability. The detailed dynamic model of the TL inverter is developed first. Next, three control strategies: (1) constant peak current (CPC), (2) constant active current (CAC), and (3) constant active power (CAP) with low voltage ride through (LVRT) and dynamic voltage support (DVS) capabilities are proposed to improve STVS. The impacts of different level of PV penetrations and LVRT capability of TL-PV inverters on the STVS are explored. Moreover, countermeasures, such as LVRT with CAC and CAP controls and DVS by the TL-PV systems are designed and implemented. Several case studies are carried out on an IEEE 4 bus system first, and later extended to IEEE 13 node test feeder. The results show that DVS can further improve STVS in residential DNs. In addition, CAP and CAC control strategies can speed-up the postdisturbance voltage recovery compared with the conventional CPC control.

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.

New approaches for operating distribution networks are required to handle highly volatile voltage profiles resulting from distributed generation capacities with intermittent feed-in characteristics connected at the medium and low voltage level. This paper discusses the use of a power-electronics-based inline voltage regulator in a low voltage network. Simulations for one year are carried out to investigate the influence of the regulator on a network's voltage profile and to derive a mission profile for the device. Based on this mission profile an analysis of the stresses on the power semiconductors is carried out to illustrate the process of extracting the stresses relevant for a specific component from the mission profile of the device.