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This paper presents a mathematical model for the prediction of the probabilities of reverse power flow exceeding predefined critical thresholds at feed-in points of a distribution network. The parametric prediction model is based on hourly forecasts of global horizontal irradiation and uses copulas, a tool for modeling the joint probability distribution of two or more strongly correlated random variables with non-Gaussian (marginal) distributions. The model is used for determining the joint distribution of forecasts of global horizontal irradiation and measured solar power supply at given feed-in points, where respective sample datasets were provided by Deutscher Wetterdienst and the N-ERGIE Netz GmbH. It is shown that the fitted model replicates important characteristics of the data such as the corresponding marginal densities. The validation results highlight strong performance of the proposed model. The copula-based model enables to predict the distribution of solar power supply conditioned on the forecasts of global horizontal irradiation, thus anticipating great fluctuations in the distribution network.

In order to improve the efficiency of battery charging and discharging in a wide conversion gain, a dual-transformer-based full bridge converter using a block capacitor was proposed. By adding the blocking capacitor in the primary side of one transformer, an extended zero voltage switching (ZVS) range is obtained in a wide output voltage range, which is achieved by regulating the secondary voltage of the transformers to match the output voltage according to the voltage-second balance in both boost and buck modes. Besides, a mirror-symmetrical modulation is introduced in reverse power flow to avoid a limited ZVS range of the traditional dual-transformer converter. The power characteristics and ZVS range are analyzed in detailed. The analysis results and transformer current are compared with the published dual-transformer converter and the conventional dual active bridge (DAB) converter to demonstrate the advantages. Finally, a 300W prototype was built and tested to verify the effectiveness of the proposed converter.

The proliferation of rooftop solar PV has caused reverse power flow in low voltage distribution networks leading to elevated voltage levels. As the voltage is raised, PV inverters reduce output power to combat voltage rise and may result in inverter shutdowns causing PV curtailment (loss of PV output power). Residential battery storage can store excess PV energy and hence reduce reverse power flow, over voltage and PV curtailment. This study aims to determine the reduction in PV curtailment achieved by the installation of optimally sized residential battery storage. A method to calculate the reduction in PV curtailment and the reduction in corresponding financial losses incurred by PV owners and the energy market is presented. The method is applied to an 11-kV feeder in South Australia along with prevailing feeder and inverter voltage limits. Results show that with the installation of optimally sized battery storage, PV curtailment and the corresponding financial losses can be reduced by more than 50%. Refereed/Peer-reviewed

The increasing penetration of distributed generations (DGs) has brought huge challenges to distribution networks operation, such as reverse power flow and overvoltage. Under this background, an optimal active and reactive power dispatch (OARPD) method is proposed in this paper. Considering the three-phase unbalance property, the bus injected model (BIM) of power flow is established while a novel high precision linearized method is proposed. Based on the linearized power flow model, the multi-objective OARPD model which aims to minimize networks losses while maximize the absorption of renewable energy is constructed. Moreover, to ensure the system safe operation and ameliorate the adverse effects caused by single-phase integration of DG, a novel voltage unbalance constraint is established. Finally, examples have been used to demonstrate the validity and effectiveness of the proposed method.

This paper presents an analysis of the system effects of reverse power flow in distribution feeders. Continued increases in the number of small-scale photovoltaic (PV) panel installations within the network has led to low or reverse power flows in distribution feeders at times of high solar energy availability, and substantial weather-induced load variation, among other impacts. In the event of a large loss of generation, under-frequency load shedding of these distribution feeders is one tool that network operators use to arrest the frequency decline. The penetration of distributed PV generation leads to low availability of load to shed, or the chance of inadvertently removing generation, which can lead to power system failure. This paper explores these effects on the largest power system in Western Australia and suggests methods to mitigate the impact of increasing DER penetration on under-frequency load shedding schemes.

Battery energy storage (BES) has the ability to solve many power system problems especially in systems with renewable energy resources integrated. Due to the intermittent nature of solar photovoltaic (PV) generation, different problems have arise such as voltage fluctuation and reverse power flow. Besides, duck curve issue has become more significant with the increasing amount of PV integrated in the power system as first raised by the Californian Independent System Operator. Studies on these issues has become important in order to solve the steep ramp and over generation problems caused by duck curve issue. The duck curve issues based on general Malaysia load profile and PV pattern are studied in this paper. Besides, the feasibility of BES in solving these issues with suitable BES capacity is investigated. The results show that the BES has the ability to solve the duck curve issues through proper control of BES charging and discharging operation.

Integration of the renewable energy sources (RES) in distribution systems is accompanied with a lot of challenges to power system protection, control and operation. This integration can cause reverse power flow that affects the voltage stability of the power system. To avoid the power system instability, the monitoring of the integration of RES is necessary. In this paper a hybrid algorithm is proposed to monitor reverse power flow, and then it was tested on the IEEE-39 and IEEE-118 node test feeders.

Increasing penetration rate of renewable energy in distribution network (DN) require effective measure for self-balancing. Considers the profit of multi investment entities with distributed energy resources (DERs) in a district DN, this paper proposed an incentive-based optimal operation method. This is a win-win situation for both the utility grid and the investors of DERs. On the one hand, the demand fluctuation and reverse power flow is reduced to delay the investment of gird expansion; the other part is the multi investment entities can benefit from the coordinated response process. The case study demonstrates the effectiveness of the proposed approach.

Integration of distributed generation (DG) in existing distribution networks has been studied thoroughly during the past years as a measure of reducing grid's power losses. However, the optimal DG placement, known as ODGP, toward loss minimisation, has not been studied in depth by considering the possible impact of the reverse power flow (RPF) caused by extended penetration of distributed energy resources. This study uses a constriction factor embedded local particle swarm optimisation algorithm along with the appropriate particle formulation that solves the ODGP problem by taking into account the impact of possible RPF. In this study, the idea of RPF modelling is introduced by providing extended versions of IEEE test systems. Modified versions of the IEEE 30-bus and IEEE 33-bus test systems are modelled and results are presented in order to highlight the impact of RPF on the ODGP problem solution. The mathematical formulation is given, results and analysis for both extended systems are presented, while the importance of RPF for different conditions is assessed.

Significant growth in PV penetration worldwide has introduced intriguing challenges for power utilities and consumers alike. This include financial losses resulting from overvoltage-induced PV curtailment during times of high PV generation. This paper examines these issues by first developing a methodical approach to quantify the impacts of PV penetration in terms of reverse power flow, overvoltage and undervoltage events. A real distribution feeder in South Australia is analysed against various PV penetration levels. The simulation model developed utilises residential load profile of South Australia and voltage regulation limits of the feeder and the inverter as set by the Australian standard. Results show that increase in PV penetration reduces the instances of undervoltage, however the instances of overvoltage increase substantially. The latter leads to inverter shutdowns when the voltage exceeds the nominal maximum voltage of the inverters. Maximum possible PV generation loss due to inverter shutdown is evaluated and some recommended solutions are presented. The financial loss due to PV curtailment has been estimated from different perspectives, namely, using feed-in-tariff, retail price and the pool price (market price). In the context of rapidly evolving regulatory frameworks and financial models for renewable energy, power utilities will need to take these financial losses into account when conducting cost-benefit analysis for possible network upgrades for increasing the PV hosting capacity of the network. Refereed/Peer-reviewed

The impact of PV generation distributed in a low voltage transmission line depends on many factors: The distribution lines and PV generators characteristics, its location, operational control, local meteorological conditions, electricity consumption profile, and the electricity cost variation. An atypical and challenging behavior of photovoltaic distributed generation (DG) insertion in consumer units (CUs), implies in some circumstances, as the reverse directionality of the power flow between the load equipped with a photovoltaic system generator and the electrical grid, when a CU contains a distributed generation and low power consumption, the power flow will be directed to the power electric grid. In this work, the modeling of a low-voltage real feeder was performed, setting the variables of the system under real operating conditions. As result, voltage levels variability throughout the feeder, the electrical losses, and the asymmetry between the phases were observed. Through simulation scenarios, the occurrence of voltage increase under different penetration scenarios of distributed generation was verified and there was a 10% increase in reference voltage as well as the occurrence of higher electrical losses by reverse current, reaching 1200% more with a DG penetration, in the massive presence of the photovoltaic generator. The mitigatory action used in this work was able to attenuate the negative impacts to the feeder circuit, ensuring the integrity grid and the consumer unit.

The growth of photovoltaic systems (PV) and battery energy storage systems (BESS) will become a challenge for distribution players. In this way it is important to understand how these systems can impact on the distribution grid operation. For this, a study was developed considering the insertion of PV on IEEE 13 buses test feeder, based on different penetration levels. These levels were calculated contemplating two different parameters: the one most used in Brazil, and the parameter that consists in an extended criterion used worldwide. Considering these possibilities, different penetration levels of photovoltaic were defined. In conjunction with photovoltaic generation, a BESS was inserted in the same feeder, in order to evaluate the impacts of this system. From the simulations was possible to evaluate the tap changes, the voltage profile, power losses and the total energy, including if there was reverse power flow at any moment during one day.

The increasing amount of power plants connected to the distribution networks is pointing out issues about energy balances of local communities as well as observability and management of the energy flows by the Distribution System Operator. This paper presents a real life Demand Response campaign carried out by the local Distribution System Operator to reduce the Reverse Power Flow caused by the increasing amount of energy produced locally by distributed generators from not programmable energy sources. Innovative near-real time smart meters and advanced software developed under the Nobel GRID and the WiseGRID projects were used for the trial. Furthermore, these findings and actual data have been used for running simulations at the primary substation level for a complete year. The encouraging results obtained, especially when large energy consumers are involved, have shown the effectiveness of these tools and how they can enable the Distribution System Operator to use Demand Response strategies for increasing grid efficiency and control.

This paper proposes a decentralized charging control method of a battery energy storage system (BESS) that can prevent the over-capacity of a pole transformer in low-voltage (LV) distribution systems due to reverse power flow from the photovoltaic generation system. The distribution system operator provides the charging parameters defined as the relationship between the state-of-charge (SoC) and the charging threshold determined by using only the LV-distribution system configuration and the demand-side information to customers. Each BESS charges the power according to the provided parameters. A high charging amount can be maintained by automatically changing the charging mode based on the change in SoC. Results of the numerical simulation demonstrate that the proposed method can prevent the over-capacity of PTr and maintain the high charging amount of a BESS in LV-distribution systems. Further, the maximum power flow at the distribution substation and the distribution losses in MV-distribution system can be reduced.

DC-feeding Microgrid (DCMG) which can integrate plural DC-driven facilities by using information is considered as a future energy system for rural shore area. To balance supply and demand in the DCMG, a set of fuel cells and electrolyzer (FCE) systems is proposed as an energy storage system instead of conventional battery systems. DCMG including FCE, PV and DC loads are assumed, the mode controlling method for FCE to balance supply and demand is proposed in this paper. As a result, FCE is controlled by proposed method and can balance supply and demand without reverse power flow to utility grid.

In this paper a novel approach regarding the optimal penetration of Distributed Generation (DG) in Distribution Networks (DNs) towards loss minimization is proposed. More specific, a Local Particle Swarm Optimization (PSO) variant algorithm is developed in order to define the optimal active and reactive power generation and/or consumption requirements for the optimal number and location of nodes that yield loss minimization. Thus, the proposed approach provides the optimal number, siting and sizing of DGs altogether. In addition, based on the optimal power requirements of the resulted nodes, a combination of potential DG types to be installed is recommended. The proposed objective function in this paper is also innovative since it embeds the constraint of reverse power flow to the slack bus by the formation of a new penalty term. The proposed methodology is applied to 30 and 33 bus systems. The results indicate the optimal number, locations, and capacity of DG units, which were calculated simultaneously. Finally, the impact of the predefined amount of permissible reverse power flow to the optimal solution is also examined through two scenarios: the first considers zero reverse power flow and the second unlimited reverse power flow.

The number of installed photovoltaic (PV) systems has been increasing in an unprecedented rate every year throughout the world. In some situations, the PV systems can provide more power than the demand in certain parts of a network and cause reverse power flow, which the traditional distribution networks are not designed for. Consequently, these instances may result in adverse interactions between PV systems and voltage regulation devices such as step voltage regulators (SVRs). This can potentially drive voltage magnitudes beyond acceptable limits and possibly damage consumers’ appliances. In the literature, such interaction cases with consideration of realistic three-phase four-wire unbalanced networks have not yet been reported. Therefore, this study analyses the interaction between SVR and PV systems in a real-world network by utilising the quasi-static time-series technique for a long-term statistical assessment. This evaluation focuses on examining voltage regulation issues in an unbalanced three-phase four-wire network along with an open-delta SVR configuration, and the corresponding solution is proposed to resolve the concerning issues. The results of this study will provide valuable information on interaction characteristics to academia and utilities for assessing large-scale PV system integration.

This paper investigates and analyzes the impacts of reverse power flow on the power system connecting elements (transformers and cables). For effective investigation and analysis, the paper groups the network under investigation into Zones A and B. Zone A is directly connected to a wind farm. Zone B is far from the wind farm. Different wind energy penetration levels are simulated. The results show that the elements experience reverse power flow at different penetration levels depending on their location and distance from the point of common coupling. Reverse power flow incurs additional element losses. In Zone A, loading and losses increase with reverse power flow, while Zone B experiences loss reduction with increase in reverse power flow. The elements operate within acceptable thermal ratings.

This paper performs a power flow modelling of a distribution grid considering the presence of electric vehicles (EVs) and distributed generation, in this case, photovoltaic panels (PV). Thus, this work aims to analyse the impacts on the distribution transformer in different levels of electric vehicle and distributed generation penetrations. The simulations are performed in three stages: 1st Stage: Modelling of different levels of EVs penetration in relation to the total amount of houses: 25%, 50%, 75% and 100%; 2nd Stage: Network analysis with penetration of EVs and PVs of equal magnitudes of 25%, 50%, 75% and 100%; 3rd Stage: Viability of the maximum penetration of EVs recharge with the aid of FV distributed generation. The results show the importance of distributed generation to relieve the distribution transformer load. However, a reverse power flow is observed due to PV penetration, which can be mitigated with a planned and coordinated insertion in the right proportions of EVs and PVs.

In this paper we propose a linear program (LP)-based algorithm to schedule battery storage co-located with residential solar photovoltaics (PV), when excess generation is compensated via net metering. While the objective of this LP-based approach is to maximize the operational savings that accrue to customers, an undesirable consequence to the utility is reverse power flow during the peak pricing period. We show in this paper that it is possible to balance the objective of the utility in limiting reverse power flow, with the customer objective of increasing operational savings, in the context of net metering. To balance the specified utility and customer objectives we employ a quadratic program (QP)-based algorithm, which explicitly penalizes reverse power flow. To complete our assessment of net metering, both the LP-based and QP-based scheduling algorithms are applied to measured load and generation data from 145 residential customers located in an Australian distribution network. The results of this case study confirm the absence of reverse power flow when all customers employ a QP-based battery schedule, with the majority of customers exhibiting operational savings.

This chapter introduces the Optimal Distributed Generation Placement problem towards power and energy loss minimization. Several solving methods are applied in order for the most suitable to emerge. Apart from technical and DG constraints, recent raised issues due to high Distributed Generation penetration like the reverse power flow effect is considered as well. The load and generation variability and their impact in integrating Renewable Energy Sources are examined, aided by the use of Capacity Factors implementation. In addition, the impact of Optimal Distributed Generation Placement problem in conjunction with Network Reconfiguration and Optimal Energy Storage Systems Placement is introduced aiming to examine how joined management schemes could be efficiently combined in order to maximize the potential loss and energy reduction.

Photovoltaic (PV) penetration in Low-Voltage (LV) networks is expected to increase in the following years, posing a series of problems in the operation pf low-voltage networks. Among the most important challenges imposed, is the reverse power flow caused by high injected energy from distributed PVs during peak irradiation hours. This is the reason of voltage rises above the permissible limits. Amongst other solutions, such as active power curtailment and reactive power absorption, the installation of distributed Energy Storage Systems (ESS) seems to be an attractive solution since it can absorb surplus power locally, avoiding curtailment methods, power flow losses on the feeder and grid reinforcements. As the cost of storage is decreasing, ESS are expected to be increasingly adopted by prosumers. This work evaluates the influence of such systems on the voltage profile of LV feeders and on the self-consumed energy of prosumers. Intensive simulations on a benchmark feeder assess the conflicted benefits of power system operators and ESS owners.

Increasing penetration level of photovoltaic (PV) distributed generation (DG) into distribution networks will have many impacts on nominal circuit operating conditions including voltage quality and reverse power flow issues. In U.S. most studies on PVDG impacts on distribution networks are performed for west coast and central states. The objective of this paper is to study the impacts of PVDG integration on local distribution network based on real-world settings for network parameters and time-series analysis. PVDG penetration level is considered to find the hosting capacity of the network without having major issues in terms of voltage quality and reverse power flow. Time-series analyses show that distributed installation of PVDGs on commercial buses has the maximum network energy loss reduction and larger penetration ratios for them. Additionally, the penetration ratio thresholds for which there will be no power quality and reverse power flow issues and optimal allocation of PVDG and penetration levels are identified for different installation scenarios., To be published (Accepted) in: 12th IEEE PES PowerTech Conference, Manchester, UK, 2017

The low voltage (LV) distribution cable networks were installed some decades ago but the new paradigm in electric power engineering generates new requirements from these old assets. The distributed generation, storage and new appliances can cause high variation of load and reverse power flow, nevertheless the LV cable grid was not designed to these new stresses. The aggregate load and generation can surpass the rated capacity of the cable lines causing short term temperature increasing. This temperature stress can decrease the expected lifetime of the cable lines. In this study the short term thermal overload of LV distribution cables was investigated. The experiments were executed on PVC insulated LV cable samples and electrical and mechanical properties of the cable jacket were investigated. The effect of these short-term overloads on the expected lifetime of cables is introduced and non-destructive measurement for tracking the effect of the short term thermal overloads on the cable is suggested.

This paper deals with the analysis of the customer voltage characteristic in distribution system interconnected with large scale PV system. There would be many power quality issues which are caused by reverse power flow of PV system interconnected with distribution system. In order to analyze the effect of PV system on the customer voltage, detailed modeling method of distribution system and modified modelling method of PV system are proposed using PSCAD/EMTDC in this paper. So far, less than dozens KW of PV system can be simulated with the existing modelling method. Therefore, a new modeling method which can simulate the large scale PV system is proposed by considering the relationship equation on the phase and voltage in the current control algorithm. From the simulation result of proposed modelling method, it is confirmed that an optimal operation method in distribution system is suggested by analyzing the effect of PV system on customer voltage.

Distributed generators (DG) using renewable energy sources (RESs) have been attracting special attention within distribution systems. However, a large amount of DG penetration causes voltage deviation and reverse power flow in the smart grid. Therefore, the smart grid needs a solution for voltage control, power flow control and power outage prevention. This paper proposes a decision technique of optimal reference scheduling for a battery energy storage system (BESS), inverters interfacing with a DG and voltage control devices for optimal operation. Moreover, the reconfiguration of the distribution system is made possible by the installation of a loop power flow controller (LPC). Two separate simulations are provided to maintain the reliability in the stable power supply and economical aspects. First, the effectiveness of the smart grid with installed BESS or LPC devices is demonstrated in fault situations. Second, the active smart grid using LCPs is proposed. Real-time techniques of the dual scheduling algorithm are applied to the system. The aforementioned control objective is formulated and solved using the particle swarm optimization (PSO) algorithm with an adaptive inertia weight (AIW) function. The effectiveness of the optimal operation in ordinal and fault situations is verified by numerical simulations.

This paper describes the impact on the voltage profiles of a secondary distribution network in the presence of Small Scale Distributed Generation (SSDG) units. The Penetration Levels of these SSDG units are varied and the effect on the voltage is simulated and analysed. The study also describes how the size of each SSDG unit affects the maximum penetration level of SSDG in the low voltage network while maintaining the voltage within statutory limits. The Case Study is a detailed model in DIgSILENT Power Factory® of a highly residential area with all network components modelled using manufacturer's data. Actual load profiles of consumers have been recorded and used for the simulation as well as recorded typical photovoltaic generation profile for Mauritius. The key contribution of this paper is the determination of the maximum amount of SSDG that secondary distribution networks can accommodate while maintaining the voltage within statutory limits. The results demonstrate that penetration level varies with the size of the installed SSDGs and for the different sizes simulated, the penetration level can be as low as below 10% for large SSDG (8.7 kW) and up to 60% for smaller size SSDG units (4.35 kW). No overloading of existing low voltage overhead cables has been observed in all the cases, even with reverse power flow.

Existing technologies can mitigate voltage fluctuation and reverse power flow effectively. At the same time, complementing solar PV with energy storage resources and flexible loads creates opportunities to earn new revenues from wholesale electricity markets, enhancing both the reliability value and the monetary value of these clean energy resources.

Recently, photovoltaic generation (PV) has attracted a great attention as one of green power generations. Accordingly a large amount of PV systems will be installed in residential areas in the coming years. In such scenario, reverse power flow caused by PV in feeders may cause some problems such as voltage rise over upper limits in the distribution line, and the reverse power flow into the distribution substation. Battery energy storage system (BESS) is a promising option to solve the above both problems at the same time. However, the effect of BESS depends on location of BESS. Therefore, it is necessary to consider an appropriate location in the residential distribution system to install BESS to obtain an optimal effect. This paper investigates an optimal placement pattern of BESS in the residential distribution system with certain patterns of PV installation. It has been made clear that the obtained results can determine the best placement pattern of BESS with the minimum required BESS capacity and power loss.

This paper develops an interconnection test devices for photovoltaic(PV) systems composed of distribution system simulator, PV systems simulator and control and monitoring systems using the LabVIEW S/W, and simulates the customer voltage characteristics considering the 3 parameters on the introduction capacity for PV systems, system configuration and load factor. This paper also proposes a new calculation algorithm for voltage profile to make a comparison between calculation values and test device values. The results show that the test results for the normal operation characteristics of PV systems is very practical and effective.Key Words : PV Systems, Interconnection, Reverse Power Flow, Test Device, Customer Voltage 본 연구는 2010년도 지식경제부의 재원으로 한국에너지 기술평가원(KETEP)의 지원을 받아 수행한 연구 과제입니다. (No. 20101020300430) * 교신저자 : 노대석(dsrho@kut.ac.kr)접수일 10년 09월 12일 수정일 10년 10월 19일 게재확정일 10년 11월 19일 1. 서 론 정부의 녹색성장정책에 의하여, 2030년까지 전체 에너지원 중 신에너지전원의 비중을 전체 에너지원의 11%정도로 확대하는 정책('09년 현재 2.2%)을 적극적으로 추진하고 있다. 그러나 신에너지전원의 확대보급 활성화방안에 따라 지자체와 발전사업자 등의 도입계획은 많은 반면, 아직 국내에는 대용량 신에너지전원의 계통연계에 대한 기술기준 및 체계적인 선로운영 기술기준이 미흡한 실정이다.[1-5] 특히 충남 천안 목천의 해비태트 마을에 설치된 30여대의 태양광발전이 저압배전선로에 설치되어 운용되는 동안, 낮에는 태양광 발전량이 상승하여 계통으로 유입하는 역조류가 발생하여 수용가의 전압이 240V까지 상승하는 과전압 현상이 발생된 사례가 보고되고 있다 . 또한, 대용량 분산전원(태양광, 풍력 등)이 연계된 고압선로의 선로전압조정장치(SVR)가 분산전원의 발전량에 의한 과전압 현상으로 기기의 오동작이 발생되는 실계통의 문제점이 다수 보고되고 있는 실정이다.[6-9]이러한 배경 하에, 본 논문에서는 배전계통의 운용특

The typical distribution systems have the power flow from distribution substations (sources) to customers (load) only as one direction. However, in the case where new energy power sources are connected to distribution systems, the output variations of new energy sources to distribution systems, which is so called reverse power flow, may cause the bi-directional power flow. So, the reverse power flow has severe impacts on typical power system, for example power quality problems, protection coordination problems, and so on. Therefore, this paper proposes the algorithm for Multi-functional protection devices in distribution systems in the case where new energy sources are interconnected. The proposed algorithm is verified to show the effectiveness by simulating and experimenting the prototype systems.

The number of installation of Distributed Generators (DG) such as photovoltaic and wind generations has been rapidly increasing in the world. Penetration of DG can contribute to reduce CO2 emissions and conserve energy. On the other hand, since reverse power flow from DG to distribution system occurs exceed of the upper limit of adequate range of voltage, various voltage control methodologies have been proposed in order to keep voltage within the secure range. This paper describes several advanced voltage control technologies and shows the trend and future perspective about the control of distribution system with many DGs.

A set of three scenarios has been created in order to examine the incorporation of extensive penetrations of micro-generators into electricity networks (termed ‘highly distributed power systems’). The scenarios have been created as a synthesis of the Future Network Technologies scenarios and the UK domestic carbon model, and yields energy use and carbon dioxide emissions of the UK housing stock from inputs of household numbers, house type, thermal efficiency, appliance efficiency, as well as the number and efficiency of micro-generators used. The centralized supply mix also varies between scenarios and features extensive penetrations of large-scale renewables. The scenarios illustrate the scale of change required to reduce CO2 emissions by 60 per cent by 2050, which has substantial impacts for electricity network operation. Moving from a centralized system to the one where one-third of electricity comes from distributed sources poses significant challenges including: reverse power flow on networks, load balancing, storage requirements, phase unbalance, harmonics, and ancillary services.

This paper discusses reverse power flow from a home cogeneration system (H-CGS) in terms of energy conservation and influence on electric power systems. Data for actual electricity and hot-water demand observed in a family including two adults and two children for a year were used as a case study for a typical installation. When the reverse power flow is allowed except for during late night, in consideration of the influence on the electric power system, the reduction in annual primary energy consumption can be increased by about 40% relative to that in the operation without reverse power. The reverse power flow is large during the daytime in winter season, because the power output of H-CGS is large in order to meet the large hot-water demand. Even if reverse power is allowed throughout a day, the primary energy conservation is almost the same as that in part-time reverse power operation, while the reverse power during late night is as large as that during daytime. Finally, the economic value of reverse power flow as a measure for reducing CO2 emission was evaluated. The result shows that the economic value of reverse power flow in PR operation corresponds to 23,000 yen/t-C. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 91(10): 11– 19, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10162

Increasing penetration of Distributed Generation (DG), when not planned appropriately by the Distribution Network Operator may lead to opposite results that are displaced as externalities on adjacent grids. Reverse Power Flow (RPF) by means of an upstream power flow leaving the grid under study and heading to the neighbouring ones could be such an issue and need to be considered and modelled accordingly. This paper introduces two implementations of constriction factor Embedded-Local PSO Variant algorithms along with the appropriate particle formulation that focus on the Optimal Distributed Generation Placement (ODGP) problem solving, by taking into account the impact of possible RPF. Both RPF methods are applied to either radial or meshed IEEE test systems and a detailed comparison is presented. Focus is given on how the integration of RPF would affect the final solution to the ODGP problem, but the same RPF modelling strategies could be applied under different target functions as well.

The rapidly increasing number of implemented photovoltaic (PV) systems in the German distribution grid in recent years has led to power quality issues due to the intermittent generation and reverse power flows in periods of low demand. In order to decrease this impact, different solutions are being investigated. The aim of this study is to analyze the maximum possible grid relief by using residential PV storage systems and different reactive power control strategies from the viewpoint of a distribution system owner. To compare the different voltage control method scenarios the hosting capacity is used as a performance indicator.

NIE Networks' distribution system is heavily connected with Distributed Generation (DG) resulting in significant reverse power flows at many primary substations. Amongst other issues, this has resulted in DG saturation at substations where NIE Networks, in the absence of network reinforcement, are unable to issue additional DG connection offers. This paper seeks to inform the industry on some of the more prevalent issues associated with operating a distribution system in reverse power flow and the current solutions employed within NIE Networks to overcome these issues.

Distributed Generators (DGs) using Renewable Energy Sources (RESs) have a huge economical and environmental potential. However, high penetration of DGs in distribution systems cause voltage deviations beyond the statutory range, and can cause reverse power flow toward the substation transformer. It is essential to control and maintain the distribution voltage within proper range to ensure both a stable power supply and good power quality. To accomplish this, an auto-tap-changer pole transformer (ATCTr) is introduced to solve this problem. However, the ATCTr is more expensive than ordinary pole transformers. Minimizing the voltage deviation as well as minimizing the introduction cost of an ATCTr have a trade-off relationship. Accordingly, this paper presents the application of multi-objective optimization methods in order to minimize the voltage deviation while simultaneously minimizing the number of introduced ATCTrs and finding an optimum placement of the ATCTrs to attain optimum operation of the distribution system.

The novel thyristor voltage regulator (TVR) for power distribution lines is discussed. It has faster response time, lighter weight, and higher maintainability compared with the existing TVR's. The newly developed “jumping-tap method” demonstrated high-speed response of 0.1 second. Thanks to this method, a big voltage disturbance caused by motor starting, for example, could be compensated. Reverse power flow cause judgement is discussed.

The integration of renewable energy resources (RESs) in power systems poses many research challenges. Research shows that the RES output may exceed the consumed power during the day. Consequently, the direction of the power flow on distribution lines can be reversed during some periods. As the voltage regulator is normally designed for unidirectional power flow, this may cause voltage violations on the distribution feeder. Therefore, most utilities try to set a penetration level (PL) limit for safe operation. On the other hand, time varying and unbalanced loading are the main characteristics of distribution systems. Moreover installation of intermittent and nondispatchable photovoltaic (PV) devices increases the control problems of distribution system. This paper presents an impedance-based monitoring method for detection of distribution system current behavior. It will be shown that by utilizing this monitoring technique, not only the small variation of PV PL can be easily detected, but also some fast transients such as the effect of cloud movement on PV system can be monitored. This monitoring technique employs only local measurements of bus voltages and line current to measure the apparent impedance seen at the installation point. The practical application of measured impedance as a monitoring technique shows its effectiveness for distribution system monitoring in presence of various PV PL. 2015 IEEE. Scopus 2-s2.0-85027948194

The integration of solar PVs which is projected to increase over the years creates concerns over stability. Reverse power flow occurs due to high PV penetration into the power system network. PV placement at proper locations in a transmission system is essential to maintain voltage stability. Improper placement will caused voltage stability of the system to be affected. However, if the PVs are connected at a strategic location it will lead to a more stable system. This paper presents a methodology for PV source placement in the transmission system while maintaining the stability of the. Voltage Stability Index (VSI) will be used as an indicator to measure the stability status of the system. Two test systems will be used for simulation for this research, the IEEE 30 Bus and 57 Bus Test System. The simulation results showed that proper placement of the PV source in the transmission system will lead to better stability to the system.

Presents a collection of slides covering the following topics: community scale energy storage; LV networks; reverse power flow; and PV generation.

Indirect matrix converter (IMC) using two stages configuration is topologically more flexible than 3×3 direct matrix converter (DMC). For grid integration of ac type distributed generators, the ac/ac converters need voltage boost function, which can't be achieved by traditional IMC due to its limited input-to-output voltage transfer gain 0.866. Alternatively, reverse power flow operation of IMC can be implemented to meet voltage boost requirement for distributed generation interface. Intuitively, only the generator side power needs to be controlled, since the power will be spontaneously transferred to the grid side due to the lack of energy storage in IMC. However, open-loop operation of grid side (current source side) converter will lead to uncontrollable grid side reactive power. This paper proposes control schemes of IMC with controllable grid side reactive power by means of controlling both the generator and grid side currents coordinately with properly designed control loop. Simulation results are provided to validate the effectiveness of the control schemes for the proposed matrix converter.

We have developed an optimal management planning method for the efficient use of a photovoltaic generation system with heat pump water heater and battery storage. This plan can prevent shortage of hot water while minimizing the cost and maximizing customer convenience and can deal with multiple scenarios corresponding to uncertainties in forecasting PV output, hot water and electricity demand. A simulation was performed to analyze daily operation with the proposed planning method in terms of year-round hot water demand, electricity demand, and PV output. An experiment was also conducted using the heat pump water heater to demonstrate the proposed method.

A procedure for minimizing the accumulated line power losses of radial distribution feeder over the day, namely line energy loss, has been developed. It determines the optimal size and location of a Photovoltaic Distributed Generation (PVDG) unit that minimizes the line energy loss, while avoiding reverse power flow along the feeder. The procedure considers the concept that the PVDG production varies independently from the changes in feeder demand, which most likely results in a peak mismatch for both. With such mismatch the PVDG unit can produce only part of its capacity at the time the feeder meets its peak load demand. Hence, the objective of minimizing the line energy loss is more appropriate in this application than that of minimizing the line peak power loss. However, dealing with energy-based quantities needs a sort of calculations for each time interval over the whole daily duration. In this essence a suitable method has been derived to rate the line energy loss of the feeder at only one time interval over the day, namely Feasible Optimization Interval (FOI). The procedure has been applied successfully on two 11kV radial distribution feeders within Abu Dhabi network. The application demonstrated that the optimal solution resulting in minimum line power loss at the FOI is the same resulting in minimum line energy loss over the day.

Japanese government plans to introduce photovoltaic (PV) systems 20-fold by 2020 compared to the 2005 level, and then grid-connected PV systems are expected to increase rapidly. At the same time, however, there is concern that a large scale PV systems introduction might bring an excess of supply when the electricity demand is low such as in spring or autumn in Japan. Meanwhile, heat pump water heaters (HPWHs) are highly efficient water heaters and have been introduced rapidly. If hot water is stored in the daytime using HPWHs, it will contribute to absorb economically a part of the excess of PV output. In this paper, we propose a use of residential HPWHs in the daytime as a means of PV reverse power flow restriction. And we evaluate how the difference of the actual demand patterns influences on PV reverse power flow restriction and HPWH power consumption.

Various tests were performed to examine the quality of power, the inetgrity of the grid, and safety, pointing out problems and investigating methods of counteracting them