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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.

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 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.

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

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.

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

This paper presents an analysis of the reverse power flow capability of on-load tap-changers with the aim to find the penetration level of distributed generation that can be connected to the network. An in-detail analysis of the switching sequence during tap changing is presented first. The physical constraints that limit the switching process are then identified, and calculation of the reverse power flow capability is done by solving the optimisation problem.

The research carried out to investigate the ability of power transformers to facilitate the required power flows associated with the anticipated high penetrations of small scale embedded generation (SSEG), within small-scale energy zones (SSEZs) is described. A small-scale energy zone is defined as a section of low-voltage, network with a high penetration of SSEGs, controllable loads and energy storage units. SSEZs, coupled with active control techniques, have the potential to assist the growth of SSEGs by removing network constraints and enabling blocks of aggregated and controlled SSEGs to participate more effectively in energy markets and network operational tasks. The research focused on identifying the reverse power flow and thermal-rating constraints imposed by power transformers. The analysis was performed using an approved UK generic PSCAD/ EMTDC electrical network model, with varying levels of SSEGs. Simulations were carried out examining cases with a uniform distribution of SSEGs contained within a number of SSEZs. It was observed that in some cases the reverse power flow capability of the primary transformers would exceed if each customer installed an SSEG with a rating of approximately 1 kW.

The paper describes a bilateral high frequency DC/AC convertor for uninterrupted power supply applications. The proposed convertor can also function as a battery charger without any additional power circuit components. Moreover, this convertor provides ohmic isolation between the DC source and the load at high switching frequencies for the forward and reverse power flow modes of operation. Consequently, the convertor exhibits high power density.