Grid integrated renewable DG systems: A review of power quality challenges and state-of-the-art mitigation techniques

Increased energy demands due to rapid industrialization, environmental concerns with fossil fuel–based generation, diminishing fossil energy resources, transmission network congestion, and technical performance deterioration are the motivations behind the integration of small renewable distributed generation (DG) units and turning the existing power systems into a restructured one. Optimizing the technical benefits offered by DG placement is a well-known challenge for distribution network operators (DNOs) for both fossil and renewable energy resource–based DGs, but renewable DG systems have several power quality (PQ) challenges associated additionally. Power quality is a very significant characteristic of renewable DG systems because today's loads are more sensitive to PQ disturbances and penetration of renewable energy as well as nonlinear loads is proliferating in distribution power networks. So the need for innovative power quality improvement (PQI) techniques becomes inevitable due to ongoing reformation in traditional distribution networks by the integration of renewable energy. This article presents a comprehensive analysis of power quality challenges with grid integration of renewable DG systems and current research status of associated mitigation techniques. Firstly, this paper puts emphasis on theoretically illustrating all the crucial power quality challenges associated with grid integration of renewable energy, and secondly, a thorough survey, of all PQI techniques introduced till date, is elaborated along with highlighting the opportunities for future research. Furthermore, all the crucial power quality issues, the impact of high penetration of renewable energy and mitigation techniques on power quality, are demonstrated also by simulating a grid integrated PV-based DG system in MATLAB/Simulink. This article is believed to be very beneficial for academics as well as industry professionals to understand existing PQ challenges, PQI techniques, and future research directions for renewable energy technologies.     

A novel method to investigate voltage stability of IEEE-14 bus wind integrated system using PSAT

The maximum demand of power utilization is increasing exponentially from base load to peak load in day to day life. This power demand may be either industrial usage or household applications. To meet this high maximum power demand by the consumer, one of the options is the integration of renewable energy resources with conventional power generation methods. In the present scenario, wind energy system is one of the methods to generate power in connection with the conventional power systems. When the load on the conventional grid system increases, various bus voltages of the system tend to decrease, causing serious voltage drop or voltage instability within the system. In view of this, identification of weak buses within the system has become necessary. This paper presents the line indices method to identify these weak buses, so that some corrective action may be taken to compensate for this drop in voltage. An attempt has been made to compensate these drops in voltages by integration of renewable energy systems. The wind energy system at one of the bus in the test system is integrated and the performance of the system is verified by calculating the power flow (PF) using the power system analysis tool box (PSAT) and line indices of the integrated test system. The PF and load flow results are used to calculate line indices for the IEEE-14 bus test system which is simulated on PSAT.     

Optimal planning of distributed generation systems in distribution system: A review

This paper attempts to present the state of art of research work carried out on the optimal planning of distributed generation (DG) systems under different aspects. There are number of important issues to be considered while carrying out studies related to the planning and operational aspects of DG. The planning of the electric system with the presence of DG requires the definition of several factors, such as: the best technology to be used, the number and the capacity of the units, the best location, the type of network connection, etc. The impact of DG in system operating characteristics, such as electric losses, voltage profile, stability and reliability needs to be appropriately evaluated. For that reason, the use of an optimization method capable of indicating the best solution for a given distribution network can be very useful for the system planning engineer, when dealing with the increase of DG penetration that is happening nowadays. The selection of the best places for installation and the preferable size of the DG units in large distribution systems is a complex combinatorial optimization problem.This paper aims at providing a review of the relevant aspects related to DG and its impact that DG might have on the operation of distributed networks. This paper covers the review of basics of DG, DG definition, current status of DG technologies, potential advantages and disadvantages, review for optimal placement of DG systems, optimizations techniques/methodologies used in optimal planning of DG in distribution systems. An attempt has been made to judge that which methodologies/techniques are suitable for optimal placement of DG systems based on the available literature and detail comparison(s) of each one.     

Integration and development of energy and information network in the Pan-Arctic region

The Global Energy Interconnection is an important strategic approach used to achieve efficient worldwide energy allocation. The idea of developing integrated power, information, and transportation networks provides increased power interconnection functionality and meaning, helps condense forces, and accelerates the integration of global infrastructure. Correspondingly, it is envisaged that it will become the trend of industrial technological development in the future. In consideration of the current trend of integrated development, this study evaluates a possible plan of coordinated development of fiber-optic and power networks in the Pan-Arctic region. Firstly, the backbone network architecture of Global Energy Interconnection is introduced and the importance of the Arctic energy backbone network is confirmed. The energy consumption and developmental trend of global data centers are then analyzed. Subsequently, the global network traffic is predicted and analyzed by means of a polynomial regression model. Finally, in combination with the current construction of fiber-optic networks in the Pan-Arctic region, the advantages of the integration of the fiber-optic and power networks in this region are clarified in justification of the decision for the development of a Global Energy Interconnection scheme.     

Towards a future with large penetration of distributed generation: Is the current regulation of electricity distribution ready? Regulatory recommendations under a European perspective

The European Energy Policy promotes renewable energy sources and energy efficiency as means to mitigate environmental impact, increase security of supply and ensure economic competitiveness. As a result, the penetration levels of distributed generation (DG) in electricity networks are bound to increase. Distribution networks and distribution system operators (DSOs) will be especially affected by growing levels of DG. This paper reviews the current regulation of distribution in the European Union Member States, focusing on those aspects that might hinder the future integration of DG. Several regulatory issues that may hinder a successful integration of DG have been identified. Recommendations to improve the current situation are proposed. Regarding economic signals sent to DG, connection charges and cost-reflective use-of-system charges together with incentives to provide ancillary services are the key aspects. Concerning DSOs regulation, unbundling from generation and supply according to the European Electricity Directive, incentives for optimal planning and network operation considering DG, including energy losses and quality of service, and innovation schemes to migrate to active networks are the most relevant topics.     

Wind power investment within a market environment

Within an existing transmission network, this paper considers the problem of identifying the wind power plants to be built by a wind power investor to maximize its profit. For this analysis a future target year is considered and the loads at different buses are represented by stepwise load–duration curves. The stochastic nature of both load and wind is represented via scenarios. The considered electric energy system operates under a pool-market arrangement and each producer/consumer is paid/pays the Local Marginal Price (LMP) of the bus at which it is located. The higher the wind penetration is, the lower the resulting LMPs. To tackle this problem a stochastic bilevel model is proposed, whose upper-level represents the wind investment and operation decisions with the target of maximizing profits; and its lower-level represents the market clearing under differing load and wind conditions and provides LMPs. This model can be recast as a mixed-integer linear programming problem solvable using commercially available branch-and-cut solvers. The proposed model is illustrated using an example and two case studies.     

Increasing penetration of renewable and distributed electricity generation and the need for different network regulation

The amount of decentralised electricity generation (DG) connected to distribution networks increases across EU member states. This increasing penetration of DG units poses potential costs and benefits for distribution system operators (DSOs). These DSOs are regulated since the business of electricity distribution is considered to be a natural monopoly. This paper identifies the impact of increasing DG penetration on the DSO business under varying parameters (network characteristics, DG technologies, network management type) and argues that current distribution network regulation needs to be improved in order for DSOs to continue to facilitate the integration of DG in the network. Several possible adaptations are analysed.     

Dynamic model of wind energy conversion systems with variable speed synchronous generator and full-size power converter for large-scale power system stability studies

This paper presents a dynamic model for variable speed wind energy conversion systems, equipped with a variable pitch wind turbine, a synchronous electrical generator, and a full power converter, specially developed for its use in power system stability studies involving large networks, with a high number of buses and a high level of wind generation penetration. The validity of the necessary simplifications has been contrasted against a detailed model that allows a thorough insight into the mechanical and electrical behavior of the system, and its interaction with the grid. The developed dynamic model has been implemented in a widely used power system dynamics simulation software, PSS/E, and its performance has been tested in a well-documented test power network.     

Probabilistic load flow using Monte Carlo techniques for distribution networks with photovoltaic generators

Connections of distributed generation (DG) systems to distribution networks are increasing in number, though they may often be associated with the need of costly grid reinforcements or new control issues to maintain optimal operation. Appropriate analysis tools are required to check distribution networks operating conditions in the evolving scenario. Load flow (LF) calculations are typically needed to assess the allowed DG penetration level for a given network in order to ensure, for example, that voltage and current limits are not exceeded.

The present paper deals with the solution of the LF problem in distribution networks with photovoltaic (PV) DG. Suitable models for prediction of the active power produced by PV DG units and the power absorbed by the loads are to be used to represent the uncertainty of solar energy availability and loads variation. The proposed models have been incorporated in a radial distribution probabilistic load flow (PLF) program that has been developed by using Monte Carlo techniques. The developed program allows probabilistic predictions of power flows at the various sections of distribution feeders and voltage profiles at all nodes of a network.

After presenting theoretical concepts and software implementation, a practical case is also discussed to show the application of the study in order to assess the maximum PV peak power that can be installed into a distribution network without violating voltage and current constraints. A comparison between Deterministic Load Flow (DLF) and PLF analyses is also performed.     

Impact of residential photovoltaic power systems on the electric utility in Cairo, Egypt

The impact of utility-interactive residential photovoltaic (PV) power systems on the electric utility was studied. Power flow analyses were performed before and after the introduction of PV, on a subtransmission and distribution network model of an actual residential utility feeder serving a suburban area of Helwan in Cairo, Egypt. The changes in bus voltages and utility power factor were used to assess the impacts caused by the PV introduction. PV systems were examined at different penetration levels and were introduced in the low- and high-voltage buses of the distribution circuit. PV power factors as low as 0·7 were used to account for various power conditioner designs. PV-utility interconnection at the high-voltage distribution level is recommended since it results in acceptable voltage regulation throughout the network as well as a good utility power factor.     

新型负荷接入环境下的配电网分布式电源规划

随着电动汽车以及储能技术的不断成熟,电动汽车及储能设备等新型负荷的不确定性给分布式电源接入配电网的规划工作带来了新的挑战。基于机会约束,建立了一种考虑新型负荷特性的配电网分布式电源规划模型,该模型既包括电动汽车与储能设备等新型负荷,也包括分布式风电、光伏发电等典型分布式电源,并应用概率潮流和遗传算法对模型进行求解。对IEEE33节点测试系统的测试结果表明,接入新型负荷后系统不确定性增强、总体收益有所下降,验证了所建立的电源规划模型处理负荷及分布式电源不确定性问题的可行性。     

分布式发电引起的电压波动和闪变

从并网分布式发电（DG）的输出功率波动出发。分析了分布式发电引起电网电压波动和闪变的主要原因。随后提出了基于潮流计算的闪变预测算法，用于识别闪变值最大的母线。基于matlab／simulink的电磁暂态仿真被用来准确计算电压波动和闪变。最后给出了一个算例，分析了机组爬坡和退出以及机组功率波动时的闪变情况。仿真结果显示，逆变型分布式电源引入的电压闪变很小，异步发电机的功率波动是造成电网电压闪变的主要原因。     

5G通信基站节能供电系统运行控制策略研究

5G通信基站耗电量较大,引入分布式供电(DG)单元能对其进行一定的电能补充,但DG单元易受气象条件的影响,导致通信基站节能供电系统运行不稳定.为提高通信基站节能供电系统运行的稳定性,提出了一种基于直流母线电压信息自动切换的控制策略,系统内各单元可根据当前直流母线电压状态实现并网、孤岛模式的无缝切换.仿真结果表明,所提控...     

A flexible perturb & observe MPPT method to prevent surplus energy for grid-failure conditions of fuel cells

Energy management is a critical issue for the economical and optimum operation of grid integrated renewable energy systems. In conventional grid integrated systems, the control methods are operated according to the design criteria for grid connection modes and cause surplus energy for low-loading conditions under grid-failure situations. For this purpose, in this paper, a flexible control strategy is improved basis on perturb & observe MPPT, and it is purposed to improve the system efficiency under grid-connection and grid-failure modes of renewable energy systems. In this way, it is aimed to ensure optimized power delivering capability with optimum load voltages/currents at desired values, and it also prevents overloading under grid-failure mode. To show the proposed method's validity, the algorithm of control method is embedded in a function block and performed for grid connection & grid-failure modes under different load conditions. The performance results show that the flexible control strategy prevents surplus energy under the grid-failure mode and reduces the power losses compared to the conventional method. Also, the proposed method increases the load-side power quality. The results show that THD values are significantly reduced to fewer than the conventional perturb & observe method.     

动态无功补偿实时监测系统的设计与实现

针对传统无功补偿监测系统难以实时随负载的变化而进行快速精确调节尤其是在故障时存在无功监测的数据处理量大、无法实时判断并记录的问题,构建了一种基于现场总线和无线通信网络的动态无功补偿实时监测系统,即在分析传统无功补偿监测系统特点的基础上,探讨了基于现场总线的无线通信网络的实现形式,通过在虚拟仪器平台上将过程控制中的现场总线和实时操作系统相结合,采用无线专用网络和普通网络完成主从站和站级补偿节点间的通信。在实验室环境下对系统的测试结果表明,该系统监测灵活、高效,避免了数据的冗余处理,提升了大量无功监测数据的高吞吐量。     

Future development of the electricity systems with distributed generation

Electrical power systems have been traditionally designed taking energy from high-voltage levels, and distributing it to lower voltage level networks. There are large generation units connected to transmission networks. But in the future there will be a large number of small generators connected to the distribution networks. Efficient integration of this distributed generation requires network innovations. A development of active distribution network management, from centralised to more distributed system management, is needed. Information, communication, and control infrastructures will be needed with increasing complexity of system management. Some innovative concepts such as microgrids and virtual utilities will be presented.     

Life-cycle assessment of diesel, natural gas and hydrogen fuel cell bus transportation systems

The Sustainable Transport Energy Programme (STEP) is an initiative of the Government of Western Australia, to explore hydrogen fuel cell technology as an alternative to the existing diesel and natural gas public transit infrastructure in Perth. This project includes three buses manufactured by DaimlerChrysler with Ballard fuel cell power sources operating in regular service alongside the existing natural gas and diesel bus fleets. The life-cycle assessment (LCA) of the fuel cell bus trial in Perth determines the overall environmental footprint and energy demand by studying all phases of the complete transportation system, including the hydrogen infrastructure, bus manufacturing, operation, and end-of-life disposal. The LCAs of the existing diesel and natural gas transportation systems are developed in parallel. The findings show that the trial is competitive with the diesel and natural gas bus systems in terms of global warming potential and eutrophication. Emissions that contribute to acidification and photochemical ozone are greater for the fuel cell buses. Scenario analysis quantifies the improvements that can be expected in future generations of fuel cell vehicles and shows that a reduction of greater than 50% is achievable in the greenhouse gas, photochemical ozone creation and primary energy demand impact categories.     

Improved artificial neural network method for predicting photovoltaic output performance

To ensure the safety and stability of power grids with photovoltaic (PV) generation integration, it is necessary to predict the output performance of PV modules under varying operating conditions. In this paper, an improved artificial neural network (ANN) method is proposed to predict the electrical characteristics of a PV module by combining several neural networks under different environmental conditions. To study the dependence of the output performance on the solar irradiance and temperature, the proposed neural network model is composed of four neural networks, it called multi- neural network (MANN). Each neural network consists of three layers, in which the input is solar radiation, and the module temperature and output are five physical parameters of the single diode model. The experimental data were divided into four groups and used for training the neural networks. The electrical properties of PV modules, including I–V curves, P– V curves, and normalized root mean square error, were obtained and discussed. The effectiveness and accuracy of this method is verified by the experimental data for different types of PV modules. Compared with the traditional single-ANN (SANN) method, the proposed method shows better accuracy under different operating conditions.     

天然气大客车发动机与传动系的匹配分析

介绍了在开发低排放天然气大客车中,利用自行开发的汽车性能模拟计算软件,对选择的3 种天然气发动机与传动系统的匹配作了分析,并进行了动力性能的模拟计算,使开发的新型大客车的性能最佳,为天然气大客车的设计开发提供指导。     

Design of an integrated process for simultaneous chemical looping hydrogen production and electricity generation with CO2 capture

This study was aimed at proposing a novel integrated process for co-production of hydrogen and electricity through integrating biomass gasification, chemical looping combustion, and electrical power generation cycle with CO₂ capture. Syngas obtained from biomass gasification was used as fuel for chemical looping combustion process. Calcium oxide metal oxide was used as oxygen carrier in the chemical looping system. The effluent stream of the chemical looping system was then transferred through a bottoming power generation cycle with carbon capture capability. The products achieved through the proposed process were highly-pure hydrogen and electricity generated by chemical looping and power generation cycle, respectively. Moreover, LNG cold energy was used as heat sink to improve the electrical power generation efficiency of the process. Sensitivity analysis was also carried out to scrutinize the effects of influential parameters, i.e., carbonator temperature, steam/biomass ratio, gasification temperature, gas turbine inlet stream temperature, and liquefied natural gas (LNG) flow rate on the plant performance. Overall, the optimum heat integration was achieved among the sub-systems of the plant while a high energy efficiency and zero CO₂ emission were also accomplished. The findings of the present study could assist future investigations in analyzing the performance of integrated processes and in investigating optimal operating conditions of such systems.