Accurate power sharing among multi-DG resources in a microgrid

In this paper, a sliding mode (SM)-based direct active and reactive power control for the distributed generations (DGs) in microgrid is presented. The grid-connected microgrid contains two three-phase DGs that are photovoltaic (PV) units, and three single-phase DGs consisting of fuel cell (FC), PV, and battery. In the proposed strategy, controlling of the active and reactive powers is carried out for the single-phase and three-phase DGs without any phase angle tracking of the network voltage or synchronization transformations. The proposed robust control strategy improves power sharing and regulates power components injected by the DGs, and it is tested under balanced and unbalanced loads.     

Fuel-cell sharing for a distributed hybrid power system

This paper investigates the benefits of sharing a proton exchange membrane fuel cell (PEMFC) in a distributed hybrid power system. The PEMFC is usually used as backup power in stationary hybrid power systems; however, in that scenario, it might be working only 2% of the time while incurring 20% of the system expenses. Therefore, this paper examines the potential of sharing a PEMFC among multiple power systems. We develop a distributed hybrid power system that comprises several immovable power stations and a fuel-cell vehicle (FCV). Each power station is equipped with solar panels and batteries, while the FCV contains a PEMFC module and can move among the stations to provide sustainable power as needed. We propose power management strategies and show that the total system costs can be significantly reduced by 10.83% and 17.89% when sharing one FCV between three and twelve power stations, respectively. We also design experiments to demonstrate the feasibility of the proposed distributed hybrid power system. In the future, the developed model can be extended to provide further cost reductions by optimizing distributed hybrid power systems with multiple FCVs.     

面向提高微网中分布式电源配置的电力优化模型

针对微电网中分布式电源优化配置问题,文章从经济性、环保性和电能质量的角度,将电压偏差、线路损耗、经济成本和碳排放目标两两组合作为优化目标,以微电网系统的供电可靠性为约束条件,建立了微电网中分布式电源优化配置模型。在传统NSGAⅡ算法的基础上,提出了一种改进的NSGAⅡ算法用于求解含约束的多目标优化模型。通过仿真,验证了优化模型和改进算法是合理有效的。     

Risk-based optimal operation of power,heat and hydrogen-based microgrid considering a plug-in electric vehicle

The growing interest in integrating variable renewable energy resources (RES), besides global concerns about greenhouse pollution, brings multiple challenges for eco and environmentally-friendly operation of systems. Meanwhile, the simultaneous energy supply can improve energy efficiency and mitigate the fluctuation of RES compared with a single-energy system. Therefore, this paper seeks to investigate the optimal scheduling of heating, power, and hydrogen-based microgrid incorporated with RES and plug-in electric vehicles (PEV). The fuel-cell-based hydrogen and electrolyzer facilities are integrated into the multi-energy system to investigate the power-to-hydrogen and hydrogen-to-power technologies in the model. Besides typical electric and thermal loads, the proposed system can directly sell hydrogen to hydrogen-based industrial applications. The PEV as a flexible resource is employed to facilitate the integration of solar energy. Due to the substantial uncertainty from solar energy, price, load, and EVs' arriving and departing times, the risk management of the model based on the conditional value-at-risk is developed to show the operator's behavior against the random inputs and their risk. Results show that integrating the hydrogen storage and plug-in electric vehicle in the model results in a daily cost reduction of up to 9.28%.     

考虑用电优质系数的微电网分段混合策略优化调度

考虑需求侧响应的并网型微电网调度常忽略光伏出力特性对可控负荷调度的影响,且缺乏完善的需求侧评价指标。文章提出一种PVP&LS(Photovoltaic Priority&Load Shifting)分段混合调度策略,PVP策略依据预测光伏出力,以弃光率最小为目的调控可控负荷;LS策略以降低峰谷差率为目的,对上阶段剩余可控负荷移峰填谷。同时,提出了改进的用电优质系数模型,不仅避免调控过度,还可量化用户感受。最后通过自适应遗传算法仿真对比,运行成本减少了3.91%,用电优质系数增加了4.09%,弃光率下降了10.2%。     

Stabilization and control of tie-line power flow of microgrid including wind generation by distributed energy storage

High penetration of wind generation in electrical microgrids causes fluctuations of tie-line power flow and significantly affects the power system operation. This can lead to severe problems, such as system frequency oscillations, and/or violations of power lines capability. With proper control, a distribution static synchronous compensator (DSTATCOM) integrated with superconducting magnetic energy storage (SMES) is able to significantly enhance the dynamic security of the power system. This paper proposes the use of a SMES system in combination with a DSTATCOM as effective distributed energy storage (DES) for stabilization and control of the tie-line power flow of microgrids incorporating wind generation. A new detailed model of the integrated DSTATCOM-SMES device is derived and a novel three-level control scheme is designed. The dynamic performance of the proposed control schemes is fully validated using MATLAB/Simulink.     

Life cycle energy and environmental analysis of a microgrid power pavilion

Microgrids—generating systems incorporating multiple distributed generator sets linked together to provide local electricity and heat—are one possible alterative to the existing centralized energy system. Potential advantages of microgrids include flexibility in fuel supply options, the ability to limit emissions of greenhouse gases, and energy efficiency improvements through combined heat and power (CHP) applications. As a case study in microgrid performance, this analysis uses a life cycle assessment approach to evaluate the energy and emissions performance of the NextEnergy microgrid Power Pavilion in Detroit, Michigan and a reference conventional system. The microgrid includes generator sets fueled by solar energy, hydrogen, and natural gas. Hydrogen fuel is sourced from both a natural gas steam reforming operation and as a by‐product of a chlorine production operation. The chlorine plant receives electricity exclusively from a hydropower generating station. Results indicate that the use of this microgrid offers a total energy reduction potential of up to 38%, while reductions in non‐renewable energy use could reach 51%. Similarly, emissions of CO₂, a key global warming gas, can be reduced by as much as 60% relative to conventional heat and power systems. Hydrogen fuels are shown to provide a net energy and emissions benefit relative to natural gas only when sourced primarily from the chlorine plant. Copyright © 2006 John Wiley & Sons, Ltd.     

Ensemble learning for optimal active power control of distributed energy resources and thermostatically controlled loads in an islanded microgrid

To achieve an effective coordination between the secondary control and the tertiary control of load frequency control (LFC), a new optimal active power control (OAPC) is constructed for real-timely changing the operating points of distributed energy resources (DERs) and thermostatically controlled loads (TCLs) in an islanded microgrid. A large number of TCLs are integrated as a load aggregator (LA) for participating the secondary control of LFC, which can enhance the dynamic response performance due to their much faster response speeds compared with that of distributed generators. Since OAPC is a nonsmooth and nonlinear optimization with a quite short implementation period, a novel model-free ensemble learning (EL) is proposed to rapidly obtain a high-quality optimal solution for it. EL based OAPC is composed of multiple sub-optimizers and a learning concentrator, where each sub-optimizer is responsible for providing the exploitation and exploration samples to the learning concentrator, while the reinforcement learning based concentrator is mainly used for knowledge learning and knowledge transfer. Case studies are thoroughly carried out to verify the performance of EL based OAPC in an islanded microgrid with 12 DERs and 900 TCLs.     

Analysis of installed capacity and operation strategy for distributed combined heating and power systems

分布式热电联产系统是一种临近用户的先进能源系统,系统构型、装机容量和运行策略的选择对系统节能性、环保性和经济性有重要影响。本研究以某办公大楼为对象,根据其全年实时运行数据,分析了其热电负荷特征;同时,为该办公楼构建了分别以微燃机和内燃机为动力单元的两种不同CHP系统构型方案,建立了相应的变工况能量平衡模型。进一步探讨了系统在以热定电与以电定热、变工况运行与额定运行、有储热与无储热、24 h连续运行与早起晚停等不同运行策略下动力机组装机容量对该办公楼经济性、节能性和环保性的影响规律。同时运用多目标评价指标来对系统不同装机容量和运行策略下的收益综合评估,并引入了混沌粒子群优化算法来找到系统最大的综合收益,结果表明,该办公楼应用CHP系统后全年的经济性、节能性和环保性较传统的单一功能模式分别提高了22.85%、17.45%、25.06%。     

Effects of low radiation on the power quality of a distributed PV-grid connected system

We have previously investigated effects of radiation levels on power quality of a number PV-grid interactive systems in Thailand, in terms of harmonics and voltage variation at the point of common coupling (PCC). In this paper, we focus on the nature of components of complex power (actual, reactive and apparent power) of inverter output of a PV-grid interactive system due to low radiation, below 400 W/m². The system being investigated has an array of 4.2 kWp and representative of roof top units. It is observed that a PV array supplies increasing real power, in magnitude and as percentage of complex power, at high values of radiation. At low radiation level when the array does not provide enough output power, reactive power is drawn from distribution transformer and fed into an inverter and loads. Based on results from the test site and long term radiation data of Bangkok, we then estimate energy available from low radiation from a hypothetical PV-grid interactive unit in Bangkok of a similar size. It can be seen that for a tropical climate like Thailand a significant amount of energy, 20–30% of radiation energy, is in the form of reactive power. Methods must be devised to capture this low radiation energy and converted into real power form.     

Optimal operation of autonomous microgrid including wind turbines

This paper gives a novel hybrid optimization method to find optimal sitting and operation of an autonomous MG at the same time. The operation is optimized via finding the optimal droop gain parameters of DGs. The optimization problem is formulated as a multi-objective problem where the objectives are applied to minimize the fuel consumption of DGs and to improve the voltage profile and stability of MG subject to operational and security constraints. A hybrid algorithm, named HS-GA, is developed to solve the paper optimization problem. A new formulation of power flow is derived to run the proposed algorithm where the steady state frequency of system, reference frequency, reference voltage and droop coefficients of DGs, based on a droop controller, are considered as optimization variables. The performance of the paper approach is compared with other optimization and non-optimization methods in MG with 33and 69 buses using MATLAB. The performance of the proposed method is compared with a method that the parameters of DGs are pre-determined without conducting any optimization process. The results show, which optimized droop parameters improves the operation of the MG.     

带蓄能装置的分布式冷热电联产系统运行优化研究

建立带蓄能装置的分布式冷热电联产系统优化运行的数学模型,分析系统应用常规优化方法和敏感性分析法时各设备的运行策略。针对典型案例的分析表明:通过敏感性分析法的应用,可以解明蓄能装置蓄释状态的变化对系统运行策略产生的影响,在没有额外增加系统日运行能耗费用的情况下,蓄能装置可在更稳定的状态下进行蓄能或释能,减少因蓄释能策略大幅度的变化给装置本身带来的负担,有利于延长其使用寿命。     

Development of FPGA based power flow monitoring system in a microgrid

In recent decades, smart grid has become increasingly attractive to both energy producers and consumers. Amongst the main challenges for the successful realization of smart grid includes the integration of renewable energy resources, real time demand response and management of intermittent energy resources. Apart from smart grid, the development of micro-grids should take into consideration of issues such as the system performance, modelling, monitoring and controlling of the micro-grids. In particular, the recent advancements in information and communication technologies (ICTs) could facilitate the effective development of the future micro-grid system. The goal of the study is design of a system, based on FPGA, which monitors the power flow of the Microgrids. First of all a MG system installed in the laboratory of Firat University Electrical and Electronics Engineering Department consists of 1.2 kWp grid connected PV system, 5 kW micro hydro turbine, 0.5 kW wind turbine and 0.1 kW fuel cell unit was introduced. Afterwards, for smart-grids, a system of power flow that has a powerful high sampling rate was dwelt upon. During implementations, the data collected from the power system was transmitted to the FPGA cards located in open area by wireless data-monitoring card. This study has contributed to studies of other researchers by means of the monitoring system which has a high sampling frequency.     

微电网的并离网平滑切换控制策略研究

针对光储微电网并离网切换过程中的平滑过渡问题,提出了一种适用于主从控制与对等控制相结合条件下的控制策略,通过离网过程中对电压相位进行积分控制,并网过程中对电压的相位和幅值进行无差调节控制,实现并离网切换过程的平滑过渡,提高电能质量,保证微电网系统中重要负荷的正常稳定运行。文章通过在Matlab/Simulink平台下搭建光储微电网仿真模型,对所提出的控制策略的有效性和可行性进行了验证。     

含有虚拟阻抗的微源逆变器微网小信号稳定性分析

微网渗透率升高使微网系统惯性减小,受到扰动之后微网易发生振荡失稳。文章引入虚拟阻抗,提出一种适用于低压微网的改进型下垂控制,减小线路阻抗的影响。在此基础上建立微网系统的小信号模型,通过计算系数矩阵特征根的形式判断系统的稳定性,并在Matlab/Simulink软件中搭建相应的模型,通过时域仿真图判断系统的稳定性。     

Optimal lay-out and operation of combined heat & power (CHP) distributed generation systems

The paper presents an optimization model of a distributed cogeneration system with a district heating network, applied to a real city centre situation. The distributed urban cogeneration system includes both a set of micro-gas turbines, located inside some public buildings, and a centralized cogeneration system based on a Internal Combustion Engine. The objective function adopted for the optimization is the Total Annual Cost for owning, maintaining and operating the whole system. To face the problem a Mixed Integer Linear Program (MILP) is defined and solved by a commercial software. Starting from the thermal and electrical demand of the buildings, the MILP model allows to define the possible installation of the centralized cogeneration ICE (Internal Combustion Engine) and the number of microturbines in the different buildings, the optimal lay-out of the district heating network and the optimal operation strategy for the whole system as well. In particular the energy performance and global CO₂ emissions are evaluated.     

Optimal management of hydrogen storage in stochastic smart microgrid operation

This paper presents an energy management and reserve scheduling scheme in order to optimally operate a 17-bus Low Voltage (LV) grid-tied microgrid, powered by photovoltaics, a wind turbine and a Fuel Cell (FC) utilizing on site hydrogen production and storage. Since high Renewable Energy Resources (RES) penetration is assumed, the expected deviations due to their intermittency are accounted for by the reserve provision by the FC system, in order to deviate as little as possible from the scheduled energy demand injected by the upstream grid. All these are incorporated into the operating cost of the microgrid assuming penalization of unscheduled power injections from the grid. The intermittency of RES and load are incorporated in the model by assuming known probability density functions for the forecasting errors. Then, energy and reserve scheduling is performed utilizing the Harmony Search algorithm in order to minimize the expected operating costs of the examined system by optimal reserve and energy provision from the stored/generated hydrogen. For that purpose, hourly optimizations are performed for a given year to assess the value on-site hydrogen generation and FC technologies add to microgrid operation and Distributed Generation (DG) in general. The purpose is to prove the use of hydrogen storage systems in effective uncertainty balancing. The hydrogen storage system appears to effectively counter the intermittency of renewables in moderate penetration, reducing the uncertainty costs. In higher renewable penetrations, due to uncertainty being already accounted for by the storage, the benefits of the RES penetration are even greater.     

Load research as a tool in electric power system planning,operation, and control—The case of Jordan

Electric load research involves the systematic collection and analysis of customers’ electrical energy as well as demand requirements by time-of-day, month, season, and year; consumption patterns; socio-economic and demographic influencing factors; and willingness-to-pay for electricity. The information created by load research are the bases for all studies and analyses conducted by the electricity company to plan, monitor, operate, and control the power system. Several attempts were carried out in Jordan to create this very important body of knowledge. Studies and analyses are conducted regularly to update the information. This paper presents the author's experience in conducting load research investigations. These efforts culminated in three distinct contributions, which are still very useful in planning and operation of the power system in Jordan. (1) The first contribution by the author is related to creating a huge database of energy and electricity consumption characteristics, trends, and driving forces. The database is being continuously updated and as such constitutes a very basic tool for all demand forecasting and other planning studies. (2) The second contribution involves the estimation of the cost of un-served (unmet) electrical energy due to outages. This estimate, which is still being used as reference for planning studies carried out in Jordan, was first coined by the author at 1.0US$/kWh. (3) The final contribution concerns the use of the information in the load research database and the accumulated experience in determining peak load composition. This effort created the “near-exact” estimate of the characteristics and constitutions of the peak load divided among the various consuming sectors as well as among the various end-uses in Jordan. The results of these contributions are still being used by the electricity sector in Jordan until this day, either as unique information or as a guideline or reference to more recent estimates. More importantly, the efforts, as outlined in the three contributions above, have established a good base and reference point for further ongoing activities to collect, analyze, and use the information by various entities in the electricity sector in Jordan. However, the efforts need to be properly coordinated and entrusted with a single entity to ensure a better quality of information and avoid conflicting decisions.     

Optimal operation of microgrid using hybrid differential evolution and harmony search algorithm

This paper proposes the generation scheduling approach for a microgrid comprised of conventional generators, wind energy generators, solar photovoltaic (PV) systems, battery storage, and electric vehicles. The electrical vehicles (EVs) play two different roles: as load demands during charging, and as storage units to supply energy to remaining load demands in the MG when they are plugged into the microgrid (MG). Wind and solar PV powers are intermittent in nature; hence by including the battery storage and EVs, the MG becomes more stable. Here, the total cost objective is minimized considering the cost of conventional generators, wind generators, solar PV systems and EVs. The proposed optimal scheduling problem is solved using the hybrid differential evolution and harmony search (hybrid DE-HS) algorithm including the wind energy generators and solar PV system along with the battery storage and EVs. Moreover, it requires the least investment.