Multi-agent system for energy resource scheduling of integrated microgrids in a distributed system

This paper proposes a multi-agent system for energy resource scheduling of an islanded power system with distributed resources, which consists of integrated microgrids and lumped loads. Distributed intelligent multi-agent technology is applied to make the power system more reliable, efficient and capable of exploiting and integrating alternative sources of energy. The algorithm behind the proposed energy resource scheduling has three stages. The first stage is to schedule each microgrid individually to satisfy its internal demand. The next stage involves finding the best possible bids for exporting power to the network and compete in a whole sale energy market. The final stage is to reschedule each microgrid individually to satisfy the total demand, which is the addition of internal demand and the demand from the results of the whole sale energy market simulation. The simulation results of a power system with distributed resources comprising three microgrids and five lumped loads show that the proposed multi-agent system allows efficient management of micro-sources with minimum operational cost. The case studies demonstrate that the system is successfully monitored, controlled and operated by means of the developed multi-agent system.     

基于一致性的微网分布式能量管理调度策略

基于多智能体一致性理论,设计了具有完全分布式特征的微网能量管理调度策略,以解决集中式控制方式通信压力大和无法满足即插即用要求的问题。以可控发电单元和储能单元运行成本最低为目标函数,结合微网功率平衡和发电单元出力的约束条件,建立了分布控制式微网最优经济调度模型。根据多智能体及一致性理论设计了微网的分布式能量管理调度算法,给出了该方法的具体实施步骤。通过在IEEE-14节点微电网系统中的仿真算例,验证了所提出调度策略的正确性和有效性。     

单相级联准Z源逆变器有限集模型预测控制

以单相级联准Z源逆变器(quasi-Z-Source Cascaded Multilevel Inverter,qZS-CMI)为研究对象,以提高动态响应速度和降低开关频率为研究目标,提出一种优化有限集模型预测控制策略。首先,在分析不同工作状态对qZS-CMI状态变量的影响后,建立其离散时间模型。其次,以MPPT作为输入电流参考,根据所建立的离散时间模型,对准Z源网络的输入电流、输出电容电压、负载电流进行预测,并引入评价函数中,实现qZS-CMI系统的多变量综合协同控制。然后,将平均开关切换次数引入评价函数,优化系统的开关损耗。通过所提模型预测控制方法,无需输出电流控制环和直流侧电压控制环,降低了控制参数的调节难度,提高了系统的动态响应速度。最后,通过建立仿真模型验证了所提算法的有效性和正确性。     

Cooperative control of battery energy storage systems in microgrids

This paper proposes a cooperative control of battery energy storage (BES) units within a microgrid (MG) which includes two control subsystems for charge and discharge operation mode of the BES. In addition, the proposed cooperative control strategy provides accurate reactive power sharing among the BES units. During discharge operation, the proposed strategy utilizes a SoC-based droop control in order to avoid promptly depleting of the BES units, by dedicating the highest priority to their SoC level and respecting their power rating. This is achieved without any disturbance in the power balance of the MG. In addition, during charge operation of the BES units, the proposed control method uses a proportional-integral (PI) controller to limit the BES absorbing power and match it with the available surplus power from the renewable energy sources (RESs). This in turn avoids any power imbalance within the system. Finally, to utilize the extra capacity of the BES converters and also to avoid overloading of RESs, a new adaptive virtual impedance (AVI) strategy is proposed here which provides accurate reactive power sharing by imposing a virtual impedance in series with the coupling impedance of each BES and RES unit. The system performance is validated through extensive simulations carried out in PSCAD/EMTDC software.     

Controlling and optimizing resilient distributed energy resources and microgrids with a demand-side operation platform

Moving to true grid resiliency requires multiple distributed energy resources, but these DERs must be properly controlled for each installation’s needs. This article answers these DER and microgrid resiliency questions and suggests some best practices for optimal financial and operational control in our New Energy Landscape.     

Valuation of distributed energy resources in active distribution networks

In concert with the transformation of conventional passive power distribution system, distributed energy resources (DERs) have progressively become participants in the provision of electricity services in active distribution networks (ADNs). In this paper, we propose a systematic valuation process to quantify the value of DERs in the ADN context. The paper first provides comprehensive insights into the impacts of DERs on ADN and the society as a whole. Given the technological, locational, and temporal diversity of DERs, a two-part scheme is developed to value and compensate DER portfolios proposed by customers and independent third parties. In particular, DERs are valued for their benefits and costs in both short and long terms. An integrated resource planning model is formulated to quantify the value of a given DER portfolio to be installed, where bi-level optimization techniques are applied to coordinate decisions on ADN planning and operations. In order to determine the short-term operation benefits of the DER portfolio on a continuous basis, a retail market operation model is developed based on peer-to-peer energy transactions among prosumers, when the impacts of DERs on ADN operations are monetized by distribution locational marginal prices. It is finally concluded in the paper that the proposed valuation scheme will not only contribute to the proactive investment of DERs in ADN but also help enhance the role of DERs in offering affordable, reliable, resilient and sustainable electricity services to customers.     

A distributed secondary scheme with terminal sliding mode controller for energy storages in an islanded microgrid

Different levels of the stored energy is the main challenge in control of the distributed energy storages (DESs) in an islanded microgrid. The conventional power-droop and the secondary distributed controllers of distributed generators (DGs) does not consider the long time-span dynamics of state of charge (SoC) of the DESs. Subsequently, the DESs with lower initial SoCs are discharged before other DESs. Besides, the SoC-droop primary control results in further deviation of the frequency of the microgrid. In this paper, the secondary control scheme is employed to share the power mismatch, match the SoCs of the DESs, and regulate the frequency and voltage of the microgrid. The proposed scheme has distributed cooperative architecture, and employs distributed terminal sliding mode controller (DTSMC) for the state regulators, and proportional controller for distributed power-sharing and SoC-matching. The proposed scheme organizes the controllable DGs, the DESs with limited SoCs, and the uncooperative DGs with unknown generation, through communicating between the neighbor cooperative DGs and DESs. Performance of the designed DTSMC is verified for the changes of communication topology, time-delays, data drop-outs, load variations, and external disturbances. DTSMC provides finite-time convergence, fast transients, and improved robustness.     

直流微电网潮流控制器与分布式储能协同控制策略

针对直流微电网互联变换器提出一种能根据两端直流母线电压判断自身传输功率方向与大小的智能控制策略。该策略首先将两个直流微电网之间的互联变换器作为微电网潮流控制器(MicrogridPowerFlowController,MPFC)来控制互联线路上的潮流。然后提出一种微网自适应功率下垂控制方法使MPCF与分布式储能协同控制直流母线电压。最后使用Matlab/Simulink仿真验证该控制方法能够有效提高系统的稳定性和效率,并且能够减小因不需要的功率流动所带来的功率损耗及储能的充放电次数。     

船舶综合能源管理系统研究综述

随着传统能源日益短缺，船舶动力系统正向新能源化升级转型，但新能源出力的不确定性也为系统的经济、安全运行带来挑战。基于此，传统船舶能源管理已不再适用，综合型能源管理系统亟需归纳梳理。针对以上情况，从国内外新型智能船舶政策入手，对比分析了各国船舶能源管理系统发展情况。对典型能源管理拓扑和船舶微网拓扑进行梳理，并基于“互联网＋智慧能源”的架构阐明船舶能源管理模式变革。总结分析了船舶综合能源管理的上层能源优化调度、底层协调控制策略以及与智能算法的应用结合。归纳了油-电混合动力推进、柴油机余热混合式推进、新能源电力混合动力推进3种典型船舶动力系统的应用架构。最后指出船舶的不确定性能源管控、多能源协同机制、数据驱动以及多层级EMS设计才是未来的发展趋势。     

孤岛运行模式下微网实时能量管理策略

针对包含柴油发电机、光伏发电、储能装置以及负荷的独立微网系统,提出孤岛运行模式下微网实时能量管理策略。实时监测储能装置数据,对下一时刻储能装置能量状态进行预测,结合净负荷功率大小采用相应的调度策略。柴油发电机通常关闭作为备用电源,充当电压/频率支撑单元的储能装置不接受功率调度,通过留有一定调节裕量以自动吸纳微网内的剩余功率,非电压/频率支撑单元的储能装置接受功率指令调度参与负荷供电。当储能装置能量状态接近下限时,考虑柴油发电机计划开机时间提前将其开启,保证负荷不间断供电。柴油发电机投入运行后,建立能量优化模型。最后,通过实验验证所提策略的合理性,为孤岛运行模式下微网能量管理的实际工程应用提供指导以及参考。     

含分布式混合储能系统的光伏直流微网能量管理策略

为了更好地管理大规模分布式光伏发电单元,将光伏直流微网划分为不同区域,且在不同区域配置了相应容量的混合储能单元与区域控制器以实现区域自治。根据各区域光伏电池输出功率与负荷功率间的关系以及储能单元荷电状态(SOC)的不同将系统分为5种运行模式,给出了不同运行模式下的能量管理策略,设计了光伏电池Boost变换器与储能双向DC/DC变换器的控制策略。最后,在Simulink中搭建了一个含多区域的光伏直流微网仿真模型。结果表明,所提方法在保证系统稳定运行的前提下,优化了各元件的出力。     

An economic evaluation for an autonomous independent network of distributed energy resources

This paper proposes a method for the economic evaluation of an autonomous independent network of distributed energy resources. There are existing proposals for such networks; the system that we are proposing and analyzing in this study is called Microgrid. Microgrid is a new framework of power delivery system that is formed by small, modular generation systems connected to each other to create a small autonomous grid. This paper estimates the total costs to consumers in a Microgrid with optimized operation of distributed generators and energy storage systems. This estimation includes not only installation and operation costs but also the additional expenses to construct the Microgrid itself. In addition, power interruption costs are also taken into account to consider the reliability enhancement created by the Microgrid. The paper attempts to determine whether or not it is economical for consumers to form this kind of autonomous independent network.     

A three-phase community microgrid comprised of single-phase energy resources with an uneven scattering amongst phases

This paper considers a three-phase, low voltage community network with both grid-connected and autonomous modes of operation, which is composed of a group of residential houses and some single-phase, converter-interfaced distributed energy resources (DER) with equal and arbitrarily scattering of the DERs among the phases. The vigorous operation of such a microgrid system is examined with the proposed management techniques. In such a network, it is highly probable for one phase to have a high generation capacity while the other phases experience a higher demand; a technically challenging problem for a network operating in autonomous mode. In this paper, it is proposed for the single-phase DERs of such a system to operate under a droop-based voltage control technique while an appropriate technique is proposed to facilitate the transmission of the excess power from one phase to other phases. The proposals are validated by extensive digital simulations in PSCAD/EMTDC for several scenarios to demonstrate the feasibility of operating such a system and the efficacy of the proposed techniques.     

Stochastic frequency-security constrained energy and reserve management of an inverter interfaced islanded microgrid considering demand response programs

This paper addresses a novel security constrained energy management system of a microgrid which considers the steady-state frequency. Microgrid frequency as a key control variable, continuously exposes to be excursed of its nominal value due to unpredictable intermittencies arise from renewable sources and/or load consumptions. Moreover, great utilization of inertia-less inverter-interfaced distributed energy resources intensifies potential frequency excursions. As a result, energy and reserve resources of a microgrid should be managed such that the microgrid frequency lies within secure margins. To that end, a new objective function on the basis of the frequency dependent behavior of droop-controlled distributed generations is formulated using a mixed integer linear programming. It is aimed to optimize the microgrid frequency according to the economic and environmental policies. Besides, to seek the active participation of the consumers into proposed frequency management approach, a linearized ancillary service demand response program is also proposed. In addition, to properly model the impacts of microgrid various uncertainties in the frequency management approach, a two-stage stochastic optimization algorithm is employed. Simulations are performed in a typical microgrid which operates in the islanded mode during a 24 h scheduling time horizon. The numerical results show the impressiveness of the proposed frequency aware energy management system while concurrently managing the microgrid security and economical aspects. Furthermore, it is demonstrated that utilization of demand response programs economizes the microgrid frequency management approach.     

Extraneous instabilities arising in power systems with non-synchronous distributed energy resources

This short communication describes an extraneous instability that can be observed when solving time domain simulations for power systems with inclusion of non-synchronous distributed energy resources such as those based on voltage source converters and asynchronous generators. The instability object of the paper is caused by the interaction of (i) synchronous machines modeled using a synchronous reference speed and (ii) non-synchronous generators whose controllers depend on a d − q transformation. The paper also provides two simple solutions able to remove such extraneous instabilities. The New England 39-bus benchmark system is used for testing the proposed solutions.     

基于微网技术的家庭能源管理系统研究

家庭能源管理系统是未来智能电网在配电侧发展的重要研究方向。以包含光伏发电、蓄电池储能和家庭负荷的家庭直流微电网系统为研究对象,研究了各个单元的基本控制策略,并提出了基于微网技术的家庭微网能量调度策略。系统的工作模式包括并网工作模式和离网工作模式,通过能量调度策略来维持系统功率平衡和直流电压稳定。在Matlab/Simulink下搭建了家庭直流微网系统并对该控制策略进行仿真验证。仿真结果表明,系统在并网运行模式和离网运行模式下均能保持直流侧电压稳定,验证了家庭能源管理系统的正确性和有效性。     

Analysis and visualization method for understanding the voltage effect of distributed energy resources on the electric power system

While adding distributed energy resources (DER) to a distribution circuit will affect numerous aspects of operation, bus voltage is a critical aspect that must be maintained within acceptable limits. It is therefore critical to: (1) quantify how DER installation will affect the voltage, (2) visualize the voltage change, and (3) predict the voltage change of the alternatives within the DER operational space. These three goals are achieved through the development of a simple voltage change potential (VCP) visualization method that can be determined using the basic characteristics of an inverter-based DER installation. The VCP results compare favorably with equivalent complete non-linear Matlab/Simulink™ models of DER implementation in distribution circuits at a fraction of the computational time. Calculation of VCP also enables a new control method that uses circuit information and simple equations to provide situation-dependent and optimal voltage regulation.     

Retail pricing responses to the challenge of distributed energy resources

The recent growth in distributed energy resources has raised issues of how to ensure that utilities recover allowed fixed costs for customer and distribution system services. This paper presents the issues related to DER in the context of both traditional cost-of-service and rate design methods, and economically efficient retail pricing. The objective is to clarify certain misconceptions and recommend retail pricing solutions.     

Economic framework for compensating distributed energy resources: Theory and practice

We offer an economic framework for analyzing the compensation that DERs should receive for energy exported to the grid. This economic framework requires that the prices paid to DER owners be based upon the forward-looking, economic costs that their utility avoids when it buys the energy from the customer. We explain why this results in efficient ‘build or buy’ and ‘purchase and install’ decisions of the utility and DER customer, respectively.     

面向园区的光储型微电网设计与应用

为满足园区重要负荷在配电网失电后的可靠供电以及园区并网下的经济运行需求,设计了一种集光伏发电、储能装置、负荷等可控设备于一体的园区光储型微电网。开展了系统的容量配置和控制架构设计,研发了微电网中央控制器和园区能量管理系统等关键模块。园区微电网中央控制器提供的并离网下模式切换控制方法,在配电网发生故障时可快速切换运行模式,保障了园区重要负荷的稳定供电,最大化减小了配电网故障带来的影响。园区能量管理系统提供的经济调度模型,以最小运行费用为目标,通过商业软件CPLEX求解,给出了园区各设备在多场景下的最优运行结果。设计的系统已在某产业园成功应用,通过实测数据证明了所设计系统的合理性。