Coupling an adaptive protection system with an energy management system for microgrids

Energy Management Systems (EMS) are control schemes in charge of defining the optimal scheduling of dispatchable units in a microgrid. Output set points from the EMS could be exploited in other control loops that may benefit from the microgrids expected behavior improving their operation. In this context, this paper proposes a novel coupled operation of an EMS with an Adaptive Protection System (APS), such that the information of the EMS serves to compute the parameters of the protective devices deployed in a microgrid. This aspect is formalized in the present proposal based on already developed APS and EMS frameworks. To evaluate the performance of the proposal, the microgrid installed in Huatacondo, north of Chile, was used as a test-bed. The obtained results indicate that considering the information provided to the APS form the EMS improves the overall performance of the microgrid in case of failure, despite the operating conditions. This also indicates that moving towards an integrated design of the EMS and APS might enhance the behavior (robustness) of a microgrid (as a whole) in case of failures or contingencies.     

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。     

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.     

考虑风光可靠性的微电网混合储能优化配置

储能装置在微电网中发挥着不可替代的作用,在微电网中有很大的市场应用前景。文中在配置储能容量时考虑风电机组与光伏机组的可靠性,采用序贯蒙特卡洛法模拟风电机组、光伏机组的正常运行、故障概率;对于蓄电池与超级电容器具有优势互补的特点,利用离散傅里叶变换法对一个周期内的不平衡功率进行频谱分析,建立规划周期内综合费用最小为目标的配置模型,确定混合储能的最佳容量。算例分析表明,当考虑风电机组与光伏机组可靠性时,混合储能配置的额定容量大于不考虑可靠性时的额定容量,为进一步研究微电网的储能规划提供借鉴。     

考虑储能电池的微电网群双层优化调度策略

储能电池是微电网中的重要组成单元,在进行调度时对其进行保护可以有效提高系统的经济性和可靠性.为此,本文充分考虑充放电速率和充放电深度对储能电池的影响,结合交替方向乘子法和模型预测控制,提出了一种微电网群的双层分布式调度策略.其中,上层以微电网群总体运行成本最小为目标对各微电网进行调度;下层则对各微电网内部分布式电源的出...     

From microgrids to aggregators of distributed energy resources. The microgrid controller and distributed energy management systems

Microgrids are a collection of distributed energy resources (DER) within a specific boundary, with a control system for their management and operations at the point of interconnection with the distribution utility. As microgrid concepts evolve, they are being applied to aggregations of DER outside boundaries with appropriate controls for operation with transmission and distribution utilities and participation in markets. This article marks this evolution and points towards the common functionalities of microgrid controllers and distributed energy management systems for integration of DER into transmission and distribution operations and markets.     

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.     

电动汽车和能量云在家庭微网中的协同调度研究

随着电动汽车(EV)的快速发展,EV分布式储能的特性广泛受到关注和重视。但EV的首要特征仍是移动工具,EV并不具备传统储能单元所固有的稳定性和持续性。为了减小EV入网后无序充放电的不利影响,高效合理地发挥EV的储能特性和优化微网系统的能源管理,文中以家庭微网为背景,提出了一种能量云运营商运营下EV和共享储能协同运作的电力调度体系结构。能量云运营商既是共享储能设备的提供商,也是EV聚合参与电能调度的代理商。此外,能量云体系下的能量交易服务还支持用户之间的能量交互。在考虑EV和储能折旧成本的情况下,以用户的用电成本最小为目标建立了优化模型。家庭微网的实例研究验证了文中策略的合理性和经济性,能量交易服务能使所有参与者获利,进一步降低用电成本。     

Electrical machines based DC/AC energy conversion schemes for the improvement of power quality and resiliency in renewable energy microgrids

The power quality and resiliency (or self-healing capacity) characteristics of a renewable energy based microgrid (REM) are limited majorly due to their inherent dependency on the static power electronics based energy conversion devices. Whereas, conventional electrical machines based power plants possess good power quality and resiliency characteristics due to their high inertia and control features. So, the REMs’ research need to be shifted towards making its operation similar to conventional electrical machines based power plant. With this intent, this paper proposes two DC/AC energy conversion schemes that are designed based on the theory of electrical machines such as DC Motor (DCM) and Doubly Fed Induction Generator (DFIG). The first scheme is a rotary inverter (named as RDCMIGI) that replaces the conventional static power electronic inverter with a real DCM-DFIG set. The second scheme is a static inverter (named as VDCMIGI) that uses a pulse width modulated power electronic inverter, whose modulating signals are generated through a closed loop virtual DCM-DFIG based control system. These two schemes emulate the behavior of electrical machines based conventional power plant in REM, which leads to the improvement of power quality through the smooth control of voltage/frequency and resiliency through the injection of necessary moment of inertia. For the analysis, the conventional/proposed energy conversion schemes are modeled in MATLAB/Simulink® and are tested during various uncertainties. From the results, it is observed that the proposed DC/AC energy conversion schemes have effectively improved the power quality and resiliency, and thereby, leverages REMs as better future grids.     

Optimization of a battery energy storage system using particle swarm optimization for stand-alone microgrids

The main challenge in integrating a Battery Energy Storage System (BESS) into a microgrid is to evaluate an optimum size of BESS to prevent the microgrid from instability and system collapse. The installation of BESS at a random size or non-optimum size can increase in cost, system losses and larger BESS capacity. Thus, this paper proposes the new method to evaluate an optimum size of BESS at minimal total BESS cost by using particle swarm optimization (PSO)-based frequency control of the stand-alone microgrid. The research target is to propose an optimum size of BESS by using the PSO method-based frequency control in order to prevent the microgrid from instability and system collapse after the loss of the utility grid (e.g., blackout or disasters) and minimize the total cost of BESS for 15 years installation in the microgrid. Then, the economical performance of BESS with modern different storage technologies is investigated and compared in the typical microgrid. Results show that the optimum size of BESS-based PSO method can achieve higher dynamic performance of the system than the optimum size of BESS-based analytic method and the conventional size of BESS. In terms of BESS economical performance with modern storage technologies, the installation of the polysulfide–bromine BESS is likely to be more cost-effective than the installation of the vanadium redox BESS for 15 years installation in the typical microgrid. It is concluded that the proposed PSO method-based frequency control can improve significantly power system stability, grid security, and planning flexibility for the microgrid system. At the same time, it can fulfill the frequency control requirements with a high economic profitability.     

新基建下储能技术典型应用场景分析

2020年,我国提出新型基础设施建设（新基建）国家战略。储能产业作为新基建政策中的主导产业,应向着高质量、低成本、大规模的方向发展。本文针对新基建政策内5G基站、数据中心、特高压输电、城际高速铁路和城市轨道交通、新能源汽车充电桩等领域,调研国内外各类型储能技术在这些领域内的储能配备以及应用实例,并对新基建背景下的储能技术进行了展望,提出了国家各部委政策应统一协调,顶层设计,成体系推进,探索合作机制和商业模式,以及各省应结合具体情况,出台相应配套实施细则等建议,进一步推进我国储能技术的高效发展。     

Why capacity markets are the Fitbits of the electric utility industry

Expanding upon the findings of the 2017 General Accounting Office Review identifying the failure of FERC to develop methodologies to determine the efficacy of RTO electric capacity markets, this article explains in detail why it is likely that capacity markets structured only for the sale of bare megawatts to load-serving utilities through an auction capacity are as lacking as Fitbits are in providing a rounded picture of their users’ health. As currently constituted, capacity markets can never capture all relevant attributes that determine the types of generating resources constructed nor fully reconcile federal and state policies that concurrently affect development of generation.     

微电网并网标准研究

根据现有的国内外相关标准和规范,从电力系统的角度初步研究了微电网并网、并网运行以及解列过程的技术要求。提出了微电网并网的基本要求和并网准则,基于配电网可靠性考虑,对微电网并网时接入点、接入容量和接入方式提出了要求。对微电网接入电网引起的电能质量、有功功率和无功功率控制、电压调节、继电保护、通信、监测和电能计量等问题进行了分析。将微电网的解列分为正常解列和事故解列,着重强调事故解列时孤岛区域的划分原则及解列要求。通过对微电网接入电网所需考虑的关键问题进行分析探讨,为制定微电网的接入标准提供了一定的基础。     

谐波对低压微电网运行的影响

由小容量分布式电源、储能装置和负荷组成的低压微电网,因供电方式灵活及可充分利用各种可再生能源等优点,越来越受到人们的重视。但由于微电网容量小,且大量采用电力电子装置实现组网,其运行更易受到谐波的影响。分析低压微电网中谐波的主要来源,即微电网自身的非线性负荷产生的谐波、微电源电力电子接口产生的谐波和配电网的谐波渗透,阐述其影响及微电网与传统大电网的不同之处。介绍微电网的运行方式和并网控制策略,并通过仿真分析非线性负载和配电网侧谐波电压渗透对微电网正常运行的影响。     

考虑源荷不确定的多园区微网与共享储能电站协同优化运行

共享储能作为一种新兴能源存储技术正在迅速发展。为提高含共享储能电力系统的经济性,提出一种基于源荷不确定性的两阶段鲁棒多园区微网与共享储能合作博弈模型。首先,建立共享储能主体和各园区微网主体间的电能交易优化运行模型。其次,考虑可再生能源及负荷的不确定性,建立园区微网的两阶段鲁棒调度模型。然后,基于纳什谈判理论建立多园区微网-共享储能多主体合作运行模型,并将其等效为合作成本最小化子问题与电能谈判支付子问题。为了保护各主体隐私,运用交替方向乘子法对上述两个子问题进行分布式求解。最后,通过算例验证所提合作运行模型以及分布式算法的有效性。仿真结果表明共享储能与各园区微网协同优化运行能够减少各主体的运行成本。     

A hybrid method for simultaneous optimization of DG capacity and operational strategy in microgrids utilizing renewable energy resources

Recently, microgrids have attracted considerable attention as a high-quality and reliable source of electricity. In this work energy management in microgrids is addressed in light of economic and environmental restrictions through (a) development of an operational strategy for energy management in microgrids and (b) determination of type and capacity of distributed generation (DG) sources as well as the capacity of storage devices (SD) based on optimization. Net Present Value (NPV) is used as an economic indicator for justification of investment in microgrids. The proposed NPV-based objective function accounts for the expenses including the initial investment costs, operational strategy costs, purchase of electricity from the utility, maintenance and operational costs, as well as revenues including those associated with reduction in non-delivered energy, the credit for reduction in levels of environmental pollution, and sales of electricity back to the utility. The optimal solution maximizing the objective function is obtained using a hybrid optimization method which combines the quadratic programming (QP) and the particle swarm optimization (PSO) algorithms to determine the optimum capacity of the sources as well as the appropriate operational strategy for the microgrid. Application of the proposed method under different operational scenarios serves to demonstrate the efficiency of the proposed scheme.     

微电网并网验收试验规范的研究

依据现有的国内外相关标准和规范,对验证微电网在并/解列过程以及并网运行中是否满足相关技术要求所必须进行的验收试验进行了研究。结合对微电网并网/解列及并网运行过程中的技术要求,给出了验收试验应具备的条件、测量仪器设备、验收试验的一般流程和验收标准等。重点针对并解列操作、并网运行时的电能质量参数、逆功率保护和短路保护等关键操作、运行参数和保护功能的验收试验进行了设计,给出了相应的测试方法、具体步骤和验收标准。该研究为制定微电网接入验收试验规范提供了较好的基础和依据。     

Assessing the contribution of microgrids to the reliability of distribution networks

The emergence of microgeneration has recently lead to the concept of microgrid, a network of LV consumers and producers able to export electric energy in some circumstances and also to work in an isolated way in emergency situations. Research on the organization of microgrids, control devices, functionalities and other technical aspects is presently being carried out, in order to establish a consistent technical framework to support the concept.