Optimal Scheduling for Flexible Regional Integrated Energy Systemwith Soft Open Point

The Regional Integrated Energy System(RIES)has brought new modes of development,utilization,conversion,storage of energy.The introduction of Soft Open Point(SOP)and the application of Power to Gas(P2G)technology will greatly deepen the coupling of the electricity-gas integrated energy system,improve the flexibility and safety of the operation of the power system,and bring a deal of benefits to the power system.On this background,an optimal dispatch model of RIES combined cold,heat,gas and electricity with SOP is proposed.Firstly,RIES architecture with SOP and P2G is designed and its mathematical model also is built.Secondly,on the basis of considering the optimal scheduling of combined cold,heat,gas and electricity,the optimal scheduling model for RIES was established.After that,the original model is transformed into a mixed-integer second-order cone programming model by using linearization and second-order cone relaxation techniques,and the CPLEX solver is invoked to solve the optimization problem.Finally,the modified IEEE 33-bus systemis used to analyze the benefits of SOP,P2G technology and lithium bromide absorption chillers in reducing systemnetwork loss and cost,as well as improving the system’s ability to absorb wind and solar and operating safety.

Two-stage Optimization for Active Distribution Systems Based on Operating Ranges of Soft Open Points and Energy Storage System

Due to the lack of flexible interconnection devices,power imbalances between networks cannot be relieved effectively.Meanwhile,increasing the penetration of distributed generators exacerbates the temporal power imbalances caused by large peak-valley load differences.To improve the operational economy lowered by spatiotemporal power imbalances,this paper proposes a two-stage optimization strategy for active distribution networks(ADNs)interconnected by soft open points(SOPs).The SOPs and energy storage system(ESS)are adopted to transfer power spatially and temporally,respectively.In the day-ahead scheduling stage,massive stochastic scenarios against the uncertainty of wind turbine output are generated first.To improve computational efficiency in massive stochastic scenarios,an equivalent model between networks considering sensitivities of node power to node voltage and branch current is established.The introduction of sensitivities prevents violations of voltage and current.Then,the operating ranges(ORs)of the active power of SOPs and the state of charge(SOC)of ESS are obtained from models between networks and within the networks,respectively.In the intraday corrective control stage,based on day-ahead ORs,a receding-horizon model that minimizes the purchase cost of electricity and voltage deviations is established hour by hour.Case studies on two modified ADNs show that the proposed strategy achieves spatiotemporal power balance with lower cost compared with traditional strategies.

Voltage Unbalance Compensation in Distribution Feeders Using Soft Open Points

Soft open points(SOPs)are power electronic devices that may replace conventional normally-open points in distribution networks.They can be used for active power flow control,reactive power compensation,fault isolation,and service restoration through network reconfiguration with enhanced operation flexibility and grid resiliency.Due to unbalanced loading conditions,the voltage unbalance issue,as a common problem in distribution networks,has negative impacts on distribution network operation.In this paper,a control strategy of voltage unbalance compensation for feeders using SOPs is proposed.With the power flow control,three-phase current is regulated simultaneously to mitigate the unbalanced voltage between neighboring feeders where SOPs are installed.Feeder voltage unbalance and current unbalance among three phases are compensated with the injection of negative-sequence and zero-sequence current from SOPs.Especially in response to power outages,three-phase voltage of isolated loads is regulated to be balanced by the control of SOPs connected to the feeders under faults,even if the loads are unbalanced.A MATLAB/Simulink model of the IEEE 13-bus test feeder with an SOP across feeder ends is implemented,and experimental tests on a hardware-in-the-loop platform are implemented to validate the effectiveness of the proposed control strategy.

Soft Open Point Planning in Renewable-dominated Distribution Grids with Building Thermal Storage

With an increasing integration of intermittent distributed energy resources(DERs),the consequent voltage excursion and thermal overloading issues limit the self-sufficiency of distribution networks(DNs).The concept of soft open point(SOP)has been proposed as a promising solution to improve the hosting capacity of DNs.In this paper,considering the ability of building thermal storage(BTS)to increase the penetration of renewable energy in DNs,we provide an optimal planning framework for SOP and DER.The optimal planning model is aimed at minimizing the investment and operational costs while respecting various constraints,including the self-sufficiency requirement of the DN,SOP,building thermal storage capacity and DER operations,etc.A steady-state SOP model is formulated and linearized to be incorporated into the planning framework.To make full use of the BTS flexibility provided by ubiquitous buildings,a differential equation model for building thermal dynamics is formulated.A hybrid stochastic/robust optimization approach is adopted to depict the uncertainties in renewable energy and market prices.IEEE 33-bus feeder and a realistic DN in the metropolitan area of Caracas are tested to validate the effectiveness of the proposed framework and method.Case studies show that SOP/BTS plays a complementary and coordinated coupling role in the thermo-electric system,thereby effectively improving the hosting capacity and self-sufficiency of DNs.

Successive MISOCP Algorithm for Islanded Distribution Networks with Soft Open Points

An optimal operation scheme is of great significance in islanded distribution networks to restore critical loads and has recently attracted considerable attention.In this paper,an optimal power flow(OPF)model for islanded distribution networks equipped with soft open points(SOPs)is proposed.Unlike in the grid-connected mode,the adequacy of local power generation in distribution networks is critical for islanded systems.The proposed approach utilizes the power output of local distributed generations(DGs)and the benefits of reactive power compensation provided by SOPs to allow maximum loadability.To exploit the available resources,an optimal secondary droop control strategy is introduced for the islanded distribution networks,thereby minimizing load shedding.The formulated OPF problem is essentially a mixed-integer nonlinear programming(MINLP)model.To guarantee the computation efficiency and accuracy.A successive mixed-integer second-order cone programming(SMISOCP)algorithm is proposed for handling the nonlinear islanded power flow formulations.Two case studies,incorporating a modified IEEE 33-bus system and IEEE 123-bus system,are performed to test the effectiveness of the proposed approach.

Reconfiguration of Active Distribution Networks Equipped with Soft Open Points Considering Protection Constraints

The purpose of active distribution networks(ADNs)is to provide effective control approaches for enhancing the operation of distribution networks(DNs)and greater accommodation of distributed generation(DG)sources.With the integration of DG sources into DNs,several operational problems have drawn attention such as overvoltage and power flow alteration issues.These problems can be dealt with by utilizing distribution network reconfiguration(DNR)and soft open points(SOPs).An SOP is a power electronic device capable of accurately controlling active and reactive power flows.Another significant aspect often overlooked is the coordination of protection devices needed to keep the network safe from damage.When implementing DNR and SOPs in real DNs,protection constraints must be considered.This paper presents an ADN reconfiguration approach that includes DG sources,SOPs,and protection devices.This approach selects the ideal configuration,DG output,and SOP placement and control by employing particle swarm optimization(PSO)to minimize power loss while ensuring the correct operation of protection devices under normal and fault conditions.The proposed approach explicitly formulates constraints on network operation,protection coordination,DG size,and SOP size.Finally,the proposed approach is evaluated using the standard IEEE 33-bus and IEEE 69-bus networks to demonstrate the validity.

Multi-stage Coordinated Robust Optimization for Soft Open Point Allocation in Active Distribution Networks with PV

To optimize the placement of soft open points(SOPs)in active distribution networks(ADNs),many aspects should be considered,including the adjustment of transmission power,integration of distributed generations(DGs),coordination with conventional control methods,and maintenance of economic costs.To address this multi-objective planning problem,this study proposes a multi-stage coordinated robust optimization model for the SOP allocation in ADNs with photovoltaic(PV).First,two robust technical indices based on a robustness index are proposed to evaluate the operation conditions and robust optimality of the solutions.Second,the proposed coordinated allocation model aims to optimize the total cost,robust voltage offset index,robust utilization index,and voltage collapse proximity index.Third,the optimization methods of the multiand single-objective models are coordinated to solve the proposed multi-stage problem.Finally,the proposed model is implemented on an IEEE 33-node distribution system to verify its effectiveness.Numerical results show that the proposed index can better reveal voltage offset conditions as well as the SOP utilization,and the proposed model outperforms conventional ones in terms of robustness of placement plans and total cost.

Control Strategy for DC Soft Open Points in Large-scale Distribution Networks with Distributed Generators

Development of power electronic devices and their implementation in power distribution networks significantly improves not only the easier integration of distributed generation into distribution networks but also the further refinement of control algorithms specialized in the application of power management procedures in distribution systems.Implementation of DC Soft Open Points(DCSOP)for closing loops in distribution networks could serve as one of the most representative examples of the use of power electronic devices as management resources in modern distribution networks.The paper describes the possibilities of the application of DCSOP used for loops closure and power flow control in medium voltage distribution networks with integrated distributed generators.Considering all the benefits of loops closure and the controllability of the DCSOP,it is considered as a management resource capable of achieving the desired/optimal state in the distribution network.The management strategy proposed in this paper covers two cases:the first case is where an adequate communication infrastructure is available when all DCSOP operations are based on Optimal Power Flow(OPF)calculations,and the second case is when OPF results are unavailable for some reason(most often due to communication interruptions)and DCSOP operations are based on processing available data using a neural network-based algorithm.The proposed management strategy has been implemented and tested on an IEEE 33 distribution test network with integrated distributed generators.The simulation results,described in this paper,can serve not only as a basis for further scientific research but also as a basis for the practical implementation of real controllers based on the proposed algorithm and its application in practice,and in real distribution networks.

Multi-stage expansion planning of energy storage integrated soft open points considering tie-line reconstruction

With the rapid development of flexible interconnection technology in active distribution networks(ADNs),many power electronic devices have been employed to improve system operational performance.As a novel fully-con-trolled power electronic device,energy storage integrated soft open point(ESOP)is gradually replacing traditional switches.This can significantly enhance the controllability of ADNs.To facilitate the utilization of ESOP,device loca-tions and capacities should be configured optimally.Thus,this paper proposes a multi-stage expansion planning method of ESOP with the consideration of tie-line reconstruction.First,based on multi-terminal modular design characteristics,the ESOP planning model is established.A multi-stage planning framework of ESOP is then presented,in which the evolutionary relationship among different planning schemes is analyzed.Based on this framework,a multi-stage planning method of ESOP with consideration of tie-line reconstruction is subsequently proposed.Finally,case studies are conducted on a modified practical distribution network,and the cost-benefit analysis of device and multiple impact factors are given to prove the effectiveness of the proposed method.

主动配电网潮流的全纯嵌入计算方法

配电网潮流计算是进行配电网规划和运行的重要基础。目前,配电网潮流求解方法主要有牛拉(Newton Raphson,NR)法和前推回代(forward backward substitution,FBS)法两大类,但NR法和FBS法在潮流收敛性和计算效率等方面均存在一定的不足。全纯嵌入法(holomorphic embedding method,HEM)是一种求解非线性潮流方程的新方法,它可以有效避免NR法和FBS法在配电网潮流求解过程中出现的上述问题,但现有HEM未充分考虑配电网中各类型分布式电源(distributed generation,DG)和智能软开关(soft open point,SOP)控制方式的多样性,且未构建计及负荷电压特性和频率特性的潮流模型,难以适用于不同运行模式下配电网潮流计算。针对上述问题,提出一种可求解含多类型DG和SOP且可运行在并网/孤岛模式的主动配电网统一全纯嵌入潮流计算方法。首先,根据负荷静态电压和频率特性,构建计及配电网频率和节点电压影响的负荷节点全纯嵌入潮流模型;其次,根据DG不同的控制方式以及配电网不同的运行模式,将DG所连节点等效为不同节点类型,构建各类DG的全纯嵌入潮流模型;再次,考虑SOP不同控制方式,构建SOP全纯嵌入潮流模型;从次,依据全纯嵌入潮流模型等式左右两侧同次幂级数系数相等原则,推导配电网各全纯函数幂级数系数的求解递推关系式,进而计算各全纯函数的各项幂级数系数,借助解析延拓理论求取电压和频率逼近值,实现配电网潮流的准确求解;最后,通过修改的IEEE-33节点测试系统和IEEE-123节点测试系统验证所提方法准确性和有效性。

Synergetic optimization operation method for distribution network based on SOP and PV

The integration of distributed generation brings in new challenges for the operation of distribution networks,including out-of-limit voltage and power flow control.Soft open points(SOP)are new power electronic devices that can flexibly control active and reactive power flows.With the exception of active power output,photovoltaic(PV)devices can provide reactive power compensation through an inverter.Thus,a synergetic optimization operation method for SOP and PV in a distribution network is proposed.A synergetic optimization model was developed.The voltage deviation,network loss,and ratio of photovoltaic abandonment were selected as the objective functions.The PV model was improved by considering the three reactive power output modes of the PV inverter.Both the load fluctuation and loss of the SOP were considered.Three multi-objective optimization algorithms were used,and a compromise optimal solution was calculated.Case studies were conducted using an IEEE 33-node system.The simulation results indicated that the SOP and PVs complemented each other in terms of active power transmission and reactive power compensation.Synergetic optimization improves power control capability and flexibility,providing better power quality and PV consumption rate.

含SOP的交直流混合配电网日前优化调度

为实现交直流混合配电网的高效运行,提出一种含智能软开关的交直流配电网优化调度方法。在对应用于交直流配电网的智能软开关工作原理进行阐述的基础上,建立含智能软开关的交直流配电网优化调度模型。通过线性化和凸松弛技术,将所建立的非线性优化模型转化为二阶锥规划模型,并且采用改进的50节点算例分析验证模型的有效性。算例结果表明,基于所建模型得到的智能软开关运行策略能够降低配电网运行损耗及改善电压越限的情况,显著提高混合配电网的经济性。

多电压等级配电系统智能软开关协同配置

配电网逐步发展成为光伏、电动汽车等新型源荷的主要承载平台,面临的电压越限和线路过载等问题逐步加剧。柔性配电装置具有良好的调控能力,成为提高配电网运行灵活性的有效手段。已有的柔性化升级主要面向中压或低压配电网,多电压等级配电网柔性互联的潜力被忽视。因此,该文开展多电压等级配电系统智能软开关协同配置方法研究。首先,提出多电压等级配电系统智能软开关协同配置策略;其次,在计及源荷不确定性影响下,考虑源荷典型场景的概率化波动,建立多电压等级配电系统智能软开关协同配置模型。最后,为实现大规模优化配置模型的可靠收敛,采用凸差规划算法进行求解。选取实际配电网算例对优化配置模型和求解算法进行验证,结果表明,所提方法可以有效解决多电压等级配电系统智能软开关协同配置问题,支撑配电网承载高比例新型源荷,在提高系统运行安全性的同时具有更好的经济效益。

基于运行状态分级的柔性互联台区自适应优化调度

柔性互联装置的接入改变了配电台区的原有形态,能够实现不同台区的灵活互动,但现有的调度策略难以平衡系统运行经济性和电压质量的关系。对此提出一种基于运行状态分级的自适应优化调度策略。考虑到系统运行状态对优化调度策略的影响,依据配电台区的电压将系统运行状态分为正常模式、预警模式和二次电压恢复模式,并基于此构建适用于多级运行状态的优化调度模型。为实现不同优化目标下的协调运行,提出一种自适应系统运行状态的权重系数调节方法。所提出的优化调度模型和权重系数调节方法在IEEE 33节点系统算例中进行仿真验证。结果表明,该策略可以根据系统运行需求自主调节优化目标的权重系数,能够在保证系统经济运行的同时有效降低电压越限风险,并减小二次电压恢复模式下的柔性负荷波动。

考虑可平移负荷和智能软开关的主动配电网故障恢复方法

在配电网发生故障后,主动配电网能够实现用户侧参与功率的实时供需平衡,满足故障后的负荷恢复。用户参与配电网的调度也是提升故障后负荷恢复比例的途径之一,可平移负荷具有较强的可控性,有效提升了主动配电网的灵活性,智能软开关等新兴可控设备的接入,也使负荷的快速供电成为可能。本文建立了考虑可平移负荷和智能软开关的主动配电网故障恢复模型,并考虑了负荷的重要性系数。通过改进的IEEE 33节点算例进行仿真分析,构建单一故障、多点故障、短时故障的场景,验证了本文所提出方法的有效性以及可控装置对故障后负荷恢复量的提升。

考虑闭式潮流优化分布的主动配电网供电恢复方法

主动配电网具有灵活的调节能力和快速可靠的运行能力,但柔性多状态开关(SOP)、分布式电源等多种设备的存在,使供电恢复模型复杂,需要研究故障后供电恢复快速决策方法。提出了一种考虑闭式潮流优化分布的主动配电网负荷恢复方案快速决策方法。模拟故障切除后配电网所有联络开关闭式运行状态,基于二阶锥规划求解最优潮流,退出电压低、传输功率小的线路,形成利于供电恢复的配电网含SOP良性网络拓扑。建立基于负荷的功率因数与分级负荷权重的负荷恢复模型,制定负荷供电恢复方案,保证失电负荷严格按优先级获得最大的恢复水平。通过IEEE33、IEEE69节点配电系统进行算例分析,结果表明所提方法能兼顾计算的准确性和快速性。

考虑配电网灵活性的分布鲁棒优化调度

针对新能源占比不断增加导致的配电网线路过载和灵活性不足问题,提出一种考虑配电网灵活性的分布鲁棒优化调度方法。首先,考虑节点灵活性资源的功率支撑作用、网络灵活性资源智能软开关的系统潮流优化,提高配电网灵活运行能力;其次,考虑供需平衡和功率传输能力提出了灵活性裕度和线路容量裕度灵活性评价指标;然后,以灵活性裕度、线路容量裕度最优和运行成本最小为目标,构建基于数据驱动的两阶段分布鲁棒优化模型,通过列与约束生成算法对模型求解。最后,通过算例仿真验证了所提模型对提升配电网经济灵活运行的有效性。

前景导向的主动配电网智能储能软开关规划方法

分布式可再生能源大量并网成为必然趋势,合理的设备规划可以提升配电系统运行灵活性,保证可再生能源的有效消纳。智能储能软开关(soft open points integrated with energy storage system,ESOP)具有时空双尺度运行灵活性,有利于分布式能源并网。因此,考虑规划决策者不完全理性特点,提出一种配电网ESOP规划方法。首先,建立了含ESOP的配电网运行模型;然后,提取出多种面向高渗透率可再生能源并网下的ESOP规划经济性指标;最后,基于前景理论描述不完全理性特征,构建了配电网功率损失减少、购电成本减少、弃风弃光惩罚减少及投资成本属性的前景值模型,以年度综合前景值最大为目标构建ESOP的规划模型。通过线性化凸松弛等手段将原规划模型转化为混合整数二阶锥规划模型。改进的IEEE33节点系统与实际配电网算例结果表明,ESOP可以通过时序特性和柔性互联特性提升配电网消纳能力和运行经济性;同时,决策者对于各属性的重视程度和期望值会对规划结果产生影响。

基于智能储能软开关的多馈线共享储能鲁棒性规划

通过固定位置接入的储能,空间调节能力受到限制,难以应对配电网不同馈线上出现的灵活性不足问题。为此,可以将储能接入智能软开关(SOP)的直流端口,形成基于智能储能软开关(E-SOP)的多馈线共享储能,实现储能功率在不同馈线间的灵活转供。建立了一种多馈线共享储能多目标双层鲁棒规划配置模型。该模型采用多面体不确定性区间刻画随机性源-荷的功率波动范围;规划层确定多馈线共享储能的配置方案,运行层以新能源消纳、网损降低、功率支撑以及电压治理等综合目标最优,确定“最恶劣”场景下的最优运行方式。随后,采用对偶法和列与约束生成算法(C&CG)完成模型求解。通过IEEE 33节点系统进行算例分析与对比验证,结果表明多馈线共享储能可有效提升储能利用率,改善配电网运行灵活性。

配电网柔性度对分布式发电消纳的影响规律和机理分析

电力电子柔性化和分布式发电(DG)消纳是配电网研究的2个热点问题,揭示了配电网柔性度对DG消纳的影响规律和机理。首先,介绍了配电网柔性度的概念,并改进了柔性度的定义。然后,以典型接线模式和IEEE RBTS-Bus4扩展算例为研究对象,观察随柔性度升高时DG消纳率的变化,并分析规律和机理。研究发现,配电网柔性化并非都能提升DG消纳,存在一个起效条件:智能软开关(soft open point,SOP)某一侧馈线存在DG相对负荷的盈余,同时另一侧存在DG缺额。然而满足起效条件后,消纳率和柔性度之间的规律性仍未显现。提出分析消纳提升限制条件和按SOP安装次序观察的2种方法,发现了隐藏的规律:当存在消纳提升可用空间且无SOP容量限制下,或者同一SOP安装次序下,柔性度和消纳率才具有正相关关系。发现的规律机理为指导配电网的柔性化发展和DG消纳提供了新的理论依据。