Research on Scheduling Strategy of Flexible Interconnection Distribution Network Considering Distributed Photovoltaic and Hydrogen Energy Storage

Distributed photovoltaic(PV)is one of the important power sources for building a new power system with new energy as the main body.The rapid development of distributed PV has brought new challenges to the operation of distribution networks.In order to improve the absorption ability of large-scale distributed PV access to the distribution network,the AC/DC hybrid distribution network is constructed based on flexible interconnection technology,and a coordinated scheduling strategy model of hydrogen energy storage(HS)and distributed PV is established.Firstly,the mathematical model of distributed PV and HS system is established,and a comprehensive energy storage system combining seasonal hydrogen energy storage(SHS)and battery(BT)is proposed.Then,a flexible interconnected distribution network scheduling optimization model is established to minimize the total active power loss,voltage deviation and system operating cost.Finally,simulation analysis is carried out on the improved IEEE33 node,the NSGA-II algorithm is used to solve specific examples,and the optimal scheduling results of the comprehensive economy and power quality of the distribution network are obtained.Compared with the method that does not consider HS and flexible interconnection technology,the network loss and voltage deviation of this method are lower,and the total system cost can be reduced by 3.55%,which verifies the effectiveness of the proposed method.

Research on power electronic transformer applied in AC/DC hybrid distribution networks

The AC/DC hybrid distribution network is one of the trends in distribution network development, which poses great challenges to the traditional distribution transformer. In this paper, a new topology suitable for AC/DC hybrid distribution network is put forward according to the demands of power grid, with advantages of accepting DG and DC loads, while clearing DC fault by blocking the clamping double sub-module(CDSM) of input stage. Then, this paper shows the typical structure of AC/DC distribution network that is hand in hand. Based on the new topology, this paper designs the control and modulation strategies of each stage, where the outer loop controller of input stage is emphasized for its twocontrol mode. At last, the rationality of new topology and the validity of control strategies are verified by the steady and dynamic state simulation. At the same time, the simulation results highlight the role of PET in energy regulation.

Two-stage Optimal Dispatching of AC/DC Hybrid Active Distribution Systems Considering Network Flexibility

The increasing flexibility of active distribution systems(ADSs)coupled with the high penetration of renewable distributed generators(RDGs)leads to the increase of the complexity.It is of practical significance to achieve the largest amount of RDG penetration in ADSs and maintain the optimal operation.This study establishes an alternating current(AC)/direct current(DC)hybrid ADS model that considers the dynamic thermal rating,soft open point,and distribution network reconfiguration(DNR).Moreover,it transforms the optimal dispatching into a second-order cone programming problem.Considering the different control time scales of dispatchable resources,the following two-stage dispatching framework is proposed.d dispatch uses hourly input data with the goal(1)The day-ahea of minimizing the grid loss and RDG dropout.It obtains the optimal 24-hour schedule to determine the dispatching plans for DNR and the energy storage system.(2)The intraday dispatch uses 15-min input data for 1-hour rolling-plan dispatch but only executes the first 15 min of dispatching.To eliminate error between the actual operation and dispatching plan,the first 15 min is divided into three 5-min step-by-step executions.The goal of each step is to trace the tie-line power of the intraday rolling-plan dispatch to the greatest extent at the minimum cost.The measured data are used as feedback input for the rolling-plan dispatch after each step is executed.A case study shows that the comprehensive cooperative ADS model can release the line capacity,reduce losses,and improve the penetration rate of RDGs.Further,the two-stage dispatching framework can handle source-load fluctuations and enhance system stability.

Battery Storage Configuration of AC/DC Hybrid Distribution Networks

The upscaling requirements of energy transition highlight the urgent need for ramping up renewables and boosting system efficiencies.However,the stochastic nature of excessive renewable energy resources has challenged stable and efficient operation of the power system.Battery energy storage systems(BESSs)have been identified as critical to mitigate random fluctuations,unnecessary green energy curtailment and load shedding with rapid response and flexible connection.On the other hand,an AC/DC hybrid distribution system can offer merged benefits in both AC and DC subsystems without additional losses during AC/DC power conversion.Therefore,configuring BESSs on an AC/DC distribution system is wellpositioned to meet challenges brought by carbon reductions in an efficient way.A bi-level optimization model of BESS capacity allocation for AC/DC hybrid distribution systems,considering the flexibility of voltage source converters(VSCs)and power conversion systems(PCSs),has been established in this paper to address the techno-economic issues that hindered wide implementation.The large-scale nonlinear programming problem has been solved utilizing a genetic algorithm combined with second-order cone programming.Rationality and effectiveness of the model have been verified by setting different scenarios through case studies.Simulation results have demonstrated the coordinated operation of BESS and AC/DC hybrid systems can effectively suppress voltage fluctuations and improve the cost-benefit of BESSs from a life cycle angle.

Reverse Droop Control-based Smooth Transfer Strategy for Interface Converters in Hybrid AC/DC Distribution Networks

Hybrid AC/DC distribution networks are promising candidates for future applications due to their rapid advancement in power electronics technology.They use interface converters(IFCs)to link DC and AC distribution networks.However,the networks possess drawbacks with AC voltage and frequency offsets when transferring from grid-tied to islanding modes.To address these problems,this paper proposes a simple but effective strategy based on the reverse droop method.Initially,the power balance equation of the distribution system is derived,which reveals that the cause of voltage and frequency offsets is the mismatch between the IFC output power and the rated load power.Then,the reverse droop control is introduced into the IFC controller.By using a voltage-active power/frequency-reactive power(U-P/f-Q)reverse droop loop,the IFC output power enables adaptive tracking of the rated load power.Therefore,the AC voltage offset and frequency offset are suppressed during the transfer process of operational modes.In addition,the universal parameter design method is discussed based on the stability limitations of the control system and the voltage quality requirements of AC critical loads.Finally,simulation and experimental results clearly validate the proposed control strategy and parameter design method.

基于线性化方法的交直流混合配电系统网架规划

随着配电系统中直流设备的大量接入,交直流混合配电系统得到越来越广泛的应用。为适应交直流混合配电系统中不同交直流(AC/DC)类型的负荷或电源的接入,提出一种新的交直流混合配电系统网架结构规划方法,该方法考虑了网架交直流配置的所有可能性。首先以二进制网络矩阵描述配电系统的网架结构;其次建立网架单层规划模型,将规划变量和运行变量同时进行优化以提升全局寻优能力;最后将单层规划模型进行线性化处理,转换为混合整数线性规划问题以提升求解效率。仿真结果表明,所提方法能够为配电系统中不同交直流类型的负荷和电源的接入提供最佳的网架配置方案,相比于传统的纯交流规划方案具有更好的经济性和供电能力,在算法上与经典遗传算法求解的双层规划方法相比,具有更好的全局寻优能力和计算效率。

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。

高比例分布式可再生能源交直流混合配电网运行调控:科学问题与技术框架

随着分布式可再生能源发电与中低压直流组网技术的快速发展,未来配电网必然向复杂的交直流混合形态演进,其运行调控技术面临许多新的挑战。在高比例分布式可再生能源交直流混合配电网(HR-HDN)运行调控技术发展需求分析的基础上,提炼出HR-HDN运行调控技术的3个科学问题,并以多类型可控设备协同、源-网-荷-储高度互动化和市场化需求为研究主线,从稳定控制、故障主动防御与恢复、电力市场机制辅助调控以及“平台+数据”数字化集成调控4个方面,提出了HR-HDN的运行调控技术框架。最后,对HR-HDN运行调控关键技术的未来发展进行了展望。

考虑光伏随机性的交直流混合配电网鲁棒机会约束安全域模型

为实现高比例光伏接入下交直流混合配电网的安全评估,构建了交直流混合配电网的鲁棒机会约束安全域模型。首先,提出一种基于区间划分的自适应带宽核密度估计方法,以获取光伏预测误差概率分布,构建光伏出力机会约束不确定集合;其次,采用功率与节点电压幅值比值为状态变量,在已有交流线性化潮流模型的基础上推导一种交直流混合配电网线性化潮流模型;然后,提出交直流混合配电网鲁棒机会约束安全域的概念和模型,结合列与约束生成算法和径向迭代搜索算法生成可观测的鲁棒机会约束安全域空间。最后,算例分析验证了所提模型能够在鲁棒机会约束安全域上准确、直观的反映光伏出力的随机性,进而为交直流混合配电网的准确安全评估提供支撑。

基于固态断路器主动注入式直流故障测距方法

随着直流配电网的快速发展与深化应用,准确可靠的故障测距技术对直流故障检修和恢复至关重要。该文提出一种基于固态断路器(SSCB)主动注入式直流故障测距方法。首先,利用SSCB开断主动注入不同脉冲宽度的信号,并检测注入脉冲首末端和反射波首末端的时间差作为注入波形传播时间间隔,能够减小采样频率带来的误差。然后,提取电缆线路电压线模量作为检测量,削弱正负极线路之间的耦合作用,获得稳定波速。最后,基于小波变换原理提出改进自适应模极大值方法来检测脉冲首末端时刻,减小噪声和过渡电阻对测距精度的影响。仿真结果表明,基于SSCB主动注入式测距方法在直流配电网单极接地和极间短路故障情况下均能够实现准确且快速的定位。

Coordinated voltage regulation of hybrid AC/DC medium voltage distribution networks

In a hybrid AC/DC medium voltage distribution network, distributed generations(DGs), energy storage systems(ESSs), and the voltage source converters(VSCs)between AC and DC lines, have the ability to regulate node voltages in real-time. However, the voltage regulation abilities of above devices are limited by their ratings. And the voltage regulation efficiencies of these devices are also different. Besides, due to high r/x ratio, node voltages are influenced by both real and reactive power. In order to achieve the coordinated voltage regulation in a hybrid AC/DC distribution network, a priority-based real-time control strategy is proposed based on the voltage control effect of real and reactive power adjustment. The equivalence of real and reactive power adjustment on voltage control is considered in control area partition optimization, in which regulation efficiency and capability are taken as objectives.In order to accommodate more DGs, the coordination of controllable devices is achieved according to voltage sensitivities. Simulations studies are performed to verify the proposed method.

考虑柔性资源多维价值标签的交直流配电网灵活调度

可再生能源高渗透率使得交直流配电网面临严重的随机性和波动性,充分挖掘柔性资源调控潜力可以有效地降低可再生能源带来的网络运行风险。针对当前交直流配电网优化调度主要考虑电压源型换流器(VSC)的调控能力,对VSC与柔性资源协同研究不足的问题,提出一种考虑柔性资源多维价值标签的交直流配电网灵活调度方法。首先,考虑柔性资源调控特性差异,构建了包含响应时段、调节能力、调节成本及响应意愿的多维价值标签评估体系,准确全面地评估柔性资源聚合调控潜力范围;其次,以运行成本最小为目标函数,柔性资源多维价值标签为约束,建立交直流配电网两阶段鲁棒日前优化调度模型,并采用嵌套列和约束生成算法(C&CG)及强对偶理论进行求解;最后,通过改进的IEEE 33节点交直流配电网仿真结果表明,所提方法能够充分发挥柔性资源的调控潜力和协同能力,同时可有效提高模型求解效率和求解精度。

基于半正定规划的交直流主动配电网三相有功无功联合优化

交直流主动配电网作为未来配电网的主要发展形态,实现其有功无功资源的协同优化控制具有重要的研究意义。然而配电网负荷单相接入和分布式发电三相功率不一致,将导致配电网三相不平衡现象越发严重。为了应对交直流主动配电网的三相不平衡问题,提出考虑相间耦合与三相不平衡度限制的三相有功无功联合优化方法。首先,建立考虑相间耦合的原始三相潮流模型并对其进行升维映射;其次,采用半正定松弛方法,推导了交直流主动配电网各子系统的完整三相潮流模型以及序分量形式下的三相电压不平衡度约束;再次,提出以总运行成本最小化为目标函数的交直流主动配电网三相有功无功联合优化模型;最后,采用改进IEEE 33节点、69节点、141节点和1056节点交直流配电网算例分析,验证了该文所提方法的有效性。

基于双智能体深度强化学习的交直流配电网经济调度方法

随着大量直流电源和负荷的接入,交直流混合的配电网技术已成为未来配电网的发展趋势.然而,源荷不确定性及可调度设备的类型多样化给配电网调度带来了巨大的挑战.本文提出了基于分支决斗深度强化网络(branching dueling Q-network,BDQ)和软演员-评论家(soft actor critic,SAC)双智能体深度强化学习的交直流配电网调度方法.该方法首先将经济调度问题与两智能体的动作、奖励、状态相结合,建立经济调度的马尔可夫决策过程,并分别基于BDQ和SAC方法设置两个智能体,其中,BDQ智能体用于控制配电网中离散动作设备,SAC智能体用于控制连续动作设备.然后,通过集中训练分散执行的方式,两智能体与环境进行交互,进行离线训练.最后,固定智能体的参数,进行在线调度.该方法的优势在于采用双智能体能够同时控制离散动作设备电容器组、载调压变压器和连续动作设备变流器、储能,同时通过对双智能体的集中训练,可以自适应源荷的不确定性.改进的IEEE33节点交直流配电网算例测试验证了所提方法的有效性.

基于数据驱动多面体集合的交直流混合配电网鲁棒调度方法

针对现有配电网鲁棒调度方法缺乏对不确定参数相关性问题的考虑,提出了一种基于数据驱动多面体集合的交直流混合配电网鲁棒调度方法。首先,构建分布式光伏出力的传统多面体集合,利用历史数据驱动形成了相关性包络图,通过弯曲多面体集合边界,建立了相关性多面体集合模型。然后,在此基础上,针对相关性多面体集合存在鲁棒性差和保守性大的问题,建立了数据驱动的多面体集合模型。进一步,建立了基于数据驱动多面体集合的交直流混合配电网鲁棒调度模型,并采用列与约束生成(column and constraint generation,CCG)算法对鲁棒调度模型进行求解。最后,改进的IEEE33节点系统仿真结果表明,基于数据驱动多面体集合的交直流混合配电网鲁棒调度方法可以减少优化结果的保守性,提高其鲁棒性,证明了所提出方法的有效性。

考虑灵活性的交直流混联配电网分布鲁棒优化运行

为适应未来配电网交直流混联的配电方式、应对新能源不确定性带来的运行灵活性调节量不足问题,提出一种考虑灵活性的交直流混联配电网两阶段分布鲁棒优化运行模型。首先,在交直流混联配电网架构下,分析其灵活性资源供需关系,定义上调/下调灵活性裕度指标;其次,综合考虑系统中各类约束,构建描述配电网经济性、新能源消纳性与灵活性的优化运行模型,结合数据驱动生成的风光典型场景,采用基于综合范数距离的分布鲁棒优化方法处理风、光出力不确定性,并根据优化变量的出力特性构建两阶段分布鲁棒优化运行模型;最后,对模型进行凸性转化与求解,通过修改的33节点交直流混联配电网算例验证模型的有效性。

基于改进分析目标级联法的交直流混联配电网分布式优化运行

交直流混联的配电方式是未来配电网的一种重要发展方向,为克服其中各子系统分属不同利益主体而带来的功率信息传递的限制,提出了一种基于改进分析目标级联法的交直流混联配电网分布式优化运行方法。首先,针对交直流混联配电网的直流、换流站和交流区域,分别建立包含自身区域运行优化与区域间交互功率运行优化的模型;其次,采用分布式优化的思想,将交互功率作为共享变量,对模型目标函数进行解耦,并在传统的分析目标级联法中引入一个平衡系数,来解决因惩罚乘数初值选择不当,子系统函数项与惩罚项权重不平衡情况下算法性能不好的问题,在一致性约束下迭代求解分布式模型;最后,通过算例仿真,进行模型的有效性、改进算法性能以及分布式模型通用性的验证。

含能量路由器的交直流混合配电网潮流计算

能量路由器(energy router,ER)作为新兴电力电子设备,可以实现电能在电力系统中的灵活分配。分析ER对系统的影响,研究以ER为配电枢纽的交直流混合配电网潮流计算方法,对实现配电网的优化运行具有重要意义。文中首先基于改进交替迭代法建立ER的稳态潮流模型,并对ER直流端口采用下垂控制策略,结合传统解耦法,提出一种适用于含ER的配电网交直流解耦迭代潮流计算方法。以含有多个ER的IEEE 14节点和IEEE 69节点配电系统为算例进行仿真计算,验证所提方法的正确性与收敛性。为分析ER对系统运行的影响,对不同场景下IEEE 69节点测试系统进行仿真计算,证明ER在系统中可以支撑节点电压,减小系统运行损耗。

计及SOP损耗的交直流配电网三相区间状态估计

随着分布式电源及智能软开关(SOP)等新型设备投入配电网运行,需要对交直流配电网进行精确的状态估计。首先构建了交直流配电网的区间状态估计模型,考虑三相不对称性与交直流之间的耦合;其次,为计及SOP的损耗,增设SOP两侧支路电流作为状态变量,完善了区间状态估计中的雅克比矩阵;最后采用基于迭代运算的线性规划方法进行区间状态估计。在修改IEEE33节点算例上进行仿真,结果表明所提方法能保证计及SOP损耗的状态估计结果的准确性。

基于冗余矢量的T型三电平双向变换器中点电位平衡模型预测控制

T型三电平双向变换器因其具有损耗小、输出电能质量高等优势适合应用于低压交直流混合配电网互联等场景。针对T型三电平双向变换器存在直流侧中点电位不平衡等问题,模型预测控制因其易于实现多目标优化的特点具有良好的应用价值。为了解决传统有限集模型预测控制(FCS-MPC)权重因子整定困难,中点电位控制效果不佳的问题,提出一种基于冗余矢量的中点电位平衡模型预测控制,利用冗余小矢量的特性实现对中点电位平衡的控制,避免了权重因子的选择。在此基础上,利用代价函数计算矢量的作用时间并预测输出最优开关序列,提升系统的稳态性能。最后,通过实验测试验证了所提策略的有效性。