State coordinated voltage control in an active distribution network with on-load tap changers and photovoltaic systems

Decreasing costs and favorable policies have resulted in increased penetration of solar photovoltaic(PV)power generation in distribution networks.As the PV systems penetration is likely to increase in the future,utilizing the reactive power capability of PV inverters to mitigate voltage deviations is being promoted.In recent years,droop control of inverter-based distributed energy resources has emerged as an essential tool for use in this study.The participation of PV systems in voltage regulation and its coordination with existing controllers,such as on-load tap changers,is paramount for controlling the voltage within specified limits.In this work,control strategies are presented that can be coordinated with the existing controls in a distributed manner.The effectiveness of the proposed method was demonstrated through simulation results on a distribution system.

Multiple Dispatching Reactive Power and Voltage Coordinated Control Method

This paper studies the reactive power and voltage coordinated control scheme. According to the characteristics of Hunan power grid, the coordinated schemes about Hunan power grid with Central China Power Grid, as well as Changsha power grid are proposed. At the same time, this paper builds a two-way interactive and multiple dispatching reactive power and voltage coordinated control mode, and can be successfully applied in Hunan power grid. The operation results show that this control scheme fulfills the ability of large power grids in optimal allocating of resources, effectively integrates the reactive power resources of the entire grid, achieves the purpose of reducing power grid loss, improving voltage quality, reducing the operating numbers of the reactive power equipment.

Hierarchical Coordinated Control for Power System Voltage Using Linear Temporal Logic

The paper proposed an approach to study the power system voltage coordinated control using Linear Temporal Logic (LTL). First, the hybrid Automata model for power system voltage control was given, and a hierarchical coordinated voltage control framework was described in detail. In the hierarchical control structure, the high layer is the coordinated layer for global voltage control, and the low layer is the power system controlled. Then, the paper introduced the LTL language, its specification formula and basic method for control. In the high layer, global voltage coordinated control specification was defined by LTL specification formula. In order to implement system voltage coordinated control, the LTL specification formula was transformed into hybrid Automata model by the proposed algorithms. The hybrid Automata in high layer could coordinate the different distributed voltage controller, and have constituted a closed loop global voltage control system satisfied the LTL specification formula. Finally, a simple example of power system voltage control include the OLTC controller, the switched capacitor controller and the under-voltage shedding load controller was given for simulating analysis and verification by the proposed approach for power system coordinated voltage control. The results of simulation showed that the proposed method in the paper is feasible.

Coordinated voltage control of renewable energy power plants in weak sending-end power grid

The utilization of renewable energy in sending-end power grids is increasing rapidly,which brings difficulties to voltage control.This paper proposes a coordinated voltage control strategy based on model predictive control(MPC)for the renewable energy power plants of wind and solar power connected to a weak sending-end power grid(WSPG).Wind turbine generators(WTGs),photovoltaic arrays(PVAs),and a static synchronous compensator are coordinated to maintain voltage within a feasible range during operation.This results in the full use of the reactive power capability of WTGs and PVAs.In addition,the impact of the active power outputs of WTGs and PVAs on voltage control are considered because of the high R/X ratio of a collector system.An analytical method is used for calculating sensitivity coefficients to improve computation efficiency.A renewable energy power plant with 80 WTGs and 20 PVAs connected to a WSPG is used to verify the proposed voltage control strategy.Case studies show that the coordinated voltage control strategy can achieve good voltage control performance,which improves the voltage quality of the entire power plant.

Research on On-Line Coordinated Control Strategy to Improve the Voltage Vulnerability after Disturbance

The on-line coordinated control strategy among multi-voltage controls is important to keep voltage security in post-fault systems. Based on the wide area measuring information, the energy function, which can qualify the impacts of the different control actions on voltage of different nodes, is proposed. And then, considering the impacts of different control actions on the node voltage being treated as a weight matrix, the energy margin is used as the objective function and the reactive power margin is innovatively used as the constraint to regulate the control actions globally according to the weight values. At last, the objective functions are solved to get the optimal global coordinated control strategies. The proposed method is identified in an IEEE-30 Bus system and the simulation results show that it effectively improves the voltage stability.

Improved Voltage Control Strategy for Photovoltaic Grid-Connected System Based on DoubleLayer Coordination Control

An improved automatic voltage coordination control strategy （AVCCS） based on ;automatic voltage control （AVC） and battery energy storage control （BESC） is proposed for photovoltaic grid-connected system （PVGS） to mitigate the voltage fluctuations caused by environmental disturbances. Only AVC is used when small environ- mental disturbances happen, while BESC is incorporated with AVC to restrain the voltage fluctuations when large disturbances happen. An adjustable parameter determining the allowed amplitudes of voltage fluctuations is introduced to realize the above switching process. A benchmark low voltage distribution system including ]？VGS is established by using the commercial software Dig SILENT. Simulation results show that the voltage under AVCCS satisfies the IEEE Standard 1547, and the installed battery capacity is also reduced. Meanwhile, the battery＇s service life is ex- tended by avoiding frequent charges/discharges in the control process.

Research on Volt/Var Control of Distribution Networks Based on PPO Algorithm

In this paper,a model free volt/var control(VVC)algorithm is developed by using deep reinforcement learning(DRL).We transform the VVC problem of distribution networks into the network framework of PPO algorithm,in order to avoid directly solving a large-scale nonlinear optimization problem.We select photovoltaic inverters as agents to adjust system voltage in a distribution network,taking the reactive power output of inverters as action variables.An appropriate reward function is designed to guide the interaction between photovoltaic inverters and the distribution network environment.OPENDSS is used to output system node voltage and network loss.This method realizes the goal of optimal VVC in distribution network.The IEEE 13-bus three phase unbalanced distribution system is used to verify the effectiveness of the proposed algorithm.Simulation results demonstrate that the proposed method has excellent performance in voltage and reactive power regulation of a distribution network.

LCC-MMC混合三端直流输电系统送端交流故障下的不间断运行协调控制策略

为实现基于电网换相换流器与模块化多电平换流器(LCC-MMC)的混合三端直流输电系统送端交流故障下的直流低电压穿越,提出兼顾传输容量与响应速度的自适应电压协调控制策略及有功功率分配策略。在维持故障期间功率续传的前提下,定量分析了模块化多电平换流器(MMC)的降压值以减少传输功率的绝对值损失量,并设计MMC根据本地直流电流偏差快速减投子模块总数的降压方式;考虑到半桥型MMC的调制比约束,设计正极MMC定量吸收无功功率与负极MMC动态调整交流电压参考值的换流站极间协同控制策略;同时,为抑制从站的过电流及避免送端严重交流故障时主站的潮流反转,提出各受端换流站有功功率自适应调整的控制方式。最后通过对输电系统送端交流电压跌落不同幅度时的故障穿越效果进行仿真分析,验证了所提控制策略的有效性。

基于牵引网电压和空载电压的多储能系统区间能量管理策略

近年来,随着“双碳”政策的推动,储能技术在城市轨道交通中的应用愈发广泛,呈现出点到线的发展趋势。当一条线路中有多站安装储能装置时,想要进一步提升储能系统的节能效果,必须要解决不同站储能装置的充放电策略个性化设计,以及多储能间协调控制这两个问题。因此,该文提出一种基于实时牵引网电压和空载电压的多储能系统区间能量管理策略。该策略基于多个牵引变电站的空载电压和牵引网电压,对能量管理区间内的列车状态和列车剩余功率进行辨识,基于此计算区间内储能装置的充放电阈值基准值初值及基准值变化的斜率。为进一步提升节能和稳压效果,该策略基于充放电周期、牵引网电压超限频次及储能系统的荷电状态(SOC)等参数,对基准值及其更新斜率进行实时校正。该文在北京地铁的实际线路中进行了验证,结果表明,相较于基于本站空载电压的能量管理策略,提出的策略在降低系统能耗和稳定牵引网电压方面都具有显著的改善效果。

基于储能有功功率与OLTC协调的配电网电压控制

高比例光伏系统接入配电网会引起电压越限,传统无功电压调整方案在高阻抗比配网中失效,利用储能系统有功功率实现电压控制的技术方案被广泛采用,但现有技术方案中的储能系统在电压控制过程中可能产生过度充放电问题。针对这些问题,提出了一种基于储能有功功率与有载调压变压器(on-loadtapchanger,OLTC)协调的配电网电压控制策略。在分析光伏接入对配电网电压影响的基础上,利用测量得到的电压数据控制储能有功功率,实现对接入节点电压水平的快速调控;同时在OLTC控制环节加入储能荷电状态参考量,利用节点电压信息与储能荷电状态共同控制OLTC分接头动作,实现对配电网整体电压水平调控的同时避免了储能系统过度充放电。最后在IEEE 13节点系统中进行仿真验证,结果表明所提策略能够解决配电网内电压越限问题,避免储能系统过度充放电,从而延长储能系统的使用寿命,实现对配电网内资源的合理利用。

一种改进的基于电网幅值跌落的SWISS整流器协调优化控制方法

SWISS整流器因其优越的性能被广泛应用于充电桩、分布式直流电源等场合。其首要的控制目标是维持稳定的直流侧输出电压、正弦且对称的交流侧三相电流以及网侧单位功率因数。然而,当电网出现幅值跌落时,基于传统的控制方法很难同时实现上述3个控制目标。因此,该文分别提出适用于电网幅值跌落的输出电压恒定控制(constant output voltage control,COVC)方法和电流正弦对称控制(sinusoidal and symmetrical current control,SSCC)方法。前者可实现直流侧输出电压恒定无波动,但无法实现网侧电流的正弦且对称。后者可实现网侧电流正弦且对称,但无法实现直流侧电压输出恒定无波动。在此基础上,该文结合这2种控制方法的优势进一步提出一种改进的协调优化控制(improved coordination and optimization control,ICOC)方法,可实现网侧处于单位功率因数的同时,在直流侧输出电压恒定无波动和网侧电流正弦且对称之间进行协调优化,实验结果证明ICOC方法相较于COVC和SSCC具有显著的优势,与该文的理论分析一致。

基于一致性算法光伏逆变器和储能分组协调电压控制策略

针对低压配电网中光伏逆变器(PV)无功控制和储能(ESS)有功控制未充分协调的现状,提出基于一致性算法的光伏逆变器和储能分组协调电压控制策略。首先,根据不同调压设备的电压-成本灵敏度F^(U-C),提出先利用光伏逆变器无功调压再利用储能有功调压,再根据不同节点调压设备的F^(U-C)对调压设备进行分组,提出优先利用F^(U-C)数值较大的分组参与调压;然后,在光伏逆变器无功调压阶段,组内以无功利用率为一致性变量,在储能有功控制阶段,组内以荷电状态(SOC)变化量为一致性变量,组间通过协调控制共同实现关键节点电压收敛至设定值;最后,利用含分布式光伏和储能的IEEE 14节点低压配电网进行算例仿真,验证所提分组协调控制策略的有效性和正确性。

含高比例光伏的配电网分组协调电压控制策略

电压越限成为限制光伏最大接入量的重要因素,为解决大规模光伏并网所导致电压越限问题,文章提出了含高比例光伏的配电网分组协调电压控制策略。首先,根据光伏接入节点对配电网电压灵敏度不同,提出了光伏逆变器分组协调控制思想;然后,光伏逆变器组内以容量利用比和功率因数为一致性变量进行电压控制,组间通过协调控制确保关键节点电压收敛至设定值1.05 p.u.;最后,通过算例仿真验证所提控制策略能有效地抑制配电网电压越限,避免不必要的有功削减,同时在负荷、光伏波动时具有较强的鲁棒性。

Coordinated control for voltage regulation of distribution network voltage regulation by distributed energy storage systems

With more and more distributed photovoltaic(PV)plants access to the distribution system,whose structure is changing and becoming an active network.The traditional methods of voltage regulation may hardly adapt to this new situation.To address this problem,this paper presents a coordinated control method of distributed energy storage systems(DESSs)for voltage regulation in a distribution network.The influence of the voltage caused by the PV plant is analyzed in a simple distribution feeder at first.The voltage regulation areas corresponding to DESSs are divided by calculating and comparing the voltage sensitivity matrix.Then,a coordinated voltage control strategy is proposed for the DESSs.Finally,the simulation results of the IEEE 33-bus radial distribution network verify the effectiveness of the proposed coordinated control method.

A coordinated consistency voltage stability control method of active distribution grid

The presence of distributed generators(DGs)with high penetration poses new challenges in the management and operation of electrical grids.Due to the local character of DGs,they could in principle be used in emergency situations to prevent a voltage instability event of the grid.In this paper,a certain method is proposed to coordinate the operation of virtual power plant(VPP)and conventional voltage regulation device to improve the static voltage stability of distribution network with the multi-agent framework.The concept and the general framework of this coordinated control system is introduced,and the voltage instable nodes are determined based on the voltage instability indicator.The voltage coordinated control model of the distribution system is established according to the multi-agent consistency control theory and the coordinated controllers for agents are designed by solving a problem with bilinear matrix inequality constraints.The suggested method is implemented on an IEEE 33 nodes test system and the simulation results show its efficiency and validity.

含分布式光伏接入的三相牵引供电系统电压协调控制方法

牵引供电系统中光伏并网逆变器普遍处于弱可控状态且缺乏多机间协调配合,为了使分布式光伏在实现牵引能耗优化的同时,主动参与牵引网电压调控,提出了用于三相牵引供电系统的电压协调控制策略。针对含光伏的新型三相牵引供电系统拓扑,分析了系统电压-有功和无功定量关系。结合分布式光伏无功裕度及协调关系,设计了3阶段分布式电压协调控制策略,根据电压灵敏度判定各节点补偿与削减优先度,实现了分布式光伏无功协调补偿及有功优化削减,达到牵引网电压主动控制。最后,通过对系统多工况下仿真,验证策略有效性。仿真结果表明,所提协调控制策略在三相牵引供电系统复杂的运行工况下,能够在兼顾光伏能量利用率的同时,增强系统电压调控能力,解决牵引网电压越限问题,并有效降低牵引网损耗。研究通过有效利用光伏支撑牵引网电压,为机车的安全、高效运行提供保障。

Coordinated control for medium voltage DC distribution centers with flexibly interlinked multiple microgrids

From flexible interconnection among feeders to hybrid alternating current(AC) and direct current(DC)distribution structures of future smart distribution systems medium-voltage DC distribution centers with flexibly interlinked multiple microgrids(MGs) will have wide applications on the demand side. A generic coordinated control framework based on a distributed cooperation scheme is proposed for such DC centers, as opposed to centralized control structures. A novel unified control only using local measurements is proposed for these interlinking converters. During normal power disturbances, automatic coordinated power control and mutual support among sub-systems can be realized, thereby improving DC voltage and AC frequency stability to enable multiple MGs to be treated as a real unified cluster. Moreover, with this method, interlinking converters can realize seamless transition in power dispatching mode, common DC bus voltage control mode, and MG support mode without communication and control system switching. A simplified dynamic model has been developed to verify the proposed control strategy. This work is expected to provide a new solution for flexible interconnection and operational control of large-scale MG clusters.

基于“先无功–后有功”功率补偿的配电网电压协同控制策略

整县分布式光伏电源的大量开发与利用及分布式电源规模化并网对实现“碳达峰、碳中和”与“乡村振兴”两大国家战略具有重要的现实意义。由于分布式电源发电尖峰和低谷阶段与负荷峰谷时常不同步,进而导致配电系统过/欠电压问题,严重影响了电能质量,甚至威胁系统安全。针对上述问题,本文提出一种基于“先无功–后有功”功率补偿的配电网层级式电压协同控制策略。首先,建立基于“先无功–后有功”功率补偿的配电网层级式电压协同控制框架。其次,结合多微电网节点注入电流与电压的方程与功率–电压灵敏度分析,根据多节点电压越限程度,提出一种基于“先无功–后有功”功率补偿的多智能体协同调节策略,该策略先通过无功补偿器进行无功调节,当电压尚未得到有效治理时,再采用多微电网进行有功调节。再次,为了进一步满足各节点微电网有功功率调节需求,并考虑电网内部源–荷–储运行成本与污染排放,提出一种基于多目标优化的微电网内部分布式源–荷–储优化协调功率控制策略。最后,在MATLAB平台中设计了3种仿真场景以及IEEE测试系统模型对所提控制策略进行了验证。结果表明,所提出的电压协同控制方法在最经济的情况下可以实现各节点电压的综合高效治理,同时,所提出的微电网优化协调功率控制策略能使源–荷–储在绿色经济的供电模式下实时精准地满足电压治理目标下微电网有功调节的需求。仿真实验结果验证了本文所提控制策略的有效性。

级联型混合直流与UPFC的柔性潮流协调控制策略

级联型混合直流输电系统具有能抑制换相失败、传输大容量功率的优势。但当级联型混合直流低端模块化多电平换流器(MMC)采用主从控制时,若系统发生交直流故障或负荷突增,可能会产生电流不平衡问题,导致受端交流侧功率出现大范围反向传输及电压支撑能力下降。为解决该问题并增强受端电网的稳定性,针对级联型混合直流输电系统,提出一种基于统一潮流控制器(UPFC)的柔性潮流协调控制策略。研究了基于柔性交流输电(FACTS)设备统一潮流控制器(UPFC)的级联型混合直流系统柔性潮流控制特性,针对系统故障及大扰动时出现的功率返送及电压稳定性问题,提出基于UPFC的频率支撑策略和基于动态限幅的电压支撑策略。该策略将送端侧故障带来的功率扰动转移到受端交流系统UPFC所在线路,利用UPFC功率补偿能力进行协调,同时基于动态限幅控制策略,采用无功优先控制方式提高换流站无功输出能力。最后,在PSCAD–EMTDC平台搭建了含受端交流系统的级联型混合直流输电系统模型。首先,仿真了LCC直流电流指令值下降过程,结果表明,本文所提基于UPFC的协调控制策略可以有效地减小交流系统频率波动,抑制功率返送现象;其次,仿真了系统负荷突增过程,验证了动态限幅控制策略能更好地提升MMC对交流系统的电压支撑能力;最后,仿真了连锁故障过程,结果表明,所提协调控制策略能有效地实现对系统频率和电压支撑,抑制功率波动,提高了级联型混合直流系统及受端电网的稳定性。因此,本文提出的级联型混合直流与UPFC的柔性潮流协调控制策略具有有效性和可行性。

基于集群动态划分的配电网无功电压自律-协同控制

针对高渗透率分布式光伏接入配电网导致的电压越限问题,以及传统集中式控制面临的通信延时、计算量大与控制设备过多等问题,提出一种基于集群动态划分的配电网无功电压自律-协同控制方法。首先,建立日前集中式无功电压优化模型,安排离散无功补偿设备投退计划,日内调度以节点电压偏差最小为目标建立日内无功电压滚动优化模型,结合同步型交替方向乘子法实现各集群间的分布式协调控制;然后,通过群内本地电压实时控制抑制群内节点电压的波动;最终,以改进的IEEE 33节点系统及某地实际60节点配电网为例,验证了该方法的正确性与有效性。