Power Flow Calculation for VSC-based AC/DC Hybrid Systems Based on Fast and Flexible Holomorphic Embedding

The power flow(PF)calculation for AC/DC hybrid systems based on voltage source converter(VSC)plays a crucial role in the operational analysis of the new energy system.The fast and flexible holomorphic embedding(FFHE)PF method,with its non-iterative format founded on complex analysis theory,exhibits superior numerical performance compared with traditional iterative methods.This paper aims to extend the FFHE method to the PF problem in the VSC-based AC/DC hybrid system.To form the AC/DC FFHE PF method,an AC/DC FFHE model with its solution scheme and a sequential AC/DC PF calculation framework are proposed.The AC/DC FFHE model is established with a more flexible form to incorporate multiple control strategies of VSC while preserving the constructive and deterministic properties of original FFHE to reliably obtain operable AC/DC solutions from various initializations.A solution scheme for the proposed model is provided with specific recursive solution processes and accelerated Padéapproximant.To achieve the overall convergence of AC/DC PF,the AC/DC FFHE model is integrated into the sequential calculation framework with well-designed data exchange and control mode switching mechanisms.The proposed method demonstrates significant efficiency improvements,especially in handling scenarios involving control mode switching and multiple recalculations.In numerical tests,the superiority of the proposed method is confirmed through comparisons of accuracy and efficiency with existing methods,as well as the impact analyses of different initializations.

Modeling load distribution for rural photovoltaic grid areas using image recognition

Expanding photovoltaic(PV)resources in rural-grid areas is an essential means to augment the share of solar energy in the energy landscape,aligning with the“carbon peaking and carbon neutrality”objectives.However,rural power grids often lack digitalization;thus,the load distribution within these areas is not fully known.This hinders the calculation of the available PV capacity and deduction of node voltages.This study proposes a load-distribution modeling approach based on remote-sensing image recognition in pursuit of a scientific framework for developing distributed PV resources in rural grid areas.First,houses in remote-sensing images are accurately recognized using deep-learning techniques based on the YOLOv5 model.The distribution of the houses is then used to estimate the load distribution in the grid area.Next,equally spaced and clustered distribution models are used to adaptively determine the location of the nodes and load power in the distribution lines.Finally,by calculating the connectivity matrix of the nodes,a minimum spanning tree is extracted,the topology of the network is constructed,and the node parameters of the load-distribution model are calculated.The proposed scheme is implemented in a software package and its efficacy is demonstrated by analyzing typical remote-sensing images of rural grid areas.The results underscore the ability of the proposed approach to effectively discern the distribution-line structure and compute the node parameters,thereby offering vital support for determining PV access capability.

基于微分代数模型的AC/DC系统非线性控制器设计

针对电力系统实际负荷以及直流系统本身的非线性特性,在微分代数模型的基础上,将M导数、M括号以及MIMO微分代数系统反馈线性化技术运用到交直流并联系统非线性控制器设计中。在系统的M关系度小于系统阶数及其满足一定的条件时,可得到微分代数系统模型的Bronovsky标准形式,并对交直流混合(AC/DC)系统中发电机励磁控制和直流系统整流侧定电流控制律进行了深入研究。针对一个含有AC/DC的单机无穷大系统(SMIBs)进行实例仿真,研究结果表明所设计的非线性控制器与传统的PID控制器相比具有较好的阻尼特性,能进一步提高系统的动态稳定性。该控制器的设计方法可以很方便地应用于多机交直流并联系统的稳定性控制。

求解大规模AC/DC最优潮流的连续递推内点算法

提出连续递推的内点算法框架,以期解决原始–对偶内点法求解大规模交直流系统最优潮流收敛难的问题。基于牛顿法的连续递推思想,将一阶KKT(Karush-Kuhn-Tucker)非线性方程组转化为自治常微分方程组,可采用多种数值积分方法求解,进而获得不同于传统牛顿法的新方向,改善了原始–对偶内点法的收敛性。多达11585条线路的5个大规模实际系统的计算表明,该算法步长大、收敛性好、鲁棒性强,特别适合求解大规模交直流系统在苛刻运行条件下的最优潮流问题,具有广阔的应用前景。

AC/DC系统潮流计算的部分直流变量消除法

为克服AC/DC系统的潮流计算方法中的变量消除法的不足,提出了部分直流变量消除法.该方法的模型中将换流器等效为依赖于换流器端交流电压和控制角的PQ负荷.计算时,只需规定换流器直流侧的无功功率,而且当直流系统控制方式发生变化后不需重新推导Jacobian矩阵中的偏导公式.数值算例表明该方法具有较高的灵活性,与变量消除法相比计算效率可提高5%左右.

计及非线性负荷的AC/DC系统控制策略

详细研究了带非线性负荷的交直流并联系统发电机励磁控制和直流系统控制,将M导数、M括号以及MIMO微分代数系统反馈线性化技术应用到交直流并联多机系统非线性控制器设计中,提出了具有微分代数形式的零动态设计。通过合理选择输出量作为坐标变换量,得到微分代数系统模型的Bronovsky标准形式。针对一个含有AC/DC的多机系统进行仿真,研究结果表明,所设计的非线性控制器与传统的PID控制器相比具有较好的阻尼特性,该控制器能进一步提高系统的动态稳定性。

AC/DC电源线自动绕扎系统的设计与实现

针对原AC/DC电源线绕扎设备存在的问题,设计了一个AC/DC电源线自动绕扎系统。介绍系统的工艺流程与结构组成,给出系统的硬件电路设计和软件程序流程。该系统在实际生产环节中可代替4~5人的人工操作岗位,使AC/DC电源线的生产效率提高5~7倍。

一种实用的多端DC──AC系统潮流计算方法

介绍了一种新的ＭＴＤＣ—ＡＣ潮流计算方法，其特点是将各换流器分别经诺顿定理等效为一带换流内阻的电流源。首先给出各单元直流系统的网络方程和换流器方程，运用给定量经网络方程推出控制方程，再用牛顿法进行潮流选代计算。此方法灵活实用，并附有算例证明。

Identification of the Worst-case Static Voltage Stability Margin Interval of AC/DC Power System Considering Uncertainty of Renewables

Calculation of static voltage stability margin(SVSM)of AC/DC power systems with lots of renewable energy sources(RESs)integration requires consideration of uncertain load growth and renewable energy generation output.This paper presents a bi-level optimal power flow(BLOPF)model to identify the worst-case SVSM of an AC/DC power system with line commutation converter-based HVDC and multi-terminal voltage sourced converter-based HVDC transmission lines.Constraints of uncertain load growth’s hypercone model and control mode switching of DC converter stations are considered in the BLOPF model.Moreover,uncertain RES output fluctuations are described as intervals,and two three-level optimal power flow(TLOPF)models are established to identify interval bounds of the system worst-case SVSM.The two TLOPF models are both transformed into max–min bi-level optimization models according to independent characteristics of different uncertain variables.Then,transforming the inner level model into its dual form,max–min BLOPF models are simplified to single-level optimization models for direct solution.Calculation results on the modified IEEE-39 bus AC/DC case and an actual large-scale AC/DC case in China indicate correctness and efficiency of the proposed identification method.

Optimal power flow calculation in AC/DC hybrid power system based on adaptive simplified human learning optimization algorithm

This paper employs an efficacious analytical tool,adaptive simplified human learning optimization(ASHLO)algorithm,to solve optimal power flow(OPF)problem in AC/DC hybrid power system,considering valve-point loading effects of generators,carbon tax,and prohibited operating zones of generators,respectively.ASHLO algorithm,involves random learning operator,individual learning operator,social learning operator and adaptive strategies.To compare and analyze the computation performance of the ASHLO method,the proposed ASHLO method and other heuristic intelligent optimization methods are employed to solve OPF problem on the modified IEEE 30-bus and 118-bus AC/DC hybrid test system.Numerical results indicate that the ASHLO method has good convergent property and robustness.Meanwhile,the impacts of wind speeds and locations of HVDC transmission line integrated into the AC network on the OPF results are systematically analyzed.

多端DC—AC系统的潮流计算

对于含多端直流输电网络的交直流电力系统,本文提出了一种对交流和直流系统分别采用牛顿法进行顺序迭代潮流计算的数学模型和算法。该算法可以有效地考虑换流器的各种控制方式,同时确定换流变压器分接头的位置。算例表明,本算法的数学模型灵活具有通用性,收敛性好。

Analysis of Commutation Failure in Multi-Infeed HVDC System under Different Load Models

HVDC technology has been widely used in modern power system. On one hand, HVDC has the advantages of economy, high efficiency and strong controllability. While on the other hand, it makes the dynamic characteristics of the power system becoming more and more complex. That puts forward a new challenge to system stability and raises new questions for power system simulation. This paper focuses on the interaction between AC and DC systems, especially the problem of commutation failure caused by AC system fault. Based on the data of China Southern Power Grid, this paper calculates the fault regions that may cause commutation failure and calculates the system critical clearance time under different load models, analyzes the impacts of different load models on commutation failure and the stability of AC/DC hybrid system.

Automated Two-stage Conversion of Hourly Optimal DC Flow Solution to AC Power Flow

Conversion of hourly dispatch cases derived using DC optimal power flow(DCOPF)to AC power flow(ACPF)case is often challenging and requires arduous human analysis and intervention.This paper proposes an automated two-stage approach to solve ACPF formulated from DCOPF dispatch cases.The first stage involved the use of the conventional Newton Raphson method to solve the ACPF from flat start,then ACPF cases that are unsolvable in the first stage are subjected to a hotstarting incremental method,based on homotopy continuation,in the second stage.Critical tasks such as the addition of reactive power compensation and tuning of voltage setpoints that typically require human intervention were automated using a criteriabased selection method and optimal power flow respectively.Two datasets with hourly dispatches for the 243-bus reduced WECC system were used to test the proposed method.The algorithm was able to convert 100%of the first set of dispatch cases to solved ACPF cases.In the second dataset with suspect dispatch cases to represent an extreme conversion scenario,the algorithm created solved ACPF cases that satisfied a defined success criterion for 77.8%of the dispatch cases.The average run time for the hotstarting algorithm to create a solved ACPF case for a dispatch was less than 1 minute for the reduced WECC system.

基于多项式混沌展开的交直流系统全纯嵌入概率潮流计算方法

为快速、准确量化分析风电出力不确定性对交直流电力系统潮流分布的影响,提出一种基于多项式混沌展开(PCE)的交直流电力系统全纯嵌入概率潮流计算方法。该方法首先根据风电出力的概率分布特征选择最优正交基函数,构造近似风电出力概率分布特征的PCE表达式;其次,将该PCE表达式引入交直流电力系统的全纯嵌入潮流方程中,构建基于PCE的交直流电力系统全纯嵌入概率潮流计算模型;再次,通过Galerkin投影将所构建的全纯嵌入概率潮流计算模型转化为高维确定性全纯嵌入潮流计算模型;然后,借助确定性全纯嵌入潮流模型求解方法,实现对所转化的高维确定性全纯嵌入潮流模型的求解,并根据所得PCE逼近系数计算交直流电力系统潮流的概率分布特征;最后,通过修改的PJM 5节点、IEEE 30节点和IEEE 118节点交直流测试系统算例验证所提方法的准确性和有效性。

双绕组感应发电机交直流集成发电系统的自抗扰控制策略

针对双绕组感应发电机交直流集成发电系统,为实现简单易调、性能优越、负载适应力强的发电控制,该文提出一种基于线性自抗扰控制器的交直流电压控制策略,通过交流电压和直流电压与控制绕组和功率绕组的传递函数模型,构建交直流电压的线性扩张状态观测器,同时对交流电压有效值、直流电压和电压扰动进行观测,并利用电压和扰动观测值设计线性误差反馈控制律,对交直流电压进行控制。最后,通过仿真和实验验证该控制策略提高电压扰动抑制能力和负载适应性,同时各模块参数可独立设计、控制器结构简单,避免需要较多传感器及降低调参难度。

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。

分布式电源对配电网潮流计算的影响研究

配电中接入的分布式电源的增多,潮流计算时,传统的前推回代法无法满足精度要求。对系统研究发现,分布式电源的出力和接入位置对配电网的网损有不同的影响,阐述了分布式电源潮流计算模型,并引入了一种带有PV节点无功修正的分布式电源配电网潮流计算方法。通过对IEEE14节点系统进行仿真验证,证明了所提算法的有效性和收敛性。研究结果显示:新提出的方案和技术能够更加高效地解决带有分布式电源的配电网潮流问题。

含多类型直流的交直流混联电网潮流计算方法适用性分析

作为电网发展的新阶段,交直流混联电网呈现多类型直流参与、大规模交直流互联的特点,而关于统一迭代和交替迭代2种潮流计算方法的适用性尚未得到深入分析。为此基于含多类型直流的交直流混联电网对2种潮流计算方法的运算性能进行对比研究。推导了含常规直流、柔性直流、混合直流的交直流混联电网潮流模型,进而提出了相应的统一迭代法和交替迭代法。通过3个交直流混联电网测试系统和南方电网实际系统数据验证了潮流模型的有效性和潮流算法的准确性,结合系统负荷水平、系统强度、直流嵌入规模等因素对2种潮流计算方法的收敛性能和计算速度进行对比分析。研究结果表明,在含多类型直流的交直流混联电网中进行潮流计算时,统一迭代法的计算效率比交替迭代法高。

面向交直流混联系统的潮流计算数据生成策略

随着电力系统中多类型直流线路占比的逐步提升,调度系统与异构平台间的潮流数据交换需求明显增大,亟需研究新形态下交直流混联系统的潮流计算数据生成问题。该文从拓扑转换、网络拓扑分析、设备建模以及数据生成策略4个主要步骤,实现含交直流系统的基于可扩展标记语言的通用信息模型(common information model/extensible markup language,CIM/XML)数据到潮流计算输入数据的转换。首先,该文从设备间开关拓扑的角度,进行深度优先算法(depth first search,DFS)搜索和设备拓扑拼接,实现开关/节点模型到母线/支路模型的转换;其次,在筛选出活拓扑岛、剔除不带电设备后,着重分析了CIM/XML中换流器建模对交直流节点选取的影响,进而提出了直流节点选取规则和具备普适性的直流数据生成策略。最后,以某地调度500kV及以上交直流网络导出的CIM/XML数据为算例,潮流计算结果与数据采集与监视控制系统(supervisory control and data acquisition,SCADA)量测数据比对验证所提策略的有效性。

基于连续潮流法的含双端VSC-HVDC交直流系统负荷裕度分析

为了分析含双端VSC-HVDC交直流系统的静态电压稳态特性,结合交替求解法和连续潮流法给出一种交直流连续潮流法。根据初始输入得到初始解确定负荷增长方向,引入负荷裕度参数。通过调节VSC-HVDC的控制策略,最终得到系统不同情况下的负荷裕度,采用左特征向量乘子法对系统进行负荷裕度灵敏度计算。对含双端VSC-HVDC的IEEE39节点系统和IEEE118节点系统进行建模仿真,得出了系统负荷裕度以及负荷裕度灵敏度近似线性的变化规律。直流线路功率流向对系统负荷裕度的影响相反,验证了方法的有效性。