Mathematical Modeling of Multiple Capacitor Coupled Substations (CCS) Impact on Transmission Lines and Approaches for Ferroresonance Suppression

Rural electrification remains a critical challenge in achieving equitable access to electricity, a cornerstone for poverty alleviation, economic growth, and improved living standards. Capacitor Coupled Substations (CCS) offer a promising solution for delivering cost-effective electricity to these underserved areas. However, the integration of multiple CCS units along a transmission network introduces complex interactions that can significantly impact voltage, current, and power flow. This study presents a detailed mathematical model to analyze the effects of varying distances and configurations of multiple CCS units on a transmission network, with a focus on voltage stability, power quality, and reactive power fluctuations. Furthermore, the research addresses the phenomenon of ferroresonance, a critical issue in networks with multiple CCS units, by developing and validating suppression strategies to ensure stable operation. Through simulation and practical testing, the study provides insights into optimizing CCS deployment, ultimately contributing to more reliable and efficient rural electrification solutions.

Mitigation of Transients in Capacitor Coupled Substations Using Traditional RLC Filter Techniques

This article presents an extensive examination and modeling of Capacitor Coupled Substations (CCS), noting some of their inherent constraints. The underlying implementation of a CCS is to supply electricity directly from high-voltage (HV) transmission lines to low-voltage (LV) consumers through coupling capacitors and is said to be cost-effective as compared to conventional distribution networks. However, the functionality of such substations is susceptible to various transient phenomena, including ferroresonance and overvoltage occurrences. To address these challenges, the study uses simulations to evaluate the effectiveness of conventional resistor-inductor-capacitor (RLC) filter in mitigating hazardous overvoltage resulting from transients. The proposed methodology entails using standard RLC filter to suppress transients and its associated overvoltage risks. Through a series of MATLAB/Simulink simulations, the research emphasizes the practical effectiveness of this technique. The study examines the impact of transients under varied operational scenarios, including no-load switching conditions, temporary short-circuits, and load on/off events. The primary aim of the article is to assess the viability of using an established technology to manage system instabilities upon the energization of a CCS under no-load circumstances or in case of a short-circuit fault occurring on the primary side of the CCS distribution transformer. The findings underscore the effectiveness of conventional RLC filters in suppressing transients induced by the CCS no-load switching.

Multi-objective planning model for simultaneous reconfiguration of power distribution network and allocation of renewable energy resources and capacitors with considering uncertainties

This research develops a comprehensive method to solve a combinatorial problem consisting of distribution system reconfiguration, capacitor allocation, and renewable energy resources sizing and siting simultaneously and to improve power system's accountability and system performance parameters. Due to finding solution which is closer to realistic characteristics, load forecasting, market price errors and the uncertainties related to the variable output power of wind based DG units are put in consideration. This work employs NSGA-II accompanied by the fuzzy set theory to solve the aforementioned multi-objective problem. The proposed scheme finally leads to a solution with a minimum voltage deviation, a maximum voltage stability, lower amount of pollutant and lower cost. The cost includes the installation costs of new equipment, reconfiguration costs, power loss cost, reliability cost, cost of energy purchased from power market, upgrade costs of lines and operation and maintenance costs of DGs. Therefore, the proposed methodology improves power quality, reliability and security in lower costs besides its preserve, with the operational indices of power distribution networks in acceptable level. To validate the proposed methodology's usefulness, it was applied on the IEEE 33-bus distribution system then the outcomes were compared with initial configuration.

Modeling of a Lithium-Ion Capacitor and Its Charging and Discharging Circuit in a Model-Based Design

For several years now, electric vehicles (EVs) have been expected to become widely available in the micro-mobility field. However, the insufficiency of such vehicles’ battery-charging and discharging performance has limited their practical use. A hybrid energy storage system, which comprises a capacitor and battery, is a promising solution to this problem;however, to apply model-based designs, which are indispensable to embedded systems, such as the electronic control units used in EVs, a simple and accurate capacitor model is required. Within this framework, a lithium-ion capacitor (LIC) model is proposed, and its charging and discharging performances are evaluated against an actual LIC. The model corresponds accurately to the actual LIC, and the results indicate that the proposed LIC model will work well when used with Model-Based Design (MBD).

Improvements to Temperature, Warburg Impedance, and Voltage Computations for a Design-Based Predictive Model for Lithium-Ion Capacitors

An earlier study manipulated the Butler-Volmer equation to effectively model a lithium-ion capacitor’s (LIC) energy storage as a function of its constituent components and charge current. However, this model had several shortcomings: computed temperature values were too low, voltage was inaccurate, and the model required Warburg impedance values that were two orders of magnitude higher than experimental results. This study began by analyzing the model’s temperature and voltage computations in order to justify output values. Ultimately, these justifications failed. Therefore, in situ temperature rise was measured during charge cycles. Experimental results indicated that temperature increases minimally during a charge cycle (<1%). At high current densities (≥150 A·kg-1) temperature increase is negligible. After it was found that LIC temperature change is minimal during a charge cycle, the model accurately computed LIC voltage during the charge cycle and computed Warburg impedance that agreed with values derived from earlier experimental studies, even falling within the measurements’ precision error.

含废旧矿井抽蓄电站的源-荷-储协同控制调频研究

针对新能源在电网中渗透率不断提高导致系统调频容量和频率响应能力不足的问题,提出一种含废旧矿井抽蓄电站的源-荷-储协同控制调频方法。首先,建立了电解铝工业负荷、废旧矿井抽蓄电站和超级电容频率响应模型。然后,基于模型预测控制理论,以系统状态量和控制量的加权函数最小为目标,设计区域信息互动的分布式模型预测控制器,并提出含废旧矿井抽蓄电站的源-荷-储协同控制调频方法。最后,将分布式模型预测控制器应用在所提源-荷-储协同控制方法中,并在改进的IEEE标准两区域LFC模型中进行仿真。结果表明所提方法可以缩短频率恢复时间,减小最大频差值,改善系统调频动态性能。

电容电压平衡的四电平有源中性点钳位逆变器的改进模型预测电流控制

多电平有源中点钳位(ANPC)逆变器具有功率器件电压应力小、电流谐波低和器件损耗可调控等优点,被广泛应用于工业驱动中。针对四电平ANPC(4L-ANPC)逆变器的控制与调制研究相对较少,现有的调制方案实现复杂,中点电压(NPV)控制难度较大。因此,该文针对三相4L-ANPC逆变器,提出一种改进的有限集模型预测电流控制(FS-MPCC)算法,避免了复杂的调制过程。首先,使用仅包含电流误差的代价函数对位于六边形顶点的6个大电压矢量进行寻优;其次,对参与第一步寻优的大矢量划分扇区,使用包含电流误差和电容电压误差的代价函数对最优大矢量所在扇区的所有电压矢量滚动寻优,得到目标电压矢量并作用于逆变器;最后,仿真和实验结果表明,与传统的FS-MPCC相比,所提方法在降低系统计算负担的同时,还具有较好的控制性能和电容电压平衡能力。

考虑电容电压平衡的混合型MMC调制波分配策略

针对过调制运行下混合型模块化多电平换流器半桥与全桥子模块之间的电容电压不均衡问题,提出一种桥臂调制波内部动态分配控制方法。首先分析混合型模块化多电平换流器子模块电容电压差异的产生机理;然后提出一种桥臂调制波分配方法,以两种子模块电容周期能量积累差异为控制对象,通过调制波初步分配和限幅环节动态修正调制波在半桥与全桥子模块之间的分配比例,最终生成相应的调制信号;最后,通过仿真与硬件在环实验验证所提策略的有效性。

考虑结电容和跨导非线性的辐射频段EMI分析模型

宽禁带WBG(wide band gap)半导体电力电子器件由于其开关频率高、开关速度快、寄生参数大等特点从噪声源头引发了越来越严峻的电磁干扰问题。然而,传统的噪声源研究主要集中在30 MHz传导频段以内,如何评估噪声源在30~300 MHz较高频率范围内的辐射频段产生的影响仍存在不确定性,因此提出1种改进的WBG器件电磁干扰分析模型,与传统的非对称梯形波电磁干扰模型相比,首次详细考虑了WBG器件的结电容和跨导体的非线性特性,评估了非线性参数对辐射频段噪声的影响,并进一步提出该模型在辐射频段噪声源抑制中的应用。仿真结果验证了所提计算方法的准确性,基于SiC器件的硬件测试结果与理论分析相吻合。

基于共轭梯度法的金属化薄膜电容器热点温度反演

热点温度是影响金属化薄膜电容器(metallized film capacitors,MFC)绝缘寿命的重要因素之一,但由于其无法直接测量,因此通常采用热仿真分析或温度反演的方法获得。该文提出了基于共轭梯度法(conjugategradient method,CG)的热点温度反演模型,建立了内部传热过程的温度分布目标函数,采用有限差分法求解电容器温度场,再通过CG对内部温度分布进行迭代求解。同时,通过交流温升试验校核了仿真模型以及反演模型。研究结果表明:热点温升与表面温升存在线性关系,热点温度出现在MFC中央靠近芯轴处,反演模型与仿真模型最大误差为4.35%,说明该模型可实现现场工况下的温度分布、热点分布等的有效预测。

一种低耦合电容的高压SiC MOSFET驱动隔离电源设计

高压SiC MOSFET更快的电压变化率dv/dt,导致其驱动遭受更严重的共模干扰,而现有高隔离电压驱动电源大多又存在耦合电容高、共模瞬态抗扰度(CMTI)能力弱、转换效率低等问题,因此该文设计一种兼具高隔离电压、高转换效率的低耦合电容驱动隔离电源。首先,基于有源钳位反激变换器,提出一种驱动隔离电源耦合电容等效简化解析模型,并通过仿真、实验验证解析模型可行性;其次,基于该模型分析耦合电容影响因素及其优化方法,为低耦合电容的驱动电源设计提供参考;最后,通过实验评估所提低耦合电容高压SiC MOSFET驱动隔离电源性能。结果表明,该文驱动隔离电源额定转换效率约80%,工频耐压高达18 kV,且耦合电容不足2 pF,CMTI能力强。

基于MPC的耦合电感飞跨电容双向DC/DC变换器功率均衡解耦控制策略

耦合电感功率变换器因耦合电感阻抗、电感值等参数差异易导致功率不均衡。针对耦合电感飞跨电容双向DC/DC变换器,提出一种基于模型预测控制(MPC)的功率均衡解耦控制策略。通过对变换器原理进行分析,建立基于电感电流解耦的数学模型,得到包括电感电流和飞跨电容电压等6个控制变量的解耦控制方法。在此基础上,提出基于MPC的功率均衡解耦控制策略。同时,为降低MPC算法的运算负荷,根据解耦控制模型重构模型预测价值函数,实现各控制变量独立动态寻优,使系统能在稳定控制输出电压及飞跨电容电压的同时,实现两相耦合电感的功率均衡控制。最后,通过理论分析及实验对所提策略进行有效验证。

动车组充电机直流支撑电容寿命评估方法研究

充电机是动车组直流供电系统的核心环节,而直流支撑电容是充电机中的关键元件,如何准确评估直流支撑电容的寿命状态对充电机的故障预测及修程修制的合理安排具有十分重要的意义。针对此问题,对动车组充电机直流支撑电容失效机理进行分析,研究不同失效模式对电容退化程度的影响及对应的失效判据;在此基础上,提出一种基于阿伦尼斯模型的电容双应力加速寿命模型;为验证所提模型的正确性,开展基于不同纹波电流和温度的加速寿命实验,通过加速寿命实验确定电容实际失效时间,其与电容双应力寿命模型计算所得的电容理论失效时间相比,误差小于8.7%,验证了所提电容双应力加速寿命模型的正确性。在此基础上,进一步提出动车组充电机直流支撑电容寿命评估方法,实现动车组充电机直流支撑电容在实际运营工况下寿命的准确评估。

应用于FeRAM设计的铁电电容宏模型

本文结合实际铁电存储器的基本电路单元和读写原理,基于Preisach理论和铁电电畴矫顽电压概率密度函数一维分布近似提出了用于电路仿真的铁电电容宏模型。模型采用与spice兼容的Verilog-A语言实现,能够准确描述铁电电容的非饱和滞回特性,以及电压任意变化时的铁电电容变化。模型仿真结果与实验数据符合良好,可为铁电存储器(FeRAM)设计提供可靠的参考。

开关电源滤波电容失效的故障诊断模型构建

高压滤波电容失效作为开关电源常见的故障之一,直接影响其稳定运行。为实现在不损坏开关电源结构的前提下,完成故障的高效诊断,本次提出一种基于改进深度置信网络的故障诊断模型(DBN-DF模型)。该模型可利用数据采集装置,对开关电源所在的电网电压进行隔离、滤波等处理,并根据电网电压畸变特性,判断开关电源滤波电容失效百分比,最终输出故障类别,完成故障诊断。经试验验证,DBN-DF模型相较于传统的DBN和BP模型,对于高压滤波电容故障诊断的准确性更高,且随着故障次数的增加,模型真确率准确率也相应提升,最终趋于稳定。说明该模型具有较高的实践应用价值。

六边形变换器在全功率抽水蓄能系统中的应用研究

在抽水蓄能系统中,可调速机组可以适应更宽的水头范围,提高机组运行效率。六边形变换器(Hexverter)作为一种高压大容量变换器,可以解决目前变速抽水蓄能系统中变流装置容量小、能量转换效率低以及调速慢等问题。本文提出了基于六边形变换器的全功率抽水蓄能控制系统,对六边形变换器的一般数学模型进行了分析,提出的基于网侧和机侧两种频率的多重解耦控制策略可以实现网侧和机侧功率的控制以及机侧输出电压电流频率灵活可调,基于零序网络的桥臂直流电压平衡控制策略可以实现桥臂直流均压。最后通过仿真和实验验证了六边形变换器在全功率抽蓄系统的应用的有效性。

直流支撑电容器圆元件的散热模型与仿真研究

随着自愈干式金属化薄膜电容器应用范围的不断扩展,其散热方式与内部温升问题成为了重要的理论与工程问题。鉴于此,本文基于直流支撑电容器圆元件的发热规律,分析了电容器元件圆柱状整体均匀发热时发热体的热流分布。进一步,结合电热对偶原理,建立了圆元件热计算模型,并通过微分单元积分,得到了圆元件的热阻计算公式。最后,通过试验验证了圆元件的热计算模型的正确性,且提出了圆元件热计算的验证方法,为直流支撑电容器圆元件的发热提供理论与试验参考。

开关电容DC-DC转换器:从变压器模型到电路的演进

开关电容(Switched Capacitor,SC)DC-DC转换器在很多领域有着广泛的应用。为应对大电压转换比(Voltage Conversion Ratio,VCR)的情况,前人提出了诸多拓扑结构。常用的拓扑结构包括Dickson,Cockcroft-Walton,Series-Parallel,Ladder,Fibonacci,Divider等等。这些拓扑结构有着各自的性能特点,适用于不同的场景。然而,对于这些不同的拓扑结构是如何产生的,本质的区别是什么,各自的优缺点是什么,并无直观的解释和分析。因此,该文从开关电容DC-DC转换器的等效变压器模型入手,分析了各个拓扑之间的本质区别,并展示了从等效模型到实际电路的演进过程,解释了规则和原因。

基于分数阶模型的Dickson型开关电容变换器时域特性分析

基于分数阶模型,对Dickson型开关电容变换器(SCCs)的时域特性进行了分析。通过建立分数阶微分方程模型,研究了分数阶效应对电路性能的影响。融合Dickson型开关电容拓扑结构,分别对基于分数阶模型的Dickson型升压SCCs和降压SCCs进行了建模与分析,证明了分数阶模型的准确性和可靠性。该研究进一步验证了分数阶预估校正法(F-ABM)在电路分析中的有效性,并强调了在设计和优化SCCs电路时考虑分数阶效应的重要性。

基于平均值模型的感应子脉冲发电机电容器重频充电系统分析

基于平均值模型对感应子脉冲发电机电容器重频充电系统进行了研究。分析了次暂态磁链在充电过程中的变化规律,以及次暂态磁链的变化对充电性能的影响。仿真和计算结果表明,次暂态磁链在充电过程中逐渐变小。当充电时间与发电机的电磁时间常数相当时,充电过程中次暂态磁链下降会导致充电电压明显降低,因此必须考虑次暂态磁链变化的影响。进一步研究了具有恒流控制功能的励磁电源对充电过程中调节作用的影响,并指出为了降低发电机对绝缘性能的要求,在重频充放电脉冲模式下励磁电流应该采用逐渐上升的方式。