Influence of source impedance on the performance of a fixed filter-thyristor controlled reactor (FF-TCR) type compensator

The influence of source impedance on the performance of a fixed filter-thyristor controlled reactor (FF-TCR) type compensator to improve the power factor of a thyristor controlled inductive load has been described. It is shown that the compensator gives better power factor improvement at higher source impedance, i.e. with a weak supply system. However, even with a small source impedance (i.e. a good supply system), a reasonable improvement in power factor is realized. The FF-TCR compensator keeps the distortion of the terminal voltage waveform within reasonable limits. The results obtained from the analysis of the lossy FF-TCR compare very well with the results obtained experimentally. This type of compensator is recommended strongly for industrial use.     

Force-Commutated Reactive-Power Compensator

A reactive-power compensator (RPC) is a type of static var compensator (SVC) that is used to dynamically correct power factor to prevent voltage variation (flicker) in ac power sources due to large dynamic loads. It also minimizes total source current. Thus the application of an RPC or SVC to a load may allow addition of substantial new load to existing feeders or substations. A reactive-power compensator suited to industrial ratings (1.0-25 MVA) is described. It utilizes a force-commutated current-source bridge to provide both leading and lagging reactive power. The ability to operate both leading and lagging can reduce by 2:1 the ratings of the RPC itself and the capacitors and magnetics associated with it. The characteristics of the power circuit, the means used to control it, and the resulting dynamic performance is described. Speed of response compares favorably to the thyristor-controlled reactors now in common use as SVC's at higher MVA ratings. This RPC is suited to compensate any balanced three-phase dynamic load.     

铜电解整流装置用并联混合型有源电力滤波器

为解决铜电解装置运行时产生的电网谐波污染和低功率因数问题,提出了在10kV侧安装并联混合型有源电力滤波器进行谐波抑制和无功补偿的综合补偿方案并介绍了混合滤波器的系统构成,混合型有源滤波器的无源部分由滤除11、13次谐波,同时补偿无功功率的11、13次两个无源支路构成。有源部分采用注入式拓扑结构,用来动态滤除11、13次以外的其它次谐波。有源部分对改善无源部分的滤波性能和抑制无源部分与系统等效阻抗之间的谐振发挥了重要作用。给出的现场运行结果表明:研制的并联混合型有源电力滤波器能有效的抑制谐波和进行无功补偿。     

A new approach to an individual‐phase reactive power compensator for nonsinusoidal and unbalanced three‐phase systems

Many researchers have attempted to clarify the definitions of active power, reactive power, active current, reactive current, etc. for unbalanced and nonsinusoidal three‐phase situations. The so‐called pq theory has given a new definition of instantaneous reactive power, and it has been discussed and developed by many authors. In this paper, the merits and demerits of the instantaneous reactive power compensator are discussed. It is shown theoretically that applying instantaneous reactive power compensation to unbalanced three‐phase systems has a serious disadvantage in that it causes third‐order harmonic currents on the source side, which problem cannot be avoided. To overcome this problem the authors propose a new approach, and name it the “quasi‐instantaneous” reactive power compensator. It compensates individual‐phase reactive currents. The basic principles of the quasi‐instantaneous reactive current compensator are discussed in detail, and its validity is confirmed using digital simulation. In particular the authors show that the power factor of each phase becomes unity on the source side, but the source currents remain unbalanced when the proposed method is applied. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 73–81, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1162     

基于磁能恢复开关的单相串联补偿器的研究

作为一种新的无功补偿装置,不论负载阻抗如何变动,磁能恢复开关都能自动地校正功率因数,并且还具有结构简单、容易控制和损耗低等许多优点。基于磁能恢复开关的单相串联补偿器中,磁能恢复开关能够吸收并恢复负载电感中的磁场能量,实现无功功率的补偿。仿真分析获得了很高的功率因数,直流输出电压具有较小的纹波,并在实验中得到了验证。     

配电网自动无功补偿装置研制

为使配电网的无功补偿更加方便灵活,对高短路阻抗变压器型的新型可控电抗器与固定电容器组合作为配电网的自动无功补偿装置进行了研究。通过调节高短路阻抗变压器二次侧的晶闸管触发角,可以实现配电网中无功功率的动态自动无级补偿。根据变电站参数,合理选取电容器组和可控电抗器的容量,能实现变电站低压侧母线无功功率的自动跟踪和无级补偿。通过备用电容器投切的滞环控制律的设计,以减少电容器组的投切次数。对某一实际系统进行仿真测试的结果表明该装置能够实现无功的动态无级补偿,并具有良好的动态响应性能,对提高配电网的功率因数和抑制配电网的电压波动有明显效果。     

Design and Implementation of Adaptive Neuro–Fuzzy Inference System Based Control Algorithm for Distribution Static Compensator

This article focuses on the design and implementation of a distribution static compensator using an adaptive neuro–fuzzy inference system based controller. The distribution static compensator is controlled to provide power quality improvement, such as power factor correction, harmonics compensation, load balancing, and voltage regulation. Active and reactive power fundamental components of load currents are extracted using d-q theory. A distribution static compensator is realized using a voltage source converter. Both simulation and experimental results prove the effectiveness of the control algorithm under non-linear loads. The adaptive neuro–fuzzy inference system based controller works satisfactorily for power factor correction and harmonics reduction under balanced as well as unbalanced load conditions. Test results clearly depict the dynamics of the performance of the system under steady state as well as dynamics under load change and load unbalancing.     

Combined compensation structure of a static Var compensator and an active filter for unbalanced three-phase distribution feeders with harmonic distortion

A combined reactive power compensation method of a static Var compensator (SVC) and an active filter is described in this paper for unbalanced three-phase distribution feeders with harmonic distortion. The SVC acts as a classic reactive power compensator for load balancing and power factor correction. The small rating active filter is used to improve filtering characteristics of the passive filter in SVC and suppress possible resonance between the system impedance and the passive filter. The control signals are derived from the calculation of instantaneous active and reactive powers of the distribution feeder. Simulation results carried out by the electromagnetic transients program (EMTP) show that the proposed reactive power compensation configurations can effectively balance currents, correct power factor, and eliminate harmonic currents.     

静止无功补偿器与有源电力滤波器联合运行系统

提出一种具有功率因数校正、补偿负载不平衡和滤除电网谐波电流的静止无功补偿器(static var compensator,SVC)和有源电力滤波器(active power filter,APF)联合运行系统电路结构。其中,SVC由晶闸管控制电抗器(thyristor controlled reactor,TCR)及固定电容器(fastness capacitor,FC)组成,主要用来快速补偿无功,并通过对其三相不对称控制来消除电网三相不对称和负序电流;APF部分主要用来消除电网及SVC引起的谐波电流,同时抑制固定电容器与电网等效阻抗间可能的串并联谐振。在分析SVC和APF联合运行系统基本工作原理的基础上,对联合运行时的控制方法进行研究。仿真和实验结果证明了该联合运行系统的可行性。     

谐振阻抗型混合有源滤波器的原理及其补偿特性

针对变电站在谐波治理的同时需要具备一定的无功静补能力的特点和要求,在分析传统谐波治理方法特点和不足的基础上,提出一种新型拓扑结构--谐振阻抗型混合有源滤波器(resonant impedance type hybrid active power filter,RITHAF)。在对RITHAF基本工作原理进行分析的基础上,深入研究其控制为电压源和电流源的不同策略,指出将RITHAF控制为电流源时具有更加优良的性能。为对RITHAF性能进行分析,定义谐波源谐波抑制函数和电网谐波抑制函数,并以此为指标研究电网阻抗变化、无源滤波器失谐对RITHAF补偿特性的影响。仿真及实验结果表明,RITHAF具有良好的谐波治理和无功补偿能力,适用于中高压系统的应用。     

一种改进的混合静止同步补偿器

作者设计了一种改进混合静止同步补偿器,该补偿器由一个三相电压源型逆变器和补偿电容组成,通过控制三相逆变器输出电压相对于系统电压的相位差间接控制补偿器的输出无功功率。该补偿器能进行补偿功率双向连续调节,控制简单,动态响应速度快,输出电流不含低次谐波,特别是在补偿感性无功功率时,该补偿器直流侧电容电压低,可减小开关器件的应力,降低补偿器损耗,提高装置的运行效率。在理想情况下,上述逆变器容量仅为最大补偿容性无功功率的1/4。文中分析了补偿器的工作原理,推导了补偿器和逆变器的功率公式,并分析了二者的关系。最后通过实验验证了该补偿器的可行性和有效性。     

Use of the homotopy method for excitation control of generators for multimachine power system

It is important to consider the stabilization problem for a large-scale power system. This paper uses a dynamic compensator based on observer theory such that desired poles are placed for a closed-loop multimachine power system. Since the system dimension is large, it is difficult to apply a conventional dynamic compensator method to an excitation control problem for a multimachine power system. The homotopy method is introduced to solve fundamental nonlinear equations which are required for observer synthesis. To show the effectiveness of the proposed method an excitation control of generators for a multimachine power system is considered. From the simulation result, it is shown that the present method is useful in stabilizing a multimachine power system.     

基于谐波小波的并联无源滤波器组阻抗特性测试

电力系统中存在大量的无功补偿／并联滤波器组,通常由电容、电感及电阻组合而成,接在从6kV到500kV的电网中,既起无功补偿的作用又能滤除特定的高次谐波。每套滤波器组都有其特定的频率阻抗特性,通过频率阻抗特性的检测可以确定滤波器组的滤波特性是否有变化。通过测录滤波器在外部暂态过程中电流和电压的波形,借助谐波小波的滤波特性,通过适当的变换来得到被测滤波器组的频率阻抗,这样将大大简化频率阻抗特性的测试。通过对计算机仿真和现场实测波形的处理,验证了这种阻抗频率特性测试方法的可行性。     

Distributed-series compensator for controlling voltage in distribution line with clustered distributed generations

A method of controlling voltage profile in distribution line with many distributed generations (DGs) using distributed-series compensator (D-SC) is proposed. These DGs are assumed to be clustered photovoltaics (PVs) which are installed at residential area. A large power injected by PVs may result in reverse power flow from PVs to main source, which can lead to overvoltage in the distribution line. To mitigate this problem, it is proposed to install D-SCs close to pole transformer of the distribution line. A D-SC is a series compensator that can imitate characteristic of negative resistance and reactance, while reverse power flow occurs in distribution line. This is carried out by injecting active and reactive power to the distribution line through voltage injection. Providing active power for the D-SC is done by a bidirectional rectifier which is connected to the secondary side of a pole transformer. The effectiveness of the proposed method is achieved by the improvement of voltage profile with small capacity of D-SC and bidirectional rectifier. Theoretical analysis is discussed and simulation results are shown to verify the proposed method. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

单相PWM整流器输入电流波形的改善技术

PWM整流器是一种新型的功率因数校正方式,具有高功率因数、输入电流波形正弦、能量可双向流动、动态响应性能较快等优点。为提高其工作性能,阐述了单相PWM整流器的工作原理、控制方法,分析了输入电流波形中低次谐波(主要是3次)产生的原因,推导了其计算公式,并提出了采用低通滤波器和采用补偿器来改善电流波形的方法。仿真和实验的验证结果表明:加入低通滤波器可有效地改善输入电流波形,但却恶化了系统的动态性能;加入直流电压动态补偿器,可更好地改善输入电流波形,系统的动态性能不但不会恶化,反而稍微有所改善。     

一种大功率低开关应力三相Buck功率因数校正电路

针对三相单开关Buck功率因数校正器的开关电压应力过大的问题,文章提出一种通过外加辅助元件使开关器件等效阻抗不相等的电压钳位型三相两开关Buck功率因数校正器。相较于传统的三相单开关Buck功率因数校正器,所提方案在保持控制方法简单的同时,有效地降低开关管电压应力,以及电源制造成本,同时电路的输入特性具有电流源的特性,具有较强的短路故障抑制能力通过对电路结构在稳定工作时各个时段工作过程的分析,建立数学模型,给出利用开关等效阻抗不相等实现电压钳位的设计方法,分析该电路高功率因数低开关电压应力的原理。最后,制作一台5kW的实验验证样机,稳定运行时功率因数为1,谐波含量不足5%,证明该电路的优越性和可行性。     

A cyclodissipativity characterization of power factor compensation of nonlinear loads under nonsinusoidal conditions

Recently, it has been established that power factor (PF) improvement for nonlinear loads with nonsinusoidal source voltage is equivalent to imposing the property of cyclodissipativity to the source terminals. Using this framework, the classical capacitor and inductor compensators were interpreted in terms of energy equalization. The purpose of this brief note is to extend this approach in three directions. In the result reported in the literature, the supply rate is a function of the load, which is usually unknown, stymieing the applicability of the technique for compensator synthesis. Our first contribution is a new cyclodissipativity condition, which is also equivalent to PF improvement, but whose supply rate is now function of the compensator. Second, we consider general lossless linear compensators, instead of only capacitive or inductive compensators. As a result, we show that the PF is improved if and only if a certain equalization condition between the weighted powers of inductors and capacitors of the load is ensured. Finally, we exhibit the gap between the ideal compensator, namely the one that achieves unitary PF, and the aforementioned equalization condition. This result naturally leads to the formulation of a problem of optimization of the parameters of the compensator. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of Source Impedance on the Steady-State Performance of Thyristor Controlled Circuits

General mathematical relations are developed for the power factor and harmonic contents of the currents and metering voltages of thyristor controlled inductive loads fed from a source having significant impedance. This impedance has previously been neglected; it could be that of the supply feeder or transformer. The general relations developed cover the special cases described in the literature. Numerical solutions and the results obtained by an analogue computer study agree with those of actual tests. The voltage regulation caused when feeding a thyristor controlled load is slightly less than when feeding an uncontrolled load of the same power and equal power factor. The voltage regulation decreases with decrease of power factor for the same thyristor controlled load.     

分布式电源系统中变换器的输出阻抗与稳定性分析

稳定性问题是分布式电源系统的关键问题,它由源变换器的输出阻抗和负载变换器的输入阻抗共同决定.采用理论分析和实验相结合的方法,对连续导电模式(continuous conduction mode,CCM)下Buck型DC-DC变换器输出阻抗的小信号模型、影响因素及优化设计方法进行研究,为制定分布式电源系统中变换器的阻抗标准提供了参考依据.给出一种实用的电流扰动测试法,可以测量变换器的输入、输出阻抗以及级联变换器的阻抗比.采用此方法对搭建的一个级联式DC-DC变换器系统的阻抗比进行测量,并根据阻抗比禁止区对系统的稳定性进行判断.     

基于同步对称分量法的静止无功补偿装置

该文提出了基于同步对称分量法的无功补偿导纳计算方法。该方法以电网三相正序电压为同步参考坐标，再利用旋转对称分量法可以方便地得到电网需要补偿的导纳值。文中提出的三相电压提取方法能有效地消除电网电压的畸变干扰，以电压为同步坐标的旋转对称分量法可消除电流中谐波的影响，从而可准确地计算出电网需要补偿的导纳值。基于该方法设计的静止无功补偿装置无需硬件锁相环，能够快速、准确地补偿对称／不对称负荷的无功功率，维持电压的稳定。采用PSCAD软件的仿真和实验结果证明，基于同步对称分量法的补偿导纳计算方法具有较好的效果。