非正弦非平衡电力系统视在功率研究

电力系统中非线性元件的急剧增加,造成电流电压波形的畸变和不对称日益严重.尽管非正弦波形下有功功率的定义已确定无疑,但视在功率的定义存在争议,导致功率因数的差异.对工业界广泛使用的算术视在功率和矢量视在功率与IEEE1459-2000试行标准中有效视在功率的定义进行了对比分析,通过线损和视在功率的关系证明了传统定义的局限性和有效视在功率定义的科学性;以三相不对称的牵引电力网为例,根据德昌牵引变电所实测数据进行了仿真试验,通过计算结果的分析,证实了有效视在功率在实际应用中的现实意义.     

非正弦波及不对称下三相功率因数的定义

尽管三相不对称下功率因数定义已有多种公式,但在非正弦波形又不对称下的功率因数定义依然存有争议。本文从单相非正弦波形下无功功率的时域分析定义出发,导出三相不对称时视在功率的公式,从而获得非正弦波形又不对称下三相功率因数的计算公式。     

非正弦三相非平衡系统视在功率定义的研究

针对非正弦三相不平衡系统下视在功率的定义尚未达成统一的问题，利用MALTAB分别对算术、矢量和有效视在功率3种计量方法建立仿真模型，并分析比较3种不同视在功率平方与线路损耗的线性度关系，得到能正确反映线路损耗的视在功率计量方法。通过实例分析表明在非正弦三相非平衡系统下，现有的算术和矢量视在功率计量方法存在很大的问题，而IEEE STD.1459-2010试行标准中推荐使用的有效视在功率能够准确反映线路损耗大小，可以为电能计量的正确考核提供依据。     

一种计算三相不对称系统视在功率的新方法--BG法

视在功率是一个重要的电气物理量，在三相不对称系统中有两种不同的视在功率定义，即算术视在功率和相量视在功率，多年来这两个视在功率的争议不断，不同的功率定义导致了不同的计算结果及测量手段上的混乱，本对现行的视在功率的定义进行了讨论，介绍了计算三相不对称负载和非正弦交流电路视在功率的一种新算法——BG法。     

基于等效的视在功率计算新方法

在电力系统电压、电流波形畸变和不对称的条件下,目前视在功率求解还没有一种认可的方法,导致功率因数计算数值不一致。针对该问题,首先详细分析影响电能传输的因素,然后采用拉格朗日乘数法推导分析一种单等效视在功率计算方法,最后在考虑影响电能传输的不同因素条件下将所提方法分别与矢量视在功率、算数视在功率、双等效视在功率进行对比分析,以研究不同视在功率实际应用特性。算例结果表明,所提方法能够体现不同不利因素对电能传输的影响,且影响程度越大,功率因数越小。     

基于双重等效的现代视在功率定义方法

不对称、非正弦条件下三相电力系统的视在功率定义目前仍然存在争议.针对这一问题本文系统地介绍了当前占主流地位的两种观点,即理论法和实践法.这两种方法关于视在功率定义,皆是基于保持电压效应和电流效应不变而实现对负载传输的最大有功功率.在前人研究思路的基础上,提出了一种基于双重等效概念的新的视在功率定义方法,称为双重等效法.将该方法与另外两种方法作了详细的比较研究,并通过实例分析了三种不同视在功率定义方法的应用特性,结果表明:双重等效法的视在功率计算不受线路参数影响,具有更广泛的适用性与合理性.     

正弦电路瞬时功率理论研究

针对研究近一个世纪还没有解决的瞬时无功功率界定与定义的问题,该文认为应从原始瞬时有功功率,瞬时无功功率界定来研究瞬时功率理论,首先分析了现有功率定义中存在的缺陷,系统地给出了正弦稳态电路瞬时有功电流、无功电流、瞬时有功功率、无功功率,视在功率、平均有功功率,平均无功功率和平均视在功率的定义,并且将该定义应用于正弦对称三相电路运行特性分析。     

不平衡畸变负荷无功功率理论综述

为了给电气化铁路等典型三相不平衡、畸变负荷的电能量计量提供物理概念更为清晰、明确的无功功率定义,文中较全面地梳理了具有代表性和较广泛认可度的几种功率理论,从原理上比较了它们在无功功率定义上的不同,之后,使用电气化铁路实测信号进行了仿真计算,从应该对无功进行补偿、监测、管理和收费等应具有指导意义考虑,选择并确定以IEEE 1459标准阐述的功率理论作为非正弦、不平衡电路或系统的无功功率定义。依据该理论,通过测量基波正序无功功率、非基波等效视在功率、不平衡视在功率等,来评价电能的利用效率,从而可帮助电力公司及用电企业更科学、合理地实施供用电管理。     

非接触电能传输系统不对称PWM调制的研究

在非接触电能传输(CPT)系统中,为提高系统的效率和可靠性,在不改变原有谐振功率变换器结构的基础上,采用不对称PWM调制,通过调整全桥逆变器的控制角α就可以有效地控制系统的传输功率。在进行等效电路模型分析的基础上,分析了不对称PWM调制的工作原理和工作特性。在CPT系统中不对称PWM调制方式实现了ZVS软开关,表明该调制方法的合理性。     

非正弦条件下无功功率定义分析与展望

非正弦电路中,有功功率定义已被公认,无功功率的定义却一直还没有定论。本文描述了在非正弦波形下有关无功功率的三种定义,其一是时域分析法,其二是频域分析法,其三是三相电路瞬时无功功率;对已提出的一些无功功率定义做了详细的分析和评述;最后总结了新的无功功率理论应该满足的要求。     

Non-fundamental effective apparent power defined through an instantaneous power approach

This paper proposes a new definition of non-fundamental effective apparent power based on an analysis of instantaneous power flows. This new instantaneous power approach for the calculation of the non-fundamental effective apparent power extends, and adapts for new electrical conditions, the procedure applied by IEEE Std. 1459 for the quantification of active and reactive power in single-phase systems.This proposed approach is based on the analysis of per-phase and three-phase instantaneous power flows when a three-phase four-wire balanced non-linear load is connected to an ideal power network that supplies a set of positive-sequence fundamental voltages. The per-phase and three-phase instantaneous power flows caused by positive-, negative-, and zero-sequence harmonic load currents are analyzed. The results obtained for the load zero-sequence harmonic currents disagree with the results obtained when applying IEEE Std. 1459. As a consequence, a new definition of the effective quantities is proposed. A comparison between the new definitions and IEEE Std. 1459 definitions is made in the paper.     

牵引供电系统功率因数计量方法的研究

文章对牵引供电系统常见的变压器接线方式下电网三相不平衡度和谐波情况进行了理论分析,分别采用算术功率因数、矢量功率因数和等效功率因数三种定义方法,对三相不平衡、非线性的牵引供电系统功率因数计算进行了讨论,并且分析仿真了牵引供电系统三相不平衡度和谐波对三种功率因数计量的影响。理论分析及计算实例表明,IEEE Std.1459-2010标准中推荐使用的等效功率因数能准确计算三相不平衡非线性系统的功率因数,为电能计量的正确考核提供科学依据。     

Discussion of power definitions contained in the IEEE Dictionary

This tutorial paper discusses the drawbacks of the definitions of various types of powers found in the IEEE Standard Dictionary of Electrical and Electronics Terms (IEEE Std. 100-88). With the exceptions of instantaneous power and active power, all remaining kinds of “powers” are nonphysical. The concept of power factor in polyphase circuits is ambiguous. Examples that illustrate the shortcomings of many power definitions are included. The impact of these definitions on current power/energy metering practices are discussed. It is recommended that some definitions be either changed or eliminated from the IEEE Dictionary     

Summary of IEEE standard 1459: definitions for the measurement of electric power quantities under sinusoidal, nonsinusoidal, balanced, or unbalanced conditions

This paper describes the new IEEE Standard 1459, Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced or Unbalanced Conditions. The information is presented in the context of historical events that explain the reasons for new definitions. The new definitions originate from S/sub e/, the effective apparent power definition attributed to F. Buchholz and W. Goodhue. The resolution of S/sub e/ extends from well-established concepts. The need for the separation of 60/50-Hz powers from the non-60/50 Hz-powers is emphasized. The standard serves users who want to evaluate the performance of modern equipment or to design and build the new generation of instrumentation.     

A new IEEE Std 1459-2000—Compatible time-domain formulation for apparent power

This paper presents the development of new time-domain equations related to the definition of apparent power. These equations are compatible with the IEEE Std 1459-2000 Standard. When the application of these formulations involves an adequate quantity of samples, thus obeying the Nyquist Criterion, they can be utilized without restrictions regarding distortion, imbalance and asymmetry. Thus, they may be used in numeric meters for power measurements. In addition, unlike the above-mentioned standard, they do not oversimplify with respect to the phase and neutral resistance ratio or the percentage of delta-connected and wye-connected loads.     

光伏接入牵引供电系统对电能质量的影响

提出将光伏系统作为牵引负荷电源之一,与电力系统共同给牵引负荷供电的方案。光伏系统在27.5k V侧接入牵引供电系统,分析牵引负荷特性和光伏系统输出特性,推导计算光伏系统接入前、后对电力系统侧电能质量的影响;针对不同工况对光伏接入后电能质量的影响进行仿真分析,基于实测负荷数据对光伏系统接入前、后电能质量的影响进行验证。结果表明:所研究的光伏接入方案对电力系统侧三相电压不平衡度不产生影响,对三相谐波畸变率以及功率因数的影响与接入光伏系统的大小有关。     

牵引供电方案设计中谐波谐振问题研究

为了评估牵引供电系统的谐波谐振特性,从牵引供电系统设计角度出发,建立牵引供电系统谐波特性仿真模型和牵引负荷谐波发射模型。研究牵引供电方案中外部电源系统短路容量大小和馈线电缆长度变化对牵引供电系统谐振特性的影响规律。在供电方案综合评判中引入谐波谐振特性分析,研究牵引供电方案与牵引负荷谐波特性匹配问题及其对供电质量的影响。研究结果表明,牵引供电设计参数的变化对谐波谐振特性影响显著,通过优化牵引供电方案可以减少甚至避免发生谐波谐振。     

A new reactive,distortion and non-active power measurement method for nonstationary waveforms using wavelet packet transform

The definitions of power components that are contained in the IEEE Standard 1459-2000 [IEEE Std. 1459-2000, Definitions for the measurement of electric quantities under sinusoidal, non-sinusoidal, balanced or unbalanced conditions, 2000] are based on the Fourier transform (FT) which is suitable only for the case of stationary waveforms. However, for nonstationary waveforms, the FT produces large errors. Therefore, the power components based on this transform become inaccurate. A new approach based on the wavelet packet transform (WPT) for defining these power components is developed in this paper. The advantages of using the wavelet transform are that it can accurately represent and measure nonstationary waveforms, providing uniform frequency bands while preserving both time and frequency information. In addition, this paper addresses the problem of choosing the most appropriate mother wavelet for power components measurements. The results of applying both approaches to stationary and nonstationary waveforms show that the currently used definitions according to the IEEE Standard 1459-2000 result in large errors for the case of nonstationary waveforms while the proposed approach (WPT based) gives more accurate results in this situation.