基于波形相似的谐波及无功电流检测

非线性负荷所产生的谐波对电网造成了极大的危害,本文分析了现有的谐波及无功电流检测方法,从最小能量损耗的分析入手,得到了与之密切相关的电压和电流的波形所满足的条件,并以电压和电流的最小能量误差为判据,提出了一种基于波形相似理论的谐波及无功电流检测方法。通过PSCAD仿真验证了该检测方法的有效性和正确性。     

一种检测单相电路无功与谐波电流的跟踪算法

有源滤波器是改善电能质量的一种有效手段,它要求快速准确地检测出负载电流中的谐波和无功分量.针对单相系统瞬时谐波与无功检测方法算法复杂的问题,根据有功和无功功率定义,提出一种检测单相瞬时无功与谐波电流的快速跟踪算法.该方法通过在一个计算周期内,用低通滤波器和锁相环电路得到与电源电压基波同相频的标准正弦波与负载电流乘积后,采样存入采样数据存储队列,然后比较队列中基波周期前后一段数据来快速跟踪有功电流,从而得到实际补偿的谐波和无功电流.仿真表明该方法正确可行,在一个周期内可以实现对补偿电流的准确提取,而且对电流变化跟踪效果好,防干扰能力强.算法简单快速,只需两个乘法器,易于实现.     

Harmonic analysis for industrial customers

A power flow program is developed to analyze the harmonic distortion of a power system with various types of harmonic loads. The proposed program can be applied to solve the harmonic current flow, voltage harmonic distortion factor, resonance frequency, and current amplification factor at every bus in the system. In this study, a large metal factory is selected for the harmonic power flow analysis. The current waveforms at every bus are measured and analyzed to determine various orders of harmonic components. These harmonic currents are used in the computer simulation to determine the harmonic voltage distortion factor at the buses of the system, and the variations of resonance impedance and amplification factor with frequencies are investigated. Finally, the program is used to calculate the harmonic load flow when the metal factory is expanded by including a new plant in the power system, and proper filters are designed to alleviate the harmonic problems     

基于双CPU的有源电力滤波器

介绍了控制系统采用数字信号处理器(DSP)和单片机相结合的双CPU并联有源电力滤波器.该有源电力滤波器的控制策略基于瞬时无功功率理论,实时检测负载电流,计算出相应的基波分量后与其相减,得出需要补偿的谐波电流和无功电流,然后控制逆变桥上的大功率电子开关管,使之输出所需的补偿电流,达到抑制谐波和补偿无功的效果.采用双CPU的控制系统,提高了滤波器的实时跟踪能力.经过用户考核及现场测试,证明投入该有源电力滤波器后,电网供给的电流波形得到了很大的改善,谐波源对电网的影响大大减小.     

基于无功功率方向法的主谐波电流来源判别

针对目前谐波电流造成特定线路各元件损耗难以明确其来源的问题,提出一种基于无功功率方向法来判别引起公共连接点（point of common coupling,PCC）处的主谐波电流来源方法。通常情况下,系统侧和用户侧谐波源流过特定线路各元件造成的损耗大小,可由两侧各自贡献的谐波电流大小区分,故以谐波电流指标为判别依据。以电网中谐波阻抗基本性质为基础,结合PCC处谐波电压和电流实测信息,利用基本电路原理和不等式约束条件,在谐波无功功率方向法的思路与判别条件下,推导得出了仅根据谐波电压和电流的相角差,就可直接判别主谐波电流来源的方法。最后,通过多种实际工程场景的实测数据,验证了该方法的有效性,使用中的便捷性反映了该方法在工程实用中的价值。     

A time-domain three-phase power system impedance modeling approachfor harmonic filter analysis

A time-domain method for impedance modeling of an unbalanced, three-phase power transmission and distribution network using three-phase measurements of bus voltage and injected current waveforms is presented. An impedance model seen at a bus where a harmonic filter is to be installed is calculated for each harmonic frequency, and the effect of placing the filter at the bus is then analyzed at these frequencies. As the configuration or operating condition of the power system varies, the estimated model changes accordingly, provided updated measurements are available. Hence, the effect of the harmonic filter under different system configurations or operating conditions is analyzed, and the information from this analysis is used for online harmonic filter control. Impedance models estimated by the proposed method are applied in filter design and performance analysis with actual recorded data, and the results are presented     

TIME DOMAIN ESTIMATION TECHNIQUES FOR HARMONIC LOAD MODELS

ABSTRACT

In this paper we present two novel time domain techniques for load modelling in the presence of harmonics. In the first technique, the harmonic contents of the load voltage and current waveforms are assumed to be known in advance. The second technique uses samples of the load voltage and current waveforms directly. The least errors square parameter estimation algorithm is used to estimate the load resistance, inductance and capacitance. The residual current associated with incomplete extraction of the parameters for all significant signal frequencies is also estimated. We also identify harmonics that are not common between the load voltage and current waveforms. The proposed techniques are applied to synthetic and actual recorded data. The paper's conclusions are based on comparing the results obtained using both techniques.     

A genetic based algorithm for measurement of power system disturbances

This paper introduces genetic algorithms (GA) as a powerful tool for monitoring and supervising power system disturbances generated due to dynamic performance of power systems. Monitoring power system disturbances involves monitoring fundamental voltage magnitude and its frequency as well as harmonic and sub-harmonic voltage magnitudes and their frequencies under different operating conditions for power quality evaluation purposes. The proposed method is based on genetic algorithms optimization technique. The method uses digital set of measurements for the voltage or current waveforms at power system bus to perform the estimation process digitally. The algorithm is tested using different simulated data to monitor power quality. Three different study cases are considered in this work. In the first part, the estimation of voltage flicker levels and its frequency is presented and discussed. In the second part, the frequency of a bus voltage signal that is contaminated with harmonics is estimated. The harmonic contents are also estimated in this case. In the third part, the analysis of a damped sub-harmonic signal is presented. Effects of number of samples, sampling frequency and the sample window size are studied. Effects of GA parameters and operators, such as population size, crossover, mutation probabilities and niching are also studied. Results are reported and discussed.     

高压无功功率自动检测补偿系统

在大型电力电子装置的供电系统中,往往存在着大量的谐波干扰,致使功率因数难以测量,无功功率不易补偿。为此,本文提出了一种新的高压无功功率自动检测补偿系统。通过对电流波形进行数字滤波,准确地确定了功率因数。同时,采用非线性控制技术,较好地解决了无功功率的自动补偿问题,试验证明,该系统稳定可靠,节能效果明显。     

基于FBD法有源电力滤波器谐波电流检测方法

介绍了一种基于FBD法的有源电力滤波器谐波电流检测方法,分析了基波有功电流和基波无功电流、谐波电流、基波负序电流和任意次谐波电流等的检测原理。该方法采用锁相环产生参考电压,将负载电流投影到参考电压上,通过低通滤波器可以准确检测出各种电流分量,并且在电网电压畸变情况下,该方法同样适用。Matlab/Simulink仿真结果证实了该方法的正确性和有效性。     

变压器发生直流偏磁时的谐波分析和治理

介绍了一种计算变压器直流偏磁时绕组励磁电流的数学模型,对励磁电流进行傅立叶变换后。计算得到各次谐波分量。对单相交流变压器绕组流过不同直流电流时变压器绕组的励磁电流各次谐波分量的含量和变化规律进行仿真研究,并探讨优化选择500kV变压器低压侧无功补偿电容器组参数配置的原则．有效吸收变压器产生的谐波,防止无功补偿设备发生谐波放大而损坏电容器设备。     

A new control strategy for active power line conditioner (APLC) using adaptive notch filter

This paper proposes a new adaptive control algorithm for a three-phase current-source shunt active power-line conditioner (APLC) operating under unbalanced and distorted network conditions. This control scheme aims at compensation of network’s reactive power, elimination of active power’s oscillating components, compensation of network current and voltage harmonic contents resulting in sinusoidal waveforms, and equilibrating the drawn power from the source evenly between the three-phases. Unlike many of the existing methods, the proposed strategy does not require any coordinate transformations or complicated calculations. The reference signals for the hysteresis-band current controlled voltage-source converter (HBCC-VSC) are generated by passing the measured current and voltage signals through two layers of modified adaptive notch filters (ANFs). To ensure superb performance and minimum total harmonic distortion (THD) level of the power system, parameters of the HBCC-VSC are obtained using differential evolution (DE) optimization algorithm. The proposed strategy is simple, easily implementable, and robust against uncertainty or variations of power system parameters and loads. The effectiveness of the proposed control scheme is validated by simulation results of a selected network under various load and power system conditions.     

ip-iq检测法的单周控制三电平有源电力滤波器

并联型有源电力滤波器APF可以有效补偿由非线性负载产生的谐波和无功功率电流。为了实现单独对谐波分量、无功功率分量进行补偿,或者对谐波和无功功率分量同时进行补偿这些不同的补偿目标,同时为了满足大功率、高电压和输出电流波形畸变小的需要,提出了将中点箝位变换器和ip-iq电流检测法应用于单周控制有源电力滤波器的方法。采用ip-iq电流检测算法可分离出负载电流中的谐波分量、无功功率分量,且电网电压波形畸变不影响检测结果,故可提供不同补偿目标的参考信号。理论推导和仿真结果表明,该法能分别单独补偿谐波分量、无功功率分量,或者同时补偿谐波和无功功率分量,而且电网电压波形畸变不影响补偿效果。通过将ip-iq电流检测法运用于单周控制三电平有源电力滤波器,既实现多种补偿目标,又具有电网电压波形畸变不影响补偿效果、单周控制策略简单、三电平变换器输出电流波形畸变小的优点。     

Design aspects of synchronous PWM rectifier-inverter systems underunbalanced input voltage conditions

A complete analysis of a synchronous front-end PWM rectifier-inverter system under unbalanced input voltage conditions is presented. The analysis includes the harmonic assessment of input/output current and voltage waveforms. It is shown both theoretically and experimentally that input voltage unbalance generates uncharacteristic low-frequency harmonic components in the input and output currents. Special emphasis is given to the generation of a DC component in the inverter output voltage in the case in which the output frequency is twice the input frequency. System design curves for different degrees of unbalance for all major system components are reported. Key predicted results are confirmed experimentally     

基于阶梯波与瞬时值反馈混合控制的光伏并网级联逆变器

针对传统光伏并网系统结构存在的问题,提出了一种新的阶梯波与电流瞬时值反馈混合控制的光伏并网级联逆变器方案。该方案一部分级联单元采取梯形波控制,一部分级联单元采取带电流瞬时值反馈的倍频正弦脉冲宽度调制,2个部分串联叠加形成输出电压。逆变器输出电压的谐波分析表明:调节正弦脉冲宽度调制波的移相角可以调节输出电压幅值和功率因数;逆变器输出电压低频谐波主要由阶梯波引起,为输出滤波器的设计提供了理论依据。对阶梯波调制逆变器的触发角提出了一种简易算法,该算法适用于电压级差不等模式且可实现触发角在线计算。实验结果表明,该方案结构简单,可靠性高,能有效降低开关损耗。     

改进型的i_d-i_q谐波检测方法研究与仿真

准确、快速、易于实现的谐波检测方法对有源电力滤波器的控制十分重要。在总结现有谐波检测理论的基础上提出了一种谐波检测方法,该方法不受电源电压畸变影响。通过对三相电源电压的预处理分离出电压正序分量,进而利用d-q变换实现了电流基波正序有功分量的准确检测。研究结果表明,该算法在理想电网电压和畸变电网电压条件下,均能获得正确的基波正序有功和无功电流,为在有源电力滤波系统中实现对谐波电流、无功电流和不对称分量的综合补偿提供了合理的参考指令电流。     

Fast tracking of transient power system signals using fuzzy LMS algorithm

The paper presents an adaptive least mean squares (LMS) algorithm for the fast estimation of voltage and current signals in power networks. The new estimator is based on the use of linear combiners. The learning parameter of the proposed algorithm is constrained by two variable parameters which causes an automatic suitable adjustment of the step size using a fuzzy gain scheduling method to provide fast convergence and noise rejection for the tracking of fundamental and harmonic components from distorted signals. Several numerical tests have been conducted for the adaptive estimation of fundamental and harmonic components from simulated waveforms from power networks supplying converter loads and switched capacitors.     

Powers in nonsinusoidal situations-a review of definitions andphysical meaning

The author expands on the physical meaning of the reactive power in nonsinusoidal situations. The sinusoidal waveform case is surveyed, viewing the active current as a component of identical waveform with the voltage. This approach, when extended to nonsinusoidal waveforms, supports Fryze's model for apparent power, S²=p ²+Q²_F. It is proved that the total reactive power Q_F is composed from four distinctive types of elementary reactive powers. Each of the basic reactive powers is identified as the amplitude of an oscillation of instantaneous power. The separation of Q_F in Q ₁, the reactive power at the system frequency, and in Q_H, the reactive power at harmonic frequencies, is recommended as an effective mean for monitoring filter efficacy and power-factor compensation. Two major recommendations are supported by the results of this study: abolish the power model using distortion power, and measure the active power of the system frequency separately from the active power of the harmonics     

Harmonic Reduction in Synchronous Chopper-Converter Combinations

The synchronous chopper-converter combination has previously been shown to be suitable for moderate to high power ac/dc converter applications. Operation at unity displacement factor, however, was seen to be accompanied by a significant increase in the harmonic compensation requirements. Techniques for reducing the input harmonic current levels in the synchronous chopper-converter combination are investigated. Operating the synchronous chopper at higher frequencies allows selective harmonic elimination but results in restricted output voltage control. The use of a multiphase synchronous chopper yields greatly improved input characteristics but requires additional power components. A compromise solution involves a single-phase chopper operated at different frequencies over its operating range.     

New digital filter for unbalance distorted current and voltage estimation in power systems

This paper presents a novel algorithm for identifying and measuring the symmetrical components of distorted three phase voltage or current waveforms in electrical power systems. The proposed algorithm is capable of estimating the symmetrical components as well as the harmonic contents of a given unbalanced distorted signal. The proposed technique is based on stochastic estimation theorem. The problem is formulated as an estimation problem and presented in state space form. The proposed algorithm used to estimate the positive, negative and zero components of unsymmetrical waveforms as well as the harmonic content of a given distorted signal. Application of the proposed algorithm has been conducted on various test cases. Among which a practical simulated power system has been implemented using EMTP. Various scenarios are carried out to simulate realistic situations of unsymmetrical waveforms. Effects of bad data on the solution accuracy are also studied. The speed of convergence is examined by changing the estimator initial conditions. Results obtained show that the proposed technique can estimate and track the symmetrical components of non-stationary three phase unbalance voltage or current waveforms in noisy environments. Fast accurate solutions are guaranteed regardless of the initial conditions. It is also shown that bad measurements have no effects on the final accuracy of the estimation.