电力谐波

摘要

目前电力系统谐波危害已经引起了各个部门的关注，为了整个供电系统的供电质量，必须对谐波进行有效的检测和治理。

关键字：电力谐波 检测 治理

前言

随着我国工业化进程的迅猛发展，电网装机容量不断加大，电网中电力电子元件的使用也越来越多，致使大量的谐波电流注入电网，造成正弦波畸变，电能质量下降，不但对电力系统的一些重要设备产生重大影响，对广大用户也产生了严重危害。目前，谐波与电磁干扰、功率因数降低被列为电力系统的三大公害，因而了解谐波产生的机理，研究和清除供配电系统中的高次谐波，对改于供电质量、确保电力系统安全、经济运行都有着十分重要的意义。

一、电力系统谐波危害

①谐波会使公用电网中的电力设备产生附加的损耗，降低了发电、输电及用电设备的效率。大量三次谐波流过中线会使线路过热，严重的甚至可能引发火灾。

②谐波会影响电气设备的正常工作，使电机产生机械振动和噪声等故障，变压器局部严重过热，电容器、电缆等设备过热，绝缘部分老化、变质，设备寿命缩减，直至最终损坏。

③谐波会引起电网谐振，可能将谐波电流放大几倍甚至数十倍，会对系统构成重大威胁，特别是对电容器和与之串联的电抗器，电网谐振常会使之烧毁。

④谐波会导致继电保护和自动装置误动作，造成不必要的供电中断和损失。 ⑤谐波会使电气测量仪表计量不准确，产生计量误差，给供电部门或电力用户带来直接的经济损失。

⑥谐波会对设备附近的通信系统产生干扰，轻则产生噪声，降低通信质量;重则导致信息丢失，使通信系统无法正常工作。 ⑦谐波会干扰计算机系统等电子设备的正常工作，造成数据丢失或死机。 ⑧谐波会影响无线电发射系统、雷达系统、核磁共振等设备的工作性能，造

成噪声干扰和图像紊乱。

二、谐波检测方法

1.模拟电路

消除谐波的方法很多，即有主动型，又有被动型；既有无源的，也有有源的，还有混合型的，目前较为先进的是采用有源电力滤波器。但由于其检测环节多采用模拟电路，因而造价较高，且由于模拟带通滤波器对频率和温度的变化非常敏感，故使其基波幅值误差很难控制在10%以内，严重影响了有源滤波器的控制性能。近年来，人工神经网络的研究取得了较大进展，由于神经元有自适应和自学习能力，且结构简单，输入输出关系明了，因此可用神经元替代自适应滤波器，再用一对与基波频率相同，相位相差90度的正弦向量作为神经元的输入。由神经元先得到基波电流，然后检测出应补偿的电流，从而完成谐波电流的检测。但人工神经网络的硬件目前还是一个比较薄弱的环节，了其应用范围。

2.傅立叶变换

利用傅立叶变换可在数字域进行谐波检测，电力系统的谐波分析，目前大都是通过该方法实现的，离散傅立叶变换所需要处理的是经过采样和A/D转换得到的数字信号，设待测信号为x(t)，采样间隔为 t秒，采样频率 =1/ t满足采样定理，即 大于信号最高频率分量的2倍，则采样信号为x(n t)，并且采样信号总是有限长度的，即n=0，1„„N-1。这相当于对无限长的信号做了截断，因而造成了傅立叶变换的泄露现象，产生误差。此外，对于离散傅立叶变换来说，如果不是整数周期采样，那么即使信号只含有单一频率，离散傅立叶变换也不可能求出信号的准确参数，因而出现栅栏效应。通过加窗可以减小泄露现象的影响。

3.小波变换

小波变换已广泛应用于信号分析、语音识别与合成、自动控制、图象处理与分析等领域。电力谐波是由各种频率成分合成的、随机的、出现和消失都非常突然的信号，在应用离散傅立叶变换进行处理受到局限的情况下，可充分发挥小波变换的优势。即对谐波采样离散后，利用小波变换对数字信号进行处理，从而实现对谐波的精确测定。小波可以看作是一个双窗函数，对一信号进行小波变换相当于从这一时频窗内的信息提取信号。对于检测高频信息，时窗变窄，可对信号的高频分量做细致的观测；对于分析低频信息，这时时窗自动变宽，可对信号的

低频分量做概貌分析。所以小波变换具有自动“调焦”性。其次，小波变换是按频带而不是按频点的方式处理频域信息，因此信号频率的微小波动不会对处理产生很大的影响，并不要求对信号进行整周期采样。另外，由小波变换的时间局部可知，在信号的局部发生波动时，不会象傅立叶变换那样把影响扩散到整个频谱，而只改变当时一小段时间的频谱分布，因此，采用小波变换可以跟踪时变和暂态信号。

三、电力系统谐波治理

限于篇幅问题，本文在此只介绍基于改造谐波源本身的谐波抑制方法，基于改造谐波源本身的谐波抑制方法一般有以下几种。

（1）增加整流变压器二次侧整流的相数

对于带有整流元件的设备，尽量增加整流的相数或脉动数，可以较好地消除低次特征谐波，该措施可减少谐波源产生的谐波含量，一般在工程设计中予以考虑。因为整流器是供电系统中的主要谐波源之一，其在交流侧所产生的高次谐波为tK 1次谐波，即整流装置从6脉动谐波次数为n=6K 1，如果增加到12脉动时，其谐波次数为n=12K 1(其中K为正整数)，这样就可以消除5、7等次谐波，因此增加整流的相数或脉动数，可有效地抑制低次谐波。不过，这种方法虽然在理论上可以实现，但是在实际应用中的投资过大，在技术上对消除谐波并不十分有效，该方法多用于大容量的整流装置负载。

（2）整流变压器采用Y/ 或 /Y接线

该方法可抑制3的倍数次的高次谐波，以整流变压器采用 /Y接线形式为例说明其原理，当高次谐波电流从晶闸管反串到变压器副边绕组内时，其中3的倍数次高次谐波电流无路可通，所以自然就被抑制而不存在。但将导致铁心内出现3的倍数次高次谐波磁通(三相相位一致)，而该磁通将在变压器原边绕组内产生3的倍数次高次谐波电动势，从而产生3的倍数次的高次谐波电流。因为它们相位一致，只能在 形绕组内产生环流，将能量消耗在绕组的电阻中，故原边绕组端子上不会出现3的倍数次的高次谐波电动势。从以上分析可以看出，三相晶闸管整流装置的整流变压器采用这种接线形式时，谐波源产生的3n(n是正整数)次谐波激磁电流在接线绕组内形成环流，不致使谐波注入公共电网。这种接线形式的优点是可以自然消除3的整数倍次的谐波，是抑制高次谐波的最基本方法，

该方法也多用于大容量的整流装置负载。 （3）尽量选用高功率因数的整流器

采用整流器的多重化来减少谐波是一种传统方法，用该方法构成的整流器还不足以称之为高功率因数整流器。高功率因数整流器是一种通过对整流器本身进行改造，使其尽量不产生谐波，其电流和电压同相位的组合装置，这种整流器可以被称为单位功率因数变流器(UPFC)。该方法只能在设备设计过程中加以注意，从而得到实践中的谐波抑制效果。 （4）整流电路的多重化

整流电路的多重化，即将多个方波叠加，以消除次数较低的谐波，从而得到接近正弦波的阶梯波。重数越多，波形越接近正弦波，但其电路也越复杂，因此该方法一般只用于大容量场合。另外，该方法不仅可以减少交流输入电流的谐波，同时也可以减少直流输出电压中的谐波幅值，并提高纹波频率。如果把上述方法与PWM技术配合使用，则会产生很好的谐波抑制效果。该方法用于桥式整流电路中，以减少输入电流的谐波。

当然，除了基于改造谐波源本身的谐波抑制方法，还有基于谐波补偿装置功能的谐波抑制方法，它包括加装无源滤波器、加装有源滤波器、装设静止无功补偿装置(SVC)等等，在此就不再详细论述。

四、结论

随着现代信息技术，计算机技术和电子技术的发展，电能质量问题已越来越引起用户和供电部门的重视。应用先进的电能质量测试仪器不仅能大大提高电能质量的监测与治理水平，同时还可建立先进可靠的电能质量监测网络，及时分析和反映电网的电能质量水平，找出电网中造成电能质量谐波及故障的原因，采取相应的措施，为保证电网的安全、稳定、经济运行提供重要的保障。

参考文献

[1]电能质量－公用电网谐波 GB／T14549-1993[J]

[2]吕润馀．电力系统高次谐波．[M]．北京：中国电力出版社，1998 [3]陈伟华． 电磁兼容实用手册．北京： 机械工业出版社，1998

Power system harmonic detection and treatment

Abstract

Power system harmonics harm has been caused concern in various sectors, in order to supply the quality of the entire power supply system must be effective on the harmonic detection and treatment.

Keywords: harmonic detection control

Preface

With the rapid development of China's industrialization process, increasing installed capacity of power grid in the use of power electronic devices more and more, resulting in a large number of harmonic current into the power grid, resulting in sine wave distortion, power quality decline, not only for power Some important equipment systems have a significant impact on the majority of users also had a serious harm. Currently, the harmonics and electromagnetic interference, lower power factor is listed as the three major power system pollution, and thus to understand the mechanism of harmonic generation, research, and clear the power supply system of high harmonics of the change in the quality of power supply, Ensure power system security, the economy is of great significance.

I the power system harmonics hazards

① harmonics in the utility grid will produce an additional loss of power equipment and reduce the generation, transmission and efficiency of electrical equipment. A large number of third-harmonic heat flow through the middle line will, in serious cases may lead to fire.

② harmonics will affect the normal operation of electrical equipment, so that mechanical vibration and noise generated by the motor such failure, severe localized overheating transformers, capacitors, cables and other equipment overheating, insulation aging, deterioration, reduced equipment life, until the final damage.

③ harmonics can cause power grid resonance, the harmonic current amplification may be several times or even ten times, the system will pose a major

threat, especially for capacitors and reactors in series with them, often makes the burning of resonant power.

④ harmonics will lead to protection and automatic device malfunction, resulting in unnecessary power interruptions and losses.

⑤ Harmonic will inaccurate measurement of electrical measuring instruments, resulting in measurement error, to the electricity sector and electricity users direct economic losses.

⑥ harmonic devices will interfere with nearby communications systems, ranging from noise and reduce the communication quality; weight have resulted in loss of information, the communication system can not work properly.

⑦ harmonics can interfere with computer systems and other electronic devices work properly, resulting in data loss or crashes.

⑧ harmonics will affect the radio transmission systems, radar systems, nuclear magnetic resonance device performance, resulting in image noise and disturbance.

II the harmonic detection

1.Analog circuit

There are many ways to eliminate harmonics, that is proactive, there are passive; both passive and also active, and there are mixed, the present is the use of more advanced active power filter. But because of its many links with analog circuit testing, and thus a higher cost, and because the simulation of the frequency and band-pass filter is very sensitive to temperature changes, so it is difficult to control the fundamental amplitude error of less than 10% have a serious impact on source filter control performance. In recent years, artificial neural network research has made great progress, because neurons in adaptive and self learning ability, and the structure is simple, clear relationship between input and output, so it can replace neural adaptive filter, and then a pair with the base the same wave frequency, the sine of 90 degrees of phase vectors as the input neurons. Obtained by the fundamental current of neurons first, and then detected to be compensated current, thus completing the detection of

harmonic current. But the artificial neural network hardware is still a relatively weak link, limiting its scope of application.

2.Fourier transform

Fourier transform can be harmonic detection in the digital domain, the power system harmonic analysis, the current mostly by this method, the discrete Fourier transform of the need to address is the result of sampling and A / D conversion by the digital signal, set to be measured signal x (t), the sampling interval t s, sampling frequency = 1 / t to meet the sampling theorem, that is, the signal is greater than 2 times the highest frequency component, the sampled signal x (nt), and the sampling signal is always limited length, ie n = 0,1 ... ... N-1. This is equivalent to the infinite made a truncated signal, resulting in the leakage phenomenon of the Fourier transform, resulting in errors. In addition, the discrete Fourier transform, if not an integer period sampling, even if it contains only a single frequency signal, discrete Fourier transform can not find the exact parameters of the signal, hence the fence effect. Window leaks can be reduced by the impact of the phenomenon.

3.Wavelet transform

Wavelet transform has been widely used in signal analysis, speech recognition and synthesis, automatic control, image processing and analysis and other fields. Harmonic frequency components from a variety of synthetic, random, very sudden appearance and disappearance of the signal, in the application of discrete Fourier transform processing has been limited in the case, give full play to the advantages of wavelet transform. Namely, the discrete harmonic sampling, the use of wavelet transform for digital signal processing, in order to achieve accurate measurement of harmonics. Wavelet can be seen as a double-window function, the wavelet transform of a signal from a time-frequency window is equivalent to the information extraction signal. For the detection of high frequency information, narrowing the time window can be high-frequency components of the signal to do meticulous observation; for the analysis of low-frequency information, then automatically widened time window can be done on the profile of low frequency signal analysis. Therefore, wavelet transform has an automatic \"focus\" of. Secondly, the wavelet transform is based on frequency

band and not by way of processing the frequency domain information, so small fluctuations in signal frequency does not have a huge impact on the deal, does not require the entire cycle of signal sampling. In addition, the wavelet transform of the time the local shows, the local fluctuation in the signal, the Fourier transform did not like the impact spread throughout the spectrum, but only a short time to change the spectrum was, therefore, can track when using wavelet transform variable and transient signals.

III the power system harmonic control

Due to space limitations, this paper only describes this transformation of harmonic sources based on their harmonic suppression method, based on the transformation of the source itself harmonic harmonic suppression method generally have the following.

（1）increasing the rectifier transformer secondary side rectification of the phase number

For components with the rectification of equipment to maximize the number of rectifier phase or pulse number, can be better to eliminate low order characteristic harmonics, the measure can reduce the harmonic content generated by harmonic sources, generally be considered in engineering design. Rectifier is the power supply system as the main source of harmonics, resulting in the exchange side of the high harmonics is tK 1 harmonics, which harmonics rectifier pulse number from 6 to n = 6K 1, if the increased 12 pulse, its harmonic is n = 12K 1 (where K is a positive integer), 5,7, etc. so that you can eliminate harmonics, thus increasing the number of phases or pulse rectifier number, which can effectively inhibit the low order harmonic wave. However, although this approach can be achieved in theory, but in practice the investment is too large, technically not very effective to eliminate harmonics, the method used for large-capacity rectifier load.

（2）rectifier transformers are Y / or / Y connection

The method can inhibit multiple of 3 times higher harmonics, to rectifier transformers / Y connection in the form as an example how this works, when the high

harmonic current from the thyristor playing a transformer secondary winding, one of the 3 multiple times higher harmonic currents there was no way through, so naturally there was not inhibited. But the core will lead to a multiple of 3 times within the emergence of high harmonic magnetic flux (phase three-phase line), and the flux in the transformer primary winding to generate a multiple of 3 times higher harmonic force, resulting in a multiple of 3 times of high harmonic currents. Phase because they are the same, only generated within the circulation in the form of windings, the energy consumed in the resistance of the windings, so the primary winding terminals will not be a multiple of 3 times higher harmonic force. As can be seen from the above analysis, three-phase thyristor rectifier transformer rectifier wiring using this form, the harmonic source generated by 3n (n is a positive integer) harmonic excitation current in the wire windings to form circulation, does not result in harmonic into the public grid. Advantage of this connection is the natural form of a multiple of 3 times to eliminate the harmonic, is the most basic high harmonics method is also used for large-capacity rectifier load.

（3）Try to use high power factor rectifier

Multiple use of rectifier to reduce harmonics is a traditional method, this method is not enough to call rectifier consisting of high power factor rectifier. High power factor rectifier is to transform itself through the rectifier, so try not to generate harmonic current and voltage in phase with its combination of devices, such rectifiers can be referred to as unity power factor converter (UPFC). This method can only be pay attention to the design process equipment, resulting in the practice of harmonic suppression.

（4）Multiple of the rectifier circuit

Multiple of the rectifier circuit, is about more than square wave superposition, to eliminate the low frequency harmonics, which are close to the sine of the staircase. The more important number, the closer the sine wave, but the circuit is also more complex, so this method is generally used for large capacity applications. In addition, the method can not only reduce the AC input current harmonics, but also can reduce the DC output voltage of the harmonic amplitude, and increase the ripple frequency.

If the above method in conjunction with the PWM technique, it will produce good harmonic suppression. The method used for bridge rectifier circuit to reduce input current harmonics.

Of course, in addition to the source itself is based on the harmonic transform harmonic suppression method, as well as harmonic compensation devices based on the harmonic function method, which includes the installation of passive filters, active filters installed, the installation of static var compensator devices (SVC), and so, in this no longer discussed in detail.

IV conclusion

With modern information technology, computer technology and electronic technology, power quality problems has increasingly become a user and the electricity sector attention. The application of advanced power quality testing equipment can not only greatly improve the power quality monitoring and governance, but can also establish an advanced power quality monitoring network of reliable, timely analysis and reflect the level of the grid power quality, identify power harmonics and power quality caused the causes and take appropriate measures to ensure grid security, stability, economic operation to provide important protection.

References

[1] Power Quality - Public harmonic GB/T14549-1993 [J]

[2] Lui Yun remaining. High power system harmonics. [M]. Beijing: China Electric Power Press, 1998

[3] Chen Weihua. EMC Practical Manual. Beijing: Mechanical Industry Press, 1998