Determination of the utility harmonic impedance based on measurements is a significant task for utility power-quality improvement and management. Compared to those well-established, accurate invasive methods, the noninvasive methods are more desirable since they work with natural variations of the loads connected to the point of common coupling (PCC), so that no intentional disturbance is needed. However, the accuracy of these methods has to be improved. In this context, this paper first points out that the critical problem of the noninvasive methods is how to select the measurements that can be used with confidence for utility harmonic impedance calculation. Then, this paper presents a new measurement technique which is based on the complex data-based least-square regression, combined with two techniques of data selection. Simulation and field test results show that the proposed noninvasive method is practical and robust so that it can be used with confidence to determine the utility harmonic impedances.

Utility Harmonic Impedance Measurement Based on Data Selection

This paper presents a new noninvasive method for calculating utility harmonic impedance at the point of common coupling (PCC). The proposed method is based on a statistical signal-processing technique, known as independent component analysis (ICA). The complex ICA technique is applied to the equations derived from Northon equivalent circuit model at the PCC in order to estimate the utility harmonic current values. Then, the estimated values of the utility harmonic current are used in an optimization problem to calculate the utility harmonic impedance. Due to considering the utility harmonic current variations in utility harmonic impedance calculation, the proposed method is relatively robust against the background harmonic fluctuations. The results obtained from computer simulation and a real case study verify the effectiveness of the proposed method.

A Novel Method for Noninvasive Estimation of Utility Harmonic Impedance Based on Complex Independent Component Analysis

Harmonics produced by residential loads have become an increasing concern in recent years due to the extensive adoption of power-electronic-based home appliances. This paper presents analysis on extensive field data collected from various locations of residential distribution systems in North America. The degree of cancellation of harmonic currents from different sources is determined. A comparative study on the harmonic characteristics of residential, commercial, and industrial feeders is also conducted. The results show that the harmonic current distortion levels of residential feeders are much higher than those of the industrial and commercial feeders. The third harmonic is the most pronounced component and the low-order harmonic currents from different homes tend to add to each other, i.e., the harmonic cancellation effect is much less than those claimed in the literature.

Characteristics of Harmonic Distortions in Residential Distribution Systems

Based on fast independent component analysis, a new method is proposed to calculate the utility harmonic impedance. Since the utility harmonic change is negligibly dependent on the customer, four independent components are obtained by demixing X-Y orthogonal components of voltage and current fluctuations at the point of common coupling. Then, mixing coefficients can be figured out by ordinary least square. Finally, the utility harmonic impedance is calculated according to the linearity of mixing coefficients. The disturbance of the utility harmonic is reduced to a certain extent by this method, which is because the joint impact of both sides is taken into account. According to analyses of simulation and field test cases, it is proved that utility harmonic disturbances can be effectively restrained by the proposed method; thus, more accurate utility harmonic impedance can be obtained.

A New Method to Calculate the Utility Harmonic Impedance Based on FastICA

This study presents a new method for determining the harmonic contributions (HCs) of utility and consumer at the point of common coupling (PCC). The proposed method is based on a well-known statistical signal processing technique, the so-called complex independent component analysis (ICA). The complex ICA technique is applied to the harmonic voltage and current measured at the PCC to estimate the parameters of the Northon equivalent circuit model. Then, the HCs of utility and consumer are calculated through quantitative indices defined by the superposition method. The proposed method is robust against the background harmonic disturbances and works well in resonance condition. Moreover, the impact of consumer harmonic impedance is appropriately considered in calculations. The effectiveness of the proposed method is verified through the computer simulation and the real case study.

Method for determining utility and consumer harmonic contributions based on complex independent component analysis

This paper presents a new method to calculate the utility harmonic impedance and the harmonic voltage emission level at the point of common coupling (PCC). Since harmonic current at the PCC commonly exhibits negligible dependence on the utility side background harmonic, the variable item of the background harmonic in the deviation formulation can be eliminated by using the covariance characteristic of random vectors. And then, the utility harmonic impedance, the customer harmonic voltage emission level, and the background harmonic can be calculated in real time. Based on the analysis results of the simulation and the field test case, it shows that the proposed method is effective to reduce the calculation errors caused by the fluctuation of background harmonic, and satisfactory results can be achieved.

Assessing Utility Harmonic Impedance Based on the Covariance Characteristic of Random Vectors

The interharmonic group concept adopted by the IEC 61000-4-7 is very useful for addressing the need to monitor interharmonics in power systems. This paper shows that grouping spectral bins into interharmonics and harmonic components of 5 Hz resolution could yield misleading information for cases where an interharmonic component's frequency is very close to a harmonic frequency. Since interharmonics in such cases can cause more severe waveform modulation, the interharmonic grouping scheme needs to be improved. A signal-processing method that can separate interharmonic and harmonic components in close proximity is, therefore, proposed in this paper to address this need. The method is based on the estimation of leakage values caused by interharmonics, at harmonic frequencies. Simulation studies and field data analysis showed that the proposed method was able to extract interharmonic and harmonic components correctly. Moreover, this paper also discusses how to apply the method to enhance the spectral grouping scheme of the IEC 610004-7.

A Method to Improve the Interharmonic Grouping Scheme Adopted by IEC Standard 61000-4-7

Interharmonic components can often be seen from the discrete Fourier transform (DFT) results of measured voltage or current waveforms. These components may be caused by various factors, such as transient waveform distortions or noises. They are not necessarily related to the real interharmonics. This letter presents a simple method to verify the existence of a genuine interharmonic component contained in the DFT results. The method can also reveal the characteristics of the component. The method has been demonstrated on various field measurement data that contain genuine and false interharmonic components.

http://www.ece.ualberta.ca/~apic/papers/Power_Quality/2012-A%20Method%20to%20Determine%20the%20Existence%20of%20Genuine%20Interharmonics.pdf

A Method to Determine the Existence of Genuine Interharmonics

The interharmonic group concept adopted by the IEC 61000-4-7 is very useful for addressing the need to monitor interharmonics in power systems. This paper shows that grouping spectral bins into interharmonics and harmonic components of 5Hz resolution could yield misleading information for cases where an interharmonic component's frequency is very close to a harmonic frequency. Since interharmonics in such cases can cause more severe waveform modulation, the interharmonic grouping scheme needs to be improved. A signal processing method that can separate interharmonic and harmonic components in close proximity is, therefore, proposed in this paper to address this need. Field data analysis showed that the proposed method was able to extract interharmonic and harmonic components correctly.

Jin Hui

Papers

Assessing Utility Harmonic Impedance Based on the Covariance Characteristic of Random Vectors

Utility Harmonic Impedance Measurement Based on Data Selection

A Method to Improve the Interharmonic Grouping Scheme Adopted by IEC Standard 61000-4-7

A Method to Determine the Existence of Genuine Interharmonics

An improved interharmonic grouping scheme based on IEC 61000-4-7