Hooman Erfanian Mazin

Assessing the Collective Harmonic Impact of Modern Residential Loads—Part I: Methodology

The proliferation of power-electronic-based residential loads has resulted in significant harmonic distortion in the voltages and currents of residential distribution systems. There is an urgent need for techniques that can determine the collective harmonic impact of these modern residential loads. These techniques can be used, for example, to predict the harmonic effects of mass adoption of compact fluorescent lights. In response to the need, this paper proposes a bottom-up, probabilistic harmonic assessment technique for residential feeders. The method models the random harmonic injections of residential loads by simulating their random operating states. This is performed by determining the switching-on probability of a residential load based on the load research results. The result is a randomly varying harmonic equivalent circuit representing a residential house. By combining multiple residential houses supplied with a service transformer, a probabilistic model for service transformers is also derived. Measurement results have confirmed the validity of the proposed technique. The proposed model is ideally suited for studying the consequences of consumer behavior or regulatory policy changes.

Determining the Harmonic Impacts of Multiple Harmonic-Producing Loads

Identifying harmonic sources in a given power system is an important task for utility power quality management. This paper presents a new class of harmonic source identification problems: how to quantify the harmonic impact of several known harmonic-producing loads on the harmonic levels observed at a network location. The paper first defines the problem and proposes a harmonic impact index to theorize the problem. The paper then presents a statistical-inference-based method to estimate the index. The data required for this analysis are the harmonic voltage and current magnitudes continuously collected by the existing power quality monitors. The characteristics of the proposed method are investigated through case studies. Finally, additional applications and improvements of the proposed method are discussed.

A Study on the Harmonic Contributions of Residential Loads

This paper presents a measurement technique to determine the harmonic sources and impedances of residential houses at the utility metering point. The results are then applied to quantify harmonic and current contributions of the residential premises. Four residential houses are investigated by using the proposed method. The characteristics of the load-side harmonic impedances and sources are studied, and their harmonic contributions are determined. The results show that voltage distortion is affected mainly by background harmonic sources that exist within the supply system. The current harmonics are affected by the residential loads and the supply system.

A method to determine the harmonic contributions of multiple loads

This paper presents a data correlation based idea and associated technique for determining the individual harmonic impact of multiple harmonic-producing loads scattered in a power system. The technique uses continuously recorded voltage and current data at each load point. The data are processed to determine the degree of association among the harmonic level at a measurement point and the behaviors of loads monitored. The results, degree of association, can be used to estimate the harmonic impact of each load. A real life case is used to illustrate the proposed technique. It is found that the technique can reveal the harmonic impact of the loads if the data points are selected judiciously.

A Novel Genetic Programming Approach for Frequency-Dependent Modeling

Frequency-dependent modeling of devices and systems is a common practice in several fields, such as power systems, microwave systems, and electronics systems. The modeling process usually involves converting the tabulated frequency-response data into a compact equivalent circuit model. The main drawback of the currently existing methods such as vector fitting is that the obtained model is often nonpassive, leading to unstable simulations. In order to overcome this problem, this paper proposes a genetic programming (GP) approach to generate equivalent circuits with guaranteed passivity. The proposed method starts with a nonoptimal initial equivalent circuit. Both the elements and the topology of this circuit are then evolved by the proposed GP-based method, and an accurate equivalent circuit is obtained. Key ideas and detailed algorithms are presented in this paper. Finally, the performance of the proposed method is verified by using different case studies.

An Impedance-Based Approach for Identifying Interharmonic Sources

This paper proposes a new method for identifying the interharmonic source location in power systems. The method is based on the interharmonic impedances measured at the metering points, and is inspired by the fact that the impedance of interharmonic-generating loads at that frequency is much higher than that of the utility system. This method represents an improvement over the traditional power-direction method, as the new method is more robust and less prone to erroneous identification. The issues associated with data reliability are addressed, and a set of data reliability criteria is presented. The effectiveness of the new method has been verified through simulation studies and field measurements.

Data segmentation algorithms for a time-domain harmonic source modeling method

Nowadays, with a fast increasing in renewable energy applications and vast deployment of plug-in electric vehicle, power quality issue becomes more important than before because of considerable harmonic current injected into grid. To better manage these distributed energy sources/loads and reduce harmonic pollution, establishing more accurate harmonic source models for them becomes very necessary. Traditionally, harmonic source is described as a fixed-parameter model, which is not good enough to describe time-varying harmonic source. In this paper, a time-domain modeling method is firstly explained, which enables the study on time-varying harmonic source model. Then two different data segmentation algorithms to support this model based on the stability of current magnitude and phase angle are developed and explained respectively using a group of data acquired from field. One is developed from statistical perspective while the other is based on slope of curve. Comparison is presented to explain their unique characteristics and synthesizing of both algorithms is also illustrated. The results of algorithms are shown to be satisfactory.

Determining the harmonic impacts of multiple harmonic-producing loads

Identifying harmonic sources in a given power system is an important task for utility power-quality (PQ) management. This paper presents a new class of harmonic source identification problems: how to quantify the harmonic impact of several known harmonic-producing loads on the harmonic levels observed at a network location. This paper first defines the problem and proposes a harmonic impact index to theorize the problem. This paper then presents a statistical-inference-based method to estimate the index. The data required for this analysis are the harmonic voltage and current magnitudes continuously collected by the existing PQ monitors. The characteristics of the proposed method are investigated through case studies. Finally, additional applications and improvements of the proposed method are discussed.

On the reliability of real measurement data for assessing power quality disturbances

This paper is primarily focused on assessing the reliability of real recorded data, which is used for several applications in analyzing power quality disturbances. The prime goal becomes, for that reason, to develop a set of reliability criteria to improve the data selection. Some of the identified reliability indices are such as quantization noises, frequency resolution, energy levels, data dispersion, frequency-domain coherence and time-domain correlation. As a motivation for the presented theory, two major applications are described in this paper: the estimation of power system parameters at harmonic frequencies, and the identification of interharmonic polluting loads. These criteria are explained in detail as a guide for rejecting unreliable data used when analyzing power quality disturbances.