Walid G. Morsi

Reformulating Three-Phase Power Components Definitions Contained in the IEEE Standard 1459–2000 Using Discrete Wavelet Transform

Power components definitions contained in the IEEE Standard 1459-2000 for unbalanced three-phase systems with nonsinusoidal situations are represented in the frequency domain based on Fourier transform (FT). However, FT suffers from the high computational effort especially when the number of phases increases and it is unable to provide information concerning time content because it provides only an amplitude-frequency spectrum. On the other hand, the discrete wavelet transform (DWT) preserves both time and frequency information while reducing the computational effort through dividing the frequency spectrum into bands and thus overcomes the limitations of FT. In this paper the three-phase power components definitions contained in the IEEE Standard 1459-2000 are reformulated using the DWT and thus redefined in the time-frequency domain. Also in order to study system unbalance, the concept of symmetrical components is defined in the wavelet domain. The results obtained from applying the IEEE Standard definitions and the DWT-based definitions to balanced and unbalanced three-phase systems under nonsinusoidal operating conditions, indicate that the DWT-based definitions are very accurate and the problem of spectral leakages can be reduced by suitable choice of the mother wavelet and the wavelet family. The DWT-based definitions are useful in studying nonstationary waveforms.

A New Perspective for the IEEE Standard 1459-2000 Via Stationary Wavelet Transform in the Presence of Nonstationary Power Quality Disturbance

Power components, power factors, and pollution factor are defined according to the IEEE standard 1459-2000 based on the fast Fourier transform (FFT). However, the FFT in the presence of nonstationary power quality (PQ) disturbances results in inaccurate values due to its sensitivity to the spectral leakage problem. In this paper, a new perspective for the IEEE standard 1459-2000 definitions is introduced using the stationary wavelet transform (SWT). As a time-frequency transform, the SWT can provide variable frequency resolution while preserving time information without spectral leakage as the FFT. Moreover, unlike other time-frequency transforms, such as discrete wavelet transform (DWT), SWT possesses the time-invariance property that keeps the time and frequency characteristics throughout all of the decomposition levels. Results of different case studies including stationary, nonstationary of synthetic, and real PQ disturbances proves the effectiveness of applying the SWT over FFT or DWT.

Wavelet Packet Transform-Based Power Quality Indices for Balanced and Unbalanced Three-Phase Systems Under Stationary or Nonstationary Operating Conditions

Three-phase power-quality indices (PQIs) can be used to quantify and hence evaluate the quality of the electric power system (EPS) waveforms. The recommended PQIs are defined based on the fast Fourier transform (FFT) which can only provide accurate results in case of stationary waveforms, however in case of nonstationary waveforms even under sinusoidal operating conditions, the FFT produces large errors due to spectral leakage phenomenon. Moreover, FFT is incapable of providing any time-related information which is a required property when dealing with time-evolving waveforms since it can provide only an amplitude-frequency spectrum. Since wavelet packet transform (WPT), which is a generalization of the wavelet transform, can represent EPS waveforms in a time-frequency domain, it is used in this study to define and formulate three-phase PQIs. In order to handle the unbalanced three-phase case, the concept of equivalent voltage and current is used to calculate those indices. The results of four numerical examples considering stationary and nonstationary, balanced and unbalanced three-phase systems in sinusoidal and nonsinusoidal situations indicate that the new WPT-based PQIs are closer to the true values. In addition, phase and overall crest factors are redefined in the time-frequency domain using WPT while a new crest factor is introduced in this paper. The redefined crest factors and the new crest factor help identifying and quantifying the waveform impact based on the time-frequency information obtained from the WPT. New crest factor can only be determined via WPT, which proves the powerful of this method and its suitability to define three-phase PQIs in nonstationary operating conditions.

Defining Power Components in Nonsinusoidal Unbalanced Polyphase Systems: The Issues

Summary form only given. Defining power components for unbalanced three phase systems operating under nonsinusoidal conditions is an area of active research which spawned many theories. The approaches may be classified into two groups: the first is a bottom-up approach that extends well accepted definition of power components for single phase systems operating under ideal sinusoidal situations to the case of unbalanced three-phase systems in nonsinusoidal situations. The second group involves a top-down approach that tries to offer a definition for nonlinear polyphase systems in nonsinusoidal situations and apply it to linear single phase systems in sinusoidal situations by considering the former as the general case and the latter as a special case. This paper summarizes previously published approaches and concludes that none of the approaches in the literature can lead to power components definitions that satisfy all required power properties. Different analysis tools other than those based on frequency or time domain are recommended in this paper for future work.

Power Quality Assessment in Distribution Systems Embedded With Plug-In Hybrid and Battery Electric Vehicles

The impact of electric vehicles on power quality in electric distribution system is evaluated. Voltage deviations such as under/over voltage and voltage imbalance are probabilistically quantified using Monte Carlo. Moreover, distribution transformers overload and unbalance are assessed for different vehicle types (i.e., plug-in hybrid and battery electric), different vehicle penetration (up to 50%) while considering level 1 and level 2 charging. The results of Monte Carlo reveal that battery electric vehicles can cause more overload to distribution transformers compared to plug-in hybrid electric vehicles. Also level 2 and level 1 can be problematic resulting in secondary bus undervoltage and transformer unbalance, respectively.

Wavelet-Based Reactive Power and Energy Measurement in the Presence of Power Quality Disturbances

This paper investigates the performance of electronic reactive power/energy meters by evaluating differences that arise as a result of (1) the distinct operating principles of the meter and (2) the presence of stationary and nonstationary power quality disturbances. The paper also includes a comparative study to determine the effectiveness of using orthogonal, bi-orthogonal, or reverse bi-orthogonal wavelets for such application. Moreover, the paper identifies the reactive power quantities required for accurate assessment and monitoring of reactive energy in the presence of power quality disturbances. Finally, the paper provides recommendations on reactive power and energy measurement for future generations of smart meters.

A New Approach Based on Wavelet Design and Machine Learning for Islanding Detection of Distributed Generation

This paper presents a new approach based on wavelet design and machine learning applied to passive islanding detection of distributed generation. Procrustes analysis is used to determine the filter coefficients of a newly designed wavelet. To automate the classification process, machine learning algorithms are used to develop appropriate models. The IEEE 13-bus standard test distribution system simulated in PSCAD/EMTDC is used as a test bed to assess the performance of the proposed approach. The numerical results demonstrating the effectiveness of the proposed approach are discussed and conclusions are drawn.

Fuzzy-Wavelet-Based Electric Power Quality Assessment of Distribution Systems Under Stationary and Nonstationary Disturbances

Evaluating the electric power quality (EPQ) becomes very important task due to the widespread use of nonlinear loads, distributed energy resources (DERs) and the economic impact of poor EPQ. In a deregulated environment, having different power quality indices (PQIs) with different values has no significance unless they are combined into single value that could represent them. In this paper, a new fuzzy-wavelet packet transform based PQI is introduced that amalgamates the recommended PQIs after being redefined in the time-frequency domain using wavelet packet transform for compatibility purposes with nonstationary disturbances. In order to handle the uncertainties associated with the electric power system operations, fuzzy systems are used in this paper. In order to study the effect of wavelet filter length and the choice of the best wavelet basis function, the new fuzzy developed modules along with the reformulated PQIs are used in three case studies considering electric arc furnace load supplied from stationary low distorted voltage, stationary high distorted voltage and nonstationary distorted voltage (voltage dip) in addition to a real case study considering variable speed drive.

The most suitable mother wavelet for steady-state power system distorted waveforms

The proliferation of nonlinear load in the electric power system leads to steady-state waveform harmonic distortion. Since harmonic distortion has harmful effects on the electric power system, there is a need to analyze and hence accurately measure their values which is an issue of great concern especially in a deregulated environment. Conventional Fourier based analyzing tools have some limitations concerning frequency and time resolutions. Although wavelet transform overcomes these limitations, it suffers from the problem of spectral leakage which is related to the choice of the wavelet family and the mother wavelet used in the analysis. In order to minimize these errors, this paper presents an approach to select the most suitable wavelet family and the most suitable mother wavelet to achieve accurate measurement of steady-state harmonic distortion using the discrete wavelet transform (DWT). The proposed algorithm is simple and proves to be accurate when applied to two cases of different distortion level.

Smart grid: Challenges, research directions and possible solutions

Power system is migrating from the conventional grid to the smart grid creates many active research areas to realize the objectives and the expected requirements from it. Different challenges facing the transformation of the conventional grid into a smart grid exist and need to be addressed by future research. This paper identifies the challenges facing the development of the smart grid, future research directions and suggests possible solutions to these challenges therefore realizing the objectives and the expected requirements of the smart grid.