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Voltage sags are often manifested as the permanent or incipient faults occurred in the power system because of equipment malfunctions or failures. The incipient faults which are originally self-cleaning faults may repeatedly occur and gradually develop to a permanent fault after its first occurrence. The incipient fault detection is considered as a crucial task in predictive maintenance for power equipment such as transformers, circuit breakers, and underground cables. This paper proposes a hybrid method for incipient faults detection and classification. The proposed method firstly adopts two extraction methods and two feature measures to obtain seven peculiar features from voltage waveforms of abnormal phases recorded by power quality monitors at substations in a transmission network. Then, a feature selection method and the support vector machine combined with particle swarm optimization are applied to classify various types of incipient faults. Test results show that the proposed method contributes relatively accurate classification of incipient faults and can be employed as a useful tool for condition monitoring of major power equipment in the transmission network.

Voltage fluctuations caused by rapid reactive power consumption of loads and photovoltaic or wind generator output variations may produce flickers and cause undesired effects on electric power components and human eyes. This paper presents a hybrid approach for voltage fluctuations assessment by using a synchrosqueezing transform-based algorithm. The proposed method first gives characterization of voltage fluctuations through accurate extraction of the measured voltage envelope by the Hilbert transform. The synchrosqueezing transform and an unsupervised clustering method called mean shift are then applied to determine the number of frequency components and corresponding frequencies. It is followed by the implementation of the bandpass filters to detect the magnitude of each frequency component. The proposed hybrid method is tested by both simulations and field measurements. Results compared with other commonly seen methods show that the proposed method provides a more accurate assessment.

This paper presents a two-stage approach for planning photovoltaic solar distributed generation (PV-DG) units considering load variations by using biogeography-based optimization (BBO) method. The objective function components include the system power loss, voltage regulator tap changes, and quadratic penalty term of rms voltage profile at different load levels while against system operating constraints. The proposed method is tested using an IEEE 123-bus benchmark network and results are compared with two other nature-inspired methods to show its superiority.

This paper presents an improved dynamic voltage-current model of an ac electric arc furnace (EAF) for multiple operation stages and for the study of propagations of voltage fluctuations in a power network associated with the EAF in operating stages. The EAF model is developed based on wavelet-transform and neural-network-based methods by training actual measured EAF current and voltage data. The proposed EAF model is then implemented in an actual 161-kV power system for simulations. The voltage fluctuations at other buses due to the EAF in operation are then assessed. Simulation and measured results show that the improved hybrid EAF model is accurate and is suitable for voltage fluctuation assessment when the actual measurements in the power network are limited or not available while the EAF is in operation or before the similar types of EAFs are to be installed in the system.

Penetration of grid connected renewable energy systems and smart loads based on power electronics technology has been increasing in low and medium voltage distribution. Power Electronics is a key technology for distribution networks which can transfer electrical power from renewable energy sources to grids or generate regulated frequency and/or voltage for different loads such as variable speed drives and battery chargers. New demands for a) cost and size reduction, b) performance and quality improvement and c) flexibility on power management have promoted power electronics applications extensively in industrial, commercial and residential sectors such as transportation, utility and home appliances in recent years.

In this paper, a stochastic approach is applied to determine the photovoltaic (PV) hosting capacity in a distribution feeder. The hosting capacity is determined accounting for the four voltage quality criteria: overvoltage, voltage deviation, dynamic voltage drop, and voltage unbalance. By applying the stochastic approach, a large number of potential PV deployment scenarios are simulated in a benchmark distribution feeder. While considering the unpredictability of future PV deployments, both sizes and locations are regarded as randomly generated factors. Simulations for assessments of voltage quality impacts are quantified and PV hosting capacities are statistically determined. In addition, smart inverter functions are included to improve voltage quality and enhance PV hosting capacity.

Drastic variations of reactive power consumed by electric arc furnaces (EAFs) often lead to significant voltage fluctuations at the connecting network bus and yield noticeable flickers of lighting devices as well as cause malfunctions of the electrical equipment. If the flicker severity levels are predictable, corrective solutions such as controls of EAF electrodes and reactive power compensators can be developed to mitigate the voltage fluctuations. This paper presents a hybrid approach that combines an improved radial basis function neural network (IRBFNN) and Grey model for the forecast of flicker severity levels. Field measurements are used to train and implement the forecasting model. Test results of ΔV10, short-term flicker severity (Pst) and long-term flicker severity (Plt) obtained by the proposed and five other methods are then under comparisons. Results indicate that more accurate flicker forecast is obtained by adopting the proposed method.

With the advances of technologies, high quality of electric power is in demand. The power quality (PQ) disturbances occurred in the power system may cause voltage and current deviation from their nominals, which can result in serious damages or equipment malfunctions. Therefore, efficient detection and classification of PQ disturbances in a transmission system is of great importance for maintaining reliable system operation. This paper presents a hybrid approach to classify PQ disturbances by using support vector machine (SVM), discrete wavelet transform (DWT), and discrete Fourier transform (DFT) to extract features from a good number of actual measured PQ events occurred in a transmission system. Results show that the proposed method can provide fast and accurate classifications of the measured PQ events.

This paper proposes a discrete wavelet transform (DWT) and radial basis function neural network (RBFNN)-based method for modeling the dynamic voltage-current (v- i)characteristics of the ac electric arc furnace (EAF). The objective of the study is to develop a complete model of the EAF including different operation stages, and the model can be used as a harmonics and flicker source in its connected power system for the power-quality penetration or mitigation study, where the developed model can be embedded in the power system implemented by a commonly seen simulation tool, such as Matlab/Simulink. In the study, a combination of the DWT and the sequential RBFNN with parameters initialization algorithm is proposed to build the EAF v- i characteristics with enhanced lookup tables for different operation stages, where the field measurements of the EAF voltage and current are used to train the RBFNN for modeling the EAF load. Simulation results obtained by using the proposed model are compared with different measured data. It shows that the solution procedure accurately models the EAF dynamic v- i behavior. The proposed method also can be applied to model other highly nonlinear loads to assess the effectiveness of compensation devices or to perform relative penetration studies.

Magnitude and duration are important characteristics when performing tracking of voltage variations. Accurate characterization of voltage variations relies much on the precise identification of frequencies of the measured signals. Although the Prony's method can provide high resolution for frequency estimation, the computational burden in the root-finding process is a crucial problem. A modified Prony-based solution procedure for voltage variation tracking is proposed in this paper. By providing a set of filters, the transfer polynomial with high estimation order in Prony's model can be efficiently reduced. The performance of the proposed method is validated by testing the generated and actual measured voltage signals. Results are compared with those obtained by typical Prony's method, namely, fast Fourier transform, adaptive linear neural network, and Kalman filtering. It shows that the proposed method is more accurate regardless of interferences of the power system frequency deviation, harmonics, and interharmonics, where both voltage variations and harmonics can be simultaneously detected.

SUMMARY This paper proposes an efficient method to obtain the equivalent fundamental positive-sequence voltage for determining the shunt active power filter (APF) reference compensation currents, where the source voltage magnitude and phase angle at the fundamental frequency are detected by a simplified adaptive linear combiner neural network. The APF reference current calculator is developed and is realized on the DSP board through processor-in-the-loop (PIL) simulation for validating the effectiveness of the proposed APF control strategy, where the source voltages and the load currents are both distorted and unbalanced. In addition, results obtained based on the true positive-sequence fundamental source current after APF compensation and another classic approach are included for comparison. It is shown that results obtained by the PIL simulations with the proposed and compared methods agree very well. The proposed APF reference compensation current strategy is simple and practical, which provides a cost-effective and computationally efficient manner for the APF controller implementation with PIL simulations. Copyright © 2013 John Wiley & Sons, Ltd.

The demand of renewable energy resources has become an important issue for green power generation in many countries. With the increasing photovoltaic generation in the distribution system, voltage fluctuation problems often present in the PV-connected grid affected by the moving cloud shadows. This paper presents a study to evaluate impacts on voltage quality due to cloud shadows movement over high-penetration PVs in a distribution power system in southern Taiwan. The moving-cloud shadow model is built under Matlab/Simulink incorporated with OpenDSS and is applied to show voltage fluctuations. Results show that the developed simulation tool is suitable for assessment of the PV output versus voltage changes due to cloud moving shadow impacts.

This paper proposes an efficient backward and forward sweep algorithm for the three-phase power flow analysis of weakly meshed distribution system. In the backward sweep, the Kirchhoff's circuit laws are firstly used to calculate each line current and the upstream bus voltage of each line or a transformer branch. Next, the linear proportional principle is applied to find the ratios of the specified (or new) and the calculated bus voltages of the decomposed real and imaginary parts of the network. The compensation method is used to break meshes and to calculate the current injections at each end bus created by breaking the mesh. A useful bus indexing scheme is also proposed to determine the updated voltages at the junction and/or terminal busses for the six decomposed networks in the forward sweep. The procedure repeats and stops after the voltage mismatch of each pair of end busses of the opened mesh and the mismatch of the calculated and specified voltages at the substation bus are less than the predefined threshold value. The proposed method is tested by three IEEE benchmark systems with meshes, and with default system data and different system conditions. Results show that the proposed algorithm is efficient, accurate, and robust in comparing with the commonly used backward/forward sweep method for weakly meshed networks.

Applications of solid-state converters and inverters for adjustable speed drives (ASDs) are popular in industrial systems and lead to a significant amount of harmonic and interharmonic currents being injected into the connected system. This paper presents an accurate analytical approach for the assessment of the harmonic and interharmonic currents generated by the voltage-source inverter-fed ASDs operated under unbalanced supply voltages, where the commutaton effect of the ASD converter and the detailed motor circuit model with various load levels are included. To validate the accuracy of the proposed approach, simulation results are performed by comparing those obtained by a time-domain simulation tool and by laboratory tests. It is shown that the proposed method can effectively calculate the harmonic and interharmonic currents produced by the ASD, either under balanced or unbalanced supply-voltage conditions.

Selection of a suitable method among various techniques for assessment of harmonic and interharmonic components of a measured voltage or current waveform is not an easy task for the students. A good start is to understand the relationship between the analysis techniques and the measured parameters. In this paper, several commonly used methods for time-varying harmonic and interharmonic detection of measured waveforms are reviewed and implemented in an integrated virtual instrumentation. Compared from the aspect of frequency identification for the reviewed methods, general guidelines for performing harmonic and interharmonic detection are also developed for the educational purpose.

Field measurements of voltage and current are the most effective way for characterizing the electric response of an ac electric arc furnace that describes its nonlinear behavior. Sufficient measured information can be adopted to determine the background harmonic level in a power system, to characterize specific sources of harmonics, and to develop an appropriate nonlinear voltage–current characteristic. In this paper, a curve-fitting-based method called cubic spline interpolation is proposed to model the voltage–current characteristic of an ac electric arc furnace in the steady state. Meanwhile, the actual measured data are collected for modeling use. Two classic methods, harmonic current injections and equivalent harmonic voltage sources, for modeling the electric arc furnace load are reviewed and used to evaluate the performance of proposed model. Results obtained from the measured data and computer simulations of the three electric arc furnace models are then compared according to the voltage and current waveforms, as well as the voltage–current characteristic. It is shown that the proposed model is more accurate than the two classic approaches for harmonic assessment of electric arc furnaces and can be used for modeling similar types of nonlinear loads in the harmonic penetration study.

It is known that artificial neural network is a powerful scheme for function learning and modeling nonlinear loads. However, a direct application of artificial neural network for modeling time-varying loads may lead to inaccuracies. This paper presents an accurate neural-network-based method for modeling the highly nonlinear voltage-current characteristic of an ac electric arc furnace (EAF). The neural-network-based model can be effectively used to assess waveform distortions, voltage fluctuations, and performances of reactive power compensation devices associated with the EAF in a power system. Simulation results obtained by using the proposed model are compared with the actual measured data and two other traditional neural network models. It is shown that the proposed method yields favorable performance and can be applied for modeling similar types of nonlinear loads for power engineering studies.

Voltage fluctuations caused by rapidly changing loads in the power systems may give rise to noticeable illumination flickers of lighting equipment. The voltage flickers can also cause malfunctions in many electric devices. This paper presents a digital implementation of flickermeter in the hybrid time and frequency domains based on IEC standard 61000-4-15. In addition, this paper proposes a new demodulation method to extract the voltage envelope. Simulations and actual measurements show that the digital implementation with the proposed method yields relatively accurate flicker measurements.

This paper presents a new procedure to track the disturbance source location of voltage sags and shunt capacitor switching transients in a power system based on branch current measurements. In the proposed method, the power-quality metering locations are first determined by the sensitivity of the system fault-current level to the fault voltage. Then, a current deviation index for representing the change of each measured branch current rms magnitudes before and after the disturbance is calculated to track the disturbance source location within an area confined by the directions of the top-priority branches. The IEEE 30-bus benchmark system and an actual transmission system with recorded power-quality disturbance events are used to illustrate the usefulness of the proposed method. Simulation results obtained by the proposed method are also compared with those obtained by a previously developed approach and by actual recorded data. By observing the results, it shows that the proposed method is efficient and accurate to track the source area of voltage sags or shunt capacitor switching transients.

A new steady-state approach for determining the optimal shunt active power filter (APF) reference compensation current injections to control harmonic currents generated by the nonlinear load and for reactive power compensation under ideal or nonideal supply voltages are presented in the paper. Conventionally, the compensation currents injected by the shunt APF are determined to eliminate harmonic currents of the load. However, when considering different APF performance indices such as minimizing source current distortion and maximizing compensated load power factor, the issues related to sizing the APF to meet IEEE-519 harmonic current limits and other constraints such as current imbalance limits and minimum load power factor requirement are rarely investigated. In the paper, a new theory of APF control in the a-b-c reference frame is proposed to determine the APF current injections to meet different constraints with an optimal APF size, where the filter control strategy is formulated as a nonlinear programming problem and is solved to find the optimal current injections. Results obtained by simulations with Matlab/Simulink show that the proposed approach is more flexible and effective than the conventional approaches on compensating reactive power and harmonic currents of the load.

Summary form only given. Applications of solid-state converters for adjustable speed drives (ASDs) are popular in industrial systems. The AC/DC/AC conversion system, frequently used to provide ac voltages with adjustable frequency/magnitude in the ASDs, consists of a voltage source inverter (VSI) fed by a three-phase diode-bridge rectifier, which generates significant amount of line harmonic and interharmonic currents into the supply system and may cause undesired effects on other power system components. This paper presents an analytical approach for characterizing the current harmonics and interharmonics of the VSI-fed ASD injected into the supply system in steady state, where the circuit models for the rectifier, the dc link, the PWM inverter, and the ac motor are considered in the analysis. The accuracy of the results obtained by the proposed model is demonstrated by comparing with those obtained by using the time-domain simulation tool, Simulink of Matlab, and by laboratory tests. It is shown that the proposed approach is effective to characterize current harmonics and interharmonics generated by the ASD, while the solution accuracy and the computational efficiency are still maintained.

The shunt active power filter has proved to be a useful device to eliminate harmonic currents and to compensate reactive power for linear/nonlinear loads. This paper presents a novel approach to determine reference compensation currents of the three-phase shunt active power filter (APF) under distorted and/or imbalanced source voltages in steady state. The proposed approach is compared with three reviewed shunt APF reference compensation strategies. Results obtained by simulations with Matlab and Simulink show that the proposed approach is more effective than the reviewed approaches on compensating reactive power and harmonic/neutral currents of the load, even if the source voltages are severely distorted and imbalanced. In addition, the proposed approach yields a simpler design of the shunt APF controller.

A microgrid integrates renewable energy and other forms of distributed energy resources (DER) to serve its loads. The microgrid can increase the DER penetration and improve power quality and reliability through appropriate management. Under the normal operation, a microgrid is connected to the utility grid, and each DG provides a preset power to the network through active/reactive power control (PQ control), whereas the utility grid is responsible for supplying/absorbing any power discrepancy. When the microgrid is disconnected from the utility grid, at least one unit switches to droop control from PQ control in order to regulate the voltage and frequency in the microgrid and continue to supply power to local load. This paper adopts Matlab/Simulink to model and simulate an actual ac microgrid with proposed control strategies. Several operation conditions including grid connected mode, islanding mode and load variation are simulated. Results show that the proposed control strategies for the microgrid are effective.

This paper proposes a discrete wavelet transform (DWT) and radial basis function neural network (RBFNN) based method for modeling the dynamic voltage-current (v-i) characteristics of the ac electric arc furnace (EAF). The objective of the study is to develop a complete model of the EAF including different operation stages and the model can be used as a harmonics and flicker source in its connected power system for the PQ penetration or mitigation study, where the developed model can be embedded in the power system implemented by a commonly seen simulation tool such as Matlab/Simulink. In the study, a combination of the DWT and the sequential RBFNN with parameters initialization algorithm is proposed to build the EAF v-i characteristics with enhanced look-up tables for different operation stages, where the field measurements of the EAF voltage and current are used to train the RBFNN for modeling the EAF load. Simulation results obtained by using the proposed model are compared with different measured data. It shows that the solution procedure accurately models the EAF dynamic v-i behavior. The proposed method also can be applied to model other highly nonlinear loads to assess the effectiveness of compensation devices or to perform relative penetration studies.

This paper presents a study of applying the equivalent effective voltage concept according to IEEE Standard 1459-2010 for determining reference compensation currents of the three-phase three-wire shunt active power filter in the a-b-c reference frame. The APF reference current calculator is developed and is realized on the DSP board through processor-in-the-loop simulation for validating the effectiveness of the proposed APF control strategy.

This letter proposes a curve-fitting approach for modeling fluorescent lamp voltage-current characteristics based on measured lamp voltage and current. The fluorescent lamp conductance is considered as a series of piecewise cubic polynomials that describes the nonlinear voltage-current characteristic of the lamp. The proposed model has been tested with a 10-W conventional 60-Hz fluorescent lamp and a 20-W high-frequency energy-saving lamp. By comparing the measured and simulated results, it shows that the proposed model can accurately model the lamps for harmonic studies.

This letter presents an improved backward/ forward sweep algorithm for three-phase load-flow analysis of radial distribution systems. In the backward sweep, Kirchhoff's Current Law and Kirchhoff's Voltage Law are used to calculate the upstream bus voltage of each line or a transformer branch. Then, the linear proportional principle is adopted to find the ratios of the real and imaginary components of the specified voltage to those of the calculated voltage at the substation bus. In the forward sweep, the voltage at each downstream bus is then updated by the real and imaginary components of the calculated bus voltage multiplying with the corresponding ratio. The procedure stops after the mismatch of the calculated and the specified voltages at the substation is less than a convergence tolerance. The proposed algorithm is tested with three IEEE benchmark distribution systems. Results show that the algorithm is accurate and computationally efficient in comparing with two other commonly used methods

This letter presents a new control strategy to determine the reference compensation voltages of a series active power filter (APF) operated under nonideal supply voltages in the steady-state. By employing the proposed control strategy, the load-side voltages can be maintained as being sinusoidal and balanced. The effectiveness of the proposed control strategy is demonstrated through simulations by the use of Pspice. Results show that the expected series APF performances are achieved.

Overhead lines in a transmission system are the most vulnerable component to natural or human attacks that lead to different severities of faults and create power quality (PQ) disturbances such as voltage sags. The transmission network failure can cause the supply voltage interruptions and significant economic loss. The faulted lines or busses must be quickly identified and taking required remedial actions becomes an urgent issue to maintain the reliable power system operation. This paper gives an overview of the faulted bus or line tracking methods and performs a comprehensive assessment. Then a practical meter placement strategy for PQ monitoring is adopted to implement the proposed fault tracking algorithm. In the study two time-domain simulation tools are used to simulate and analyze the transmission system. Actual measured field data of a 345-kV transmission system is used to verify the usefulness of the proposed fault tracking algorithm.

Precisely forecasting the flicker level is important for drastic voltage fluctuations associated with the rapid reactive power consumptions of electric arc furnace (EAF) loads. This paper presents a prediction model based on grey theory combined with radial basis function neural network (RBFNN) for the forecast of flicker severity caused by the operation of a dc and an ac EAF loads, respectively. Test results based on the proposed model are compared with two other neural network methods. It shows that more accurate forecast is achieved for the flicker prediction based on the proposed method.

The operation of electric arc furnaces (EAFs) with drastic and random voltage-current characteristics creates considerable power quality problems in the connected power network. Because of the nonlinear behaviors of the EAF loads during operations, serious voltage fluctuations have been observed at busses that connect the substation transformer and cause frequent operations of the on-load tap changer (OLTC) of the transformer, which may shorten the OLTC life and affect the voltage quality. To reduce the number of switching operations of the OLTC, it is necessary to adopt mitigation solutions. This paper presents a feasibility study of installing a static var compensator (SVC) in an actual substation network supplying two large EAF loads for mitigating the voltage fluctuation and the number of OLTC operations. The effectiveness of installing the SVC at selected busses and the corresponding size are then reported.

It is known that rapid voltage fluctuations caused by electric arc furnace loads may generate significant levels of flickers, which have negative impacts to human eyes and power system components. This paper proposes a grey predictor model for the forecast of flicker levels produced by an electric arc furnace load. Actual measured data are adopted to implement the predictor model. Test results based on the proposed model are compared with two other neural network methods. It shows that more accurate forecast is achieved for the flicker prediction based on the proposed method.

It is known that artificial neural network is a powerful scheme for function learning and modeling nonlinear loads. However, a direct application of artificial neural network for modeling time-varying loads may lead to inaccuracies. This paper is to present an accurate neural network-based method for modeling the highly nonlinear voltage-current characteristic of an AC electric arc furnace. The neural network-based model can be effectively used to assess waveform distortions, voltage fluctuations, and performances of reactive power compensation devices associated with the electric arc furnace in a power system. Simulation results obtained by using the proposed model are compared with the actual measured data and two other traditional neural network models. It is shown that the proposed method yields favorable performance and can be applied for modeling similar types of nonlinear loads for power engineering studies.

Effective detection of power quality events is an important issue for maintaining reliable operations of power systems. Under different measuring environment, detection methods usually need different requirements. In this paper, the performances of several commonly seen methods for the detection of voltage sags are evaluated and compared.

Wind turbines may cause significant impacts on the power quality of their connected grid. Voltage fluctuations produced by wind turbines are usually due to wind speed variations, power and voltage fluctuations. This paper presents simulations for numerical models of two wind turbine schemes, fixed and variable speed types, by using Matlab/Simulink, where simplified analytical model of wind turbines for voltage spectral analysis are illustrated for the power quality assessment.

Model-based simulations by commercial simulation packages, such as EMTP/ATP, PSCAD/EMTDC and MATLAB/SIMULINK often provide convenience for testing and analyzing the power quality studies. Nowadays, the real-time simulation techniques are highly developed to enhance the capabilities of traditional off-line simulations. This paper presents the real-time simulation techniques for a shunt active passive filter design. A three-phase four-wire shunt active passive filter operated under non-sinusoidal source voltages which supply unbalanced linear and nonlinear loads is tested with a PC cluster-based real-time simulator. Traditional off-line simulation with variable-step solver is also included for comparison of solutions. Results indicate that satisfactory solutions are obtained with using real-time simulation techniques for the active passive filter design.

This paper presents an efficient time-domain algorithm to characterize harmonic currents generated by a cluster of adjustable speed drives operated under either balanced or imbalanced supply voltages and asymmetrical source impedances, where the Poincare map-based approach is adopted as the solution method. An actual industrial rolling mill system with several dc motor drives operating in parallel is under test to show the usefulness of the proposed method. Simulation results are compared with those obtained by actual measurements. It shows that the harmonic currents determined by the proposed method well agree with those obtained by actual measurements. The proposed algorithm is relatively accurate, computationally efficient, and robust in characterizing harmonic currents generated by the multiconverter loads.

Fluorescent lamps are increasingly used in daily life, in which the gas discharge is the lighting principle. Due to the internal nonlinear characteristics of the lamp tube, harmonic currents are produced when the voltage source is directly connected to the lamp. Furthermore, in order to maintain the stable output of the lighting device, the ballast circuit is used. In practice, accurate fluorescent lamp models for harmonic studies are of importance to understand harmonic pollutions caused by fluorescent lamps. This paper presents a fluorescent lamp dynamic conductance model by using cubic spline interpolation method. To show the usefulness of the proposed model, a 10-W conventional 60Hz fluorescent lamp and a 20-W high-frequency fluorescent lamp are under tested. The laboratory experiments are also performed to verify the accuracy of the proposed model.

IEEE Std 519-1992 is regarded as one of the most widely used power quality standards for both electric utilities and their customers. Among several difficult aspects of applying IEEE Std 519, two issues are related to modeling and measurement of harmonic currents and voltages produced by nonlinear loads. This paper intends to discuss ambiguous aspects of the modeling and measurement when applying the standard.

Field measurements of voltage and current is the most effective way for characterizing the electric response of an EAF that describe the nonlinear behavior of AC EAF loads. Sufficient measured information can be adopted to develop an appropriate EAF model. In this paper, two classic methods based on measured data, harmonic current injections and equivalent harmonic voltage sources, for the EAF load modeling are reviewed. For comparison, two advanced methods based on actual recorded data, cubic spline interpolation and radial basis function neural network (RBFNN), are also proposed to model the EAF load. A steel plant power system with EAF loads is used for field measurements and computer simulations. Comparisons between the results of measured data and simulations for the four EAF models are being made according to the voltage/current waveforms and voltage-current characteristics. It is shown that the advanced models yield better performance than classic models of the EAF.

This paper presents a fuzzy-based approach for the placement of capacitor banks in a harmonics-polluted distribution system. In the problem the objective function is the total system power loss, while the constraints are the RMS voltage and the total harmonic voltage distortion (THDv) limits at each bus, as well as the limit of the available capacitor units to be placed. In the study the system power loss, the bus RMS voltage, the THDv at each bus, and the capacitor site suitability are modeled as fuzzy membership functions. A useful solution algorithm is then proposed to find the best capacitor locations by testing an actual distribution system. Numerical experiences show that the proposed method yields favorable results for the capacitor placement problem.

This paper presents a new theory of optimization-based control strategy to determine the reference compensation voltages of a series active power filter (APF) operated under non-ideal supply voltages in the steady state. With using the proposed optimal control strategy, the load-side voltages can be flexibly maintained being balanced and sinusoidal. The usefulness of the proposed control strategy is demonstrated through simulations by using Matlab. Results show that the proposed method works well for series APF control with an optimal size.

This paper presents a simplified forward and backward approach for load flow analysis in radial distribution system. The proposed method includes two phases. At Phase I (forward sweep), the KCL and KVL are used to find the calculated voltage for each bus located at upstream of each line segment or transformer. At Phase II (backward sweep), the linear proportion concept for real and imaginary decomposition is adopted to find the ratios of real and imaginary parts of specified voltage to the calculated voltage at each upstream bus. Then, the voltage at each downstream bus is updated by real and imaginary parts of initial or calculated voltage multiplying with the corresponding ratios, respectively. The solution procedure is terminated after the mismatch of calculated voltage and specified voltage of substation is less than the tolerance value. The proposed method is tested with three IEEE distribution benchmark systems. Results show that the proposed method is effective, computationally robust, and faster than conventional forward/backward sweep and the ladder iteration method.

This paper presents a new control strategy to determine the reference compensation voltages of a series active power filter (APF) operated under non- ideal supply voltages in the steady state. With using the proposed control strategy, the load-side voltages can be maintained being sinusoidal and balanced. The effectiveness of the proposed control strategy is demonstrated through simulations by using Pspice. Results show that the expected series APF performances are achieved with adopting the new control strategy.

This paper presents a study of passive harmonic filter planning in the power system. The purpose is to find the optimal locations for harmonic filters among existing capacitor buses in the power network, based on sensitivity analysis. The planning problem is formulated as an unconstrained optimization problem. The inductor size of each shunt filter is then determined while IEEE-519 recommended harmonic voltage and voltage distortion limits are maintained at each network bus. Simulation results obtained by testing a distribution system show that the proposed approach is robust, computationally efficient and suitable for siting and sizing passive harmonic filters.