Yu-Jen Liu

A Neural-Network-Based Method of Modeling Electric Arc Furnace Load for Power Engineering 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.

On Real-Time Simulation for Harmonic and Flicker Assessment of an Industrial System With Bulk Nonlinear Loads

This paper presents application experiences of real-time simulation (RTS) techniques for harmonic and flicker studies of an industrial power system, where the system and nonlinear loads are properly modeled. A PC-cluster-based real-time parallel simulator is implemented under MATLAB/SIMULINK, where the studied system consists of an ac electric arc furnace, dc and ac motor-drive loads, and the static var compensator. Guidelines for model partition of the studied system and the solver settings under an RTS environment are reported. In addition, the most commonly used offline simulation with variable-step solver and the actual field measurements are included for comparison. Results indicate that the RTS achieves satisfactory solution accuracy within much less execution time and can be applied for more complicated studies such as installing new nonlinear loads with different levels of model complexities or designing/tuning mitigation devices of power-quality disturbances, where the repeated time-consuming analysis is required.

Mayr's Equation-Based Model for Pantograph Arc of High-Speed Railway Traction System

This letter presents an extended Mayrs equation-based model for the pantograph detachment arc of the high-speed railway traction system. The proposed model is composed of Mayrs model for arc behavior control and time-controlled switches for starting pantograph detachment and reattachment events, which are developed by MODELS language and TACS in Electromagnetic Transients Program/Alternate Transients Program. With the combination of a traction motor drive circuit, an effective simulation is performed to observe the harmonic spectrum of pantograph current that is caused by pantograph detachment arcs. By comparing this with the actual measurements for validation, it shows that the proposed arc model is useful for estimating the harmonic frequency range of the pantograph arc current and for power-quality studies.

Modeling voltage-current characteristics of an electric arc furnace based on actual recorded data: A comparison of classic and advanced models

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.

A New Approach for Modeling Voltage–Current Characteristics of Fluorescent Lamps

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.

Power quality measurements of low-voltage distribution system with smart electric vehicle charging infrastructures

The introduction of electric vehicles in currently urban transportation system becomes tendency and attractive alternation to traditional fuel cars. Electric vehicles include certain different types and are powered through electric vehicle chargers which are elements in an infrastructure that supplies electric energy for the recharging of the plug-in electric vehicles. There has been much more concern expressed over the power quality issues caused by electric vehicle chargers on low-voltage distribution systems. It is necessary to know the influence of the electric vehicle chargers impact to power grid before electric vehicles operating in scale. In this paper a field measurement is carried out on a low-voltage distribution system with 4 alternating current electric vehicle conductive chargers, that are specified by SAE 1772 standard, and a part of operated nonlinear loads. Some measured results of voltage/current trend, harmonics/interharmonics, flicker, and power quality events are discussed.

Applications of real-time simulation techniques for harmonics study of an industrial power system

Due to the increasing use of nonlinear loads, the associated power quality (PQ) problems have become a major concern to many electric utilities and their customers. For efficient and accurate analysis, the performance of computer simulation has been recognized as an important and necessary procedure to the power quality study. With the advanced development of computer and communication technologies, the real-time simulation becomes matured and provides better computational efficiency, flexible and scalable programming, and preserves a preciseness as good as conventional off-line simulation. This paper presents an application example of real-time simulation to harmonics study of an industrial power system. A cluster-based real-time simulator is executed under MATLAB/SIMULINK environment, where an industrial power system including the arc furnace and motor drives, as well as PQ mitigation devices is under test by real-time simulation techniques. In addition, the conventional off-line simulation with variable-step solver is included to compare the performance of the real-time simulation. Results indicate that the real-time simulation has a great advantage in both the computational efficiency and the system size under study than the off-line simulation, while the solution accuracy is maintained.

Grid-connected PV inverter test system for solar photovoltaic power system certification

Photovoltaic inverter, that is in charge of electric power conversion, is a critical component used in solar photovoltaic power systems. Many concerns are focused on the operation of photovoltaic inverter due to the worse designing may cause the terrible influences on safety, performance and grid interconnection characteristics of solar photovoltaic power systems. IEEE SCC21 provides a uniform standard, known as IEEE 1547 standard, for interconnection considerations of distributed resources with electric power systems. The standard focuses on the technical specifications and includes general principles, response to abnormal conditions, power quality, islanding, and test instructions and requirements for design, production, installation evaluation, commissioning, and periodic tests. This paper presents a interconnection test system for grid-connected photovoltaic inverter based on such standard. Some of the test items that described in IEEE 1547.1 standard are carried out by the proposed system to verify the overall performance. The system is now introduced into the equipment certification of solar photovoltaic power system in Taiwan; therefore, the description of photovoltaic inverter voluntary product certification system in Taiwan may also be presented in the study.

Real-time simulation on a multi-core PC platform for model-based power system harmonic study

It is typically time-consuming to obtain the time-domain responses of power system from conventional off-line simulation. With the advanced development in computer technologies, the applications of real-time simulations are introduced to power system studies for enhancing the capabilities of traditional off-line simulations. This paper presents a PC cluster-based real-time parallel simulator developed on a multi-core PC platform which is capable of speed up the execution time of simulation while the solution accuracy is maintained. A numerical example, five-bus power network, performed on MATLAB/SIMULINK is offered to illustrate the effectiveness of the used simulator.

Applications of real-time simulation techniques for shunt active power filter design

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.