G. W. Chang

Test systems for harmonics modeling and simulation

This paper presents three harmonic simulation test systems. The purpose is to demonstrate guidelines for the preparation and analysis of harmonic problems through case studies and simulation examples. The systems can also be used as benchmark systems for the development of new harmonic simulation methods and for the evaluation of existing harmonic analysis software.

Experiences with Mixed Integer Linear Programming-Based Approaches in Short-Term Hydro Scheduling

This paper describes experiences with mixed integer linear programming (MILP)-based approaches on the short-term hydro scheduling (STHS) function. The STHS is used to determine the optimal or near-optimal schedules for the dispatchable hydro units in a hydro-dominant system for a user-definable study period at each time step while respecting all system and hydraulic constraints. The problem can be modeled in detail for a hydro system that contains both conventional and pumped-storage units. Discrete and dynamic constraints such as unit startup/shutdown and minimum-up/minimum-down time limits are also included in the model for hydro unit commitment (HUC). The STHS problem is solved with a state-ofthe-art package that includes an algebraic modeling language and an MILP solver. The usefulness of the proposed solution algorithm is illustrated by testing the problem with actual hydraulic system data. Numerical experiences show that the solution technique is computationally efficient, simple, and suitable for decision support of short-term hydro operations planning. In addition, the proposed approaches can be easily extended for scheduling applications in deregulated environments.

Interharmonics: Theory and Modeling

Some of the most remarkable issues related to interharmonic theory and modeling are presented. Starting from the basic definitions and concepts, attention is first devoted to interharmonic sources. Then, the interharmonic assessment is considered with particular attention to the problem of the frequency resolution and of the computational burden associated with the analysis of periodic steady-state waveforms. Finally, modeling of different kinds of interharmonic sources and the extension of the classical models developed for power system harmonic analysis to include interharmonics are discussed. Numerical results for the issues presented are given with references to case studies constituted by popular schemes of adjustable speed drives.

An Improved Backward/Forward Sweep Load Flow Algorithm for Radial Distribution Systems

This letter presents an improved backward/ forward sweep algorithm for three-phase load-flow analysis of radial distribution systems. In the backward sweep, Kirchhoffs Current Law and Kirchhoffs 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

Modeling characteristics of harmonic currents generated by high-speed railway traction drive converters

This paper presents a study for modeling harmonic currents injected by three-level pulse-width-modulated (PWM) converters of the high-speed railway traction drive in steady-state motoring mode. An analytical solution for converter harmonics based on the double Fourier series theory is described. The time-domain simulation results obtained by the use of PSpice are then compared with those obtained by the proposed model. It is shown that the harmonic currents determined according to the proposed model agree well with those results obtained by using the time-domain simulation tool.

A Two-Stage ADALINE for Harmonics and Interharmonics Measurement

Harmonics and interharmonics may introduce operational problems of electrical and electronic equipment. Therefore, monitoring harmonics/interharmonics for improving the power quality is of importance for both electric utilities and their customers. In this paper, a cascade two-stage adaptive linear element (ADALINE) structure for both harmonics and interharmonics measurement is proposed. In addition, a simple laboratory setup implemented by MATLAB and the dedicated hardware for measuring power signals is built to verify the performance of proposed method. Results are compared with those obtained by short-time Fourier transform (STFT) and two other conventional ADALINE-based methods. It shows that the proposed method is with a better accuracy, even if the power frequency deviation and interharmonic components are present in the measured signal. The proposed method also can be adopted for harmonic/interharmonic compensation devices in real-time.

Radial-Basis-Function-Based Neural Network for Harmonic Detection

The widespread application of power-electronic loads has led to increasing harmonic pollution in the supply system. In order to prevent harmonics from deteriorating the power quality, detecting harmonic components for harmonic mitigations becomes a critical issue. In this paper, an effective procedure based on the radial-basis-function neural network is proposed to detect the harmonic amplitudes of the measured signal. By comparing with several commonly used methods, it is shown that the proposed solution procedure yields more accurate results and requires less sampled data for harmonic assessment.

A novel reference compensation current strategy for shunt active power filter control

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.

Extended Real Model of Kalman Filter for Time-Varying Harmonics Estimation

The effective harmonics estimation for measuring power signals has become an important issue in the power quality assessment. By reviewing those commonly used Kalman filter-based models, some limitations for harmonics estimation can be observed. In this paper an extended real model of Kalman filter combined with a resetting mechanism for accurately tracking time-varying harmonic components of power signals is presented. The usefulness of the proposed algorithm is demonstrated by a simple laboratory setup with LabVIEW program and the dedicated hardware for harmonics monitoring. Results show that the proposed method can achieve more accurate and robust measurement of harmonic amplitudes and phase angles for the time-varying power signals among compared methods while the uncertainty testing performances required by IEC standard 61000-4-30 are satisfied.

Modeling devices with nonlinear Voltage-current Characteristics for harmonic studies

This paper documents the modeling of harmonic sources with nonlinear voltage-current characteristics such as transformers, iron-core reactors, rotating machines, arc furnaces, energy efficient lightings, and some household electronic appliances. The harmonic generating characteristics of these apparatus are reviewed. Different modeling techniques are summarized and suggestions for the use of different models are also provided whenever possible.