Three-phase multipulse AC-DC converters (MPC) are developed for improving power quality to reduce harmonics in AC mains and ripples in DC output. This paper deals with the multipulse AC-DC converter configurations, state of art, their performance, power quality aspects, components selection considerations, latest trends, future developments, and potential applications. It is targeted to provide broad perspective on multipulse converter technology to the researchers, engineers, and designers dealing with them. A classified list of more than 250 research publications on the subject is also given for quick reference.

Multipulse AC–DC Converters for Improving Power Quality: A Review

This paper proposes an impedance-based analytical method for modeling and analysis of harmonic interactions between the grid and aggregated distributed generation (DG) inverters. The root cause of harmonic interaction/resonance problems is the impedance-network quasi-resonance between the effective output impedance of the inverter and the equivalent grid impedance at the connection point. Starting with the output impedance modeling of an inverter, a Norton model of the inverter is derived. Comparing with the switching model and the average model of the inverter, simulation results show the effectiveness of the model. This paper proposes that impedance limits should be specified and used as an extra design constraint for DG inverters in order to minimize the harmonic distortion impact on the grid. Assuming the impedance models of individual inverters and local loads within a distribution grid are known, especially in the case of new grids under construction, harmonic interactions between the grid and a certain number of DG inverters can be preliminarily estimated.

Modeling and Analysis of Grid Harmonic Distortion Impact of Aggregated DG Inverters

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.

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

A cycloconverter is a power electronic device used to convert constant voltage constant frequency AC power to adjustable voltage adjustable frequency AC power without a DC link. Cycloconverters inject significant harmonics and nonstandard frequency components (i.e., noninteger multiples of the power frequency) into power systems. The impact of cycloconverters on power quality is studied, and the relationships between power quality indices and cycloconverter control strategies are developed. Control strategies are proposed to minimize the power quality impact of the cycloconverters. An innovative group frequency concept is introduced. This is a technique whereby many frequency components in the cycloconverter voltage and current spectra are collapsed into several group frequencies, and the power quality impact of the group frequencies is the same as that of the full spectrum of the cycloconverter signals. Some concepts are illustrated by simulation, and some by measurement at a twelve pulse cycloconverter load.

The power quality impact of cycloconverter control strategies

Islanding detection is one of the most important issues for the distributed generation (DG) systems connected to an electric power grid. The conventional passive islanding detection methods inherently have a nondetection zone (NDZ), and active islanding detection methods might cause problems with safety, reliability, stability, and power quality on a power system. This paper proposes a passive islanding detection method with the zero NDZ property by considering the switching frequency from an inverter of the DG system. Moreover, the proposed method does not cause any negative effects in the aforementioned problems because it avoids applying the intended changes such as variations of reactive power and/or harmonics, which are required in the active islanding detection methods. Several case studies are carried out to verify that the proposed method can detect the islanding operation within 20 ms, which is less than 150 ms required in a recloser as the shortest mechanical reclosing (delay) time. Moreover, this value satisfies the requirement of 2 s given in IEEE Std. 1547.

New Islanding Detection Method for Inverter-Based Distributed Generation Considering Its Switching Frequency

This paper presents a review of characteristics and modeling of major power electronic types of harmonic sources for the power system harmonic analysis. The power electronic switching types of harmonic sources to be reviewed include static power converters, static var compensators (SVCs), and cycloconverters. Discussions and comtnents for applications of these harmonic sources in harmonic modeling and simulation also will be described.

G. Chang

Papers

Characteristics and Modeling of Harmonic Sources-Power Electronic Devices