| With the increasing demand for clean, reliable AC power, there is an increasing demand for UPS (Uninterruptible Power Supply) style sinewave inverters that can supply this power in cases of utility outages, remote sites, etc. While the body of knowledge dealing with the modeling and control of single-phase and three-phase three-wire (three-leg) sinewave inverters is quite extensive, there is a growing need for sinewave inverters that can supply unbalanced/non-linear three-phase loads and still maintain precise regulation of the output voltage magnitude, phase, and total harmonic distortion. In the past, various "60-Hz" transformers have been incorporated to provide a neutral point connection, most notably the {dollar}Delta{dollar}-Y configuration. As an alternative to the cost, size, weight and impedance drawbacks of these low-frequency transformers, three-phase four-wire (four-leg) inverters have been proposed, where the neutral point of the filter/load is controlled by a fourth inverter leg.; This document presents an in-depth analysis of sinewave inverters, and presents a transformation for the four-leg inverter that decouples the system into three independent single-phase equivalents; in much the same way the "qd" transformation decouples the standard three-leg inverter into two independent single-phase equivalents. The decoupling techniques developed to control the four-leg sinewave inverter build upon advanced control methods previously developed for single-phase sinewave inverters. Implementation details and experimental results are provided.; Because of the growing interest in variable-speed generation systems in which a variable speed engine-generator set is paired with a sinewave inverter, this document additionally presents research on the control and modeling of such a system. Models, computer simulations and experimental results are included. |
