Comprehensive analysis and transient modeling of symmetrical single phase PWM AC-AC voltage converters

摘要

Recently, a new family of AC-AC converters has been proposed for AC power conditioning. These converters are solid-state function equivalent to transformers with a continuously variable transformation ratio. Operating with the principle of pulse width modulated (PWM) control using gate turn-off switching devices like IGBTs have been shown to have significant performance advantages compared to older generation of thyristor based phase controlled converters. Although various techniques for realizing AC-AC power control using PWM control have been proposed in the past, few have seen wide application. This is seen to be primarily due to the complexity of the bi-directional switch requirements. In this paper, transient analysis and modeling of PWM AC-AC voltage converters with reduced number of uni-directional switches are developed and experimentally verified. It has been demonstrated that PWM AC-AC converters allow for the line current harmonics to be readily and economically filtered out, and for the load current harmonics to be almost negligible. Switching-to-supply frequency ratio plays an important role in terms of harmonic generation, distortion factor, distribution and control, through a switching frequency, in excess of several hundred hertz has almost negligible effect on the performance parameters. The developed transient modeling and its solution procedure are experimentally verified. Measured, simulated and predicted waveforms using the proposed model are shown to be very close and the model is proved to be efficient and accurate.