A series-resonant single-phase step up/down AC chopper

Abstract

A series-resonant single-phase step up/down ac chopper is presented. The main attribute of the ac chopper topology is the fact that it generates an output ac voltage larger or lower than the input ac one, depending on the instantaneous duty-cycle. This property is not found in the classical ac chopper, which produces an ac output instantaneous voltage always lower than the input ac voltage. The presented single-phase ac chopper is configured by a series-resonant conversion. The presented single-phase ac chopper is a series resonator to configure adaptively the resonant voltage robes. The synthesized sinusoidal waveform (SSW) before output filter is synthesized by a series of sinusoidal amplitude quasi-sinusoidal pulses (QSPs) following the input voltage amplitude. Because the synthesized SSW very closes sinusoidal waveform, the presented single-phase ac chopper can use a simple LC filter to filter the undesired harmonics and get the sinusoidal voltage with low total harmonic distortion (THD). The presented single-phase ac chopper is operated by constant frequency pulse width modulation control technique. Waveform syntheses for the output sinusoidal voltage are clearly analyzed and derived. A typical design example of a 600 W series-resonant single-phase ac chopper is examined to assess the system performance. The power efficiency is over 90% when the output power is at maximum output rated power. The total harmonic distortion (THD) when the output power is at maximum output rated power is within 6%.