High frequency inverters with regenerative snubber and zero voltage switching

Abstract

The function of an inverter is to change a DC input voltage and/or current to a symmetrical AC output voltage and/or current of desired magnitude and frequency. The output voltage and/or current waveforms of ideal inverters should be sinusoidal. However, the wavefroms of practical inverters are nonsinusoidal and contain certain harmonics. The harmonic contens of the output voltage and/or current cna be minimized or reduced significantly by high switching frequencies. The desire for high switching frequencies also stems from the reduction of volume and weight of smoothing devices and transfromers in power circuits, and the reduction of acoustic noise by running power circuits at ultrasonic frequencies. But the increase of the inverter switching frequency continue to exact a heavy penalty in tems of system efficiency. In this thesis, the thchniques which can incrase the inverter switching frequency without the sacriffice of system efficiency are proposed. First, a regenerative snubber for three-level high-power GTO inverter having simple construction and high efficiency is proposed. It consists of seried inductor and shunt capacitor snubers with DC/DC converter for energy recovery trapped in the snubbers. In particular, the new DC /DC converter as an essential component of regenerative snubber has very low switching loss due to resonant operation with zero voltage switching and has small size due to high switching frequency over 10KHz using power transistors. The proposed regenerative snubber is also thought to be applicable for other multi-level power GTO inverters. Second, two new zero voltage swtiching partial-resonant link AC/AC converters are proposed which overcome the shorteomings of conventional resonant ac and dc link AC/AC schemes anmd consist of only 12 unidirectional switches. The proposed converters synthesize output ac waveforms with integrals of high-frequency current pulses like series-resonant converters. But switching operations occur at zero vo...