Switching converters with magnetic amplifiers as controllable switches : I: Soft-switching converters. II: Input current shaping

Citation

Brkovic, Milivoje Slobodan (1994) Switching converters with magnetic amplifiers as controllable switches : I: Soft-switching converters. II: Input current shaping. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/y716-bs43. https://resolver.caltech.edu/CaltechETD:etd-12042007-133110

Abstract

Part I: Novel soft-switching converters combine the functions of loss-less soft-switching for all switches and secondary side output voltage regulation at constant switching frequency. This was made possible by using magnetic amplifiers in series with the rectifier diodes in the symmetrical topologies. The primary side switches are driven at constant frequency and near 50% duty ratio with small dead-time and the output voltage is regulated by pulse width modulation (PWM) control on the secondary side.

All three soft-switching topologies, half-bridge, full-bridge and push-pull, are analyzed. It was found that the multiple-output extension of these converter do not have some serious adverse effects inherent to their parent PWM converters with magnetic amplifier post-regulators.

Experimental results obtained on two different prototypes confirm the key advantages of the proposed soft-switching converters.

Part II:

Two classes of automatic current shapers are analyzed, with external and internal capacitive energy storage.

The Cuk converter with Integrated Magnetics when operated in DICM with external energy storage exhibits advantages over other automatic current shaper topologies. Unity power factor is provided automatically and by using "ripple steering" mechanism essentially zero input and output current ripples are obtained for all operating conditions. Consequently, the size of the magnetics can be significantly reduced even at very modest switching frequencies.

The requirement for fast output regulation implies that low-frequency energy is stored internally in the input current shaper. A new AC-to-DC converter which combines the functions of automatic current shaping, fast output voltage regulation, and loss-less soft-switching in a single converter is proposed. This was made possible through internal energy storage and discovery of the new modes of operation, which together, effectively decoupled the input boost-like part of the Cuk converter from its buck-like output. In order to keep the voltage stress on the switches low, the variable frequency control is required in addition to PWM control.

Another novel class of single stage AC-to-DC converters with unity power factor and fast output regulation is also proposed. These converters use a magnetic amplifier for the input current shaping, while the active switch is used for fast output regulation. By using core material for magnetic amplifiers with high saturated permeability, and operating the input stage of the converter in DICM, the linear input inductance can be replaced by the saturated inductance of the magnetic amplifier. Thus, the magnetic amplifier combines the functions of a controllable switch and a linear inductor into a single device.

The proposed method of current shaping with magnetic amplifiers is extended to the full-bridge topologies with their input, boost-like stage operated in continuous conduction mode.

Experimental results obtained on different prototypes confirm advantages of the proposed topologies.

Thesis Files