Power-control design of resonant converters
Novel design techniques are presented for load-resonant and quasi-resonant converters for use in, for example, arc-welding and fan-load power supplies. Both converters are capable of very high switching frequency over a wide range of output power, with high efficiency and the presentation of near-unity power factor to the primary power supply. Previous work, by the author and his colleagues, has produced. a frequency-domain approach to produce circuit-designs for use in load-resonant converter applications. This design technique, although simple and straight-forward to understand, suffers by requiring some rather tedious trial-and-error algebraic and arithmetic manipulations albeit computer assisted. In this thesis, a systematic way of designing such circuits, based on Gr6bner Basis ideas, is explained, developed and compared with the previous best-practice design method. By employing the Gr6bner Basis techniques to synthesize electrical circuits, an entirely novel approach to the design of series-parallel load-resonant converter circuits is presented. This has led to the formulation of a new output-power control methodology in the design of the converters. These techniques produce output-power-control designs that have superior properties, compared with other established methods, in the sense of their simplicity, robustness and flexibility. It is found that the methodology can be further extended to alter any resonant circuits and, hence enables multilevel-output power to be controlled without involving complex control and advanced mathematical theories, while still preserving the desirable characteristics of resonant switching. The technique is, in fact, far more generally useful in the circuit-design/synthesis arena than the specific load-resonant-converter application for which it was developed. The novel technique used to vary the speed of an induction motor is found to be promising. Various test results are presented based on an experimental system.