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A new soft-switched, current-driven full-bridge converter is presented. The structure utilizes a simple snubber formed by two unidirectional switches and a capacitor to realize soft-switching operation over a wide line and load range. All primary-side switches are operated with zero-current switching (ZCS) and the snubber switches are operated with zero-voltage switching. The energy used for soft-switching is self-adaptable. For a given input current, the snubber capacitor is charged to the minimum required energy for ZCS of the switches. Thus, less resonant energy is used and the conduction loss can be kept minimal. The cyclical switching operation and control of the converter will be discussed. By compromising the voltage stress on the switches and loss of duty cycle (i.e., the regulation range), an optimized design procedure of the circuit elements is derived. The input voltage range and load variation that ensure both output voltage regulation and soft switching are determined. By studying the small-signal characteristics of the entire system, a current-controlled feedback control circuit has been implemented with a DSP. The experimental results measured on a 5-kW, 530-V/15-kV prototype confirms the advantages of the proposed converter. [ABSTRACT FROM AUTHOR]

A feedback system for controlling the speed of a separately excited DC motor supplied from a 3-phase semi-converter circuit is presented. The electronic feedback structure is designed to assure that, in the starting transient state, the motor speed climbs from zero to its steady-state value within specified ‘customer’ bounds. This has to be achieved despite random variations in the characteristics of the supply voltage, of the motor and of the converter, and despite uncertain values of the load, keeping at the same time the starting current peak below a dangerous level. When feedback is applied, the system becomes highly non-linear; but owing to its quantitative approach, the design algorithm uses no small-signal linearizations. [ABSTRACT FROM AUTHOR]

A new approach for the time-domain simulation of power electronic circuits is developed. The methodology is based on stepwise identification of circuit topology. The simulation process automatically looks for a valid topology in every step. At each simulation instant, the circuit topology is transformed into a resistive network, giving another superior feature of this method: the avoidance of solving complicated s-domain or differential formulas. No small-signal approximation is assumed. Parasitic resistance of the reactive element is included in the circuit model. Several examples illustrating the generality and computational efficiency of this new method are presented. The simulated results are favourably verified with experimental measurements and available literature. © 1997 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]