Active-clamp PWM converters: design-oriented analysis and small-signal characterization

Abstract

This thesis addresses issues related to the use of an active clamp (ACL) circuit in high-frequency PWM converters with an electrical isolation.

Existing design guidelines and design trade-offs for the ACL in forward and flyback converters are reviewed, and specific properties of both circuits that are caused by the ACL are highlighted. Based on the obtained results, a robust single-switch active clamp (SS ACL) for the Weinberg converter is developed and evaluated using the Weinberg converter employed in the Space Station as an example. The ACL in the Weinberg converter provides recovery of the magnetic leakage energy, ZVS for all switches, and minimum voltage stresses on switches. Therefore, it allows a reliable high switching frequency operation without a significant increase of the switching losses. This makes the ACL Weinberg converter a prime candidate for high-voltage, high-power space distribution systems.

This thesis also investigates impacts of the ACL on dynamic behavior of all the aforementioned circuits. The investigation led to the discovery of a significant detrimental effect that the ACL can have on dynamic characteristics of the ACL forward converters operated with the ZVS. A new small-signal model that predicts that effect is derived using the state-space averaging, and necessary steps for its elimination are proposed.