Adaptive feedback stabilization in PWM-controlled DC-to-DC power supplies

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Abstract
In this article, adaptive discontinuous feedback regulators are proposed for the stabilization of switch mode controlled DC-to-DC power supplies of the buck, boost and buck-boost types. Adaptation is performed under the assumption of an unknown LC ‘input’ circuit natural oscillating frequency, unknown RC ‘output’ circuit time constant and unknown input source voltage. An average pulse-width-modulation (PWM) input-current regulation scheme, in continuous conduction mode, which accomplishes indirect stabilization of the average output load voltage, is used as the basis for the adaptive controller design. Adaptation is thus confined to the self-tuning of a (static) duty ratio synthesizer. The actual, discontinuous, adaptive PWM feedback strategy state responses exhibit remarkably good asymptotic convergence properties toward the adaptively controlled average designed responses, thus effectively compensating for the modelling error inherent in the average based feedback controller design. It is shown that only in the buck converter case, is a direct-output voltage-adaptive feedback control scheme feasible. In the boost, and the buck-boost, converter cases, the non-adaptive average output voltage regulation schemes lead to non-minimum phase closed loop situations. The performances of the proposed controllers are evaluated through computer simulations.

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