Active-clamp dc-dc converters are pulsewidthmodulated converters having two switches featuring zero-voltage switching at frequencies beyond 100 kHz. Generalized equivalent circuits valid for steady-state and dynamic performance have been proposed for the family of active-clamp converters. The activeclamp converter is analyzed for its dynamic behavior under current control in this paper. The steady-state stability analysis is presented. On account of the lossless damping inherent in the active-clamp converters, it appears that the stability region in the current-controlled active-clamp converters get extended for duty ratios, a little greater than 0.5 unlike in conventional hard-switched converters. The conventional graphical approach fails to assess the stability of current-controlled active-clamp converters, due to the coupling between the filter inductor current and resonant inductor current. An analysis that takes into account the presence of the resonant elements is presented to establish the condition for stability. This method correctly predicts the stability of the currentcontrolled active-clamp converters. A simple expression for the maximum duty cycle for subharmonic-free operation is obtained. The results are verified experimentally.
Active clamp technique has been proved to be an important topology for pulse width modulated (PWM) converters featuring zero voltage switching (ZVS). The small signal modeling and analysis of current mode controlled active clamp ZVS dc-dc converters are presented in this paper. It is identified that, damping due to lossless resistance inherent in active clamp topology is eliminated under uncompensated current mode control. The buck converter is considered to demonstrate the small signal modeling of current mode controlled active clamp ZVS dc-dc converters. The analysis is also extended to boost and buck-boost converters and the same can be extended to complete family of active clamp dc-dc converters. The small signal model of active clamp converter is compared with the hard switched converters. Simulation results for the active clamp buck converter are presented.Index Terms--Active clamp converter, current programmed control, lossless damping, small signal model, zero voltage switching,
Active-clamp dc-dc converters are pulsewidthmodulated converters having two switches featuring zero-voltage switching at frequencies beyond 100 kHz. Generalized equivalent circuits valid for steady-state and dynamic performance have been proposed for the family of active-clamp converters. The active-clamp converter is analyzed for its dynamic behavior under current control in this paper. The steady-state stability analysis is presented. On account of the lossless damping inherent in the active-clamp converters, it appears that the stability region in the current-controlled active-clamp converters get extended for duty ratios, a little greater than 0.5, unlike in conventional hardswitched converters. The conventional graphical approach fails to assess the stability of current-controlled active-clamp converters due to the coupling between the filter inductor current and resonant inductor current. An analysis that takes into account the presence of the resonant elements is presented to establish the condition for stability. This method correctly predicts the stability of the current-controlled active-clamp converters. A simple expression for the maximum duty cycle for subharmonic free operation is obtained. The results are verified experimentally.
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