Active-clamped flyback DC-DC converter in an 800 V application:
Design notes and control aspects

Darko Vračar – Predrag Pejović

   This paper presents findings for active-clamped flyback (ACF) DC-DC converter 57 W used as an auxiliary power-supply of a wireless inductive-charging system 800 V. Measurements of magnetizing and leakage inductances for three transformers demonstrated how big differences between them could be depending on chosen vendor. Comparison of simulated and measured Bode plots showed that, even when those plots were not matched, one could design a compensator that ensures stable operation. Evaluation of cross-regulation when output with low power (9.62 % of total) was regulated showed that such approach was feasible too. The switching frequency vs output-power and drain-source voltage of switch vs output-power graphs are presented for the first time. Comparison of bandwidth, phase-margin and gain-margin vs input-power, between the ACF and conventional flyback converter were discussed too. Those quantities were changeable with load and input-voltage as expected. The conventional flyback converter in DCM has higher bandwidth than the ACF which resulted in lower phase- and gain-margins. That showed that it cannot have the same compensator as an ACF.

Keywords: active-clamped flyback, Bode plots, control, cross-regulation, DC-DC converter, inductance measurement, switching-frequency change, transformer

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