Variable Frequency Control for Isolated, Nonresonant Single-Stage AC–DC Converter With a Constant DC-Link Voltage

This article proposes a system, which comprises an isolated, nonresonant single-stage ac–dc converter with variable frequency control. One of the main contributions of this article is that the proposed system ensures a stable dc-link voltage independent of power flow, which improves the reliability of the system. Moreover, it eliminates the capacitor imbalance issue when using pulsewidth modulation control in bridgeless, nonresonant single-stage converters. Due to this, a minimal output capacitance is needed to regulate the output current in low output voltage applications tightly. The proposed system shows high flexibility in controlling the current waveforms, which enables soft switching for all turn-
on
instants of the switches. A new equivalent circuit is introduced to study the steady-state operation of the proposed system accurately. Experimental and simulation results are provided for a
$250 \, \mathrm{W}$
prototype to demonstrate the superior performance of the proposed system.