A PWM Controlled Bidirectional Forward Converter With Zero Voltage Switching and Utilizing Variable Turns Ratio Transformer

A novel bidirectional forward converter with zero voltage switching (ZVS) characteristic is proposed in this article. The converter utilizes a variable turns ratio transformer, enabling the change of the operational mode. The converter includes two power <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfets</small> paralleled by two capacitors to achieve ZVS conditions and the demagnetization of the transformer core. The pulsewidth modulation control approach has been chosen to regulate the output voltage of the converter, simplifying its performance and design. Depending on the converter operation mode, the transformer turns ratio is modified using a magnetic approach to achieve the necessary voltage gain. This transformer type enhances the reliability of the converter compared to a relay-based converter. The magnetizing inductance of the transformer also holds substantial value, resulting in a notable reduction in circulating current and, consequently, a considerable improvement in converter efficiency, especially under light load conditions. The leakage inductance of the transformer plays a crucial role in energy transfer within the converter. A comprehensive theoretical analysis, small-signal analysis, and finite element analysis simulations of the transformer are presented. The validity of the theoretical analyses has been confirmed through experimental results.