A ZVZCS Full-Bridge Converter for MVDC Collection Systems Using Renewable Energy

This study proposes a full-bridge DC-DC converter incorporating zero-voltage zero-current switching (ZVZCS), based on a dual-transformer structure with two output filter capacitors. The converter is designed for seamless integration with DC collection systems in medium-voltage renewable energy applications, where stability, adaptability, and efficiency are crucial. The primary switches operate under a pulse width modulation (PWM) scheme with a fixed duty cycle to regulate voltage and power output. Under full load conditions, the main full-bridge circuit delivers the majority of the power and achieves zero-voltage switching (ZVS) due to the precise design of the main transformer’s turn ratio, significantly minimizing switching losses. To complement this, an auxiliary circuit achieves ZVZCS and handles a small fraction of the power. Efficiency can be further improved by optimizing the auxiliary transformer’s turns ratio, balancing power contribution and minimizing conduction losses. In addition to conventional control methods, a fuzzy logic controller is incorporated to enhance real-time adaptability. The fuzzy controller dynamically adjusts control signals based on varying input voltage, load conditions, and switching timing, allowing the converter to maintain soft-switching conditions even under transient disturbances or parameter drift. It replaces rigid threshold-based decision-making with linguistic rules, enabling smarter handling of system nonlinearity and uncertainty. Design characteristics, fuzzy rule base definition, and optimization strategies for the proposed converter are described in detail. To validate the effectiveness of the proposed scheme and verify the simulation results, a 200 V / 2 kV / 3 kW prototype has been developed and tested. The results demonstrate improved switching performance, better thermal management, and higher overall efficiency due to the combined use of ZVZCS and fuzzy logic control.