Novel Modulation Strategy to Eliminate Device Overvoltage Stress and Enable True ZVS Operation in the Soft-Switching Solid-State Transformer

The Soft-Switching Solid-State Transformer (S4T) is a minimal single-stage current source converter with high-frequency isolation and soft-switching across the entire load range. The 3-quadrant reverse blocking switches used in the S4T and their associated parasitic capacitances can lead to situations where the voltage across a device is higher than the total leg voltage. This results in significant overvoltage stress across the power devices and generates spurious high dv/dt transitions. This paper analyzes the source of this unique device overvoltage stress and introduces a novel modulation strategy to eliminate it and ensure true zero-voltage switching (ZVS) of all the power devices. The proposed modulation strategy applies to all S4T variants and offers a simple, no-cost solution to reduce the voltage rating requirement of the switches, enabling the scaling of the topology to higher voltage levels.