Evaluation of a Single-Phase Soft Switched AC/DC Active Front End Converter for Solid-State Transformer Applications

With the emergence of silicon carbide (SiC) power devices, and their rapid growth and development in the past few years, the demand for increasing the efficiency and power density of power converters has seen a steep rise. In certain applications, like on-board chargers (OBCs), solid-state transformers (SSTs), etc., AC/DC PWM converters are used as the active front-end converters for power factor correction. Traditional AC/DC converters are typically hard-switched which results in low efficiency and low power density. In a bid to push the limits of AC/DC converter systems, soft-switched converters are imperative. In this paper, an integrated Triangular Current Mode (iTCM) operation of a single-phase converter system is studied. This concept achieves soft-switching over the entire line cycle by using an LC branch connected to the midpoint of the phase leg. This paper discusses the concept of iTCM and studies the effect of various system and operating parameters on the converter system. A recommended design procedure for the converter system is also provided. An analysis based on the effect of the switching frequency variation is also given, and the effect of component tolerance is also studied to a small extent. Various limitations of such a converter is also studied. A 4 kW prototype is built and operated as an inverter, to validate the operation of the iTCM converter system. This study can be helpful in analyzing the practical considerations for operating an iTCM-based converter, and to understand the inherent limits of such a system.