Zero-Voltage Switching and Natural Voltage Balancing of a 3 kW 1 MHz Input-Series-Output-Parallel GaN LLC Converter

Input-Series-Output-Parallel (ISOP) LLC converters have the capability to leverage lower voltage semiconductor devices, thereby enabling applications with higher voltage requirements. The primary advantages lie in enhanced efficiency and power density attributed to improved device performance. Given the utilization of multiple modular LLC converters, the potential impact of component parameter mismatch becomes a significant concern. Specifically, issues related to input voltage sharing (IVS) and device zero voltage switching (ZVS) are critical considerations. This paper develops a precise mathematical model during deadtime to determine ZVS boundaries, taking into account parameter mismatches. Within the developed boundaries, all LLC sub-modules are assured of ZVS operation. To assess IVS performance, a mathematical model is formulated using the first harmonic approximation (FHA) equivalent circuit. To validate the proposed modeling and analysis, a 3 kW 1 MHz GaN-based ISOP LLC is constructed, comprising four modular 750W-LLC units. Experimental results showcase successful ZVS operations and natural voltage balancing of the ISOP LLC converter across a broad range of parameter mismatches.