LLC synchronous rectification using Coordinate Modulation

LLC resonant converters have gained popularity in a variety of applications due to their natural ability to provide soft switching conditions. Although LLC features good efficiency, conductive losses in the output rectifier remains a barrier to achieve enhanced efficiency, specially for high output current applications. This paper introduces a new strategy referred to as Coordinate Modulation, which is designed to drive the synchronous rectification MOSFETs. The main challenge to successfully drive synchronous rectifier is to detect/find the rectifier conduction angles with a cost-effective strategy. This paper proposes and analyzes a robust and simple detection method in the vinv - nvsec coordinate plane. The plane allows a remarkable ability to detect conduction angles with two lines, producing proper pulses to drive synchronous rectifier. In order to validate the theoretical analysis, a 1.2KW prototype LLC converter is implemented and the experimental results using the Coordinate Modulation are presented. At the nominal output power, the converter's efficiency was measured at 97.1%. In comparison with a conventional LLC converter, the proposed modulation method increases the efficiency by 3%.