Optimized Zvs Analysis and Parameter Design for LLC Converter with Parasitic Capacitance

This paper reveals the mechanism by which parasitic capacitance impacts the Zero Voltage Switching (ZVS) characteristics of LLC resonant converters. Specifically, the parasitic capacitance on the secondary side participates in the circuit's resonance during the deadtime, causing a portion of the resonant current, originally intended for ZVS, to be diverted to the transformer's secondary side. Under high output current load conditions, the interaction between the secondary side parasitic capacitance and the resonant circuit is intensified, leading to significant distortion in the resonant current that should have enabled ZVS. This distortion not only increases the losses in the switching devices but also reduces the system's efficiency and stability. By developing an accurate time-domain model, the degree of influence of parasitic capacitance on ZVS can be precisely predicted, allowing for further design optimization to mitigate this impact. A comparison of simulation and experimental results validates the accuracy of the proposed model and demonstrates that properly accounting for the influence of parasitic capacitance in the design can effectively improve the stability of ZVS.