Frequency Domain Modelling of an LCLC Resonant Converter with Capacitive Output Filter Under Hybrid Modulation

The LCLC resonant converter topology is popular and frequently used in high voltage applications as it can more accurately describe the effect of parasitic elements in high turns ratio transformers over LLC or LCC. The accuracy of the Fundamental Harmonic Approximation (FHA) analysis technique suffers from low-quality factor (Q) designs which is desired to minimize component stress. Presented in this paper is a new frequency domain model incorporating effects of both input and load side harmonics under a duty cycle-variable frequency-based hybrid modulation technique previously shown to be advantageous under light load conditions. Generalized curves of converter resonant tank gain describe its operation. Steady-state waveforms from the model and a 400V, 250W experimental prototype is used to verify the accuracy