An Improved Frequency Domain Based Analytical Model of Voltage-Fed Series LC – Parallel LC Resonant Converter with Capacitive Output Filter

The series LC-parallel LC (LCLC) resonant converter with capacitive output filter is an emerging favorite for high frequency, high output voltage applications. Existing literature utilizes conventional fundamental harmonic approximation (FHA) based techniques for steady-state analysis due to its simplicity. However, FHA results in limited accuracy when applied on low-quality factor (Q<2) tuned resonant circuits since higher-order harmonics are neglected. This paper presents an improved frequency domain-based analysis of voltage-fed LCLC resonant converter with a capacitive output filter, considering both input and load side harmonics. The proposed analysis can be utilized to study LCLC converter operational characteristics under both variable frequency control and fixed frequency phase shift control. Closed-form expressions for the performance characteristics such as voltage gain, resonant tank RMS current, and ZVS angle $(\beta)$ in terms of design specifications can be derived from the nth harmonic equivalent circuit. The proposed model is validated using PSIM based simulation studies and hardware prototype-based experimental waveforms. This model improves the accuracy over conventional FHA by 4% for low-Q range designs.