Research on LCL-T Resonant High-Voltage Capacitor Charger Including the Effect of the High-Ratio Transformer Parasitic Capacitance

High voltage capacitor charger (HVCC) is crucial for power pulse sources, and the LCL-T resonant converter is widely utilized as current-source charger. The accurate capacitance model and FHA model are the critical foundation for converter analysis and parameter design. Due to the non-negligible effect of the parasitic capacitance of the high-voltage high-ratio transformer, the parasitic capacitance is evaluated, and a transformer model is constructed. The transformer model analysis demonstrates the transformer current is discontinuous with significant harmonics, which invalidates conventional fundamental harmonic approximation (FHA) methods and causes the LCL-T converter to lose the constant output current capability. An improved FHA method based on the continuous resonant current is proposed, providing better accuracy and lower complexity. The output current characteristic and zero-voltage switching (ZVS) range are analyzed accurately, and the resonance parameters and control scheme are designed for the constant output current and full-range soft-switching. A LCL-T resonant converter prototype with 200V input voltage, 2000V output voltage, 0.4A average output current, and 95.68% maximum efficiency is made. The prototype achieves constant output current and full-range ZVS, completes the charging of the energy storage capacitor, and verifies the accuracy and effectiveness of the proposed FHA method and parameter design.