Frequency Domain Modelling of an LCC Resonant Converter with Capacitive Output Filter

Introduced over 30 years ago, the LCC resonant dc/dc converter topology with capacitive output filter is gaining renewed interest to develop the first-stage of a two-stage PV inverter and 48V to 1V VRM for server applications. Previously reported time domain and Fundamental Harmonic Approximation analysis techniques suffer from degraded accuracy at low quality factors (Q). This paper presents a frequency domain model valid for any Q by accurately deriving the expression for the parallel capacitor voltage. This general model applies to the study of the converter under variable frequency and phase shift modulation techniques. Converter characteristics can be studied using generalized curves of voltage gain (V
0
/V
i
), phase shift ($\phi$), and non-conduction angle ($\theta$) which are suitable for optimizing converter performance in terms of resonant component ratings and zero-voltage-switching (ZVS) range. The model is verified against a 380V, 250W experimental prototype.