A Generalized Study of Multiphase Parallel Resonant Inverters for High-Power Applications

A generalized study of the parallel connection of N Class-D parallel resonant (LC_P) inverters is presented. Steady-state analysis and design considerations are provided in detail, evaluating the current distribution, output power and efficiency of the circuit as a function of the number, N, of phases. Inductor equivalent series resistance and MOSFET conduction losses are considered in order to foresee and optimize the inverter efficiency. The power supplied to the load can be controlled at constant switching frequency by using the phase displacement of the output voltages of each Class-D leg, although for the interests of this specific application, only one inverter is phase shifted. The applicability of the general analysis is demonstrated on two practical designs with three and five phases, resulting in 400-W and 1-kW high-pressure sodium lamp ballasts, respectively.