Envelope analysis applied to multi-phase resonant inverters

In this paper, the fundamental approximation combined with a time-varying phasor transformation is applied to obtain a suitable envelope model of a phase-controlled triple LC_sC_p resonant inverter. The resulting model removes the high frequency component while keeping the useful information contained in the waveform envelopes. The control parameter is the phase displacement, Psi, of the midpoint voltage of one class D section referred to the others. Once the model is obtained, the small-signal analysis of the envelope variations is accomplished by adding the perturbation, phi to the control parameter, Psi. In applications such as control of gaseous discharges, the proposed constant switching frequency control is more robust under large load changes and results in lower efficiency modification with respect the nominal operation point. Spice models of the load are also easily included in the converter analysis to foresee the overall performance.