Reduced Order Model for Envelope and Small-Signal Analysis of a Phase-Controlled Triple LCpCs Resonant Inverter for Electronic Ballast Applications

In this paper, the fundamental approximation combined with a time-varying phasor transformation is applied to obtain an envelope model of a phase-controlled triple LC_pC_s resonant inverter. The resulting model removes the high-frequency component while keeping the useful information contained in the waveform envelopes. The method provides large and small-signal Spice compatible models in a straightforward manner. The inverter is controlled at constant switching frequency by the phase displacement, Psi, of the midpoint voltage of one class D section referred to the others. An approximated explicit form of the small-signal transfer function from the control angle, Psi, to the load current is obtained by using a reduced order model. The proposed overlap phase control exhibits a wide bandwidth suitable for applications such as control of gaseous discharges. Experimental results are given using a 400 W high-pressure sodium lamp as load.