Direct modeling of envelope dynamics in resonant inverters

This paper provides a direct dynamic modeling approach for envelope signals in resonant inverters driven by modulated inputs (AM or FM). Based on the sinusoidal approximation, this approach decomposes the modulated input into its fundamental component plus two dominant sidebands. The system response is then found by the summation of the responses to the three individual inputs. Following this conception, the small signal transfer functions for envelope signals in a resonant inverter are then derived. Some simple but useful results for these transfer functions are presented, which link the transfer functions of envelope signals to the transfer functions of the resonant tank and simplify hand calculations. This modeling approach is verified with simulation and experimental results by studying the dynamic responses of output current envelope to bus voltage and switching frequency.