Simplified Frequency-Domain Analysis of Improved Asymmetrical PWM Technique for DC-DC Resonant Converters

摘要

The present work introduces a frequency domain analysis of an improved asymmetrical pulse-width modulation (I-APWM) scheme for dc-dc resonant converters. By adjusting both switching frequency and duty cycle, the improved APWM scheme has been shown to extend zero voltage switching (ZVS) range at light load conditions. However, the existing time-interval analysis proposed by authors results in non-linear transcendental ZVS conditions which are resource intensive to implement on a digital microprocessor. The proposed frequency analysis uses the Fourier series to establish simple analytical solutions that determine both switching frequency and duty cycle for ZVS operation. Necessary ZVS conditions have been established for a dc-dc LLC resonant converter using the derived analytical equations. Theoretical analysis is verified by an experimental prototype of a 300W/400V dc-dc LLC resonant converter operating over an input voltage range of 25-40V.