Periodically time-variant systems and harmonic analysis of quasi-resonant converters

The time averaging equivalent circuit approach allows one to obtain a nonlinear differential equation of periodically time-variant system that can be applied to the harmonic analysis of quasi-resonant converters. The differential equation is solved by combination of harmonic balance and small parameter methods. This results in a system of algebraic equations from which a steady-state solution required for the harmonic analysis is obtained. First three equations of this system usually suffice for the practical analysis of converters. An example (zero-voltage switching quasi-resonant boost converter) is given.