A Novel Method to Predict ZVS Behavior of LLC Converters

Abstract:
Resonant converters have been gaining much attention within the recent years. However, their exact mathematical description is rather complicated making simplified calculation methods very attractive, e.g. the First Harmonic Approximation (FHA). Although the steady state solution of these simplified methods is usually quite acceptable and close to the exact solution, the prediction of the ZVS characteristic is either neglected or treated too simple. The ZVS characteristic is typically directly related to the voltage transfer function resulting in a too optimistic estimation of the operation range obtaining ZVS. This paper focuses on a more accurate investigation of the resonant LLC converter’s ZVS behavior and proposes two approximation methods allowing a fast estimation of different converter designs.