Direct ZVS start-up of a current-fed resonant inverter

Zero voltage switching (ZVS) is critical for reliable operation of standard current-fed parallel resonant inverters. Under steady-state conditions, ZVS can be achieved using common techniques such as a phase lock loop, a voltage controlled oscillator, and other integral controllers. However, during transient processes, achieving ZVS is not trivial for such controllers and consequently switch failure can occur. This paper proposes a dynamic ZVS method to solve the start-up problems by using a forced dc current. Start-up conditions are analyzed and complete dynamic ZVS control is achieved. If the ramp-up delay of practical dc power supplies is utilized, the start-up process can be controlled to be overshoot-free at no extra cost. The validity of this method is proven using both PSpice simulations and experimental results