Dynamic ZVS direct on-line start up of current fed resonant converter using initially forced DC current

ZVS (zero voltage switching) is critical for the reliable operation of normal current fed DC-AC resonant converters. In the steady state, ZVS can be achieved by many available techniques such as PLL, VCO and other integral controllers. However, during the transient process like start up, to achieve ZVS is not an easy task for these controllers and consequently switch failure may occur. Based on numerical and analytical analyses, this paper proposes a novel method using an initially forced DC current to achieve ZVS during start up. Start up conditions are discussed and complete dynamic ZVS is achieved. Considering the ramp up delay of the DC power supply, the start up can be controlled completely overshoot free at no extra cost. The validity of this method has been proven with PSpice simulations and experimental results