High performance control of the series-parallel resonant converter

The authors describe the operation, characteristics and design of a two-loop control technique for a MHz-switching series-parallel resonant converter. A resonant current feedback loop is used to determine the transistor switching instants resulting in the fourth-order converter characteristics becoming third order and, furthermore, being insensitive to operating conditions. The technique exploits the inherent delays in MHz-switching converter systems to provide well-damped dynamics. An output voltage control loop bandwidth of 100kHz is achieved.