On the stability and subharmonic susceptibility of current-mode controlled converters

The authors present stability conditions for constant switching frequency power converters with current-mode control. The conditions take fully into account the interaction of the current and voltage feedback loops, and give explicit limits for the loop gains as a function of the duty ratio and the slope of the compensation ramp. The conditions are confirmed by experiment, and it is shown that they provide more stringent limits than the conventional stability analysis. The authors also introduce the concept of subharmonic susceptibility, which is closely related to the stability conditions. This is a useful design parameter which provides a measure of the degree of stability