A Control Actuation Concept for Self-Oscillating Resonant Converters

This article presents a concept of controller actuation mechanism for self-oscillating resonant converters (SORCs). Simplicity, robustness, and cost-effectiveness are among the main features of this type of converter. Described as a self-oscillating system with an intrinsic positive-type feedback switching network, also known as the self-oscillating command circuit (SOCC), it performs its own gate drive with self-sustained frequency, designed around an equilibrium point. Designers often disregard this converter as an explicit solution for closed-loop applications, especially those that require extra layers of control, due to its inherent inability to operate under pulse frequency modulation without extra circuitry. Thus, in this article, a robust, efficient, and simple way of controlling the SORC through frequency modulation is proposed. The idea consists of varying the self-oscillating frequency through the equivalent magnetizing inductance of the SOCC, using a mechanism called variable current transformer. Thus, through the injection of a small controllable dc current, it is possible to modulate the frequency of resonant converters. This allows the self-oscillating system to follow a reference current signal, operating in closed-loop over a wide range of input voltage and load variation.