Posicast-based digital control of the buck converter

The analysis, design, and microcontroller-based implementation of a digital controller using a Posicast element are presented for the buck converter. Posicast is a feedforward compensator that eliminates overshoot in system response, but the traditional approach is sensitive to variations in natural frequency. The new method described here reduces the undesirable sensitivity by using Posicast within a feedback loop. Compared to classical proportional-integral-derivative (PID) control, the new control results in lower noise in the control signal because the controller has a lower gain at high frequency. Furthermore, the authors' experiments indicate that the new controller is less sensitive to the inherent time delay associated with a digital controller for a dc-dc converter. The authors present a straightforward method to design controller parameters from the small-signal averaged model of the converter dynamics. Experimental results for a PID-controlled converter and Posicast-type controller are also compared.