Digital controller design for a practicing power electronics engineer

Practical digital controller design for switching power converters is addressed in this paper. A simplified direct-digital design approach is proposed where digital compensation tools are analyzed in the familiar analog frequency domain. The design is based on traditional concepts and tools such as Bode plots, zero/pole insertion, and gain/phase margins. In contrast to analog redesign methods, this approach is able to accurately account for loop parasitics such as zero-order holds and computational delays and predict the system response. It does not entail the creation of a discrete-time model of the controlled plant, necessary for other direct-digital design approaches. Families of compensation zerostpoles are presented. Notably powerful are two families of complex zero pairs, able to create a sharp phase boost of 180 degrees, specifically useful for converters with high-Q filters. A numbering system is introduced that enables simple -yet optimized- number representation within a fixed-point environment. This system is utilized to model different controller blocks, and to construct a blue-print of the controller code. A design example is then used to demonstrate the design methodology. Experimental results of a matching prototype are then presented that show close correspondence to theoretical and simulation predictions.