Digital controller design for buck and boost converters using root locus techniques

Root locus techniques to design digital controllers for buck and boost converters are discussed in this paper. The small signal models of both converters are first transformed into discrete-time models using the matched pole-zero mapping method. Digital controllers are designed based on the discrete-time model using the root locus method. By selecting the poles, zeros and gain of the digital controllers, the closed-loop poles are placed at desired locations in the z-plane. The digital controllers are then implemented on a TI DSP. The root locus design method is compared with the frequency response design method. Experimental results from the buck converter indicate that the results obtained using the root locus method are comparable to the results obtained using the frequency response method, while results from the boost converter indicate the nonlinear nature of the boost converter small signal model may degrade the performance of the design using the root locus method.