Proximate Time-Optimal Digital Control for DC-DC Converters

This paper introduces an approach to near time- optimal control in DC-DC converters using a simple digital controller realization. The proposed proximate time-optimal digital (PTOD) controller is a combination of a linear PID controller operating near a reference point and a nonlinear switching surface (NSS) controller away from the reference, together with a smooth transition between the two. A capacitor current estimator enables effective switching surface evaluation and eliminates the need for current sensing. The NSS controller, which is implemented as a small Verilog HDL module, can be easily added to an existing digital PWM controller to construct the PTOD controller. In steady state, the converter operates at constant switching frequency. Simulation and experimental results are shown for a 6.5 V-to-1.3 V, 10 A synchronous buck converter.