A digital observer based current loop control for buck converters

This paper presents an approach for current sensing in digital controlled buck converters. Therefore, an observer based algorithm in a digital implementation is used as it has the advantage of not needing an additional shunt in the circuit and thus causing additional losses. The setup needs no additional a to d converter (ADC) besides the already available ones in the system. Using the observer principle a current signal is obtained, which is fed to the current loop of the controller. In order to prove the working principle of this current sensing technique a system level simulation in ScicosLab is performed and the results are presented. Subsequently these results are compared with a standard current mode control. The robustness of the algorithm is proven by simulations with a noise floor of V pp = 20 mV (peak-to-peak voltage) on the measured signals. Additionally an approach to estimate the on-resistances of the switches is presented and proved by simulations, as this parameter is required for the herein presented observer algorithm.