In this paper, an observer-based switched control law is proposed for the three level neutral point clamped (NPC) converter operating as a rectifier. Modeling the converter as a switched affine system, the proposed control is based on the well known argmin control law to track a varying state reference trajectory. A full-order observer is introduced to compute the control law with only the measure of the input and the output voltages. The control aims at tracking a state reference defined from a power analysis and three objectives are addressed: to stabilize the output at a given DC voltage, to ensure a unit power factor by having the input current and voltage on phase and to have balanced capacitor voltages on the output. Based on a unified modeling methodology, the control and the observer are easily derived from LMI conditions. An outer loop is added to regulate the output when constant perturbations are considered. The results are illustrated by simulations on MATLAB/Simulink.