This article proposes a proportional-type cascade output voltage control algorithm equipped with disturbance observers for a three-phase AC/DC converter considering a model-plant mismatch. The advantages of the proposed method are grouped into two. First, a simple first-order disturbance observer is devised for both inner and outer-loops, not only to recover the target closed-loop performance, but also to eliminate steady-state offset errors. Second, it is thoroughly verified that the entire closed-loop system driven by the proposed proportional-type cascade controller is stable. The efficacy of the proposed method is experimentally investigated using a 3 - kW AC/DC converter.