Series multi-cell converters provide many degrees of freedom. Direct control laws make perfect use of them during transient behaviours but leads to disorderly and imperfect steady-state cycles [4]. The direct command, we propose in this paper, enables the multi-cell converter to reach the optimal steady-state trajectory defined by a P.W.M. control technique. As usual, this control strategy enforce naturally high dynamic properties. Thus, it combines the best features of PWM techniques and direct control strategies. Moreover, this control scheme only needs external variables measurement (input voltage and output current). For the sake of simplicity, the control algorithm, the observer structure as well as the association of both of them are described carefully in the case of a two-cell chopper.