We consider the control problem for a class of biological models of photo-synthetic algae growth in the chemostat. These models are “variable yield” models, on the contrary to classical bioprocess models that are “constant yield” ones. We develop then a nonlinear controller for a wide class of qualitatively known variable yield models and theoretically prove the global asymptotic stability of the resulting set point for the closed loop system. Finally some simulations for Dunaliella terti-olecta growth, with realistic parameters, illustrate this proof. Moreover, the controller appears to be robust to noise and algae concentration dynamics does not depend upon feeding nutrient concentration.