This paper deals with a stabilizer for a hybrid kinematic/dynamic control scheme for humanoid robots. The proposed solution is based on a nonlinear PID regulation of the ZMP, coupled with a spherical projection in the CoM's control space. The result of such a stabilizer is a dynamically stable motion, even with large variations in the inclination of the ground. The effectiveness of this new stabilizer has been demonstrated through real-time experiments on the humanoid robot HOAP-3. The produced motion is smooth and dynamically stable.