A mechanical ventilator (10) provides pressure support ventilation (PSV) to a patient (12). A power of breathing (PoB) or work of breathing (WoB) estimator (30) generates a PoB or WoB signal (34) for the patient. An error calculator (36) computes an error signal as a difference between the PoB or WoB signal and a set point PoB or WoB value (22). A controller (20) inputs a PSV control signal (24) equal to the product of the controller transfer function and the error signal to the mechanical ventilator. A patient adaptation component (52, 54, 56, 60) fits parameters of a model of a controlled mechanical ventilation system comprising the mechanical ventilator and the patient to data comprising the PoB or WoB signal and the PSV control signal generated by the operating closed loop controller, and adjusts parameters of the controller transfer function to maintain stability of the operating closed loop controller.