Tuning Dc Brushless Motors

A method of tuning a DC brushless motor integrated in a blood pump, wherein measurement of back EMF voltage is used to detect changes in the torque requirements caused by variation in the blood characteristics or blood dynamics characteristics, the method including varying the timing of the drive signals to the motor to compensate for the changes in the torque requirements, wherein the motor comprises a rotor and a stator, the stator including at least three phases, wherein alternating driving signals are provided simultaneously to at least two of the at least three phases such that, each switching cycle is a driving cycle, for at least two of the phases that receive driving signals, and the same switching signal is a listening cycle for at least one listening phase that is non-energised during this cycle, the motor being arranged such that, for a given switching cycle, a rotation of the rotor generates in the at least one listening phase a back EMF voltage that varies between two extreme values, the method including the steps of:

• for at least one reference switching cycle:
• detecting the back EMF voltage from the at least one listening phase;
• determining the back EMF voltage corresponding to the midpoint value between the extreme values to define a reference voltage value;
• and
• calculating the time delay for the back EMF voltage to change from the midpoint value to the final extreme value to define a reference delay time;
• then, for at least one further switching cycle having a further at least one listening phase and a further set of at least two driving phases, the further cycle being subsequent to the reference cycle, with:
• monitoring the back EMF voltage in the further listening phase and, when the EMF voltage reaches a value equal to the reference voltage value;
• and
• providing a driving signal to the corresponding driving phases with a time delay with respect to the reference voltage point, equal to the reference delay time.