Electronically commutated motor and method of controlling such a motor

The present invention relates to a method of operating a three-or more-stranded electronically commutated motor which, to detect its rotor position, has a number of sensors which is fewer, by at least one, than the number of sensors intrinsically necessary for this number of strands for controlling the commutation, having the following steps: (a) within each range (120) of rotor positions in which an adequate association between sensor output signals and position is possible, a virtual rotor position signal (H3B\') is derived from the output signals (H1, H2) of said rotor position sensors (37, 38), as a replacement for a sensor which is not present; (b) within each range (122, 124) of rotor positions in which an adequate association is not possible, an estimated value (H3B\") is used for the virtual rotor position signal, which value is a function of an output signal (H1) of at least one of the existing rotor position sensors (37, 38). A preferred embodiment of the invention includes a RISC microprocessor which processes signals from two Hall sensors to derive a third \"synthetic\" sensor signal, representing rotor positions for which the two actual Hall sensors do not provide coverage. This has the advantage that the power consumed by the sensors, which sometimes exceeds that consumed by the motor itself, is reduced by up to one-third. Such power economy makes it practical to use motorized dampers in air-conditioning installations.