Abstract: A brushless direct current motor is energized by a power stage. Switches of the power stage are selectively switched by an electronic control device. In order to determine the correct commutation pattern, without using rotor position indicators such as Hall effect devices, the control device is arranged to sample the power fed to the motor. The samples, each responsive to a test signal or normal energization pulses received by the motor, in a ordered sequence define an analogue function whose parameters can be determined by mathematical analysis. The analysis applied to the samples derives the necessary commutation information and the energization signals in a rapid manner by employing a vector or complex number addition based on functions dependent on variable inductance in the operation of the motor.