A control system for an electronically commutated motor (401) can rotate smoothly to very low speeds without using a high resolution encoder and can respond to variations in load without excessive speed fluctuations. The control system can be applied to motors operating with low resolution encoders and motors operating with sensorless rotor position feedback. The electronic control system can vary the magnitude and frequency of the stator excitation applied to one or more stator phase windings, the electronic control system comprising a frequency setting section (402) and a magnitude setting section (403) characterized by the fact that the frequency setting section (402) is constrained to operate over a limited range of frequencies, the maximum frequency being a function which is closely related to the frequency associated with rotation of the rotor at the desired speed.