An electronically commutated motor (ECM) uses a microprocessor controller to sequentially energize/de-energize each winding of the stator.  This processor-based pulse control sets up the magnetic field that makes the rotor turn. The microprocessor uses a closed loop feedback mechanism to more precisely control the magnetic fields and minimize eddy current losses. This allows a brushless design to be used, so reducing points of moving physical contact. 

An ECM motor has a minimum efficiency of 70% throughout its operating range, and at low speeds is over 30% more efficient than a standard induction motor.