Question:

How do electronically commutated motors (ECMs) work? How are they are different from regular motors, and how do they manage to save energy?

Answer:

In any motor, either the rotor or the stator must have a rotating magnetic field in order to cause the motor to turn. This rotation can be accomplished by:

1. Three-phase AC power, or
2. Single-phase power with some sort of circuit element like a capacitor, inductor, or resistance to synthesize a second phase (that is timed differently from the first), or
3. An electro-mechanical commutator to switch power to different coil groups as the motor turns.

There are limitations with each of the above methods.

• Three-phase AC power is not available everywhere and the frequency and voltage are constant, which makes speed control difficult.
• Single phase power has all the shortcomings of three-phase power. In addition, phase-shifting methods produce a very imperfect rotating field and tend to introduce considerable losses in the motor. Many of the phase-shifting methods produce a very weak starting torque.
• An electro-mechanical commutator solves several of the above problems. It can accomplish wide-range speed control, and it can provide high starting torque. The limitation is that the electro-mechanical commutator has friction and wear problems that reduce efficiency and require frequent maintenance. Also, some sort of voltage controller has to be used to accomplish speed control.

Electronic commutation potentially eliminates all the above problems. Power is pulsed on and off electronically with semi-conductor devices sometimes called electronic switches, transistors, or by various acronyms that denote their design particulars. The pulsed signals power three or more circuits or coil groups within the motor. By varying the timing and duration of pulses, the electronic controller can accomplish speed control and maintain high torque at start and over a broad speed range.

Although many types of motors can be correctly called "electronically commutated" (e.g. AC motors on electronic ASDs and switched reluctance motors), the designation ECM is usually reserved for smaller variable speed motors that operate from a single-phase power source and have the electronic controller mounted in or on the motor.

Electronically commutated motors can have other features that also may be used in addition to, or instead of, ECM in their name. For example, they may or may not also be a permanent magnet motor or axial gap motor. Some are made to run directly from a DC power source. Others are made to run from an AC power source, but they rectify the AC to DC in their controllers before it is pulsed or commutated.