A Simple Introduction to Brushless Micro Motor Control

The brushless micro motor is becoming increasingly popular in sectors such as automotive (particularly electric vehicles (EV)), HVAC, white goods and industrial because it does away with the mechanical commutator used in traditional motors, replacing it with an electronic device that improves the reliability and durability of the unit.

Another advantage of a BLDC motor is that it can be made smaller and lighter than a brush type with the same power output, making the former suitable for applications where space is tight.

The advantages of brushless operation
The brushes of a conventional motor transmit power to the rotor windings which, when energized, turn in a fixed magnetic field. Friction between the stationary brushes and a rotating metal contact on the spinning rotor causes wear. In addition, power can be lost due to poor brush to metal contact and arcing.

Fundamentals of operation
The BLDC motor’s electronic commutator sequentially energizes the stator coils generating a rotating electric field that ‘drags’ the rotor around with it. N “electrical revolutions” equates to one mechanical revolution, where N is the number of magnet pairs.

Controlling a BLDC motor
While BLDC motors are mechanically relatively simple, they do require sophisticated control electronics and regulated power supplies. The designer is faced with the challenge of dealing with a three-phase high-power system that demands precise control to run efficiently.

Driving a BLDC motor
While an 8-bit microcontroller allied to a three-phase inverter is a good start, it is not enough for a complete BLDC motor control system. To complete the job requires a regulated power supply to drive the IGBT or MOSFETs (the “IGBT Driver” shown in Figure 3). Fortunately, the job is made easier because several major semiconductor vendors have specially designed integrated driver chips for the job.

In summary
BLDC motors offer a number of advantages over conventional motors. The removal of brushes from a motor eliminates a mechanical part that otherwise reduces efficiency, wears out, or can fail catastrophically. In addition, the development of powerful rare earth magnets has allowed the production of BLDC motors that can produce the same power as brush type motors while fitting into a smaller space.

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