A brushless DC (BLDC) motor is essentially a DC motor without the mechanical commutation of the brushed DC motor. BLDC motors are powered by direct current and have electronic commutation systems instead of the mechanical brushes and commutators used in brushed DC motors.

All DC motors generate a magnetic field, either via electromagnetic windings or permanent magnets. An armature, which is often a coil of wires, is placed between the north and south poles of a magnet. When current flows through the armature, the field produced by the armature interacts with the magnetic field from the magnets and eventually generates a torque and thereby motion.

For motion control applications, the most common DC motor types are the basic brushed DC motor, brushless motors, and permanent magnet motors.

In a brushed DC motor, the magnet acts as the stator. The armature is integrated onto the rotor and a commutator switches the current flow. The commutator’s function is to transfer current from a fixed point to the rotating shaft. Brushed DC motors generate torque straight from the DC power supplied to the motor by using internal commutation, fixed permanent magnets, and rotating electromagnets.

Brushed DC motors have the advantage of generally low initial cost and simple control of the motor speed. However, there are some drawbacks. At certain periods during the DC motor rotation, the commutator must reverse the current, causing reduced motor life due to arcing and friction. Consequently, brushed DC motors require more maintenance such as frequently replacing the springs and brushes which carry the electrical current, as well as replacing or cleaning the commutator. These components are important for transferring electrical power from outside the motor to the spinning coil windings of the rotor inside the motor.

BLDC motors, on the other hand, do away with mechanical commutation in favor of electronic commutation, which eliminates the mechanical wear and tear involved with brushed DC motors. In BLDC motors, the permanent magnet is housed in the rotor and the coils are placed in the stator. The coil windings produce a rotating magnetic field because they’re separated from each other electrically, which enables them to be turned on and off. The BLDC’s commutator does not bring the current to the rotor. Instead, the rotor’s permanent magnet field trails the rotating stator field, producing the rotor field.

For successful commutation, it’s important to have precise rotor position data, which is often achieved via magnetic sensing with a Hall Effect sensor, which also allows for tracking of speed and torque.

BLDC motors have quite a few advantages over their brushed counterparts. Compared to brushed DC motors, BLDC motors are more efficient due mainly to the elimination of the friction from the brushes. They’re also more reliable and typically have longer life spans as well. Getting rid of the brushes also means a decrease in EMI (electromagnetic interference) noise and no sparking from the brushes making contact with the commutator.

Some servomotor systems use brushless DC motors instead of other types of motors (either a brushed DC motor or an ac motor such as an induction motor.)

BLDC motors are used in everything from low-power applications such as consumer products to high power applications in electric vehicles and industrial equipment.

 

Content provided by Design World.