A brushless DC Motor is also known as BLDC or BL motor. Alternatively, they are also known as electronically commuted motors or synchronous DC Motors. These motors are powered by direct current using an inverter. In certain cases, such motors are powered by switching power supply which produces AC current hence driving each phase of the motor via a closed loop.
Speed and torque of the motor are controlled by a control unit which generates a pulse of current to achieve the desired result. Brushless motors have a high power to weight ratio, high speed, and electronic control. These motors serve a great purpose and are widely used in computer peripherals and power tools.
Construction of Brushless Motors:
A brushless or BLDC motor can be constructed in different configurations. Some of them are as follows:
In this configuration the permanent magnets are embedded in the rotor or in other words they are a part of the rotor itself.
In this configuration, the radial relationship between the coil and the magnet is reversed. The center core of the BLDC motor is made up of the stator coils and magnets spin with an overhanging rotor surrounding the core. This configuration, in general, has more poles, therefore they are set up in triplets to maintain the 3 core windings. Hence they produce high torque at low rpm’s.
Electric Winding Configurations:
Brushless or BLDC motors have two types of electric winding configurations:
In this configuration, the three windings are connected in series and in a triangular circuit and the power is applied to each of the connections.
This configuration is also known as a star winding. Here the windings are centrally connected in parallel circuits and power is supplied to the remaining end of each winding.
One point to be noted here is that a motor having delta configuration of the winding will give low torque at low speeds and will have higher top speed, whereas a motor having wye configuration will give high torque at low speeds but will have a low top end speed.
A motor constructed with wye winding is bound to be more efficient than the one in the delta configuration. In delta winding resistive losses are great and due to the overall configuration of the winding the parasitic electric loses are also on the higher side. There is no such thing in case of wye configuration.
How is a brushless or BLDC motor different from a normal motor?
A note: We are considering DC motors here.
Brushed motors are mechanical motors whereas brushless motors are solid-state electronics motor.
The commutator is the rotary switch which reverses the direction of the electric field inside a motor. This switch is widely used in brushed motors however it is not present in the brushless motors. This is a big difference in the construction of both the motors.
Commutator had many distinct disadvantages. The friction caused here created waste of energy hence decreasing the overall efficiency of the motor. The brush material was of a soft nature hence would get worn out easily. The resistance caused would also result in the drop in voltage. All these problems are not present in the brushless motor.
Other points of difference:
Brushed DC motors develop peak torque when stationary and increasing with the increase in velocity. This limitation is not there in case of brushless DC motor.
Brushless or BLDC motors, when compared to brushed motors, have high torque, high torque to weight ratio and increased efficiency. They also have very less electronic interference.
BLDC motors also don’t have any windings on the rotor so unlike brushed motors they do not have any relation with centrifugal forces. This makes them pretty standard used motor for specialist applications. They also consume very less power in comparison.