In a BLDC motor, the mechanical commutator used in the conventional DC motor is replaced with an electric switch circuit. A brushless DC Motor is basically a type of synchronous motor. Therefore, the magnetic field generated by the stator and the rotor revolve at the same frequency.
Since BLDC motors are commutated electronically, the windings of the stator must be energized in a sequence and the position of the rotor must be known to precisely energize a particular set of stator windings, in order to rotate the motor.
A Position Sensor or a Hall Sensor is a sensor that works on the principle of Hall Effect. Its function is to detect the position of the rotor and transform it into an electrical signal. These sensors are embedded into the stator to detect the rotor’s position. Usually, three Hall sensors are required in a BLDC motor.
BLDC motors can be controlled using feedback mechanisms to give specifically the required torque and rotation speed. Precision control, in turn, lessens energy utilization and heat generation. In certain cases, where motors are powered by battery, the precision control enhances the battery life.
BLDC motors also offer high durability and low electric noise generation owing to the lack of brushes. With brushed motors, the brushes and commutator wear down because of the continuous moving contact, and also produce sparks at the point of contact. Particularly, electrical noise is a consequence of the strong sparks that happen to take place in the areas where the brushes pass over the spaces in the commutator. Therefore, BLDC motors are often considered preferable in applications where it is important to avoid electrical noise.
The cost of a BLDC motor is relatively higher when compared to a conventional brushed DC motor. The electronic controller also elevates the overall cost of the complete setup, as in a traditional motor. A less expensive mechanical commutation setup involving brushes is used. When a BLDC motor is operated at low speed, slight vibrations take place during low-speed rotation. However, the vibrations are reduced at high speed. Due to the inherent natural vibration frequency of the BLDC motor, sometimes this natural frequency is capable of matching or coming closer to the vibration frequency of the body or plastic parts resulting in the occurrence of a phenomenon, known as resonance. However, this resonance can be minimized by adjustment. The resonance phenomenon is commonly observed in various BLDC motor based devices. The brushed DC motors are easy to operate as they have simple wiring. The positive terminal is connected to the positive wire and the negative terminal is connected to the negative wire and the motor starts rotating. However, in the case of a BLDC motor, wiring and operation of the motor are not that smooth and effortless. This is because of the involvement of electronic control and its connection to all the electromagnets.
A large constant power range is important for achieving a high vehicle efficiency. It is impossible for a BLDC motor to achieve a maximum speed greater than twice the base speed. During the manufacturing process of the BLDC motor, it might result in being dangerous because the large rare earth permanent magnets can attract scattered metal objects. In case of a vehicle crash, if the wheels spin freely and the motor is still excited by permanent magnets, high voltages will appear at the motor terminals. This can endanger the passengers or rescuers. The permanent magnet can be demagnetized by applying a huge reverse magnetomotive force and increasing the temperature. The critical demagnetization force is distinct for each permanent magnet material. Surface mounted motors of permanent magnets fail to achieve high speeds. This is because of the limitation by the mechanical strength of the assembly between the rotor yoke and the permanent magnets.
Applications of BLDC Motors
Considering the long list of advantages, BLDC motors can be used in numerous applications, ranging from automotive to industrial applications. They can be used in medical equipment, home appliances, building controls and industrial automation. They can also be used to drive vacuum machines. These brushless motors can also be used to spin hard disc drives. Here, their durability keeps the drives operating dependably over the long term. The power efficiency of these motors contributes to energy reduction in an area where this is becoming increasingly important.
Some applications that use the BLDC motors are :
Heating and ventilation