Brushless DC Motors.
Confused about motors? Understand the principle and applications of these high efficiency motors.
What is a Brushless DC Motor?
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.
Construction of BLDC Motors
A Brushless DC Motor (BLDC) is a brushless motor which is powered by a direct current voltage supply. In conventional DC motors, brushes are used to transfer the power to the rotor as they turn in a fixed magnetic field, while the brushless DC motors are commutated electronically, thereby eliminating the use of brushes. BLDC motors are broadly used in various applications owing to their high efficiency and exceptional controllability. It also has power-saving advantages as compared to other types of motor
Advantages of BLDC Motors
· Reduced motor size
· Superior thermal characteristics
· Light weight
· Longer lifetime
· No maintenance due to lack of brushes
· No sparking
· Steady operation
· Variable speed
· Excellent controllability
BLDCmotors 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.
· Limited Constant power range
· High-Speed Performance
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.