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BLDC Motor Control

What is BLDC Motor?.

A brushless DC electric motor(BLDC motor or BL motor), also known as electronically commutated motor (ECM or EC motor) and synchronous DC motors, are synchronous motors powered by direct current (DC) electricity

What are the types of BLDC Motor?

Out runner: This type of motor spins its outer shell around its windings, much like motors found in ordinary CD-ROM computer drives, defence, and Drone application. The permanent magnets spin around the static rotor. In runner: The permanent magnets spin inside the static rotor uses in actuator application, automobile and automation etc.

Why use BLDC?

It can operate at high speed in both loaded and unloaded conditions.BLDC motors have the highest running torque per cubic inch of any DC motor.BLDC motors do not have brushes, meaning they are more reliable and have life expectancies of over 10,000 hours. It has high life expectancy in continuous running application, no brushes so no spark. Safe for chemical and flammable application. This results in fewer instances of replacement or repair and less overall down time.Inner rotor Brushless DC motors have low rotor inertia, allowing them to accelerate, decelerate, and reverse direction quickly.

How BLDC Motor Control works?

In every industry there are processes some form that require adjustment for normal operation. Such adjustments are usually accomplished with variable speed drive and it consists of

  • Controller
  • Power Converter
  • Electric Motor
  • Controller: The controller generates PWM signal to the converter & hence forms the heart of the Variable speed system.Power Converter: It controls the power flow from an AC supply to the motor by appropriate control of power semiconductor switches (part of power Converter).Electric Motor: It is connected directly/indirectly to the load

    BLDC Motor

    Brushless Permanent Magnet Motors, Permanent Magnet AC motors, Permanent Magnet Synchronous Motors etc. The confusion arises because a brushless dc motor does not directly operate of a dc voltage source. However, as we shall see, the basic principle of operation is similar to a dc motor.

    A Brushless DC motor has a rotor with permanent magnets and a stator with windings. It is essentially a dc motor turned inside out. The brushes and commutator have been eliminated and the windings are connected to the control electronics. The control electronics replace the function of the commutator and energize the proper winding. The energized stator winding leads the rotor magnet, and switches just as the rotor aligns with the stator. There are no sparks, which is one advantage of the BLDC motor. The brushes of a dc motor have several limitations; brush life, brush residue, maximum speed, and electrical noise.

    BLDC Motors are potentially cleaner, faster, more efficient, less noisy and more reliable. However, BLDC motors require electronic control.

    BLDC Motor Operation

    A permanent Magnet AC motor, which has a trapezoidal back emf, is referred to as brushless DC motor (BLDC). The BLDC drive system is based on the feedback of rotor system at fixed points for commutation of the phase currents. The BLDC motor requires quasi-rectangle shaped currents fed into the machine. Alternatively, the voltage may be applied to the motor every 120°, with current limit to hold the current within motor capabilities. Because the phase currents are excited in synchronism with the constant part of the back emf, constant torque is generated. The electromagnetic torque of the BLDC motor is related to the product of phase, back emf and current. The back emf in each phase are trapezoidal in shape and are displaced by 120 electrical degree with respect to each other in 3 phase machine. A rectangle current pulse is injected into each phase so that current coincides with the ack emf waveform; hence the motor develops an almost constant toque.


    Hall Effect sensor provides the portion of information needed to synchronize the motor excitation with rotor position in order to produce constant torque. It detects the change in magnetic field. The rotor magnets are used as triggers to the Hall Sensor. A signal conditioning circuit integrated within the Hall switch provides a TTL-compatible pulse with sharp edges. Three Hall Sensors placed 120° apart, are mounted on the stator frame. The Hall Sensor digital signals are used to sense the rotor position. It ialso use for close loop system

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