What are Brushless DC Motors (BLDC)?

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Editorial Team - everything PE

Apr 17, 2024

A brushless DC (BLDC) motor is a type of synchronous direct current (DC) motor that does not use brushes for commutation. Instead, they are electronically commutated with the help of semiconductor switches. Commutation is the process of switching the current flow in the motor's windings to maintain continuous rotation. As electronic switches are used for transferring current to the coil windings, these motors are also called electronically commutated motors (ECM) or EC motors.

Construction and Working of BLDC Motors

A BLDC motor design is similar to a brushed DC motor design and comprises a rotor and a stator. The rotor consists of a permanent magnet and the stator consists of electromagnets in the form of windings. In addition, it consists of a few BLDC-specific components such as sensors and an electronic controller. Hence the main components of a BLDC motor include:

  • Rotor
  • Stator
  • Position Sensor
  • Electronic Controller

Cross Section of a BLDC Motor

Stator: The stator comprises stacked steel laminations with axially cut slots for winding. It produces a shifting magnetic force and results in the spinning of the rotor. The stator can be configured inside and surrounded by a rotor or it can be outside and enclosing the rotor. It usually consists of three different windings connected using either a star or delta pattern. A star configuration produces a higher torque level at lower speeds whereas a delta pattern produces a low level of torque at low motor rpm.

Rotor: The rotor comprises of permanent magnet made up of rare earth materials such as neodymium, ferrite, and boron. It offers a magnetic field that interacts with the stator to enable rotational motion. Depending on the application, the number of poles varies from two to eight with north (N) and south (S) poles positioned alternatively. Similar to the stator, the poles of the rotor can be configured either on the outer periphery of the rotor, embedded into the core of the rotor, or can be inserted into the core of the rotor. 

Increasing the number of poles increases the motor’s torque. However, it decreases the motor’s speed and smoothness of operation. Also, the use of high-ferrite materials for permanent magnets enhances the motor’s torque. 

Position Sensor: For a BLDC motor to electronically, its controller must be aware of the position of the rotor anytime. Hall effect position sensors are used to sense the rotor position and switch the power to the right electromagnet at the right time. Three such sensors are embedded into the stator to estimate the rotor’s position. The output of the sensor is either high or low depending on the type of pole (N or S) that has passed near it.

Electronic Controller: The electronic controller in a BLDC motor coordinates the various components to achieve precise and efficient motor control. It determines the optimal timing for commutation based on feedback from position sensors. The controller also regulates the speed and torque of the BLDC motor by adjusting the amplitude and timing of the current supplied to the windings.

Working Principle: The working principle of a BLDC motor is based on the interaction between the magnetic fields of the stator and the rotor, which is controlled by the electronic controller. The electronic controller is integrated into the motor's stator assembly. It provides a three-phase frequency-controlled supply to the stator winding and controls the flow of current based on the position of the rotor. The rotor position is detected by Hall effect sensors mounted on the stator. The controller adjusts the flow of current to the motor windings to ensure smooth and efficient operation of the motor.

Features of BLDC Motor

  • Use of rare earth material permanent magnets: BLDC motors use permanent magnets made up of rare earth materials such as neodymium, ferrite, and boron. These magnets create a strong electric field and do not require pole windings. This results in reduced electrical losses, and reduced weight and volume for these motors.
  • Brushless Design: BLDC motors replace brushes with electronic circuits to transform the DC to AC. This results in negligible spark and noise, no brush consumption, and reduced maintenance. It eliminates electrical and mechanical losses. 
  • High Efficiency: BLDC motors have an efficiency of up to 95% which leads to less energy consumption and heat generation compared to brushed motors.
  • High torque-to-weight ratio: BLDC motors often have a high torque-to-weight ratio, making them suitable for applications where weight and space are critical factors.
  • Variable Speed Control: BLDC motors offer precise control over speed and direction through electronic control systems. This makes them ideal for applications where precise speed regulation is needed.
  • Regenerative Braking: BLDC motors can act as generators during braking. They convert kinetic energy into electrical energy which is fed back to the power supply or stored for later use, improving overall energy efficiency.
  • Durability and Cost-Effectiveness: The simple and robust design of BLDC motors makes them more durable and reliable than brushed motors in harsh operating environments. Though it has a higher initial cost, its efficiency, reliability, and long-term savings in maintenance and energy costs justify the investment in high-performance applications.

Disadvantages of BLDC Motors

  • Higher Initial Cost: The high initial cost of a BLDC motor is attributed to factors such as the incorporation of electronic controllers and sensors within the assembly.
  • Fragile Electronics and Sensors: BLDC motors depend on electronic controllers and sensors for their operation which impose restrictions on the motors' suitability for rugged environments like dusty conditions.
  • Demand Gear Reduction: The high rotational speed of BLDC motors makes them impractical for low-speed applications, such as drives. In such scenarios, a gear reduction system is necessary, which leads to increased costs.

Applications of BLDC Motors

  • Electric Vehicles (EVs): BLDC motors find widespread usage in electric vehicles (EVs) for propulsion. Their efficiency and high torque-to-weight ratio make them well-suited for EV applications, extending driving ranges and enhancing overall performance.
  • Industrial Automation: BLDC motors play a crucial role in various industrial automation systems, including robotics, conveyor belts, CNC machines, and packaging equipment. Their precise speed control and robust torque capabilities enhance productivity and accuracy in manufacturing processes.
  • HVAC Systems: Heating, Ventilation, and Air Conditioning (HVAC) systems employ BLDC motors in fans and pumps to facilitate air circulation and fluid movement. These motors' energy efficiency and silent operation render them suitable for diverse HVAC applications, spanning residential, commercial, and industrial sectors.
  • Home Appliances: BLDC motors are integrated into home appliances like washing machines, refrigerators, and vacuum cleaners. Their energy-efficient operation and durability contribute to lower power consumption and extended product lifespans.
  • Aerospace: BLDC motors serve critical functions in aerospace applications, including actuation, control surfaces, and auxiliary systems. Their lightweight design and high reliability are indispensable in aerospace engineering, ensuring optimal performance and safety.
  • Consumer Electronics: BLDC motors are seamlessly integrated into various consumer electronics products such as computer cooling fans, hard disk drives, and camera autofocus systems. Their compact size, minimal noise output, and precise control capabilities enhance the functionality and user experience of electronic devices.
  • Medical Devices: BLDC motors play a vital role in numerous medical devices and equipment, including infusion pumps, surgical tools, and laboratory automation systems. Their precise motion control and unwavering reliability are pivotal in critical healthcare applications, ensuring precise and consistent performance.
  • Renewable Energy Systems: BLDC motors are used in renewable energy systems like wind turbines and solar tracking systems. Their superior efficiency and reliability play a pivotal role in maximizing energy production and optimizing overall system performance.
  • Marine Applications: BLDC motors find extensive usage in marine propulsion systems, thrusters, and auxiliary equipment aboard boats and ships. Their robust construction and corrosion resistance are essential attributes that ensure dependable operation in challenging marine environments.