Brushless DC motors (BLDC), also known as electronically commutated motors or synchronous DC motors, are a type of synchronous motor powered by direct current (DC). Essentially, a brushless DC motor utilizes a DC power input, which is converted into three-phase AC power via an inverter, to drive a permanent magnet synchronous motor with position feedback.

  Among the diverse types of motors, the brushless DC motor stands as the most ideal speed-controlled motor today. It combines the advantages of both DC and AC motors: it possesses the excellent controllability of a DC motor while also offering the benefits of an AC motor, such as simple structure, spark-free commutation, reliable operation, and ease of maintenance. Consequently, it is highly popular in the market and widely used in automotive, home appliances, industrial equipment, and other fields.

  1 Development History of Brushless DC Motors

  Brushless DC motors did not originate as the earliest product but evolved from brushed motors, featuring a structurally more complex design. A brushless DC motor consists of a motor body and a driver. Unlike brushed DC motors, it does not use mechanical brushes. Instead, it employs a self-controlled permanent magnet synchronous motor with square wave control, replacing the carbon brush commutator with Hall sensors and utilizing neodymium iron boron as the permanent magnet material for the rotor.

However, when motors first emerged in the last century, the practical motors developed were actually brushless in form.

  2 BLDC Motor Fundamentals

  2.1 Structure of Brushless DC Motors

  A brushless DC motor primarily consists of a rotor made of permanent magnet material, a stator with coil windings, and a position sensor (optional).

  Stator

  The stator structure of a BLDC motor resembles that of an induction motor. It comprises stacked steel laminations with axial slots for winding. The windings in a BLDC differ slightly from those in traditional induction motors.

  Typically, most BLDC motors feature three stator windings connected in a star or “Y” configuration (without a neutral point). Additionally, based on coil interconnection, stator windings are further categorized into trapezoidal and sinusoidal motors.

  In trapezoidal motors, both the drive current and counter-electromotive force exhibit trapezoidal shapes (sinusoidal in sinusoidal motors). Motors rated at 48 V (or below) are commonly used in automotive and robotics applications (hybrid vehicles and robotic arms).

  Rotor

  The rotor section of a BLDC motor consists of permanent magnets, typically rare-earth alloy magnets such as neodymium (Nd), samarium cobalt (SmCo), and neodymium iron boron (NdFeB).

  Depending on the application, the number of poles can vary between 2 and 8, with north (N) and south (S) poles arranged alternately. The figure below illustrates three different arrangements of magnetic poles.

(a): Magnets are placed on the outer periphery of the rotor.

(b): Known as an electromagnetic embedded rotor, where rectangular permanent magnets are embedded within the rotor's iron core.

(c): Magnets are inserted into the rotor's iron core.

  2.2 Working Principle of Brushless DC Motors

  The core working principle of brushless motor is "electronic commutation+magnetic field drive"

  Brushless motors replace traditional electric brushes with electronic components. By alternately energizing the stator coils through a controller, a rotating magnetic field is generated, which drives the permanent magnet rotor to rotate along with the magnetic field. The rotor is equipped with permanent magnets, and the stator consists of multiple sets of coil windings. The position sensor detects the rotation angle of the rotor in real time and feeds it back to the controller. The controller sequentially applies electricity to different coils based on the angle signal, forming a continuously changing rotating magnetic field. The rotor permanent magnet continuously rotates with the magnetic field under the action of magnetic attraction and repulsion, achieving power output..

 3 Brushless DC Motor Drive Methods

  Brushless DC motors employ various drive methods categorized by different approaches, each with distinct characteristics.

  By Drive Waveform:

  Square Wave Drive: This method is simple to implement and facilitates sensorless motor control.

  Sine wave drive: This method improves motor performance by delivering uniform output torque, though its implementation is relatively complex. It further divides into SPWM and      SVPWM (Spatial Vector PWM) approaches, with SVPWM offering superior results over SPWM.

  4 Advantages and Limitations of Brushless DC Motors

  Advantages:

  High output power

  Compact size and lightweight

  Excellent heat dissipation and high efficiency

  Wide operating speed range

  Low electrical noise

  High reliability and low maintenance requirements

  High dynamic response

  Minimal electromagnetic interference

  Limitations:

  Expensive electronic controllers required for motor control

  Complex drive circuitry needed

  Additional position sensors required (except for FOC)

  5 Applications of Brushless DC Motors

  Brushless DC motors are widely used across diverse application needs, such as industrial control, automotive, aerospace, automation systems, and medical equipment, serving various loads, constant-load applications, and positioning tasks.

  Industrial Control Sector

  In recent years, driven by extensive R&D and technological maturation, the adoption of brushless DC motor drive systems in industrial production has expanded significantly, establishing them as the mainstream development direction for industrial motors. Research and efforts focused on reducing production costs and enhancing operational efficiency have yielded significant benefits. Major manufacturers now offer diverse motor models to meet the needs of different drive systems. Currently, brushless DC motors are employed in industrial production sectors including textiles, metallurgy, printing, automated production lines, and CNC machine tools.

  Automotive Sector

  In addition to the core engine, there are also electric motors in parts such as wipers, electric doors, car air conditioning, and power windows. With the development of the automotive industry towards energy conservation and environmental protection, the motors used must also meet the standards of high efficiency and low energy consumption. The advantages of brushless DC motors, such as low noise, long lifespan, no spark interference, and convenient centralized control, are fully in line. With the increasing maturity of their speed regulation technology, their cost-effectiveness will become higher, and their application in various aspects of automotive motor drive will become more widespread.

  Medical Equipment Sector

  Internationally, brushless DC motors are already widely adopted, powering miniature blood pumps in artificial hearts. Domestically, they drive high-speed centrifuges for surgical instruments, infrared laser modulators in thermal imaging cameras, and temperature measurement devices.

   Home Appliance Sector

“Inverter” technology has become ubiquitous, gradually dominating the consumer market as a hallmark of Chinese home appliances. “DC inverter” technology is favored by manufacturers, showing a trend toward replacing “AC inverter” systems.

  Office Computer Peripherals and Digital Consumer Electronics

  Common household devices like printers, fax machines, copiers, hard disk drives, floppy disk drives, and film cameras all incorporate brushless DC motors in their spindle and auxiliary motion control systems.