Difference between BLDC Motor and PMSM Motor


An electromechanical energy conversion device that converts electrical energy into mechanical energy in the form of rotation of shaft is known as electric motor or simply motor. There are several types of electric motors available such as induction motor, brushed DC motor, brushless DC motor, synchronous motor, etc.

Read through this article to get a brief overview of BLDC motors and PMSM motors, how they operate, and what are the major differences between them.


What is BLDC Motor?

BLDC Motor or Brushless Direct Current Motor is a type of DC motor which does not have brush assembly for commutation, rather it uses electronic commutation system.

A BLDC motor consists of two main parts namely: stator and rotor. The rotor is a rotating part and has permanent magnets. The stator is a stationary part and has stator windings. When the stator windings of the BLDC motor are connected to a switching circuit (or control circuit), it energies the stator windings. Now, a rotor magnet tends to align with the energized stator winding (acts as electromagnet), as soon as it aligns, the next stator winding (stator electromagnet) is energized. This makes the rotor running.

The electronic control circuit used in the BLDC motor helps in obtaining unidirectional torque. For this region, the BLDC motor is also called as electronically commutated motor.

Now-a-days, the BLDC motors are becoming popular because of the following advantages:

  • High efficiency as compared to conventional DC motor.
  • More reliable
  • No sparking due to absence of brushes
  • Long lifespan, etc.

What is a PMSM Motor?

PMSM Motor or Permanent Magnet Synchronous Motor is a type of AC synchronous motor that uses permanent magnets to provide the necessary field excitation.

Just like any other electric motor, the PMSM motor also consists of two major parts namely stator and rotor. The rotor of the PMSM motor has permanent magnets mounted on it that form rotor field poles. The stator contains the stator winding. When the stator winding is energized by supplying alternating current (AC), a rotating magnetic field is produced in the air gap between the stator and rotor. This rotating magnetic field of stator interacts with the magnetic field of the rotor, i.e. the rotor poles lock with the rotating magnetic field of the stator and starts rotating at the synchronous speed.

One of the major disadvantage of the PMSM motor is that it is not self-starting. Therefore, we need to provide a variable frequency power supply. The major advantages of a PMSM motor are: high efficiency, no sparking, compact in size, high dynamic performance, etc.

Difference between BLDC Motor and PMSM Motor

Both BLDC and PMSM are types of brushless motors. However, there are many differences between these motors that are highlighted in the following table:

Basis of Difference BLDC Motor PMSM Motor
Full form BLDC Motor is the abbreviated name for Brushless Direct Current Motor. PMSM stands for Permanent Magnet Synchronous Motor.
Definition A BLDC motor is an electronically commutated DC motor which does not have carbon brushes and commutator assembly. A PMSM motor is an AC synchronous motor that uses permanent magnets to provide the necessary field excitation.
Type of motor BLDC motor is a direct current (DC) motor. PMSM motor is an alternating current (AC) motor.
Waveform of back emf The waveform of back emf of a BLDC motor is trapezoidal shaped. The waveform of back emf of a PMSM motor is sinusoidal shaped.
Torque The torque produced by a BLDC motor is comparatively lower. A PMSM motor produces higher torque as compared to BLDC motor.
Efficiency The efficiency of a BLDC motor is less, around 85% to 90%. PMSM motors are comparatively more efficient. The typical efficiency is about 92% to 97%
Switching losses At same switching frequency, a BLDC motor has less switching losses. The switching losses in a PMSM motor are high.
Core losses BLDC motor has high core losses because of harmonics. The core losses are less in a PMSM motor due to less harmonic content.
Torque ripple In BLDC motors, the torque ripples present at the commutation. There is no torque ripple at the commutation in case of PMSM motor.
Control BLDC motor uses comparatively The control algorithms used in PMSM
algorithm simple control algorithms. motors are complex and mathematically intensive.
Cost The BLDC motor is comparatively less expensive. The cost of PMSM motor is high.
Applications BLDC motors are used in hard drives, CD/DVD drives, washing machines, fans, pumps, robotics, etc. PMSM motors are used in servo drives, traction control, robotics, aerospace, power factor improvement, machine tools, etc.

Conclusion

The most significant differences between BLDC and PMSM motors is that the BLDC motor is a direct current (DC) motor, whereas the PMSM motor is an alternating current (AC) motor.

Updated on: 08-Nov-2023

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