Home Embedded Blog Brushless DC Motor vs PMSM: Find Out How These Motors and Their Motor Control Solutions Work

Brushless DC Motor vs PMSM: Find Out How These Motors and Their Motor Control Solutions Work

Motors and Motor Controller Solutions have served Automotive Industry since time immemorial!

And the ongoing innovations in Motors and the Motor Control Systems have ensured that motors are becoming integral part of diverse set of Automotive Applications.

With efficiency as the motive, Motors and Motor Control Solutions are living up to the expectations of the Automotive Industry (including the Electric Vehicle space)

Interestingly, there are two specific types of Motors that have stood the test of time and have evolved tremendously.

They are popularly known as:

  • BLDC Motors – Brushless DC Motors
  • PMSM Motors – Permanent Magnet Synchronous Motors.

While BLDC Motors have replaced the Brushed DC Motors, PMSM Motors have come across as a better alternative to AC Induction motor.

Both these Motors find application in some of the most innovative automotive applications. For instance, PMSM is now the de-facto Motor deployed in the Drivetrain of Electric Vehicles.

Likewise, applications like Electric Power Steering and HVAC systems function at their best when a BLDC Motor drives them. However, these Motors can be sometimes deployed interchangeably, depending on certain specific use-cases.oHoweverHoHH

Before we delve deeper into the applications, let’s have a little understanding of How PMSM and BLDC Motors work?

In the course, we will also try to discuss about the inherent differences between these two motors.

How PMSM and Brushless Motors work?

  1. Brushless DC Motors

    A Brushless DC motor is an upgraded version of a brushed DC Motor. The absence of brushes gives BLDC motors the ability to rotate at high-speed and increased efficiency.

    Highlights of a BLDC Motors:

    • It has two major parts- a rotor and stator.
    • Rotor is the part that moves and has Permanent Magnets as Rotor Magnets.
    • Stator is the Stationary component and is made up of Coil Windings.
    • Electric Current through the Stator Windings generates a magnetic field which rotates the Permanent Magnet of Rotor.
    • By varying the Current flowing through the stator, the speed of the Motor can be varied.
    • In most Automotive Applications, the Motor Speed is controlled electronically, using a Brushless DC Motor Controller.

    *For in-depth details regarding the Motor Control Systems, please refer to our blog.

    Advantages of BLDC Motors:

    • Ability to work at higher speed and produce constant torque
    • Durability
    • Efficiency of almost 85-90%
    • Ability to respond to the control mechanisms at high speeds
    • No sparks and less noise, as the brushes are absent
    • Ease of Motor Control (using BLDC motor controller solutions)
    • Ability to self-start
    • Gets cooled by conduction and requires no additional cooling mechanism
  2. Permanent Magnet Synchronous Motor (PMSM)

    Moving on to the Permanent Magnet Synchronous Motor, it can be seen as an AC counterpart of the Brushless DC motor.

    PMSM also comprises of a Permanent Magnet as a Rotor and a Stator with a Coil wound over it. The working of PMSM Motor is also quite similar to the BLDC motor.

    PMSM Motor

    However, the change lies in the wave form of the Back EMF which is sinusoidal in nature. This is so because the coils are wound on the Stator in a Sinusoidal manner.

    It also implies that PMSM requires Alternating Current (Sinusoidal in nature) to achieve the best performance. This type of drive current also reduces the noise produced by the motor. We will discuss the concept of Back EMF in our upcoming blog on Field Oriented Control (FOC).

    The diagram will bring more clarity.


    Advantages of PMSM Motors:

    • Higher efficiency than Brushless DC Motors
    • No torque ripple when motor is commutated
    • Higher torque and better performance
    • More reliable and less noisy, than other asynchronous motors
    • High performance in both high and low speed of operation
    • Low rotor inertia makes it easy to control
    • Efficient dissipation of heat
    • Reduced size of the motor

BLDC v/s PMSM Motors: Understanding the Motor Control mechanism

There is no major difference in motor control systems of BLDC and PMSM Motors; except the nature of the Drive Current and the detection of the Rotor Position.

While we have discussed the drive-current required for both the motors, let’s now talk about the importance of rotor position detection.

The right time to switching on the Motor Phase Current (motor commutation) is important in order to assess the correct amount of energy. In sensor-based motors, the HALL effect sensors do this job.

In a BLDC motor, the rotor position is usually detected by a set of 3 HALL effect sensors. The commutation is achieved through a six-step process. This results in small breaks in commutation which in turn causes torque ripples (periodic increase/decrease in torque output of the motor) at the end of every step.

A PMSM motor in contrast, requires only one HALL effect sensor as the commutation is continuous. Hence, the rotor position is monitored at every instance and is measured by the sensor and passed on to the PMSM Motor Controller Solution.

One of the advantages of PMSM motor is the absence of Torque ripple, which makes these motors more efficient than BLDC.

What are the Applications of BLDC and PMSM Motors in Automotive Industry?

Both BLDC and PMSM motors are widely used in the automotive industry, as both these Motors cater to the different kinds of use-cases (sometimes interchangeable.)

Brushless DC motors are durable, fairly efficient and low-cost. They can operate on high-speed and can be controlled electronically. All these attributes make these motors ideal for automotive components that are in operation, continuously.

PMSM motors on the other hand has every attribute of BLDC motor with added advantage of lesser noise and higher efficiency.

Let’s see some common applications of these motors, starting with Brushless DC Motors:

  • Electronic Power Steering Systems: The ability to work on high speed and inherent durability, make BLDC motors the preferred choice for Electronic Power Steering (EPS) Applications.

    A sensor-based BLDC motor can detect the position of the rotor and apply optimum torque to drive the steering wheel.

  • HVAC (Heating, Ventilation, and Air Conditioning) System: HVAC solutions are becoming smarter due to introduction of automation in the modern-day vehicles.

    This automation is brought about by the electronically driven motors, especially the Brushless DC Motors. These motors are controlled by Pulse Width Modulation (PWM) which makes it reliable, efficient and environment friendly.

  • Hybrid Electric Vehicle drivetrain: A large number of hybrid vehicles are integrated with Brushless DC Motor Controllers to drive the Drivetrain.

    There are several reasons for the same. Most important reason is the peak point efficiency and simple method of rotor cooling.

BLDC motors also aid in regenerative braking which is about charging the battery at every instance of braking. The Permanent magnets and the external torque work together as a generator to pulse-charge the battery.

Applications of PMSM Motors in Automobiles

  • Servo Mechanism in Automobiles: Servo mechanisms is a set of motors and motor controllers that produce motion at a higher energy level than the input applied. PMSM motors are the first choice of Motors to support such mechanism.

    This is because PMSM Motors are highly efficient, produce less noise and are resistant to wear and tear. One example is the servo brake that amplifies the force used by the driver on the brake pedals. Another example is the Servo Steering which is one step ahead of the regular power steering. This also makes use of a PMSM motor.

  • Electric Vehicle Drivetrain: Baring a few Electric Vehicles which use BLDC motors, most OEMs are deploying AC motors to power the EV drivetrain.

    And PMSM is the preferred choice. Reasons being high power density and the availability of efficient PMSM motor control solutions.

Towards the Future

New features are being introduced in the vehicles at an unprecedented rate. And motors, especially smart motor systems are at the core of such innovations.

Applications like ADAS are also driven by several small electronically driven motors.

And more importantly, as the world moves faster towards electric vehicles, the motors and motor control systems are destined to evolve at a much higher speed.

Because, that is only how the electric vehicles are going to get wider acceptance among the people who are so used to drive IC engine vehicles.

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May 28 2019
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