How Does Back-EMF Control of Sensorless Brushless Motors Work and What Brushless Motor Controllers Do I Need For This?

What exactly is back-EMF?

Back EMF stands for Back Electromotive Force.

In simple terms, the Back EMF is an electromotive force which occurs as the brushless motor turns. This acts like a generator creating electromotive resistance within the motor. Critically, motor controllers such as the ZDBL15 sensorless brushless DC motor controller can measure the back-EMF generated. As the back-EMF frequency is proportional to the motor speed this enables us to determine the exact speed of the motor.

An intelligent motor controller such as the ZDBL15 sensorless brushless motor controller can then read this force and use it to measure the actual speed of the motor. The ZDBL15 can then maintain this speed using Back EMF as a reference to measure and adjust the speed. It is this method which enables a sensorless brushless motor controller such as the ZDBL15 to be able to deliver constant speed under a variable load.

Are there disadvantages to using back-EMF in sensorless brushless motor controllers?

In a word, no. However, there are limitations.

The most notable of these is the fact that back EMF is not generated when the motor is stationary, meaning that start up is difficult. As such, the motor can take a small amount of time to settle and run efficiently. This is something that can be compensated for by requesting a sensorless BLDC controller be specifically optimised for your application.

A second (related) limitation is that at low speeds the back EMF is weak and therefore quite difficult to measure accurately. This can result in inefficient operation in the form of jumpiness. However, there are measures that can be taken to reduce or completely remove this negative impact. Talk to our team today to see how we can help you get the performance you need.

What are the main advantages of using back-EMF in the control of sensorless brushless motors?

Using back-EMF as a means of maintaining and accurately controlling motor speed in brushless DC motors is a much lower cost solution than brushless DC motors with sensors and is also much more reliable as there are less component parts which can go wrong. A sensored brushless DC motor and a sensored motor controller will become completely useless if the sensors fail. However, a sensorless brushless motor controller will be able to function reliably without risk of sensor failure.

To browse the range of ZDBL Series Brushless Motor Controllers which optimise back-EMF to deliver exceptionally accurate brushless motor control please CLICK HERE


Is a 'closed loop' sensorless brushless system right for my application?

Ultimately the question of which method of drive is best for your project or application is a subjective one which needs to be looked at and decided on a case by case basis. We are aware that this may sound like us hedging our bets but there are so many small factors that can impact on the performance of a system and its appropriateness for particular applications that it needs to be viewed in this way. 

If you would like to read more about this on our website then please have a look at our main applications and case studies page which highlights several examples of how these types of systems have been implemented. 

Category: Brushless Motor Controller FAQs
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