How does Closed Loop Control of Brushless Motors Work, What Brushless Motor Controllers Do I Need and What Are the Advantages?

What does closed loop brushless control involve?

Closed loop brushless control involves driving a motor but then monitoring the speed of the motor and using the monitored information to inform the behaviour of the driver. This then creates a closed loop in which the actual output of the motor is monitored and the controller drive adjusted according to the behaviour of the motor. This is particularly useful in applications in which there is a need to maintain an exact speed all the time or is also a useful method for monitoring for potential faults such as jams, stalls or where a sudden change in load could result in a potential undesired speed up.

There are (broadly speaking) two methods by which brushless motors can be operated in a closed loop.

The first is using a sensored brushless motor and using the onboard hall effect sensors to monitor the rotor speed and position. This can then be fed back into a brushless motor controller which can then process the information and change the way in which it drives the motor according to the core requirements of the application.

The second method involves using sensorless brushless motor controllers but then using the back electro-motive force (also known as back-EMF) to monitor the speed and number of rotations of the rotor. By using a controller which can then read the back-EMF and loop this information back into the controller it is then possible to ‘govern’ the speed of the controller

Is one method better?

Broadly speaking, most engineers would argue that using hall effect sensors is ultimately the most accurate and therefore the best route to go down if you need a closed loop brushless system. This largely because the onboard sensors can tell you exactly where the rotor is and what speed it is doing and essentially do the job of an encoder but without the additional cost of buying an encoder.

That said, sensored motors and controllers do typically cost more money which can be a downside depending on other applications.

They also are ultimately less reliable than sensorless brushless motors because there are more things that can go wrong, typically the sensors. This is an especially important factor to consider in applications where there may be lots of dust or other issues which could interfere with the sensors.

If one of these sensors breaks then the controller will not be able to operate and this could lead to an expensive repair. To learn more about the differences between sensored and sensorless brushless motors and controllers and their applications click here.

Which brushless motor controller do I need for each method?

To use the sensors on a sensored brushless motor you will need to use a sensored brushless motor controller. A sensorless brushless motor controller will be able to drive a sensored brushless motor but not by using the sensors.

For a closed loop brushless system based on back-EMF you will need a sensorless brushless motor controller such as the ZDBL15.

This sensorless brushless motor controller will be able to drive either a sensored or a sensorless brushless motor controller in a closed loop system by using the back-EMF generated to measure motor speed and determine rotor position.

The type of brushless closed loop system we would recommend will ultimately depend on the nature of the project or application that you have. Both systems have pros and cons which are technical and financial and ultimately need to be considered in the context of your specific project.

Category: Brushless Motor Controller FAQs
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