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THE QUICK ANSWER…
Yes, although starting sensorless brushless motors under load is one of the hardest aspects of operation of sensorless brushless motors.
The key to successfully using a sensorless brushless motor controller to drive sensorless brushless motors in an energy efficient and practical way is the timing of the power input into the motor coils. If the timing is slightly out then this will cause major inefficiencies within the motor and can even act as a brake on the motor’s turning.
This can also create excess heat and wasted energy (a common issue with lower cost brushless ESCs which often start to overheat and burn out relatively quickly).
When a motor is up and running it is relatively easy to know the rotor positions on a sensorless brushless DC motor as this can be detected using back EMF and then optimised at the testing and setup stage through testing and understanding the exact motor being used.
There are a huge range of applications which can be effectively dealt with using sensorless brushless motor controllers. Why not explore some of our stock range and if you have a particular application that you would like to discuss please get in touch.
Frequently Asked Questions
However, at the startup stage it is impossible for the BLDC motor driver to know the inertia on the rotor or the rotor position on a sensorless BLDC motor because there is no movement from which to gain the back EMF information which the brushless motor controller can use to pinpoint the rotor location.
It is therefore quite common for sensorless motors to jump around a little at the start if they have not been properly optimised because the brushless motor controller being used is powering on coils on an assumed position with the aim of pulling the rotor into that pattern when it will then function normally.
Hence, the often stuttered startup followed by a sudden boost as the rotor aligns with the drive pattern (this is often compared to an engine struggling to start, coughing and spluttering, before suddenly roaring into life).
The key to optimising a brushless motor controller to start under load is firstly to know the motor that you are working with and its application and then to optimise the brushless motor controller to the key specifications of this particular motor and the application. Key variables such as inertia, number of poles, inductance and more can all be used to optimise the controller to run well.
The Vert Rotor case study provides a good example of this.
Once this is done the running of the motor will be as efficient as possible and this knowledge can then be used to inform the startup sequence for the motor. Knowing the number of poles and the motor inductance is a big part of this as this can be optimised specifically for the motor.
However, advanced programming in the ZDBL range of brushless motor controllers is also carefully optimised to read changes in back-
A TAILORED SOLUTION DELIVERS THE BEST RESULTS
There is no doubt that starting a sensorless brushless dc motor under load is not the easiest aspect of motor control to master but with the ZDBL series of brushless ESCs we have come pretty close to developing a system which works well in a huge number of applications.
Sometimes this can require a significant amount of optimisation and hard work but in the long run it pays off, particularly where such performance is a key part of your application.
If you have any questions at all please do not hesitate to CONTACT US to discuss with one of our engineers.
+44 (0) 333 123 7130
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