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Efficient control of BLDC motors is easier than you think

Efficient control of BLDC motors is easier than you think

Perhaps surprisingly there are still many applications today where brushed DC motors are used. Despite their low efficiency and the electromagnetic interference they generate, they are simple to integrate and control. In many cases, such as simple children’s toys or the electric mirrors of a vehicle, they are a good match to the application. Driven only occasionally, the poor efficiency has a negligible overall impact. However, there are plenty of applications where motors run for long periods of time or even continuously, and it is here that brushed DC motors have made way for brushless solutions.

 

Brushless DC motors (BLDC) do away with the mechanical commutation, turning instead to an electronic control system that energises the motor’s coils in the correct order, at the right moment, to keep the rotor turning at the desired number of revolutions per minute. This results in a significant improvement in efficiency but at the cost of a more complex electronic control system. Whereas a conventional DC motor is commutated at precise moments due to the angular position of the commutator, the angular position of the BLDC motor has to be provided to the control electronics by some other means. Often this is implemented using one or more sensors based upon Hall technology.

 

This precise, electronically controlled commutation delivers impressive increases in efficiency compared to DC motors. However, using the angular position as provided by the Hall sensors alone to control the moment of commutation does not deliver the full efficiency such motors can achieve. As the rotation speed of the motor increases, the phases of the current and voltage move further apart from one another. If it were possible to bring these back into phase with one another, regardless of rotation speed, efficiency can be improved by several percentage points.

 

The method of achieving this is simple enough to describe: actively modify the moment of commutation (changing the lead angle) to bring voltage and current back in phase. Many approaches to this calculate a rough lead angle value for various motor RPMs, applying them as the rotation speed changes. But the lead angle is also affected by variations in motor due to production methods. For the optimum approach, the electronic control mechanism must actively match itself to the motor during operation.

 

This is where the InPAC technology from Toshiba comes in. By integrating Intelligent PhAse Control into the electronics that monitors rotor angle as well as the current drawn by the motor, the internal control mechanism can apply the appropriate lead angle across the entire range of rotational speeds required by the application. This is achieved without requiring experimentation in the laboratory during development, or applying tuning parameters during production. InPAC is available across a wide range of single-chip solutions suitable for both 3-phase and 1-phase brushless motors. Next generation products can also be used with external power stage for more flexibility.

 

To find out more about how InPAC delivers highly efficient BLDC motor control take a look at our reference design available here:

 

Click here to find out more about next generation BLDC motor control

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