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Back EMF stands for Back Electromotive Force. In simple terms, the Back EMF is an electromotive force which occurs as the brushless motor turns and acts like a generator. Critically the Back EMF generated by the brushless motor can be measured by certain types of sensorless brushless motor controller such as the ZDBL15 Brushless Motor Controller. As the frequency of the BACK EMF is directly proportional to the speed of the motor this then enables the sensorless brushless motor controller to know exactly what speed the BLDC motor is rotating at.
An intelligent motor controller such as the ZDBL15 brushless ESC can then read this force and use it to measure the actual speed of the motor. This speed can then be maintained 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?
A disadvantage of using this method is that no back EMF is generated when the motor is stationary, meaning that start up is affected by operating in open loop. As a result of this, the motor can take a small amount of time to settle and run efficiently. A second disadvantage is that at low speeds the back EMF is small and therefore can be quite difficult to measure accurately, which can result in inefficient operation. For situations where low speed is required it is worth considering either sensored motors or stepper motors.
Why not start by browsing some of the ZDBL Series of Sensorless Brushless Motor Controllers which feature BACK EMF as a key part of the way in which they operate. You can view the Vert Rotor case study to see how the ZDBL15 has been used in a high end compressor application and as always, if you have any questions, please CONTACT US.
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