Sensorless BLDC control with back-EMF filtering using a majority function

This application note describes a sensorless brushless direct current (BLDC) motor control algorithm that is implemented using dsPIC digital signal controller (DSC). The algorithm works utilizing a majority function for digitally filtering the Back-Electromotive Force (BEMF). Each phase of the motor is filtered to determine when to commutate the motor drive voltages. This control technique excludes the need for discrete, low-pass filtering hardware and off-chip comparators. It should be pointed out that all the discussions here, and the application software, assume a 3-phase motor has to be used.

The purpose of this application note is to explain the different parts of the implementation of this new sensorless BLDC motor control technique in a basic and simple form. It also shows that this new control method is a single-chip dsPIC DSC device-based solution, which does not requires external hardware except for a couple of resistors used to conditioning the BEMF signals to the dsPIC DSC device ADC operational voltage range.

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