Improved speed operation of sensorless BLDC motor drives using IIR digital filter

This paper presents improved sensorless operation of permanent magnet brushless DC motor (BLDC) based back-EMF digital filtering using the dsPIC30F6010 microcontroller. Normally, the back-EMF signal of the unexcited phase winding has significant noise distortion PWM signals which are used to vary the applied voltage, and therefore the speed of the motor. So it is relatively difficult to detect the zero-crossing event of the back-EMF waveform due to the coupled PWM noise. Improved back-EMF signal can be generated via infinite impulse response digital filter (IIR filter) so that the back-EMF looks more like ideal signal for easier zero-crossing detection. The proposed voltage controlled scheme together with IIR digital filter includes control capability for both low speed PWM control and high speed phase advance commutation to obtain an extended speed range operation. Design of IIR digital filter and control simulation are performed in Matlab Simulink to optimize the proposed control algorithm which could be particularly suitable for cost sensitive products such as air purifiers, air blowers, cooling fans, and related home appliances. Theoretical analysis and experiments are conducted over a wide operating speed range and different back EMF waveforms to validate the effectiveness of the proposed method.