Abstract:
A pulse width modulated (PWM) trapezoidal commutation drive to a brushless direct current (BLDC) motor is sine modified so that the applied drive voltage substantially matches the induced voltage generated in the BLDC motor. The values of the cosine of the angles between -30 degrees and +30 degrees are used to modify the duty cycle of the PWM drive signal dependent upon the rotor angular positions determined from the times between the zero crossing BEMF voltages measured at the unconnected motor terminals.
Abstract:
Zero-crossing detection accuracy is enhanced in a sensorless brushless direct current (BLDC) motor by increasing the PWM drive frequency in anticipation of a zero-crossing event in any one or more commutation periods. Once a zero-crossing event is detected, the PWM frequency can go back to a lower normal operating frequency. Switching losses of the power drive transistors are thereby minimized while maintaining accurate zero-crossing detection for stable operation of the BLDC motor.
Abstract:
Drive voltages to a sensorless brushless DC motor are regulated by varying the width of a single drive pulse (PWM pulse) centered in each of the commutation periods. Switching losses are thereby cut to an absolute minimum because there are only two transitions (on and off) in each drive commutation period. Back EMF zero-cross detectors determine the electrical timing relationships during each electrical cycle. Since the PWM drive pulses are always centered in each of the commutation periods, there will always be back EMF available for measurement of "zero-crossings." A digital device controls power switching transistors to produce one single PWM pulse during each of the commutation periods.