Synchronized minimum frequency pulse width modulation drive for sensorless brushless direct current motor
AssigneeMicrochip Technology Incorporated
InventorWard R. Brown
Life of this patent
Estimating the term…
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.
Claims13
A method for controlling speed of a sensorless brushless direct current motor, said method comprising the steps of:
- determining each commutation period in an electrical cycle of a sensorless brushless direct current motor by measuring back electromotive force voltage at each phase connection of the sensorless brushless direct current motor;
- generating pulse width modulation (PWM) control pulses, the PWM control pulses each having one on and one off transition during respective ones of the commutation periods, wherein each single PWM control pulse is substantially centered within its respective commutation period;
- and
- driving power switching transistors with the PWM control pulses for each of the commutation periods, wherein the power switching transistors are connected between stator coils of the sensorless brushless direct current motor and a direct current power source.
A method for controlling speed of a sensorless brushless direct current motor, said method comprising the steps of:
- determining electrical timing centers for each of a plurality of commutation periods of a sensorless brushless direct current motor by
- measuring back electromotive force voltages at each stator coil of the sensorless brushless direct current motor, and
- determining from the measured back electromotive force voltages when each of the measured back electromotive force voltages is at substantially a zero-crossing voltage value, wherein the zero-crossing voltage value is about one-half of a voltage value of a direct current power source;
- generating a single pulse width modulation (PWM) control pulse during each of the plurality of commutation periods, wherein each single PWM control pulse has one on and one off transition during its respective commutation period and the single PWM control pulse for the respective commutation period is substantially centered within that respective commutation period;
- and
- driving power switching transistors with the PWM control pulses during the plurality commutation periods, wherein the power switching transistors are connected between the stator coils of the sensorless brushless direct current motor and the direct current power source.
Dependencies are inferred from the claim text.