Slow speed operation of brushless direct current motors by gating pulse width modulation drive
AssigneeMicrochip Technology Incorporated
InventorWard R. Brown
Life of this patent
Estimating the term…
Abstract
Slow speed operation of a brushless DC (BLDC) motor is enhanced by gating off some of the PWM pulses in each commutation period. By doing so, longer PWM pulse widths may be used at PWM signal frequencies that are inaudible while still allowing desired slow speed operation of the BLDC motor. Centering the non-gated PWM pulses in each commutation period where peak back EMF occurs, further reduces losses and improves delivery of maximum torque from the BLDC motor.
Claims17
A method for controlling low speed operation of a brushless direct current motor, said method comprising the steps of:
- generating a plurality of pulse width modulation (PWM) pulses at a certain duty cycle;
- determining electrical timing centers for each of a plurality of commutation periods of a brushless direct current motor;
- gating off some of the plurality of PWM pulses in each of the plurality of commutation periods, wherein the plurality of PWM pulses not gated off are grouped toward the electrical timing centers of the plurality of commutation periods;
- and
- driving power switching transistors with the plurality of PWM pulses not gated off during the plurality of commutation periods, wherein the power switching transistors are connected between the stator coils of the brushless direct current motor and a direct current power source.
A method for controlling low speed operation of a sensorless brushless direct current motor, said method comprising the steps of:
- generating a plurality of pulse width modulation (PWM) pulses at a certain duty cycle;
- 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;
- gating off some of the plurality of PWM pulses in each of the plurality of commutation periods, wherein the plurality of PWM pulses not gated off are grouped toward the electrical timing centers of the plurality commutation periods;
- and
- driving power switching transistors with the plurality of PWM pulses not gated off 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.