Variable pulse width modulation for reduced zero-crossing granularity in sensorless brushless direct current motors
AssigneeMicrochip Technology Incorporated
InventorWard R. Brown
Life of this patent
Estimating the term…
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.
Claims13
A method for improving zero-crossing detection in a sensorless brushless direct current motor, said method comprising the steps of:
- generating a first plurality of pulse width modulation (PWM) control pulses at a first number of pulses per second until a certain time interval before a zero-crossing event is anticipated then generating a second plurality of PWM control pulses at a second number of pulses per second, wherein the second plurality of PWM control pulses at the second number of pulses per second is greater than the first plurality of PWM control pulses at the first number of pulses per second;
- detecting a zero-crossing event during the generation of the second plurality of PWM control pulses at the second number of pulses per second in at least one commutation period of an electrical cycle of a sensorless brushless direct current motor by measuring a back electromotive force voltage at an unexcited phase connection of the sensorless brushless direct current motor;
- and
- returning to generating the first plurality of PWM control pulses at the first number of pulses per second after the zero-crossing event has been detected.
A method for improving zero-crossing detection in a sensorless brushless direct current motor, said method comprising the steps of:
- generating a plurality of pulse width modulation (PWM) pulses at a first number of pulses per second until a certain time interval before a zero-crossing event is anticipated then generating the plurality of PWM pulses at a second number of pulses per second, wherein the second number of pulses per second is greater than the first number of pulses per second;
- 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;
- and
- driving power switching transistors with the plurality of PWM 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.