Bldc adaptive zero crossing detection
AssigneeMicrochip Technology Incorporated
InventorWard R. Brown
Life of this patent
Estimating the term…
Abstract
BLDC adaptive zero crossing detection compares BEMF voltages from a floating phase of a BLDC motor to a reference voltage, measures a rising time interval during a rising BEMF period when the BEMF voltages are greater than the reference voltage, and a falling time interval during a falling BEMF period when the BEMF voltages are less than the reference voltage. The reference voltage is adjusted so that the rising and falling time intervals are substantially the same, thereby causing the drive voltage to be in phase with the motor self-generated voltage, thus ensuring maximum efficiency of the BLDC motor.
Claims21
A method for zero crossing detection for a brushless direct current (BLDC) motor, said method comprising the steps of:
- driving two phases of the three phase BLDC motor with pulse width modulation (PWM) drive voltage pulses, each PWM drive voltage pulse having a period and a duty cycle, and a voltage from a power source;
- coupling an un-driven third phase of the three phase BLDC motor to a voltage comparator for comparing back electromotive force (BEMF) voltages thereof;
- comparing the BEMF voltages to a reference voltage with the voltage comparator;
- measuring a falling time interval during a falling BEMF period when the BEMF voltages are less than the reference voltage;
- storing the falling time interval;
- measuring a rising time interval during a rising BEMF period when the BEMF voltages are greater than the reference voltage;
- storing the rising time interval;
- and
- comparing the stored falling and rising time intervals, wherein
- if the stored falling and rising time intervals are substantially the same then do not change the reference voltage, and
- if the stored falling and rising time intervals are not substantially the same then change the reference voltage.
An apparatus for brushless direct current (BLDC) adaptive zero crossing detection, comprising:
- an analog-to-digital converter (ADC);
- a voltage comparator having a first input coupled to an output of the ADC, and a second output coupled to a floating phase of a BLDC motor and adapted for measuring back electromotive force (BEMF) voltages therefrom;
- an AND gate having a first input coupled to an output of the voltage comparator and a second input coupled to a pulse width modulation (PWM) period signal;
- an inverter having an input coupled to the PWM period signal;
- a set-reset (RS) latch having a set input coupled to an output of the AND gate and a reset input coupled to an output of the inverter;
- and
- a D-latch having a D-input coupled to a Q-output of the SR-latch and a clock input coupled to the output of the inverter.
A motor controller using brushless direct current (BLDC) adaptive zero crossing detection for providing pulse width modulation (PWM) drive to a BLDC motor, comprising:
- high and low side power switches coupled to each BLDC motor terminal, wherein the high and low side power switches are further coupled to a high motor supply voltage and a low motor power supply voltage, respectively, and controlled by the PWM drive, wherein each of the high and low side power switches will connect a respective one of the BLDC motor terminals to either the high motor supply voltage, the low motor power supply voltage, or neither and left floating;
- a PWM master time base;
- PWM generators coupled to the PWM master time base and respective ones of the high and low side power switches;
- an adaptive zero crossing detection circuit adapted for coupling to a floating phase terminal of the BLDC motor and for receiving back electromotive force (BEMF) voltages therefrom, wherein the adaptive zero crossing detection circuit:
- compares the BEMF voltages to a reference voltage,
- measures a rising time interval during a rising BEMF period when the BEMF voltages are greater than the reference voltage,
- measures a falling time interval during a falling BEMF period when the BEMF voltages are less than the reference voltage, and
- adjusts the reference voltage until the rising and falling time intervals are substantially the same;
- and
- a microcontroller for generating a PWM drive signal based upon the reference voltage.
A system for driving a brushless direct current (BLDC) motor using adaptive zero crossing detection, said system comprising:
- a three phase BLDC motor having first, second and third motor phase terminals;
- high and low side power switches coupled to each of the motor phase terminals, wherein the high and low side power switches are further coupled between a high power supply voltage and a low power supply voltage, respectively, and controlled by the PWM drive, wherein each of the high and low side power switches will connect respective one of the BLDC motor phase terminals to either the high motor supply voltage, the low motor supply voltage, or neither and left floating;
- a PWM master time base;
- PWM generators coupled to the PWM master time base and respective ones of the high and low side power switches;
- an adaptive zero crossing detection circuit adapted for coupling to a floating motor phase terminal of the BLDC motor and for receiving back electromotive force (BEMF) voltages therefrom, wherein the adaptive zero crossing detection circuit
- compares the BEMF voltages to a reference voltage,
- measures a rising time interval during a rising BEMF period when the BEMF voltages are greater than the reference voltage,
- determines a falling time interval during a falling BEMF period when the BEMF voltages are less than the reference voltage, and
- adjusts the reference voltage until the rising and falling time intervals are substantially the same;
- and
- a microcontroller for generating a PWM drive signal based upon the reference voltage.
Dependencies are inferred from the claim text.