Reconstruction of an average motor supply current using phase current measurement
Systems and methods for computing an average supply current to a motor include a current sensor that is configured to sense a current through the motor. A converter is configured to sample the output of the current sensor at times that are established by a trigger signal and convert the samples into digital current values. A trigger signal generator generates the trigger signal based on one or more pulse width modulated (PWM) motor control signals within a PWM cycle. An average supply current value that indicates the average supply current to the motor is computed by a controller using the digital current values received from the converter.
1. A method for computing an average supply current to a motor, the method comprising:
sensing a current through the motor with a current sensor, wherein the motor comprises three phases, wherein each of a plurality of samples of the current sensor output is indicative of a current through one or more of a first phase of the motor and a second phase of the motor;
generating a trigger signal based on one or more pulse width modulation (PWM) motor control signals within a PWM cycle;
sampling an output of the current sensor at times established by the trigger signal;
converting samples of the current sensor output into digital current values; and
computing an average supply current value using the plurality of samples by integrating each of the plurality of samples over its corresponding PWM portion, summing the integration results, and dividing the summed integration results by the PWM cycle, the average supply current value being indicative of the average supply current to the motor based on the digital current values.
2. The method of claim 1 , wherein sensing the current comprises sensing the current with one or more shunt resistors.
3. The method of claim 2 , wherein sensing the current comprises coupling inputs of an amplifier across the one or more shunt resistors.
4. The method of claim 1 , wherein generating the trigger signal comprises generating the trigger signal at a midpoint of one or more portions of the PWM cycle of the one or more PWM motor control signals.
5. The method of claim 1 , wherein converting samples of the current sensor output comprises converting the current sensor output samples using an analog to digital converter.
6. Apparatus comprising:
a current sensor configured to sense a current through a motor comprising three phases, wherein each of a plurality of samples of the current sensor output is indicative of a current through one or more of a first phase of the motor and a second phase of the motor;
a converter configured to sample an output of the current sensor at times established by a trigger signal and to convert the current sensor output samples into digital current values;
a controller configured to compute an average supply current value indicative of an average supply current to the motor based on the digital current values received from the converter using the plurality of samples by integrating each of the plurality of samples over its corresponding PWM portion, summing the integration results, and dividing the summed integration results by the PWM cycle; and
a trigger signal generator configured to generate the trigger signal based on one or more pulse width modulation (PWM) motor control signals within a PWM cycle.
7. The apparatus of claim 6 , wherein the current sensor comprises one or more shunt resistors.
8. The apparatus of claim 7 , wherein the current sensor further comprises an amplifier having inputs coupled across the one or more shunt resistors.
9. The apparatus of claim 6 , wherein the trigger signal generator is configured to generate the trigger signal at a midpoint of one or more portions of the PWM cycle of the one or more PWM motor control signals.
10. The apparatus of claim 6 , wherein the converter comprises an analog to digital converter.
11. Apparatus comprising:
means for sensing a current through a motor with a current sensor;
means for generating a trigger signal based on one or more pulse width modulation (PWM) motor control signals within a PWM cycle;
means for sampling an output of the current sensor at times established by the trigger signal;
means for converting samples of current sensor output into digital current values; and
means for computing an average supply current value indicative of an average supply current to the motor based on the digital current values, the computing means for computing the average supply current value comprising means for integrating each of the plurality of samples over its corresponding PWM portion, summing the integration results, and dividing the summed integration results by the PWM cycle.
12. The apparatus of claim 11 , wherein the sensing means comprises one or more shunt resistors.
13. The apparatus of claim 12 , wherein the sensing means comprises an amplifier having inputs coupled across the one or more shunt resistors.
14. The apparatus of claim 11 , wherein the trigger signal generating means comprises means for generating the trigger signal at a midpoint of one or more portions of the PWM cycle of the one or more PWM motor control signals.
15. The apparatus of claim 11 , wherein the converting means comprises an analog to digital converter.
16. The apparatus of claim 11 , wherein the motor comprises three phases and wherein each of a plurality of samples of the current sensor output is indicative of a current through one or more of a first phase of the motor and a second phase of the motor.
17. The apparatus of claim 16 , wherein the computing means comprises means for computing the average supply current value using the plurality of samples.