US 8,558,495 B2 · Sensorless BLDC motor control by comparing instantaneous and average BEMF voltages

Abstract

Sensorless driving of a brushless DC (BLDC) motor includes detecting a zero crossing time from back electromotive force (BEMF) voltage of the BLDC motor. An instantaneous BEMF voltage and an average BEMF voltage are compared to detect the crossover time, which can be used to change the commutation switching sequence. Since the average BEMF voltage differs for odd and even steps of the commutation switching sequence, average BEMF voltages are calculated separately for odd and even sequences and compared to instantaneous BEMF voltages to detect crossover points for the odd and even sequences. The times to commutations for the odd and even sequences are averaged to provide an average time to the next commutation cycle. The average time can be scaled by a reduction factor to reduce the effects of measurement noise.

Claims20

Dependent claims

A method of detecting back electromotive force (BEMF) for controlling a brushless DC (BLDC) motor, the method comprising:

measuring, by a microcontroller coupled to a BLDC motor, BEMF voltages during a start period of the BLDC motor;
determining, by the microcontroller, an average BEMF voltage value from the measured BEMF voltages by calculating averages based on an order of a commutation switching sequence for driving the BLDC motor, wherein calculating the averages includes:
calculating a first average value for odd steps of the commutation switching sequence, and
calculating a second average value for even steps of the commutation switching sequence;
determining, by the microcontroller, an instantaneous BEMF voltage;
and
comparing, by the microcontroller, the average BEMF voltage with the instantaneous BEMF voltage to detect a crossover time, which converges to zero crossing of the BEMF voltage.

4 more elements

A system comprising:

interface circuitry configured to couple to a brushless DC (BLDC) motor;
and
instructions stored in memory that, when executed by a processor coupled to the interface circuitry, configured to cause the processor to:
measure back electromotive force (BEMF) voltages received from the interface circuitry during a start period of the BLDC motor;
calculate an average BEMF voltage value from the measured BEMF voltages by calculating averages based on an order of a commutation switching sequence for driving the BLDC motor, wherein calculating the averages includes:
calculating a first average value for odd steps of the commutation switching sequence, and
calculating a second average value for even steps of the commutation switching sequence;
calculate an instantaneous BEMF voltage;
and
compare the average BEMF voltage with the instantaneous BEMF voltage to detect a crossover time, which converges to zero crossing of the BEMF voltage.

7 more elements

Dependencies are inferred from the claim text.

Sensorless BLDC motor control by comparing instantaneous and average BEMF voltages

Life of this patent

Sensorless BLDC motor control by comparing instantaneous and average BEMF voltages

Life of this patent

Abstract

Claims20