3-Phase BLDC Motor Sensorless Control Using MC56F8013

Tuning7.5.2.2 PER_START_PROCCMT_USThe minimum value for the period Toff.This value is used to limit the period Toff to a minimum. Therefore, the period Toff applied after everycommutation can have a minimum value of PER_START_PROCCMT_US.7.5.2.3 PER_CMTSTART_USThe commutation period used to compute the first (start) commutation period.During the start commutation state, no zero crossing has been detected before. Therefore, thecommutation algorithm must predict a value for the commutation period and start the process. This valueis used as the first predicted commutation period.To select this value, see Table 7-5.7.5.2.4 PER_TOFFSTART_USThe first (start) interval Toff after commutation (where back-EMF zero crossing is not detected).This value is the first predicted period duration Toff for the start commutation state.Setting these constants is an experimental process. It is difficult to obtain a precise formula because manyfactors involved are difficult to quantify for real drives (motor and load mechanical inertia, motorelectromechanical constants, and sometimes also the motor load, for example). Therefore, constantsmust be set for a specific motor. Table 7-5 aids in the setting of constants.Table 7-5. Recommended Start PeriodsMotor sizex_PER_CMTSTART_US[µs]x_PER_TOFFSTART_US[µs]First commutationperiod [ms]Slow motor/high load motor mechanical inertiaFast motor/high load motor mechanical inertia>5000 >10000 >10