ElmoMC SimplIQ Software Manual - Manual (Page 209)

SimplIQ Software Manual Limits, Protections, Faults and Diagnosis
MAN-SIMSW (Ver. 1.4)
13-14
ƒ The commutation is drifting (that is, Δθ changes in time)
drift can occur in two forms:
ƒ Slow drift, caused by excessive noise on the encoder lines, a damaged or dirty
encoder or a wrong encoder resolution setting. Usually, Δθ drifts slowly and,
when the motor stops, it does not drift at all. Slow drifting causes the motor to
lose torque gradually until fully stopped at the static setting of Δθ = +90º. At this
point, the current in the motor will not produce any torque. The motor will
overheat, but it will not move.
ƒ Fast drift, which can be caused by an encoder frequency reaching the encoder
filter value (EF[1] command). The drive does not sense any feedback, causing a
sudden stop and a rise in current with no torque. Δθ drifts to 0 because the rotor
angle aligns with the field angle.
13.11.2 Detection of Commutation Feedback Faults
Commutation faults can be detected if there are two sources of commutation data. The
redundant data enables a failure of one sensor to be identified by the other.
The SimplIQ drive supports commutation failure identification through the use of
redundant encoder and digital Hall sensor data. The Hall sensors provide a rough, but
direct, estimate of the commutation angle. The encoder provides high-resolution data,
but it may accumulate errors if the drive setup data is set incorrectly or if it is faulty. If
the encoder’s cumulative commutation angle differs by more than 15 electrical degrees
from the closest value to match the Hall sensor reading, an error is issued. The motor is
shut down (MO=0) and MF is set to 0x4. An error is issued when there is a commutation
discrepancy of between 15 and 45 degrees.
After detection of a commutation fault, the motor must be shut down and a proper MF
code set to be active. The motor cannot be stopped under control, because the correlation
between the motor currents and the resulting torque is not known. At the next motor
startup attempt, the motor will again seek commutation.