Elmo HARmonica, HARSFEN0602 192, Detection of Commutation Feedback Fault, Double sensor systems

HARSFEN0602ElmoHARmonicaSoftwareManual PRELIMINARYDRAFT

In this situation, the direction of the stator field is constant, and if torque is commanded, the rotor seeks equilibrium, aligned to the magnetic field.

If the motor is driven by an external speed or position controller, it will be commanded to full-torque, and dissipate the corresponding heat, without generating any motion.

The commutation is drifting (i.e.		Changes in time):
Drifting in	occur in two forms:
Slow drift:
The following reasons:
Excessive noise on the encoder lines
Damaged or dirty encoder
•Wrong encoder resolution setting
Usually drifts	slowly. When the motor is stopped,		does not drift at all.
Slow drifting will cause the motor to lose torque gradually until fully stopped at the static
setting∆θof ∆θ = ±90o. At this∆θpoint, the current in the motor will not produce any torque.
The motor shall overheat, but not move.

Fast drift:

Faulty resolver∆θ wires cause the resolver to digital∆θconverter to elude motion in its full supported speed. The motor behavior becomes bizarre, normally producing oscillations without much average torque.

14.11.3Detection of Commutation Feedback Fault

The detection of commutation faults is according to the sensors present.

Three categories are dealt:

Double sensor systems

•Resolver system

Double sensor systems

The situation is the easiest if there are two sensor systems, as happens in encoder + digital hall systems. In this case, there is a rough commutation estimate available by the digital Hall sensors, that measure the electrical angle of the motor directly.

Bad correlation between the encoder-accumulated commutation angle and the Hall sensors angle is a sign of faulty commutation.

If the accumulated commutation angle differs by more than 15 electrical degrees than its closest value that fits the Hall sensor reading, an error is to be declared. The motor is shut (MO=0) and MF is set to 0x4. This way an error is decided when the commutation is 15 to 45 degrees wrong.

After the detection of a commutation fault, the motor must be shut down and a proper MF code set active.

There is no point in trying to stop the motor under control, since we don’t know the correlation between the motor currents and the resulting torque.

At the next motor starting attempt, the motor will seek commutation again.

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