STo Step-Out (PM Motor) fault in delta drive

STo Step-Out (PM Motor) fault in delta drive troubleshooting

Description

The STo fault is specific to Permanent Magnet (PM) motor applications. Unlike induction motors, PM motors must run synchronously with the drive's rotating magnetic field. "Step-Out" means the rotor has lost synchronization with the drive's stator field. The drive no longer knows the exact position of the rotor magnets, leading to a loss of torque control and potential stalling.

Causes

1. Sudden Load Impact: A sudden shock load exceeded the magnetic "pull-out" torque of the motor, causing the rotor to slip.
2. Incorrect Parameters: The Back-EMF constant or motor inductance values entered in the drive do not match the physical motor.
3. Magnetic Saturation: Attempting to accelerate too fast (Short Accel Time) causes current saturation, weakening the magnetic lock.
4. Reverse Rotation: Start-up logic failed to detect the initial rotor position, pushing the motor in the wrong direction against the load.

Solution

Re-establish synchronization:
1. Auto-Tuning: You must perform a Rotational Auto-tuning for PM motors. This measures the exact magnetic angles.
2. Adjust Current: Increase the "PM Start Current" detection level (Group 10 or 11 parameters) to ensure the drive locks the rotor before accelerating.
3. Ramp Time: Increase Acceleration Time to allow the magnetic field to pull the heavy rotor gradually.
4. Heavy Duty Mode: Ensure the drive is set to Heavy Duty (HD) mode, as PM applications (like compressors/elevators) usually require constant torque.