Inverter Phase-Current Sensor Offset Diagnosis

Overview

The traction inverter calculates torque from phase-current feedback. A shifted zero point can make the controller see false torque or overcurrent and can mimic a motor winding fault.

Begin at zero torque. Raw offsets should remain mutually consistent and move plausibly with temperature. A single-channel shift points towards the sensor or analogue front end, while all channels moving together suggests a shared reference or supply issue.

Under load, interpret the U, V and W phase-current sum together with commanded torque and rotor position. Balanced winding resistance with distorted current feedback shifts attention to the sensor board, shielding or gate-driver interference.

Oscilloscope work on power electronics requires differential, correctly rated probes and approved access points. It is not a conventional chassis-referenced measurement.

After repair, verify phase symmetry and thermal stability across low torque, acceleration and regenerative operation rather than only completing an offset calibration.

Identity and Key Facts

System

Traction inverter and phase-current feedback

Core separation

Sensor offset, common reference, winding fault and EMI

Measurement

Zero torque plus loaded phase correlation

Zero-current test

• Compare raw sensor outputs at zero torque.
• Observe whether channels drift together or independently with temperature.
• Record common reference and sensor supply separately.

Loaded separation

• Review phase symmetry and the vector sum.
• Compare commanded torque with actual current response.
• Separate rotor-position errors from current-feedback distortion.

Noise source

• Correlate gate-driver switching edges with sensor output.
• Check shielding and low-voltage reference paths.
• Exclude cooling loss and thermal drift.

Check and Verification Sequence

• Record first-fault conditions and inverter temperature.
• Compare raw current-sensor offsets at zero torque.
• Verify the shared supply and reference.
• Check winding balance using an approved method.
• Correlate phase current, torque and rotor position under load.
• Verify across several torque regions after calibration.

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