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Common Faults and Solutions of Variable Frequency Inverter System for Electric Dynamometer

The faults of the variable frequency inverter system of the dynamometer are mostly concentrated in aspects such as energy feedback, motor control, heat dissipation and harmonics. The following is a simplified version of troubleshooting plan.

1. Abnormal energy feedback

Symptom: The DC bus voltage is too high to feed back electrical energy to the grid.
Cause: Abnormal grid voltage, IGBT module damage, or aging feedback reactor.
Solution: Install a voltage stabilizer to stabilize grid voltage; Test the IGBT drive waveform with an oscilloscope and replace the damaged module; Measure the inductance of the reactor with a bridge. Replace it when the inductance value is less than 80% of the nominal value.

2. Motor control out-of-step

Symptom: Torque fluctuation over 5%, large speed deviation.
Cause: Poor coaxiality of sensor, encoder signal interference, control parameter mismatch.
Solution: Adjust the sensor by laser alignment (deviation ≤ 0.05mm); Encoder wire with shielding and isolator; Optimize the PI parameters according to the principle of "speed loop first, then torque loop" to make the overshoot less than 5% and the fluctuation ≤2%.

3. Overheating of the power unit

Symptom: IGBT temperature > 80° C, heat dissipation failure.
Cause: Insufficient fan air volume, low water cooling flow rate, silicone thermal grease drying.
Solution: For air-cooled models, clean the filter screen, replace the fan with an air volume lower than 60% rated value; For water-cooled models, check the flow rate (±10% of the standard value) and clean the tubing; Reapply silicone grease (0.1-0.2mm thick).

4. Excessive harmonic pollution

Symptom: Grid power factor < 0.8, voltage waveform distortion.
Cause: Outdated rectification topology, improper PWM parameters.
Solution: Upgrade to 12-pulse rectification or AFE; Increase the PWM carrier frequency to 4-8kHz and set the current loop bandwidth ≥50Hz.

5. Communication synchronization fails

Symptom: Inconsistent torque across multiple devices, communication interruption.
Cause: Clock out of sync, protocol incompatible.
Solution: Enable IEEE 1588 clock synchronization (deviation ≤1μs); Unify the communication protocol and write a protocol conversion program to achieve data mapping.