Overcurrent Protection and Troubleshooting for Inverters

1. Overcurrent Protection Function
　　　　In inverters, overcurrent protection addresses sudden current surges exceeding allowable limits. Due to the limited overload capacity of power electronics, this protection is critical and highly refined.
　　　　(1) Causes of Overcurrent:
　　　　• During Operation: Sudden load shocks or mechanical jamming cause abrupt motor current spikes.
　　　　• Output Short Circuit: Short between output terminals or within the motor.
　　　　• Inverter Fault: Failure in IGBT bridge arms (e.g., due to overheating or aging) causing “shoot-through” and DC bus short circuit.
　　　　• Acceleration Overcurrent: Short ramp-up time with high inertia loads causes excessive current.
　　　　• Deceleration Overcurrent: Rapid deceleration with high inertia leads to regenerative overvoltage/current.
　　　　(2) Troubleshooting:
　　　　• Trips Immediately on Start: Check for mechanical jams, output shorts (use megohmmeter), damaged IGBTs, or insufficient motor starting torque.
　　　　• Trips During Operation: Extend acceleration/deceleration times; reduce V/F boost to lower no-load current; verify electronic thermal relay settings to prevent false trips.