The inverter output is a PWM voltage waveform. After passing through the motor windings, the output current is approximately a sine wave, lagging behind the voltage by a phase angle determined by the motor's power factor. The inverter's output current is detected by a precision resistor or current transformer, and the CPU processes this current signal.
To protect the frequency converter, it will report an overcurrent fault when the output current exceeds a certain threshold. The frequency converter will also immediately block the pulse output. This is an important and necessary method to protect the frequency converter components from damage. This fault cannot be masked.
There are many causes of overcurrent faults in frequency converters, and each case should be analyzed based on its specific circumstances. If the root cause is identified and the appropriate remedy is applied, the problem can generally be resolved.
The motor cable connects the frequency converter and the motor. Therefore, we will analyze the process from the frequency converter side and the motor side separately.
1. First, there are the effects from the inverter side.
Common causes of overcurrent in the frequency converter include:
If the acceleration time is too short, the required motor torque will be greater. Since torque is proportional to current, the current will also be very high. The acceleration time can be appropriately extended.
Enhancement function: If the voltage boost is too high during startup under V/f control, it may cause overcurrent. The voltage boost value can be appropriately reduced.
Inappropriate PID parameters: Excessive dynamic response may cause overcurrent. The filtering time should be extended, and PID should be decreased and I increased.
2. Secondly, there are the effects from the motor side.
Common causes of overcurrent in the frequency converter on the motor side include:
Short circuit to ground in motor cable: Poor cable insulation, with exposed sheaths. A megohmmeter can be used to test the cable insulation to confirm cable quality.
Motor stall: In this case, the frequency converter will try to rotate the motor with greater torque, which may cause an overcurrent fault.
3. Finally, there are hardware issues.
If the current detection mechanism inside the frequency converter is not working properly, or if there is a problem with the CPU processing mechanism, these problems cannot be solved by simply setting parameters; repair is required.
If the inverter and motor current are mismatched, it can also cause an overcurrent fault. For example, a small inverter driving a large motor, or incorrect nameplate parameters, can all cause an overcurrent fault.
