In the routine maintenance of inverters, various issues may arise, such as problems with peripheral circuits, improper parameter settings, or circuit board damages. When a fault occurs in the frequency inverter, it is essential to analyze which specific part is causing the problem. This article provides a brief overview and approaches for diagnosing and handling internal DC bus faults.
I. Static Testing
Test the Rectifier Circuit
Locate the P (positive) and N (negative) terminals of the internal DC bus in the frequency inverter. Set the multimeter to X10 resistance range and connect the red probe to the P terminal. Connect the black probe to the R, S, and T terminals one by one. The resistance should be very high, close to infinity. Repeat the same steps with the red probe connected to the N terminal. If any of the following results occur, it indicates a circuit abnormality:
A. Uneven resistance in three phases, indicating a fault in the rectifier bridge.
B.Infinite resistance when the red probe is connected to the P terminal, indicating a fault in the rectifier bridge or starting resistor.
Test the Inverter Circuit
Connect the red probe to the P terminal and the black probe to the U, V, and W terminals one by one. The resistance should be in the tens of ohms, and each phase’s resistance should be similar, with the reverse phase resistance being close to infinity. Repeat the steps with the black probe connected to the N terminal. If the results differ, it confirms a fault in the inverter module.
II. Dynamic Testing
After confirming normal results in static testing, dynamic testing or powering up the inverter can be conducted. Before and after powering up, pay attention to the following:
Before powering up, confirm that the input voltage is correct. Incorrectly connecting a 380V power supply to a 220V-rated frequency inverter can lead to damage such as capacitor, varistor, or module explosions.
Check if the various connection ports of frequency inverter are correctly connected and if there are any loose connections. Abnormal connections can lead to malfunctions or even damage to the frequency inverter.
After powering up, check the displayed fault information and preliminarily identify the fault and its cause.
If no faults are displayed, check for abnormal parameters. Reset the parameters and start the frequency inverter without connecting it to a motor. Test the voltage output of U, V, and W phases. If there are issues like phase loss or uneven three-phase output, it indicates a fault in the module or drive board.
With normal output voltage (three-phase balanced), perform a load test. It’s advisable to conduct a full-load test.
III. Fault Diagnosis
Rectifier Module Damage
Usually caused by grid voltage fluctuation or internal short circuits. Check the user’s grid conditions, such as voltage fluctuation and pollution from equipment like welding machines.
Inverter Module Damage
Typically caused by motor or cable damage and faults in the drive circuit. After repairing the drive circuit and ensuring a good drive waveform, replace the module. After replacing the driver board on-site, also check the motor and connecting cables before running the frequency inverter.
No Display After Powering Up
Usually caused by a damaged power supply or soft charging circuit, resulting in no DC power. If the starting resistor is damaged, it could also lead to this issue, or the panel may be faulty.
Overvoltage or Undervoltage Display After Powering Up
Generally caused by input phase loss, circuit aging, or circuit board moisture. Identify the voltage detection circuit and its testing points, and replace damaged components.
Overcurrent or Ground Short Circuit Display After Powering Up
Typically caused by a faulty current detection circuit, such as Hall elements or operational amplifiers.
Overcurrent Display During Startup
Usually caused by a damaged drive circuit or inverter module.
Normal Output Voltage at No Load, Overload or Overcurrent Display Under Load
This situation is often due to improper parameter settings, aging of the drive circuit, or module damage.
The above information covers common frequency inverter faults and their handling methods. For more details about frequency inverter and related industry information, please follow GTAKE official website: www.gtake.com.
