Common faults in the auxiliary control circuit of the power inverter for maintenance
Control circuits such as frequency converter drive circuits, protection signal detection and processing circuits, pulse generation and signal processing circuits are called auxiliary circuits. After the auxiliary circuit malfunctions, the cause of the malfunction is relatively complex. Except for the loss of the solidification program or the damage of the integrated block (which can only be handled by replacing the control board as a whole or the integrated block), other faults are easier to diagnose and handle.
1. Repair the drive circuit fault of the frequency converter
The driving circuit is used to drive the IGTR of the inverter, and it is also prone to faults. Generally, there are obvious signs of damage, such as device (capacitor, resistor, transistor, printed board, etc.) bursting, discoloration, wire breakage, and other abnormal phenomena, but there will not be any complete damage to the driving circuit. The processing method is generally based on the schematic diagram, and each group of driving circuits is checked, measured, replaced, compared, and other methods step by step in reverse;
Or compare and inspect with another genuine (new) driver board, and gradually find the fault point. Troubleshooting steps: First, clean and remove dust and dirt from the entire circuit board. If a broken printed circuit is found, repair the wire; Replace damaged components immediately upon detection;
Based on practical experience analysis, methods such as measurement, comparison, and substitution are used to determine suspected components. Some components require offline testing. After repairing the driving circuit, an oscilloscope should also be used to observe the output waveforms of each group of driving circuit signals. If the three-phase pulse size and phase are not equal, there are still abnormal areas in the driving circuit (mismatched parameters of replaced components can also cause such phenomena), and repeated inspection and processing should be carried out.
The damage to the driving circuit of high-power transistors is also one of the reasons for the overcurrent protection function to operate. The common phenomena of damaged driving circuits are phase loss, unequal three-phase output voltage, and unbalanced three-phase current.
2. Repair the damage to the frequency converter switch power supply
One obvious feature of damaged switching power supply is that there is no display after the inverter is powered on. For example, the Fuji G5S frequency converter adopts a two-stage switching power supply, which is based on the principle that the DC voltage of the main DC circuit is reduced from over 500V to about 300V, and then through a one-stage switch voltage reduction, the power supply outputs multiple power sources such as 5V and 24V.
Common damages to switching power supplies include breakdown of switch tubes, burning of pulse transformers, damage to secondary output rectifier diodes, prolonged use of filter capacitors, resulting in changes in capacitor characteristics (reduced capacity or high leakage current), decreased voltage stability, and easy damage to switching power supplies.
In addition, one of the common fault phenomena is that the frequency converter does not display after being powered on, and most of the reasons for such faults are also caused by damage to the switching power supply. The switching power supply of the MF series frequency converter adopts a common flyback switching power supply control method. A short circuit in the output stage circuit of the switching power supply can also cause damage to the switching power supply, resulting in no display of the frequency converter.
