With the rapid development of electronic technology, frequency converter technology has gradually matured and improved, and has been successfully applied to various fields. However, if the inverter is used improperly, it may still cause various faults or poor operation conditions, shortening the service life of the equipment. The author made a general analysis of the problems encountered during maintenance.
Although there are many kinds of inverters and circuits are continuously updated, the faults are nothing but overcurrent, overvoltage, undervoltage, overload, overheat, unbalanced outputs, and no display.
2 Overcurrent
Overcurrent is the most frequent phenomenon of inverter alarm.
2.1 phenomenon
(1) When restarting, it will trip at a raise speed. This is a very serious phenomenon of overcurrent. The main reasons are: load short circuit, mechanical parts stuck; inverter module damage; motor torque is too small and so on.
(2) Power-on jump, this phenomenon can not be reset generally, mainly due to: bad module, bad drive circuit, bad current detection circuit.
(3) When restarting, it does not immediately trip, but when accelerating, the main reasons are: too short acceleration time setting, too low current limit setting, and high torque compensation (V/F) setting.
2.2 Examples
(1) One RNB3003 3.7kW inverter jumps "OC" as soon as it starts
Analysis and Maintenance: No signs of burning were found when the lid was opened. There was no problem with the basic IGBT determination. To determine the problem further, it was good to turn on and off the high-power transistors that measured 7 units after the IGBT was removed. When measuring the drive circuit of the upper half bridge, it was found that there was a clear difference between the other two circuits. After careful inspection, it was found that the output pin of the optocoupler A3120 had a short circuit with the negative electrode of the power supply. After the replacement, the three paths were basically the same. The module is powered on and everything is running fine.
(2) One RNB3002 2.2kW inverter energized jumps "OC" and cannot be reset.
Analysis and maintenance: First check the inverter module found no problems. Secondly, there is no abnormality in checking the drive circuit. It is estimated that the problem is not in this block. It may be in the part of the over-current signal processing. After the circuit sensor is removed and the power is turned on, it shows that everything is normal. Therefore, the sensor is considered to be bad and a new one is needed. After loading the experiment, everything was normal.
3 Overvoltage
Overvoltage alarms usually occur at the time of shutdown. The main reason is that the deceleration time is too short or there is a problem with the braking resistor and the brake unit.
(1) Examples
One RNB3003 3.7kW inverter jumps "OU" when it stops.
Analysis and maintenance: Before repairing this machine, we must first understand what causes the “OU†alarm. This is because when the frequency converter is decelerating, the rotor rotor winding cuts the rotating magnetic field faster, and the rotor's electromotive force and current increase. Make the motor in the power generation state, the energy returned by the diode in the inverter circuit in parallel with the high-power switch tube to the DC link, so that the DC bus voltage rise caused by, so we should focus on checking the brake circuit, measuring the discharge resistance is no problem, When the brake pipe was measured, it was found to have broken down. After the replacement, it was powered on. There was no problem with the quick stop.
4 Undervoltage
Underpressure is also a problem we often encounter in use. Mainly because the main circuit voltage is too low (380V series is lower than 400V). The main reason is that the damage of one of the rectifier bridges or abnormal operation of the SCR three channels may cause undervoltage faults, followed by the main loop contact. Device damage, resulting in DC bus voltage loss above the charging resistor may cause undervoltage. There is a voltage detection circuit failure and undervoltage problems.
4.1 Examples
One RNB3018 18.5kW inverter jumps "LU2".
â— Analysis and maintenance: After checking that the charging resistance of the rectifier bridge of this inverter is good, but no contactor action is heard after power-on, because the charging circuit of this inverter is not using SCR but by the contactor. The suction process is completed to complete the charging process. Therefore, it is considered that the fault may be in the contactor or the control circuit and the power supply section. The removal of the contactor and the addition of the 24V DC contactor work properly. Then check the 24V DC power supply, after careful inspection of the voltage is regulated by the LM7824 regulator after the output, measuring the voltage regulator tube is damaged, find a new replacement after power-up is working properly.
5 Overheating
Overheating is also a relatively common fault. The main causes are: high ambient temperature, blocked fans, poor temperature sensor performance, and motor overheating.
5.1 Example
One RNB3022 22kW inverter customer reported to jump "OH" about half an hour running.
â— Analysis and maintenance: Because it is only after running for a period of time, there is a possibility that the temperature sensor is bad. The temperature of the inverter may be too high. After the power is turned on, the fan is found to be rotating slowly. The protective hood is full of a lot of cotton. (Because the frequency converter is used in the textile industry), the boot fan runs well after being cleaned, and does not jump this fault after several hours of operation.