1. Overcurrent

Overcurrent is the most frequent phenomenon of inverter alarm.

1.1 Phenomenon

When restarting, it will trip as soon as the speed is increased. This is a very serious phenomenon of overcurrent. The main reasons are: load short circuit, mechanical parts stuck; inverter module damaged; motor torque is too small and other phenomena caused.

It jumps after power on. This phenomenon cannot be reset. The main reasons are: bad module, bad drive circuit and bad current detection circuit.

When restarting, it does not trip immediately but when accelerating. The main reasons are: the acceleration time setting is too short, the current upper limit setting is too small, and the torque compensation setting is high.

1.2 Examples

An LG-IS3-43.7kW inverter jumps "OC" as soon as it starts

Analysis and maintenance: Opening the cover did not reveal any signs of burnout. Basically, there is no problem in online measurement of IGBT. To further determine the problem, it is very good to measure the opening and closing of 7 power transistors after removing the IGBT. When measuring the drive circuit of the upper half-bridge, there is one channel that is obviously different from the other two channels. After careful inspection, it is found that the output pin of an optocoupler A3120 is short-circuited with the negative pole of the power supply. The three channels are basically the same after replacement. The module is installed and powered on and everything works well.

When a BELTRO-VERT 2.2kW frequency converter is powered on, it will jump "OC" and cannot be reset.

Analysis and maintenance: first check the inverter module to find no problems. Second, check that there is no abnormality in the drive circuit. It is estimated that the problem is not in this area. It may be in the part of overcurrent signal processing. Remove the circuit sensor and power it up. It shows that everything is normal, so the sensor is considered to be bad. Find a new product and replace it. After loading, everything is normal with load test.

2. Overpressure

The overvoltage alarm usually occurs when the machine is shut down. The main reason is that the deceleration time is too short or there is a problem with the braking resistor and braking unit.

Examples

A Tai'an N2 series 3.7kW inverter jumps "OU" when stopped.

Analysis and maintenance: Before repairing this machine, we must first understand the cause of the "OU" alarm. This is because when the frequency converter is decelerating, the speed of the motor rotor winding cutting and rotating magnetic field is accelerated, and the electromotive force and current of the rotor increase. The motor is in the power generation state, and the feedback energy flows to the DC link through the diode in parallel with the high-power switch tube in the inverter link, which causes the DC bus voltage to rise. Therefore, we should focus on checking the brake circuit and measuring the discharge resistance. When the brake pipe was measured, it was found to have broken down. After replacement, it was powered on and operated, and there was no problem with rapid stop.

3. Undervoltage

Undervoltage is also a problem we often encounter in use. Mainly because the main circuit voltage is too low, the main reason: one of the rectifier bridge is damaged or the thyristor three circuits are not working properly may lead to the occurrence of undervoltage faults. Secondly, the main circuit contactor is damaged, resulting in DC bus voltage Loss on the charging resistor may cause undervoltage. There is also an undervoltage problem due to a fault in the voltage detection circuit.

3.1 Examples

A CT18.5kW frequency converter jumps "Uu" on power-up.

Analysis and maintenance: After checking that the charging resistance of the rectifier bridge of this inverter is good, but the contactor action is not heard after power on, because the charging circuit of this inverter does not use SCR but depends on the contactor The charging is completed to complete the charging process, so it is believed that the fault may be in the contactor or the control circuit and the power supply. Remove the contactor and add 24V DC contactor to work normally. Then check the 24V DC power supply. After carefully checking that the voltage is output after being stabilized by the LM7824 voltage regulator tube, it is measured that the voltage regulator tube is damaged, and it is normal to power on after a new product is replaced.

A DANFOSSVLT5004 frequency converter shows normal after power on, but jumps "DCLINKUNDERVOLT" after loading.

Analysis and maintenance: This inverter is special in terms of phenomenon, but if you analyze the problem carefully, it is not so complicated. The inverter also completes the charging process through the charging circuit and the contactor. It is estimated that any abnormal phenomenon is caused by the voltage drop of the DC circuit when the load is applied, and the voltage of the DC circuit is rectified by the full-wave rectification of the rectifier bridge and then provided by the smoothing of the capacitor. Therefore, the rectifier bridge should be inspected emphatically. The rectifier bridge has a bridge arm open circuit, and the problem is solved after replacing the new product.

4. Overheating

Overheating is also a relatively common failure. The main reasons are: the surrounding temperature is too high, the fan is blocked, the temperature sensor has poor performance, and the motor is overheated.

Examples

A customer of ABBACS50022kW inverter reported jumping "OH" in about half an hour of operation. Analysis and maintenance: because the fault only occurs after a period of operation, the temperature sensor is unlikely to be damaged. The temperature of the inverter may be too high. After the power is turned on, the fan turns slowly and the protective cover is filled with a lot of cotton wool. After cleaning, the fan is running well, and the fault does not jump again after running for several hours.

5. Unbalanced output

The output imbalance is generally manifested as motor jitter and unstable speed. The main reasons are: bad module, bad drive circuit, bad reactor, etc.

5.1 Examples

A Fuji G9S11KW inverter, the output voltage difference is about 100V.

Analysis and maintenance: Turn on the machine to check the inverter module online and find no problem, measure the 6-channel drive circuit and find no fault, remove the module and measure that there is a bridge high-power transistor on the road that cannot be turned on and off normally, the module has been damaged After confirming that the drive circuit is fault-free, everything is normal after replacing the new product.

　6, overload

Overload is also one of the faults where the frequency converter jumps more frequently. When we usually see the overload phenomenon, we should first analyze whether the motor is overloaded or the frequency converter itself is overloaded. Generally speaking, the motor has a strong overload capacity, as long as the motor in the inverter parameter table If the parameters are set properly, the motor overload will not occur. The inverter itself is prone to overload alarm due to the poor overload capacity. We can detect the output voltage of the inverter.

7. The switching power supply is damaged

This is the most common failure of many inverters, usually caused by a short circuit in the load of the switching power supply. Danfoss inverter uses a new pulse width integrated controller UC2844 to adjust the output of the switching power supply. At the same time, UC2844 also has current detection, voltage Feedback and other functions, when there is no display, no voltage at the control terminal, DC12V, 24V fan does not run, we should first consider whether the switching power supply is damaged.

8. SC failure

SC fault is a more common fault of Yaskawa inverter. The IGBT module is damaged, which is one of the causes of SC failure alarm. In addition, damage to the drive circuit can also easily cause SC failure alarms. In the design of the drive circuit, Yaskawa uses the drive optocoupler PC923, which is an optocoupler with an amplifier circuit dedicated to driving IGBT modules, and Yaskawa's lower bridge drive circuit uses the optocoupler PC929, which It is an optocoupler with amplifier circuit and detection circuit inside.

In addition, motor jitter, three-phase current, voltage imbalance, frequency display but no voltage output, these phenomena may be IGBT module damage. There are many reasons for IGBT module damage. The first is the failure of the external load and the damage of the IGBT module, such as short circuit of the load and stall. Secondly, the aging of the driving circuit may also lead to distortion of the driving waveform, or the driving voltage fluctuates too much and the IGBT is damaged, resulting in SC failure alarm.

9. GF ground fault

The ground fault is also a fault that is usually encountered. In addition to eliminating the cause of the problem of motor grounding, the most likely part of the fault is the Hall sensor. Due to the influence of environmental factors such as temperature and humidity, the operating point of the Hall sensor is easy. A drift occurred, causing GF to report an alarm.

10. Current limiting operation

In normal operation, we may encounter the inverter prompt current limit. For general inverters that cannot work normally and smoothly when the current limit alarm occurs, the voltage must first be lowered until the current drops to the allowable range. Once the current is lower than the allowable value, the voltage will rise again, resulting in system instability. Danfoss frequency converter adopts internal slope control to find the working point without exceeding the predetermined current limit value, and control the motor to run smoothly at the working point, and feedback the warning signal to the customer. Based on the warning information, we will check whether the load and the motor are something wrong.