Undervoltage is also a problem that we often encounter in application. The main reason is that the voltage of the main circuit is too low (220V series is lower than 200V, 380V series is lower than 400V), the main reason: a rectifier bridge is damaged or there is abnormal operation in the three thyristors, which may lead to undervoltage problems, and secondly, the main circuit contactor is damaged, resulting in DC bus voltage loss on the charging resistor. There is also a problem of undervoltage due to the problem of voltage detection circuit.
1. Phenomenon
(1) When starting from the beginning, it trips as soon as the speed is raised. This is a very serious phenomenon of overcurrent. The main reasons are: short circuit of load, stuck mechanical parts; The inverter module is damaged; The torque of the motor is too small.
(2) Jump when powered on, this phenomenon generally cannot be reset, the main reasons are: bad module, bad drive circuit, bad current detection circuit.
(3) When starting from the beginning, it does not trip immediately but accelerates, the main reasons are: the acceleration time is set too short, the upper current limit is set too small, and the torque compensation (V/F) is set high.
2. Examples
(1) A 43.7kW inverter jumps "OC" as soon as it is started
Analysis and repair: open the cover did not find any signs of burnout, online measurement IGBT (7MBR25NF-120) basically no problem, in order to further identify the problem, the IGBT is removed after measuring 7 units of high-power transistor registration and sealing are very good. When measuring the driving circuit of the upper half-bridge, it was found that one of them was significantly different from the other two, and after careful inspection, it was found that the output pin of an optocoupler A3120 was short-circuited with the negative pole of the power supply, and the three channels were basically the same after replacement. The modules are all outstanding when they are powered on.
(2) A 2.2kW inverter jumps "OC" when it is energized and cannot be reset.
Analysis and repair: The first thing to do is to check the inverter module and find no problems. Secondly, there is no abnormal phenomenon in the drive circuit, the estimation problem is not in this piece, perhaps in the overcurrent signal processing part, the circuit sensor is removed and powered on, and the display is all normal, so I think the sensor is broken, and I find a new product to replace it with a load experiment that is normal.
3. Overvoltage
The overvoltage alarm generally appears at the time of shutdown, and the main reason is that the deceleration time is too short or there is a problem with the braking resistance and braking unit.
(1) Examples
A 3.7kW inverter jumps "OU" when it stops.
Analysis and repair: Before repairing this machine, the first thing to understand is the reason for the "OU" alarm, this is because when the inverter is decelerating, the speed of the motor rotor winding cutting the rotating magnetic field accelerates, the electromotive force and current of the rotor increases, so that the motor is in a state of power generation, and the energy fed back flows to the DC link through the diode connected in parallel with the high-power switch tube in the inverter link, which causes the DC bus voltage to rise, so we should focus on looking at the braking circuit, there is no problem in measuring the discharge resistance, and the brake tube ( ET191) was found to have broken down, and after replacement, it was powered on and running, and there was no problem with rapid shutdown.
4. Undervoltage
Undervoltage is also a problem that we often encounter in application. The main reason is that the voltage of the main circuit is too low (220V series is lower than 200V, 380V series is lower than 400V), the main reason: a rectifier bridge is damaged or there is abnormal operation in the three thyristors, which may lead to undervoltage problems, and secondly, the main circuit contactor is damaged, resulting in DC bus voltage loss on the charging resistor. There is also a problem of undervoltage due to the problem of voltage detection circuit.
Example
(1) An 18.5kW inverter is powered on to jump "Uu".
Analysis and repair: After checking the rectifier bridge charging resistance of this inverter, it is good, but the contactor action is not heard after powering on, because the charging circuit of this inverter does not use thyristors but relies on the suction of the contactor to complete the charging process, so I think that the problem may be in the contactor or control loop and the power supply part, remove the contactor and add 24V DC contactor to work normally. Then check the 24V DC power supply, after careful checking, the voltage is output after the voltage stabilization of the LM7824 regulator tube, measure that the voltage regulator tube has been damaged, find a new product to replace the power on operation normally.
(2) A frequency converter, the power-on display is normal, but the load jumps "DCLINKUNDERVOLT" (DC loop voltage is low).
Analysis and repair: this inverter is more special from the phenomenon point of view, but if you carefully analyze the problem is not so complicated, the inverter is also through the charging circuit, contactor to complete the charging process, no abnormal phenomenon was found when powering on, the estimation is caused by the voltage drop of the DC circuit when the load is added, and the voltage of the DC circuit is rectified by the full wave of the rectifier bridge, and then provided by the capacitor after the flat wave, so we should focus on the rectifier bridge, and the rectifier bridge is found to have a bridge arm open circuit. The problem is solved after replacing the new product.
5. Overheating
Overheating is also a relatively common problem, the main reasons: the surrounding temperature is too high, the fan is stalled, the temperature sensor performance is poor, and the motor is overheated.
(1) Examples
A 22kW inverter was reported by a customer who jumped "OH" after about half an hour of operation.
Analysis and repair: because it is a problem after a period of operation, so the temperature sensor may not be bad, perhaps the temperature of the inverter is indeed too high, after the power is on, it is found that the fan rolls slowly, and the protective cover is filled with a lot of cotton wool (because the inverter is used in the textile industry), after cleaning, the fan runs well, and there is no problem after a few hours of operation.
6. The output is unbalanced
The output imbalance is generally manifested as motor flutter and unstable speed, the main reasons: bad module, bad drive circuit, bad reactor, etc.
(1) Examples
A 11KW inverter, the output voltage difference is about 100V.
Analysis and repair: turn over the machine and start to check the inverter module (6MBI50N-120) online no problem, measure the 6-way drive circuit and find no problem, remove the module and measure it found that there is a way bridge high-power transistor can not be turned on and closed normally, the module has been damaged, after admitting that the drive circuit is faultless, all are normal after replacing the new product.
7. Overload
Overload is also one of the problems of frequent inverter beating, usually see the overload phenomenon, we should actually analyze whether it is the motor overload or the inverter itself overload, generally speaking, the motor can be stronger because of overload, as long as the motor parameters of the inverter parameter table are set properly, it is generally unlikely that the motor will be overloaded. The inverter itself is poor because of overload, and it is very simple to have an overload alarm. We can detect the output voltage of the inverter, the current detection circuit, and other fault-prone points to eliminate the fault one by one.
(1) Examples
A 55KW inverter often jumps "OL" when running.
Analysis and repair: According to the customer, this machine was originally used on a 37kw motor, but now it is used on a 55kw motor. The parameters have not been set from the beginning, so the problem may lie in the parameters, after checking the frequency conversion current limit set to the rated current of the 37kw motor, after the parameters are set from the beginning with the load is normal.
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