Causes and treatment methods of inverter tripping fault

One. Power failure handling
If the power supply is temporarily powered off or the voltage is low, the “undervoltage” display, or the “overvoltage” display of this transient overvoltage may cause the inverter to trip and stop. Generally, the power can be restarted after the power supply returns to normal.
2. External fault handling
If the input signal is open, the output line is open circuit, phase failure, short circuit, grounding or insulation resistance is very low, the motor is faulty or overloaded, etc., the inverter will display “external” fault and trip and stop. After the fault is eliminated, it can be re-enabled.
three. Internal fault handling
If the internal fan is open or overheated, the fuse is open, the device is overheated, the memory is faulty, the CPU is faulty, etc., it can be switched to the power frequency operation without affecting the production. After the internal fault is eliminated, the inverter operation can be resumed.

In the event of an internal fault in the inverter unit, if it is within the warranty period, the manufacturer or the manufacturer’s agent should be notified as soon as possible to be responsible for the warranty. Perform the following checks based on the category and data displayed by the fault:

1. After opening the chassis, first check whether there are any broken wires, solder joints, burnt smells or deterioration of the components inside, if necessary, do the corresponding treatment in time.

2. Use a multimeter to check the resistance of the resistor and the on-off resistance of the diode, switch tube and module to determine whether to break or break down. If yes, replace it with the original nominal value and the withstand voltage value, or replace it with the same type.

3. Use the dual trace oscilloscope to detect the waveform of each working point, and use the step-by-step elimination method to judge the fault location and components.

Issues to be aware of during maintenance:

1. Strictly prevent false soldering, virtual connection, or wrong soldering, continuous soldering, or miswired, especially do not mistakenly connect the power cable to the output.

2. Power-on static check indicator, digital tube and display are normal, and the preset data is appropriate.

3. If there are conditions, a small motor can be used for the simulation dynamic test.

4. With load test.

four. Improper handling of function parameters
When the parameters are preset, the no-load test is normal. If an “overcurrent” trip occurs after loading, the starting torque setting may be insufficient or the acceleration time may be insufficient. Some may also decrease the moment of inertia after running for a period of time, resulting in “overvoltage” during deceleration. “Trip, generally modify the function parameters and then increase the acceleration time to solve.

Causes and treatment methods of inverter overcurrent

(1) Overcurrent in operation means that the drag system has an overcurrent during the working process. The reason is mainly from the following aspects: 1 The motor encounters an impact load, or the transmission mechanism is “stuck”, causing a sudden increase in the motor current.

2 The output side of the inverter is short-circuited, such as a short circuit between the output terminals and the motor, or a short circuit inside the motor.

3 The inverter itself is not working properly. For example, two inverter devices of the same bridge arm in the inverter bridge are abnormal during the alternate work. For example, due to the high ambient temperature or the aging of the inverter device itself, the parameters of the inverter device are changed, resulting in one device being turned on during the alternation process, and the other device is still turned off in the future, causing the same The “straight through” of the upper and lower devices of one bridge arm makes the short circuit between the positive and negative terminals of the DC voltage.

(2) Over-current when the speed is increased When the inertia of the load is large and the speed-up time is set too short, it means that during the speed-up process, the working efficiency of the inverter rises too fast, and the synchronous speed of the motor rises rapidly. However, the rotation speed of the motor rotor cannot be kept up due to the large inertia of the load, and as a result, the speed increase current is too large.

(3) Overcurrent in the deceleration When the inertia of the load is large and the deceleration time is set too short, it will cause overcurrent. Because the speed reduction time is too short, the synchronous speed decreases rapidly, and the rotor of the motor maintains a high speed due to the inertia of the load. At this time, the speed at which the rotor winding cuts the magnetic line is too large to generate an overcurrent.

Inverter overcurrent processing method

(1) Tripping at a speed up at start-up, this is a very serious over-current phenomenon. The main check: whether the working machine is stuck; whether there is a short circuit on the load side, check whether there is a short circuit to the ground with a megohmmeter; The module is not damaged; the starting torque of the motor is too small, and the drag system cannot be turned.

(2) Do not trip immediately when starting, but trip during operation, the main check: the speed increase time setting is too short, lengthen the acceleration time; the deceleration time setting is too short, lengthening the deceleration time; torque compensation (U/f ratio The setting is too large, causing too much no-load current at low frequencies: the electronic thermal relay is improperly set, and the operating current is set too small, causing the inverter to malfunction.

How to make the inverter “live” longer

The frequency converter is often used in electrical systems, but the service life of the frequency converter will also be shortened due to overvoltage and overcurrent, and once the inverter fails, it will cause serious failures in the entire electrical system. Therefore, the electrician is gradually paying attention to and paying attention to the maintenance and repair skills of the inverter. After all, anyone who wants to buy the inverter can live longer, so how should the inverter “longevity”?

1, the correct wiring and parameter settings. Be sure to read the manual carefully before installing the inverter, master its usage, precautions and wiring; after installation, set the parameters correctly according to the use.

2. The ambient temperature has a great influence on the service life of the inverter. When the ambient temperature is 10 °C per liter, the life of the inverter is halved, so the problem of ambient temperature and heat dissipation of the inverter must be solved.

3. V/F control is a constant torque adjustment. The vector control increases the output torque of the motor in proportion to the square of the voltage, thereby improving the output torque of the motor at low speeds.

4. If the system is operated by the power frequency/frequency conversion mode, the interlock of the power frequency output and the frequency conversion output should be reliable. Moreover, the pump should be stopped, the power frequency/frequency conversion should be stopped, and then the contactor should be operated. Since the contact sticking and the extinguishing of the large-capacity contactor arc take a certain time, the order and time of the above switching should be considered comprehensively.

5. The problem of external control signal failure. Generally, there are several cases: the signal mode is incorrect, the terminal wiring is incorrect, the parameter setting is incorrect, or the external signal itself has a problem.

6, pay attention to the relationship between speed and head. The choice of the motor and its optimal working segment are important issues. If the inverter runs below 5HZ for a long time, the motor heating becomes a serious problem.

7. The difference between overcurrent trip and overload trip. Overcurrent is mainly used to protect the inverter, and overload is mainly used to protect the motor. Because the capacity of the inverter sometimes needs to be increased by one or two gears than the capacity of the motor. In this case, the inverter does not have to overcurrent when the motor is overloaded. The overload protection is carried out by the electronic thermal protection function inside the inverter. When preset electronic thermal protection, the “current take-up ratio”, that is, the ratio of the rated current of the motor to the rated current of the inverter should be accurately preset.

Solutions to Overcurrent /Overvoltage/Undervoltage of VFD

Overcurrent is the most frequent phenomenon of inverter alarm.
1.1 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.
1.2 Examples
(1) An LG-IS3-4 3.7kW inverter jumps “OC” as soon as it starts
Analysis and maintenance: Open the cover did not find any signs of burnt, online measurement IGBT (7MBR25NF-120) basic judgment is no problem, to determine the problem, after the removal of the IGBT measured 7 units of high-power transistors turn on and off both well. 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 was short-circuited to the negative terminal of the power source. After the replacement, the three paths were basically the same. The module is powered on and everything is running fine.
(2) A BELTRO-VERT 2.2kW inverter energizes to jump “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 removing the circuit sensor and powering it on, it shows that everything is normal. Therefore, it is considered that the sensor is broken and a new one is found. After loading the experiment, everything is normal. The
2 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
A Taian N2 series 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 flows to the DC link, so that the DC bus voltage is increased, so we should focus on checking the brake circuit, measuring the discharge resistance is no problem, When the brake pipe (ET191) was measured, it was found to have broken down. After the replacement, it was powered on, and there was no problem with the quick stop.
3 Undervoltage
Underpressure is also a problem we often encounter in use. Mainly because the main circuit voltage is too low (220V series is lower than 200V, 380V series is lower than 400V), the main reason: a damaged rectifier bridge or SCR three-way work may lead to undervoltage fault Appeared, followed by the main circuit contactor damage, resulting in DC bus voltage loss above the charging resistor may cause undervoltage. There is a voltage detection circuit failure and undervoltage problems.
3.1 Examples
(1) Jump on “Uu” on a CT 18.5kW inverter.
● 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 pull-in process completes the charging process, so it is considered that the fault may be in the contactor or the control circuit and the power supply section, and the removal of the contactor alone plus the 24V DC contactor is working properly. Then check the 24V DC power supply. After careful inspection, the voltage is output after being stabilized by the LM7824 regulator. Measure the voltage regulator tube is damaged. After finding a new one, the power is normal after the replacement.
(2) For a DANFOSS VLT5004 inverter, the power-on display is normal, but jump “DC LINK UNDERVOLT” after load.
● Analysis and maintenance: This inverter is special in terms of phenomena, but if you carefully analyze the problem is not so complicated, the inverter also through the charging circuit, contactor to complete the charging process, there is no power Any abnormal phenomenon is estimated to be 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 bridge of the rectifier bridge and then provided by the capacitor after the flat wave. Therefore, the rectifier bridge should be checked and measured. The rectifier bridge was found to have an open bridge and the problem was solved after replacing the new one.

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