With the development of my country’s social economy, frequency converters have been widely used in major automation industries, and have played an important role in accelerating the development of the automation industry. But the frequency converter is an electronic component, and some faults will naturally occur. Next, we will bring you the common fault analysis of vector frequency converters. Let’s take a look.
1. The variable-frequency-drive is overvoltage
The VFD displays an overvoltage fault, usually due to thunderstorms. Because lightning is connected to the power supply of the ac drive, the voltage detector on the DC side of the ac drive is activated and tripped. In this case, usually only need to disconnect and turn on the inverter power supply again after about 1 minute. Another situation is that the frequency inverter drives a large inertia load and over-voltage occurs. In this case, one way is to lengthen the parameter of deceleration time or increase the braking resistor (brake unit); the other is to set the stop mode of the inverter to the free stop mode.
2. The variable-frequency-drive is overcurrent
The frequency inverter displays overcurrent. When this appears, first check whether the acceleration time parameter is too short and whether the torque boost parameter is too large, and then check whether the load is too heavy. If there is no such phenomenon, you can disconnect the output current transformer and the Hall current detection point on the DC side, and run after reset to see if there is an over-current phenomenon. If it is, it is likely that the IPM module is faulty, because the IPM module contains protection functions such as over-voltage, over-current, under-voltage, overload, overheating, phase loss, short circuit, etc., and these fault signals are transferred to the controller through the module control pin Fn. After the micro controller receives the fault information, it blocks the pulse output on the one hand, and displays the fault information on the panel on the other hand. So the IPM module should be replaced.
3. No failure but no operation
The frequency inverter has no fault display, but it cannot run at high speed. After checking that the inverter parameters are set correctly, and the speed control input signal is normal. After power-on operation test, the inverter DC bus voltage is only about 450V (normally should be 580V-600V), and then test the input side, one phase was found to be missing. The cause of the fault is that one phase of an air switch on the input side is in poor contact. The reason that the inverter input phase loss does not alarm and can still work in the low frequency band is because that the lower limit of the bus voltage of most inverters is 400V. Only when the bus voltage drops below 400V, the inverter will report a fault.
When two-phase input, the DC bus voltage is 380V×1.2=452V>400V. When the inverter is not running, due to the smoothing capacitor, the DC voltage can also reach the normal value. The new inverters all adopt PWM control technology. The voltage and frequency regulation is completed in the inverter bridge, so the VFD can still work normally when the input phase is lacking in the low frequency band. But due to the low input voltage and low output voltage, the asynchronous motor rotates at a low frequency and cannot go up.
4. The variable-frequency-drive is overheated and overloaded
The motor heats up and the inverter displays overload. For the inverter that has been put into operation, you need to check the load condition. For the newly installed inverter, this fault may be caused by improper V/F curve setting or problem with the motor parameter setting. Various parameters need to be set correctly. In addition, the heat dissipation performance of the motor becomes worse when the motor is working at low frequencies. this situation may also occur. At this time, a heat sink is required.
5. Failure of charging start circuit
General-purpose inverters are generally pressure-type inverters with AC-DC-AC working mode. When the inverter is just powered on, because the smoothing capacitor on the DC side is very large and the charging current is very large, a starting resistor is usually used to limit the charging current.
After the charging is completed, the control circuit short-circuits the resistance through the contact of the relay or the thyristor. The starting circuit failure is generally manifested as the starting resistance burned out, and the inverter alarm shows that the DC line voltage is faulty. Generally, in the design of the inverter, in order to reduce the volume of the inverter, a smaller starting resistance is selected, its value is mostly 10-50Ω, and the power is 10-50W; when the AC input power of the inverter is frequently turned on or the contact of bypassed contactor is not in good contact, it will cause the starting resistor to burn out. Therefore, when replacing the resistor, it is necessary to find out the cause. If the fault is caused by the input side power frequency, you need to deal with this phenomenon before you can put the inverter into use. If the fault is only caused by the bypassed contact element, you need to replace these elements.
Using a variable-frequency-drive as an asynchronous motor drive, although its reliability is very high, if it is used improperly or accidentally, it will also cause damage to the ac drive. If you want to use it well in the production process, you must be familiar with the structure principle of the VFD and understand common faults. It is especially important for operators.
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Post time: Oct-09-2021