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Today, Shanghai Kuan Ying came to tell you about the basic introduction of the inverter and the common fault analysis.
Drives are used in a wide range of applications, from small appliances to large mine grinders and compressors. About one-third of the world's energy is spent on motors that drive fixed-speed centrifugal pumps, fans and compressors, and the market penetration of inverters is still not high. A significant increase in energy power is one of the main reasons for using frequency converters.
Inverter skills are closely related to power electronics, including semiconductor switching components, drive topology, control and simulation skills, and advances in control hardware and firmware.
The inverter charging circuit is faulty. The general-purpose inverter is generally a pressure-type inverter, and the AC-DC-AC operation mode is selected. When the inverter is just powered on, because the flat-wave capacitor capacity on the DC side is very large and the charging current is very large, a starting resistor is usually used to constrain the charging current.
After charging is complete, the control circuit shorts the resistor through the contacts of the relay or the thyristor. The fault of the starting circuit is generally caused by the burning of the starting resistor, and the alarm of the inverter shows that the DC line voltage is faulty. Generally, when designing the inverter, in order to reduce the volume of the inverter, choose a small starting resistor, the value is mostly 10-50Ω, the power is 10-50W; when the AC input power of the inverter is frequently turned on, perhaps bypass When the contacts of the contactor are in poor contact, the starting resistance will burn out. Therefore, when replacing the resistor, it is necessary to find out the cause. If the fault is caused by the beginning of the input side power frequency, it is necessary to eliminate this phenomenon before the inverter can be put into use. If the fault is caused only by the bypass contact element, then there is It is necessary to replace these devices.
Analysis and treatment of overvoltage (ou) problems
The overvoltage of the inverter is concentrated on the tributary voltage of the DC bus. Under normal circumstances, the inverter DC power is the average value after three-phase full-wave rectification. If the voltage is calculated by the 380v line voltage, the average DC voltage ud=1.35 and the u line=513v. When an overvoltage occurs, the storage capacitor of the DC bus will be charged, the voltage will rise, and the overvoltage detection value will be 800vdc. When the voltage rises to the overvoltage detection value, the inverter overvoltage protection action. Therefore, for the inverter, there is a normal operating voltage scale, which is likely to damage the inverter when the voltage exceeds this scale.
There are three types of overvoltages common to inverters: ou1 speed over voltage, ou2 speed over voltage, and ou3 constant speed over voltage. The overvoltage alarm is generally presented at the time of the shutdown, the main reason being that the deceleration time is too short or there is no device braking resistor and braking unit. The inverter presents an overvoltage problem, which is generally thunderstorm. Because the lightning is connected to the power supply of the inverter, the voltage detector on the DC side of the inverter is tripped. In this case, usually only the inverter power supply must be disconnected for 1 min. Left and right, and then close the power supply, you can reset; in another case, when the inverter drives a large inertia load, its deceleration time is set to “shorter”, because in this case, the deceleration stop of the inverter belongs to regenerative braking. During the suspension process, the output frequency of the inverter decreases linearly, and the frequency of the load motor is higher than the output frequency of the inverter. The load motor is in the power generation state, the mechanical energy is converted into electric energy, and is absorbed by the smoothing capacitor on the DC side of the inverter. When this energy is large enough, a so-called "pumping phenomenon" occurs, and the voltage on the DC side of the inverter trips beyond the large voltage of the DC bus. For this problem, the "deceleration time" parameter is set long. The second is to install the brake unit to increase the braking resistance; the third is to set the suspension mode of the inverter to “free stop”. There is also a case where the frequency converter operates normally when the motor is unloaded, but cannot be started with a load. This problem is often present in a constant torque load. When encountering such problems, you should check the acceleration/deceleration time setting or increase the torque function. Therefore, the DC link voltage of the inverter rises and exceeds its protection value, which is a problem.
The motor is hot, and the inverter shows overload. It is necessary to check the load status of the inverter that is now in operation. The inverter of the new device has such a problem, it is likely that the V/F curve is not set. If there is a problem with the setting of the motor or the motor, it is necessary to set the various parameters correctly. In addition, the heat dissipation function of the motor is degraded during low-frequency operation, and this will also occur. At this time, a heat sink is required.
The inverter is selected as the asynchronous motor driver. Although its reliability is very high, if the use is improper or accidental, the inverter will be damaged. In order to use the inverter during the production process. Familiar with the structural principle of the inverter and understand the common problems. It is especially important for the technical personnel.
Emerson Inverter will continue to develop energy-efficient, efficient, sophisticated and user-friendly products with professional and unique industrial control technology. High-quality and applicable innovative products and deeply integrated solutions help users achieve economic transformation and industrial upgrading, accelerate the pace of internationalization, conquer the world with quality, and aspire to become a world-famous professional supplier of intelligent electrical!