Fault prevention in the use of the inverter - Database & Sql Blog Articles

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After the inverter is used for 6-10 years, it enters the high-risk period of the fault, and often the components burn out, fail, and the protection function frequently operate, which seriously affects its normal operation. In the actual maintenance, the abstract grasps its characteristics, grasps the law of fault handling, and can do the maintenance work of the inverter. It is the various faults that occur in the actual situation of the inverter that are dealt with and solved in time, so as to prevent problems before they occur. It is especially important to carefully analyze the cause of the failure in advance.
If there is interference source around the inverter, they will invade the inverter through the radiation or power line, causing the control circuit to malfunction, causing abnormal operation or shutdown, and even damage the inverter in severe cases. It is important to improve the anti-interference ability of the inverter itself. However, due to the limitation of the cost of the device, it is more reasonable and necessary to eliminate the interference source by taking noise suppression measures on the outside. The following measures are specific methods for implementing the “three noes” principle for noise interference: all the relays around the inverter and the control coil of the contactor need to be equipped with absorption devices to prevent the surge voltage, such as RC absorbers; Wiring distance and separation from the main line; the specified shielded circuit should be carried out according to the regulations. If the line is better, a reasonable relay method should be adopted; the grounding terminal of the inverter should be carried out according to the regulations, not the same as electric welding and power grounding. Mixed; a noise filter is installed at the input of the inverter to avoid interference introduced by the power supply line. Installation environment The frequency converter is an electronic device device and has detailed requirements for installation and use environment in its specification. In special cases, if these requirements are not met, the corresponding suppression measures must be adopted as much as possible: vibration is the main cause of mechanical damage to electronic devices. For vibration shocks, vibration and other vibration-proof measures should be used; moisture and corrosion Gas and dust will cause rust, poor contact, and low insulation of the electronic device to form a short circuit. As a precautionary measure, the control board should be treated with anti-corrosion and dustproof, and a closed structure; temperature is the life and reliability of the electronic device. Important factors, especially semiconductor devices, should be installed in accordance with the environmental conditions required by the device or to avoid direct sunlight.
In addition to the above three points, it is also necessary to regularly check the air filter and cooling fan of the inverter. For special high-cold occasions, in order to prevent the microprocessor from working properly due to low temperature, necessary measures such as setting a space heater should be taken. Abnormal power supply abnormalities are manifested in various forms, but they are roughly classified into the following three types, namely, phase loss, low voltage, power failure, and sometimes their mixed forms. Most of the main causes of these anomalies are caused by wind, snow, and lightning strikes, and sometimes due to short-circuit to ground and phase-to-phase short circuit in the same power supply system. Lightning strikes vary greatly by region and season. In addition to voltage fluctuations, some power grids or self-generating units also have frequency fluctuations, and these phenomena sometimes appear repeatedly in a short period of time. In order to ensure the normal operation of the equipment, the power supply of the inverter is also required.
If there is a direct start motor and induction cooker nearby, in order to prevent the voltage drop caused by the input of these devices, it should be separated from the inverter power supply system to reduce the mutual influence; in the case of requiring continuous operation after the instantaneous power failure, in addition to selecting the appropriate In addition to the price of the inverter, the speed reduction ratio of the load motor is also considered in advance. The inverter and the external control loop adopt the instantaneous stop compensation mode. When the voltage is restored, the overcurrent is prevented by the speed tracking and the detection of the speed measuring motor. For the equipment that requires the necessary amount of operation, the inverter should be automatically installed. Switched uninterruptible power supply unit.
The diode input and the inverter using the single-phase control power supply can continue to work in the phase loss state, but the current of the individual components in the rectifier is too large and the pulse current of the capacitor is too large. If the long-term operation will be used, the life and reliability of the inverter will be long. Cause adverse effects, should be checked and dealt with as soon as possible. The surge voltage formed by lightning strikes, inductive lightning strikes, or induced lightning strikes can sometimes cause damage to the inverter. In addition, when the power supply system has a vacuum circuit breaker on the primary side, the short circuit breaker can also generate a high surge voltage.
When the primary side vacuum circuit breaker of the transformer is disconnected, a high voltage surge spike is formed by coupling on the secondary side.
In order to prevent overvoltage damage caused by the surge voltage, it is usually necessary to apply a snubber such as a varistor at the input end of the inverter to ensure that the input voltage is not higher than the maximum voltage allowed during the main circuit of the inverter. When using a vacuum circuit breaker, an additional RC surge absorber should be formed by impact. If there is a vacuum circuit breaker on the primary side of the transformer, the inverter will be disconnected before the vacuum circuit breaker is operated in the control timing.
In the past, transistor inverters mainly had the following disadvantages: easy to trip, not easy to restart, and low overload capability. Due to the rapid development of IGBT and CPU, the inverter has improved the self-diagnosis and fault prevention functions, which greatly improves the reliability of the inverter.
If the "all-area automatic torque compensation function" in the vector control inverter is used, the cause of failure such as "insufficient starting torque" and "decreased output due to environmental conditions" will be well overcome. This function uses the high-speed calculation of the microcomputer inside the inverter to calculate the torque required at the current time, and quickly corrects and compensates the output voltage to offset the change in the output torque of the inverter caused by changes in external conditions.
In addition, since the software development of the inverter is more perfect, various fault prevention measures can be set in the inverter in advance, and the fault can be maintained after the fault is resolved, for example, restarting the motor during the free stop; The internal fault is automatically reset and keeps running continuously; when the load torque is too large, the running curve can be automatically adjusted to avoid the trip; the abnormal torque of the mechanical system can be detected.
The influence of the inverter on the peripheral equipment and the fault prevention The installation and use of the inverter will also affect other equipment, and sometimes even cause other equipment to malfunction. Therefore, it is necessary to analyze these factors and study what measures should be taken. High-order harmonics of power supply Because the current inverters almost all adopt PWM control mode, such pulse modulation forms cause high-order harmonic currents on the power supply side when the inverter is running, and the voltage waveform is distorted, which has a serious impact on the power supply system. The following treatment measures are usually adopted: the inverter is used to supply power to the inverter, and is separated from other power supply systems; a filter reactor or a plurality of rectifier bridge circuits are added on the input side of the inverter to reduce high-order harmonic components, and for the phase-in capacitor Occasionally, due to the higher harmonic current, the increase of the capacitor current causes severe heat generation. The reactor must be connected in series with the capacitor to reduce the harmonic component. The electric induction of the reactor is reasonably analyzed and calculated to avoid the formation of LC oscillation. When the motor temperature is too high and the operating range is modified for the existing motor, the motor is overheated due to the cooling capacity of the self-cooling motor at low speed. In addition, because the higher harmonics contained in the output waveform of the inverter are bound to increase the iron loss and copper loss of the motor, after confirming the load state and operating range of the motor, the following measures are taken: strong cold ventilation of the motor or Improve the motor specification grade; replace the inverter-specific motor; limit the operating range and avoid the low-speed zone. Vibration and noise vibrations are usually caused by the pulsating torque of the motor and the resonance of the mechanical system, especially when the pulsating torque coincides exactly with the mechanical resonance. The noise is usually divided into variable frequency device noise and motor noise. Different treatment measures should be taken for different installation places: In the debugging process, under the premise of ensuring control accuracy, the pulse torque component should be minimized; Resonance point, using the frequency shielding function of the inverter, these resonance points are excluded from the operating range; since the inverter noise is mainly generated by the cooling fan electromechanical device, the low noise device is selected; the reasonable setting between the motor and the inverter AC reactor to reduce the higher harmonics caused by PWM modulation. The high-frequency switch forms a spike voltage that is detrimental to the motor insulation. In the output voltage of the inverter, it contains a high-frequency spike voltage. These high-order harmonic surge voltages will reduce the insulation strength of the motor windings, especially with PWM-controlled inverters. The following measures should be taken: minimize the wiring distance from the inverter to the motor; use surges that block diodes Voltage absorption device, processing the inverter output voltage.
In short, in the application of the frequency converter, only the various conditions that meet the design work requirements and normal use can be used for long-term, safe and stable operation. If it is used in a harsh working environment, it is necessary to pay more attention to the daily maintenance and overhaul of the inverter, and to improve the environment and load fluctuation of the inverter. In order to ensure that the inverter can perform its various functions reliably, smoothly and safely, it can achieve the purpose of speed regulation operation, saving energy and reducing maintenance costs.