The frequency converter is composed of main circuit, power circuit, IPM drive and protection circuit, cooling fan and so on. Its structure is mostly in a modular or modular form. Due to incorrect use or unreasonable setting environment, the inverter may be mishandled and malfunctioned, or the expected operation may not be achieved. In order to prevent problems before they occur, it is especially important to carefully analyze the cause of the failure in advance.
1. Analysis of common faults in the main circuit:
The main circuit is mainly composed of three-phase or single-phase rectifier bridge, smoothing capacitor, filter capacitor, IPM inverter bridge, current limiting resistor, contactor and other components. Many of these common faults are caused by electrolytic capacitors. The life of an electrolytic capacitor is mainly determined by the DC voltage and internal temperature applied to both ends. The type of capacitor has been selected in the loop design, so the internal temperature determines the life of the electrolytic capacitor.
Electrolytic capacitors will directly affect the service life of the inverter. For every 10°C increase in temperature, the life will be halved. Therefore, on the one hand, the appropriate ambient temperature should be considered during installation, and on the other hand measures can be taken to reduce the pulsating current. An AC or DC reactor with improved power factor can reduce the ripple current and extend the life of the electrolytic capacitor. In the maintenance of the capacitor, the deterioration of the electrolytic capacitor is usually judged by the electrostatic capacity which is relatively easy to measure. When the electrostatic capacitance is less than 80% of the rated value and the insulation resistance is 5 MΩ or less, the electrolytic capacitor should be replaced.
2. Typical fault analysis of the main circuit:
Symptom: The inverter trips overcurrent during acceleration, deceleration or normal operation.
The first thing to distinguish is due to the load or the cause of the inverter. If it is the fault of the inverter, the history can be used to check the current at the time of trip, which exceeds the rated current of the inverter or the set value of the electronic thermal relay. If the three-phase voltage and current are balanced, then it should be considered whether there is overload. Or sudden changes, such as motor stalls.
When the load inertia is large, the acceleration time can be extended appropriately, and the process is not damaged by the inverter itself. If the current at the time of tripping is within the rated current of the inverter or within the set range of the electronic thermal relay, it can be judged that the IPM module or related part has failed. First, it is possible to determine whether the IPM module is damaged by measuring the positive and negative resistances between the main circuit output terminals U, V, and W of the inverter and the P and N terminals on the DC side. If the module is not damaged, the drive circuit has failed. (http:// copyright) If the IPM module is over-current or the inverter short-circuits to ground when decelerating, it is generally the module of the upper half of the inverter or its drive circuit is faulty; and the IPM module during acceleration Overcurrent is the failure of the module of the lower half of the bridge or its drive circuit. The cause of these faults is mostly caused by external dust entering the inverter or the environment is humid. Imported pumps.
The control loop affects the life of the inverter. It is the power supply part. It is the smoothing capacitor and the snubber capacitor in the IPM board. The principle is the same as the above, but the pulsating current passing through the capacitor here is the value that is basically not affected by the main loop load. Therefore, its life is mainly determined by temperature and power-on time. Since the capacitors are soldered on the circuit board, it is difficult to judge the deterioration by measuring the electrostatic capacity. Generally, it is estimated whether the service life is close to the service life based on the ambient temperature of the capacitor and the use time. The power supply board supplies power to the control loop, the IPM drive circuit, the surface operation display panel, and the fan. These power supplies are generally obtained by rectifying the DC voltage output from the main circuit through the switching power supply.
Therefore, if a certain power supply is short-circuited, in addition to the damage of the rectifier circuit of this circuit, it may affect other parts of the power supply. For example, the control power supply is short-circuited with the common ground due to misoperation, resulting in partial damage of the switching power supply on the power supply circuit board. A short circuit in the power supply causes other power supplies to be powered down, etc. It is usually easier to find by observing the power board.
The logic control circuit board is the core of the inverter. It concentrates on large-scale integrated circuits such as CPU, MPU, RAM, EEPROM, etc. It has high reliability, and the probability of failure itself is small, but sometimes it is completely controlled by booting. The terminals are closed at the same time, causing an EEPROM fault in the inverter, as long as the EEPROM is reset again. The IPM board contains drive and buffer circuits, as well as overvoltage and missing protection circuits. The PWM signal from the logic board is used to input the voltage drive signal into the IPM module through optical coupling. Therefore, the optocoupler on the IPM module should be measured while detecting the mode fast.
3, cooling system
The cooling system mainly includes a heat sink and a cooling fan. The cooling fan has a short life. When the service life is approaching, the fan generates vibration, and the noise increases and finally stops. The inverter has IPM overheat trip. The life of the cooling fan is limited by the bearing, which is approximately 10,000 to 35,000 h. When the inverter is running continuously, it takes 2 to 3 years to replace the fan or bearing. In order to extend the life of the fan, fans of some products only operate when the drive is running, not when the power is turned on.
4. External electromagnetic induction interference:
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. The specific methods to reduce noise interference are: on the control coils of all relays and contactors around the inverter, add absorption devices to prevent surge voltage, such as RC surge absorbers, the wiring should not exceed 20cm; try to shorten the wiring of the control loop The distance is separated from the main circuit; the distance of the twisted joint of the inverter control circuit should be more than 15mm, and the distance from the main circuit should be more than 10cm; when the inverter is far away from the motor (more than 100m), then on the one hand The cross-sectional area of ​​the wire can be increased to ensure that the line voltage drop is within 2%. At the same time, the inverter output reactor should be installed to compensate the charging current of the distributed capacitance generated by the long-distance wire. The grounding terminal of the inverter should be grounded according to the regulations. It must be grounded reliably at the special grounding point. It can not be mixed with electric welding and power grounding. The radio noise filter is installed at the input end of the inverter to reduce the input high harmonics, thus reducing the power line to The noise effect of the electronic equipment; a radio noise filter is also installed at the output of the frequency converter to reduce the line noise at its output.
5, the installation environment:
The frequency converter belongs to the electronic device device, and the installation environment is more stringent. The detailed installation environment is required in the manual. 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 dust-proof treatment, and a closed structure; temperature is an important factor affecting the life and reliability of electronic devices. 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 points, it is also necessary to check the air filter and cooling fan of the inverter regularly. For special high-cold occasions, in order to prevent the microprocessor from working properly due to low temperature, necessary measures such as setting an air heater should be taken.
A buzzer or beeper is an audio signalling device, which may be mechanical, electromechanical, or piezoelectric (piezo for short). Typical uses of buzzers and beeper include alarm devices, timers, and confirmation of user input such as a mouse click or keystroke.
1. Analysis of common faults in the main circuit:
The main circuit is mainly composed of three-phase or single-phase rectifier bridge, smoothing capacitor, filter capacitor, IPM inverter bridge, current limiting resistor, contactor and other components. Many of these common faults are caused by electrolytic capacitors. The life of an electrolytic capacitor is mainly determined by the DC voltage and internal temperature applied to both ends. The type of capacitor has been selected in the loop design, so the internal temperature determines the life of the electrolytic capacitor.
Electrolytic capacitors will directly affect the service life of the inverter. For every 10°C increase in temperature, the life will be halved. Therefore, on the one hand, the appropriate ambient temperature should be considered during installation, and on the other hand measures can be taken to reduce the pulsating current. An AC or DC reactor with improved power factor can reduce the ripple current and extend the life of the electrolytic capacitor. In the maintenance of the capacitor, the deterioration of the electrolytic capacitor is usually judged by the electrostatic capacity which is relatively easy to measure. When the electrostatic capacitance is less than 80% of the rated value and the insulation resistance is 5 MΩ or less, the electrolytic capacitor should be replaced.
2. Typical fault analysis of the main circuit:
Symptom: The inverter trips overcurrent during acceleration, deceleration or normal operation.
The first thing to distinguish is due to the load or the cause of the inverter. If it is the fault of the inverter, the history can be used to check the current at the time of trip, which exceeds the rated current of the inverter or the set value of the electronic thermal relay. If the three-phase voltage and current are balanced, then it should be considered whether there is overload. Or sudden changes, such as motor stalls.
When the load inertia is large, the acceleration time can be extended appropriately, and the process is not damaged by the inverter itself. If the current at the time of tripping is within the rated current of the inverter or within the set range of the electronic thermal relay, it can be judged that the IPM module or related part has failed. First, it is possible to determine whether the IPM module is damaged by measuring the positive and negative resistances between the main circuit output terminals U, V, and W of the inverter and the P and N terminals on the DC side. If the module is not damaged, the drive circuit has failed. (http:// copyright) If the IPM module is over-current or the inverter short-circuits to ground when decelerating, it is generally the module of the upper half of the inverter or its drive circuit is faulty; and the IPM module during acceleration Overcurrent is the failure of the module of the lower half of the bridge or its drive circuit. The cause of these faults is mostly caused by external dust entering the inverter or the environment is humid. Imported pumps.
The control loop affects the life of the inverter. It is the power supply part. It is the smoothing capacitor and the snubber capacitor in the IPM board. The principle is the same as the above, but the pulsating current passing through the capacitor here is the value that is basically not affected by the main loop load. Therefore, its life is mainly determined by temperature and power-on time. Since the capacitors are soldered on the circuit board, it is difficult to judge the deterioration by measuring the electrostatic capacity. Generally, it is estimated whether the service life is close to the service life based on the ambient temperature of the capacitor and the use time. The power supply board supplies power to the control loop, the IPM drive circuit, the surface operation display panel, and the fan. These power supplies are generally obtained by rectifying the DC voltage output from the main circuit through the switching power supply.
Therefore, if a certain power supply is short-circuited, in addition to the damage of the rectifier circuit of this circuit, it may affect other parts of the power supply. For example, the control power supply is short-circuited with the common ground due to misoperation, resulting in partial damage of the switching power supply on the power supply circuit board. A short circuit in the power supply causes other power supplies to be powered down, etc. It is usually easier to find by observing the power board.
The logic control circuit board is the core of the inverter. It concentrates on large-scale integrated circuits such as CPU, MPU, RAM, EEPROM, etc. It has high reliability, and the probability of failure itself is small, but sometimes it is completely controlled by booting. The terminals are closed at the same time, causing an EEPROM fault in the inverter, as long as the EEPROM is reset again. The IPM board contains drive and buffer circuits, as well as overvoltage and missing protection circuits. The PWM signal from the logic board is used to input the voltage drive signal into the IPM module through optical coupling. Therefore, the optocoupler on the IPM module should be measured while detecting the mode fast.
3, cooling system
The cooling system mainly includes a heat sink and a cooling fan. The cooling fan has a short life. When the service life is approaching, the fan generates vibration, and the noise increases and finally stops. The inverter has IPM overheat trip. The life of the cooling fan is limited by the bearing, which is approximately 10,000 to 35,000 h. When the inverter is running continuously, it takes 2 to 3 years to replace the fan or bearing. In order to extend the life of the fan, fans of some products only operate when the drive is running, not when the power is turned on.
4. External electromagnetic induction interference:
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. The specific methods to reduce noise interference are: on the control coils of all relays and contactors around the inverter, add absorption devices to prevent surge voltage, such as RC surge absorbers, the wiring should not exceed 20cm; try to shorten the wiring of the control loop The distance is separated from the main circuit; the distance of the twisted joint of the inverter control circuit should be more than 15mm, and the distance from the main circuit should be more than 10cm; when the inverter is far away from the motor (more than 100m), then on the one hand The cross-sectional area of ​​the wire can be increased to ensure that the line voltage drop is within 2%. At the same time, the inverter output reactor should be installed to compensate the charging current of the distributed capacitance generated by the long-distance wire. The grounding terminal of the inverter should be grounded according to the regulations. It must be grounded reliably at the special grounding point. It can not be mixed with electric welding and power grounding. The radio noise filter is installed at the input end of the inverter to reduce the input high harmonics, thus reducing the power line to The noise effect of the electronic equipment; a radio noise filter is also installed at the output of the frequency converter to reduce the line noise at its output.
5, the installation environment:
The frequency converter belongs to the electronic device device, and the installation environment is more stringent. The detailed installation environment is required in the manual. 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 dust-proof treatment, and a closed structure; temperature is an important factor affecting the life and reliability of electronic devices. 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 points, it is also necessary to check the air filter and cooling fan of the inverter regularly. For special high-cold occasions, in order to prevent the microprocessor from working properly due to low temperature, necessary measures such as setting an air heater should be taken.
A buzzer or beeper is an audio signalling device, which may be mechanical, electromechanical, or piezoelectric (piezo for short). Typical uses of buzzers and beeper include alarm devices, timers, and confirmation of user input such as a mouse click or keystroke.
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