The supplier of the frequency converter braking unit reminds you that compared to traditional electrical circuit control, the technology content of the frequency converter is relatively high. It is a device that combines strong and weak electricity, so its faults are diverse. Only by combining theoretical knowledge with practice can we continuously summarize experience. Below are 15 common questions about frequency converters:
1. What is frequency conversion resolution? What does it mean?
For digital controlled frequency converters, even if the frequency command is an analog signal, the output frequency is still given in stages. The smallest unit of this level difference is called the frequency conversion resolution. The frequency conversion resolution is usually taken as 0.015~0.5Hz. For example, if the resolution is 0.5Hz, the frequency above 23Hz can be changed to 23.5 and 24.0 Hz, so the motor's action is also followed in stages. This poses a problem for applications such as continuous roll up control. In this case, if the resolution is around 0.015Hz, it can also fully adapt to a level difference of 1r/min or less for a 4-stage motor. In addition, some models have a given resolution that is different from the output resolution.
2. What is the significance of having models with acceleration time and deceleration time that can be given separately, and models with acceleration and deceleration time that can be given together?
Acceleration and deceleration can be given separately for different types of machines, which is suitable for short-term acceleration, slow deceleration situations, or situations where strict production cycle time is required for small machine tools. However, for situations such as fan transmission, acceleration and deceleration times are relatively long, and both acceleration and deceleration times can be given together.
3. What is regenerative braking?
If the command frequency is reduced during the operation of the electric motor, it will become an asynchronous generator and work as a brake, which is called regenerative (electrical) braking. The energy consumption braking unit can release the regenerated electrical energy generated during motor speed regulation and other processes through the braking resistor to generate sufficient braking torque, ensuring the normal operation of equipment such as frequency converters.
4. Can we obtain greater braking force?
The energy regenerated from the motor is stored in the filtering capacitor of the frequency converter. Due to the capacity and voltage resistance of the capacitor, the regenerative braking force of a general frequency converter is about 10% to 20% of the rated torque. If using optional braking units, it can reach 50% to 100%.
5. What is the protection function of the frequency converter?
The protection function can be divided into the following two categories: (1) automatically performing corrective actions after detecting abnormal states, such as overcurrent stall prevention and regenerative overvoltage stall prevention. (2) After detecting abnormalities, block the PWM control signal of the power semiconductor device to automatically stop the motor. Such as overcurrent cut-off, regeneration overvoltage cut-off, semiconductor cooling fan overheating, and instantaneous power outage protection.
6. Why does the protection function of the frequency converter activate when the clutch is continuously loaded?
When connecting a load with a clutch, at the moment of connection, the motor rapidly changes from an unloaded state to an area with a large slip rate. The large current flowing through causes the inverter to trip due to overcurrent and cannot operate.
7. Why does the frequency converter stop when large motors are running together in the same factory?
When the motor starts, a starting current corresponding to its capacity will flow, and the transformer on the stator side of the motor will generate a voltage drop. When the motor capacity is large, this voltage drop will also have a significant impact. The frequency converter connected to the same transformer will make a judgment of undervoltage or instantaneous stop, so sometimes the protection function (IPE) will be activated, causing it to stop running.
8. What does stall prevention function mean?
If the given acceleration time is too short and the output frequency of the frequency converter changes much more than the speed (electrical angular frequency), the frequency converter will trip and stop running due to overcurrent, which is called stall. To prevent the motor from continuing to operate due to stall, it is necessary to detect the magnitude of the current for frequency control. When the acceleration current is too high, slow down the acceleration rate appropriately. The same applies when decelerating. The combination of the two is the stall function.
9. Is there any restriction on the installation direction when installing a frequency converter?
The internal and back structure of the frequency converter takes into account the cooling effect, and the vertical relationship is also important for ventilation. Therefore, for unit types that are installed inside the disk or hanging on the wall, they should be installed vertically as much as possible.
10. Inverter overvoltage
Overvoltage alarm usually occurs when the machine is stopped, and its main reason is that the deceleration time is too short or there are problems with the braking resistor and braking unit.
11. The temperature of the frequency converter is too high
In addition, the frequency converter also has a high temperature fault. If a high temperature alarm occurs and the temperature sensor is checked to be normal, it may be caused by interference. The fault can be shielded, and the fan and ventilation of the frequency converter should also be checked. For other types of faults, it is best to contact the manufacturer for quick and feasible solutions.
12. Overcurrent is the most frequent phenomenon of frequency converter alarm.
Inverter overcurrent phenomenon
(1) When restarting, it trips as soon as the speed increases. This is a very serious phenomenon of overcurrent. The main reasons are: load short circuit, mechanical parts stuck; The inverter module is damaged; Caused by phenomena such as insufficient torque of the electric motor.
(2) Jumping when powered on, this phenomenon generally cannot be reset, mainly due to module failure, drive circuit failure, and current detection circuit failure. The main reasons for not immediately tripping during restart but during acceleration are: the acceleration time is set too short, the current upper limit is set too small, and the torque compensation (V/F) is set too high.
13. Is it possible to directly input the motor into a fixed frequency inverter without using soft start?
It is possible at very low frequencies, but if the given frequency is high, the conditions for starting directly with the same power frequency are similar. When a large starting current (6-7 times the rated current) flows, the motor cannot start due to the inverter cutting off the overcurrent.
14. What issues should be noted when the motor operates beyond 60Hz?
When operating beyond 60Hz, the following precautions should be taken
(1) Machinery and devices should operate at this speed to the fullest extent possible (mechanical strength, noise, vibration, etc.)
(2) When the motor enters the constant power output range, its output torque should be able to maintain operation (the output power of shafts such as fans and pumps increases proportionally to the cube of speed, so attention should also be paid when the speed slightly increases).
(3) The issue of bearing lifespan should be fully considered.
What will happen if the frequency converter is not used for a long time?
1. The lubricating fluid for the bearings of the frequency converter fan has dried up, affecting its use.
2. High voltage filtering capacitors are prone to bulging if not used for a long time, while low-voltage electrolytic capacitors are prone to leakage.