Variable frequency noun definition and some frequently occurring faults

For the inverter, it is believed that many electric power practitioners are not unfamiliar. Compared with the traditional electric circuit control, the frequency converter has a high technological content and is a combination of strong and weak electricity. Therefore, its failures are various and can only be Combining theoretical knowledge with practice to sum up experience, here are 15 examples of frequently asked questions about frequency converters. Do you understand this?

1, what is the frequency resolution? has no meaning?

For digitally controlled inverters, even if the frequency command is an analog signal, the output frequency is given a step. The smallest unit of this differential is called the frequency resolution. The resolution of the frequency conversion is usually 0.015~0.5Hz. For example, if the resolution is 0.5Hz, then the upper side of 23Hz can be changed to 23.5, 24.0Hz, so the action of the motor is also followed step by step. This causes problems for the use of a continuous coil control. In this case, if the resolution is about 0.015 Hz, one step for a four-stage motor is 1 r/min or less, which can be adequately accommodated. In addition, some models have different resolutions and output resolutions.

2. What is the significance of the models that can be specified for the acceleration time and deceleration time, and the type of acceleration and deceleration time given together?

Acceleration and deceleration can be given for each type of machine, for short-time acceleration, slow deceleration occasions, or for small machine tools need to strictly specify the production of the tact time is appropriate, but for fan drive and other occasions, acceleration and deceleration time is longer, Acceleration time and deceleration time can be given together.

3. What is regenerative braking?

When the motor is running, if the command frequency is reduced, the motor becomes an asynchronous generator state operation and operates as a brake, which is called regenerative (electrical) braking.

4. Is it possible to obtain greater braking power?

The energy regenerated from the motor is stored in the filter capacitor of the inverter. Due to the relationship between the capacity of the capacitor and the withstand voltage, the regenerative braking force of the general inverter is about 10% to 20% of the rated torque. If using optional brake unit, it can reach 50%~100%.

5, inverter protection function?

The protection functions can be divided into the following two categories: (1) Corrective actions are automatically performed after detection of abnormal conditions, such as overcurrent stall prevention and regenerative overvoltage stall prevention. (2) Block the power semiconductor device PWM control signal after detecting the abnormality, and make the motor stop automatically. Such as over-current cut-off, regenerative over-voltage cut-off, semiconductor cooling fan overheating and instantaneous power failure protection.

6. Why does the inverter's protection function act when the clutch is continuously loaded?

When the clutch is used to connect the load, the motor rapidly changes from the no-load state to the area where the slip rate is large at the moment of connection, and the large current that flows causes the inverter to trip overcurrent and cannot operate.

7. In the same factory, the large-scale motor moves together and the inverter stops during operation. Why?

When the motor starts, the starting current corresponding to the capacity will flow. The transformer on the stator side of the motor will generate a voltage drop. When the motor capacity is large, the pressure drop will also have a large effect. The inverter connected to the same transformer will make undervoltage or instantaneous stop. As a result of the judgment, the protection function (IPE) may occasionally act to stop the operation.

8. What does the stall prevention function mean?

If the given acceleration time is too short, the output frequency of the inverter will change far beyond the change of the speed (electrical angle frequency). The inverter will trip due to the overcurrent and the operation will stop. This is called stalling. In order to prevent the stall from continuing to operate the motor, it is necessary to detect the magnitude of the current for frequency control. When the acceleration current is too large, the acceleration rate is appropriately slowed down. This is also true during deceleration. The combination of the two is a stall function.

9. Is there a limit to the mounting direction when installing the inverter?

The structure of the inside and the back of the inverter considers the cooling effect. The relationship between the upper and the lower is also important for ventilation. Therefore, take the longitudinal position of the unit type in the tray and hung on the wall, and install it as vertically as possible.

10, inverter overvoltage

Overvoltage alarms usually occur at the time of shutdown. The main reason is that the deceleration time is too short or there is a problem with the braking resistor and the brake unit.

11, the inverter temperature is too high

In addition, the inverter has too high temperature fault. If the temperature alarm is too high, the temperature sensor can be checked if the temperature sensor is normal. The fault can be shielded. In addition, the fan and ventilation of the inverter should also be checked. For other types of faults, it is best to contact the manufacturer for a quick and feasible solution.

12. Overcurrent is the most frequent phenomenon of inverter alarm.

Inverter over-current phenomenon

(1) When restarting, it will trip at a raise speed. This is a very serious phenomenon of overcurrent. The main reasons are: load short circuit, mechanical parts stuck; inverter module damage; motor torque is too small and so on.

(2) Power-on jump, this phenomenon can not be reset generally, the main reasons are: bad module, bad drive circuit, bad current detection circuit. When restarting, it does not immediately trip, but when accelerating, the main reasons are: too short acceleration time setting, too low current limit setting, and high torque compensation (V/F) setting.

13. Is it possible to use a soft start without putting the motor directly into a fixed frequency inverter?

It is possible to operate at very low frequencies, but if the given frequency is high then the conditions for direct start with the commercial frequency power supply are similar. A large starting current (6 to 7 times the rated current) will flow, and the motor cannot be started because the inverter cuts off the overcurrent.

14. When the motor exceeds 60Hz, what problems should be noticed?

Pay attention to the following matters when operating above 60Hz

(1) Machines and devices must be fully operational at this speed (mechanical strength, noise, vibration, etc.)

(2) The motor enters the constant power output range, and its output torque must be able to maintain the work (shaft, pump and other shaft output power increase in proportion to the cube speed, so speed should be paid attention to when it rises slightly).

(3) The bearing life problem should be fully considered.

15. What happens if the inverter is not used for a long time?

1, the frequency converter blower bearing lubricant dry, affect the use.

2, high pressure filter capacitor is not easy to bulge for a long time, low pressure electrolytic capacitor is easy to leak.