Do you know all ten problems with frequency converters?

What is the difference between voltage type and current type?

The main circuit of a frequency converter can be roughly divided into two categories: voltage type is a frequency converter that converts the DC of the voltage source into AC, and the filtering of the DC circuit is a capacitor; Current type is a frequency converter that converts the DC of a current source into AC, and its DC circuit filter is an inductor.

2. When an electric motor is driven by a power frequency source, the voltage decreases and the current increases. For frequency converter drive, if the voltage also decreases when the frequency decreases, does the current increase?

When the frequency decreases (at low speed), if the same power is output, the current increases, but under the condition of constant torque, the current remains almost unchanged.

3. What are the starting current and starting torque of the motor when using a frequency converter for operation?

Using a frequency converter for operation, the frequency and voltage increase correspondingly with the acceleration of the motor, and the starting current is limited to below 150% of the rated current (125%~200% depending on the model). When starting directly with a power supply, the starting current is 6-7 times the rated current, resulting in mechanical and electrical impacts. Using a frequency converter drive can smoothly start (with longer starting time). The starting current is 1.2~1.5 times the rated current, and the starting torque is 70%~120% of the rated torque. For frequency converters with automatic torque enhancement function, the starting torque is above 100% and can start with full load.

4. Is there no output power below 6Hz, as the manual states a speed range of 60~6Hz, which is 10:1?

Power can still be output below 6Hz, but based on the temperature rise and starting torque of the motor, the minimum operating frequency is around 6Hz. At this time, the motor can output rated torque without causing serious heating problems. The actual output frequency (starting frequency) of the frequency converter varies from 0.5 to 3Hz depending on the model.

5. Is it possible to require a constant torque for general motor combinations above 60Hz?

Usually it is not possible. At 60Hz and above (there are also modes above 50Hz), the voltage remains constant and exhibits a generally constant power characteristic, requiring the same torque at high speeds.

6. What does open-loop mean?

A speed detector (PG) is installed on the motor device used to feed back the actual speed to the control device for control, which is called a "closed loop". If it does not operate with PG, it is called an "open loop". Universal frequency converters are mostly open-loop, and some models can also use options for PG feedback. The speed sensorless closed-loop control method calculates the actual speed of the motor based on the established mathematical model and magnetic flux, which is equivalent to using a virtual speed sensor to form a closed-loop control.

7. What should I do if the actual speed deviates from the given speed?

When open-loop, even if the frequency converter outputs a given frequency, the motor's speed varies within the range of rated slip rate (1%~5%) when running with load. For situations where high speed regulation accuracy is required and even load changes require operation close to a given speed, a frequency converter with PG feedback function (optional) can be used.

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. 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.

10. Why does the protection function of the frequency converter activate when connecting the load with a clutch?

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.