1 Introduction
With the continuous advancement and development of power electronics and automation technologies, the performance of various low-voltage frequency converters has become increasingly advanced, with significant improvements in temperature rise, size, noise, functionality, and output characteristics. Consequently, the number of parameters for frequency converters has also increased, and the setting of these parameters has become more complex. Furthermore, many parameters are interrelated and mutually influential, requiring a complete understanding and comprehensive calculation of the functional characteristics of each parameter to achieve correct settings. Simultaneously, many parameters are closely related to actual usage conditions, demanding that technicians be thoroughly familiar with the entire control system to ensure the normal and efficient application of the frequency converter.
2. Frequency range setting
(1) The maximum frequency (fun04) is the highest frequency that the frequency converter can output. When setting the maximum frequency, be careful not to exceed the highest frequency that the motor can withstand. The maximum frequency is generally set to the rated frequency of the motor.
(2) The corner frequency (fun05) is the lowest frequency at which the inverter begins to output the rated voltage. The output voltage remains constant from the corner frequency. It can be set within the highest frequency range.
(3) The starting frequency (fun06) is the lowest frequency at which the inverter starts to output voltage.
The relationship between the highest frequency, the corner frequency, and the starting frequency is shown in Figure 1.
(4) The upper and lower limit frequencies (fun26, 27) are used to limit the operating frequency, restricting it to the upper and lower limit range. The relationship between the upper and lower limit frequencies and the maximum frequency is shown in Figure 2.
3V/F characteristics
The V/F characteristic of a frequency converter determines the output torque during motor startup or low-speed operation, and is one of the most important functions of the frequency converter. The LG-IH frequency converter's function group parameter (fun08) V/F curve setting provides users with four control characteristics, as shown in Figure 3. This function allows users to select the appropriate voltage-frequency curve based on the load characteristics.
(1) Curve (1) in the figure is a linear voltage-frequency curve, which is more suitable for driving constant torque loads where the ratio of output voltage to output frequency remains constant. Such as conveyor belts, mixers, etc.
(2) Curve (2) in the figure is a parabolic voltage-frequency curve, which is more suitable for driving variable torque loads with a parabolic ratio of output voltage to output frequency. Such as fans and pumps.
(3) The curve (3) in the figure is a custom voltage-frequency curve, which is used in special occasions. Users can set the ratio of output voltage to output frequency arbitrarily.
(4) Curve (4) in the figure is the automatic compensation voltage-frequency curve. It continuously detects the load status and automatically adjusts the voltage-frequency curve to automatically compensate for the torque. It is suitable for low-speed, high-torque loads.
4. Overcurrent protection characteristics
Overcurrent protection is the most important and basic protection function for the load, and it must be set correctly and reliably. Function group parameter (fun49) sets the inverter's output current to continuously exceed the current protection limit (i.e., the percentage of the inverter's rated current); function group parameter (fun50) sets the overcurrent time. Generally, the overcurrent is set to 110%, and the duration is 60 seconds.
5. Carrier frequency settings
If the motor is noisy or interferes with other control devices in the same control cabinet when the frequency converter is running, the user can adjust the carrier frequency (i.e., adjust the PWM switching frequency) within a certain range to reduce noise or interference. Generally, setting it to 2kHz is more reasonable.
6. Fault Signal Mode Selection
The fault setting function of a frequency converter is crucial. Providing safe and reliable protection for the frequency converter and its load largely relies on the converter's fault signal output port to achieve tripping in the external electrical circuitry. Therefore, the completeness of the protection function is closely related to the frequency converter's output signal setting capability.
The function group parameter (fun44) offers four setting options for users:
(1) Restart;
(2) All faults;
(3) Undervoltage + Restart;
(4) Undervoltage + All faults;
Under normal circumstances, users can choose (4) undervoltage + all faults, that is, when the input voltage is too low, the protection will activate or as long as a fault occurs, the fault relay will activate and the fault signal will be output.
7. Parameter modification and locking function
The LG-IH frequency converter has a parameter setting lock protection function to prevent unauthorized personnel from arbitrarily changing some important parameters of the frequency converter. The function group parameter (fun98) provides a parameter lock function, which is operated by entering a password each time. The parameter lock and unlock functions can alternately take effect.
8. Output signal fine-tuning settings
During operation, frequency converters need to display status signals such as operating frequency, current, and voltage on the control panel. These functions can be achieved through the output port settings. However, there is always a certain error between the analog output of the frequency converter and the instrument display. In engineering applications, the analog output of the frequency converter must be fine-tuned to obtain an accurate display.
(1) Input/output group parameter i/o36 is for fine-tuning the pulse output of the frequency instrument. The output terminals fm and cm output 0~10V, corresponding to the highest output frequency of the inverter.
For example: the inverter's maximum frequency is set to 50Hz, and the panel instrument scale is 0-10V corresponding to 0-60V.
hz; then the voltage value displayed on the panel instrument at 50 Hz = 50/60 × 10V = 8.333V, from which the fine adjustment percentage is 83.33%, therefore the parameter i/o36 should be set to 83.33%.
(2) Input/output group parameters i/o34 and 35 are for selecting the analog instrument display mode. For example, if parameter i/o34 is set to current display mode, the output terminals lm and cm will output 0~10V, corresponding to the rated output current of the frequency converter.
For example: the rated output current of the frequency converter is 115A, and the scale of the panel instrument is 0~10V corresponding to 0~120A; then the voltage value of 115A displayed on the panel instrument = 115/120×10V = 9.583V. From this, the fine adjustment percentage is 95.83%, so the parameter i/o35 should be set to 95.83%.
(3) Input/output group parameter i/o37 is for fine-tuning the current output of the frequency meter. The frequency meter also outputs a standard current signal of 4 to 20mA to display the output frequency of the inverter. It outputs 4mA below the starting frequency and 20mA at the highest frequency.
For example, if the starting frequency of the frequency converter is set to 5 Hz and the maximum frequency is set to 50 Hz, the relationship between the output frequency of the frequency converter and the current output of the frequency meter is shown in Figure 4.
9. Conclusion
Inverter parameters are numerous, typically hundreds of options. The above only introduces a few important parameter settings for the LG-IH inverter, intended for reference only. In practical work, it's not necessary to be thoroughly familiar with every parameter; understanding and correctly setting the required parameters is sufficient. Generally, the original factory values are adequate for actual operation. However, for a technician, detailed study and research of inverter parameters and functions is highly beneficial for improving professional skills. Furthermore, continuous learning allows for further exploration of inverter functions, improving operational performance and energy efficiency, and maximizing inverter utilization.
