Source：/eninews/60.html Date : 2019-05-06
Common frequency converters are selected according to the requirements of load characteristics, speed range, static speed accuracy and starting torque of production machinery; while common frequency converters adopt V / F control mode or vector control mode; the frequency conversion motor it drives is quite different from the common motor, and the frequency range it adapts to is also very large, so the long-term low-frequency operation of frequency converter does not affect the frequency converter There is no harm; however, the installation environment and ventilation performance of the inverter must be fully considered for its long-term low-frequency operation. As shown in the figure below.
In this case, the V / F control mode is used. The frequency converter changes the voltage of the motor power supply while changing the frequency of the motor power supply, so that the motor flux is kept constant. In a wide range of speed regulation, the efficiency and power factor of the motor do not decrease.
Because it is the ratio of control voltage (V) to frequency (f), it is called V / F control. Its v / F control features simple control circuit structure, low cost, good mechanical properties hardness, and can meet the requirements of smooth speed regulation of general drive.
When the output frequency of the frequency converter rises from 0Hz to the basic frequency, the output voltage rises from 0V to the V / F line of the maximum output voltage in direct proportion, which is called the basic V / F line, as shown in Figure 1.
Figure 1 defines the basic characteristic parameters of V / F. it is the most widely used form of frequency converter. When the output frequency of frequency converter rises from 0Hz to 50Hz, the output voltage rises from 0V to 380V in direct proportion.
From the above V / F characteristic parameter definition figure, we can see that there is an FL (it represents the lowest frequency of the line), FH (it represents the upper limit frequency), FB (it represents the rated frequency), Fmax (it represents the maximum frequency); for example, the maximum frequency range of this V / F converter is 50-500hz, the rated frequency is 50Hz, the basic operating frequency is 1-500hz, and the basic maximum output voltage is 1-480v;
In addition, when setting the V / F curve of the frequency converter, we must pay attention to the corresponding settings for different load properties; because the V / F curve has a variety of control settings; moreover, the multi-point voltage points should also be adjusted according to their own load conditions (0.00-100%). The default value set by the frequency converter in the factory is not necessarily suitable for themselves.