How should PID parameters be set for adjusting the liquid level using variable-frequency speed control?
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How should PID parameters be set for adjusting the liquid level using variable-frequency speed control? What is the difference from the PID parameter settings of conventional regulators? What areas need attention?
Personally, I believe that the response speed of variable-frequency speed control is slower than that of control valves; therefore, the parameters for each PID should be set to more aggressive values compared to those used with conventional controllers. In addition, attention must be paid to the selection of signals for the inverter according to the process requirements.
We have also used a regulator to supply power to the inverter, and the result has been slow performance; we still haven’t succeeded so far.
Inverters come equipped with regulators, which can also be used.
If a frequency converter is used with a centrifugal pump, changes in frequency directly result in changes in speed. There is a quadratic relationship between speed and the pump’s head (flow rate follows a linear relationship, while power follows a cubic relationship). Operating at low frequencies can result in the pump running while there is no flow at the pipe outlet. Therefore, a minimum value must be set on the inverter; this minimum value corresponds to the frequency at which there is a minimum flow rate at the pipe outlet, and it is generally between 20-30 Hz. In other words, the corresponding range is reduced; instead of 4-20mA corresponding to 0-50, it is now 4-20mA corresponding to 30-50Hz.
Simply in terms of PID parameter setting, there is actually no difference; the PID parameters still need to be adjusted using the standard methods for setting PID parameters in controllers.
Thumbs up; it really helped me understand. No wonder there are such large fluctuations. . . .
This requires some experimentation; it is similar to conventional PID control, but it is necessary to take into account the output characteristic curve of the frequency converter. In addition, the volume of the container as well as the inflow and outflow rates must also be considered