FX5U to FREQROL Inverter – Inverter Comms (Serial) PID Control – Implementation Strategy


Here we will ONLY be looking at the strategic approach of interlinking an FX5U PLC CPU with a FREQROL Inverter using Inverter communication (Which is a serial communication method).

Other than this interconnection and transition of values and commands, we will also look at how the PID control FB is being utilized and where it will be applied to allow for PLC PID control (as supposed to PID Control from the inverter itself).

The following map applies:

The essential variables (analog\integral) values used to drive a PID Control system is the SP, PV and MV – all of which can be seen pointed out above.

These values are given via the outline of PID Control;

Other than this, we see 3 function blocks which is used to interact with the inverter, being the IVCK (to read values from the inverter) and IDVR (to write values to the inverter), relative to the PLC.

It must be noticed that with this approach NO PID parameterization will be setup in the drive – as the PID control is being processed within the external PLC. The VFD will only receive a Speed Reference (Net Mode) from the PLC.