S7-200 and mitsubishi e540 communication variants

[awpe]

Hi,

I have s7-200 cpu 226 PLC, and mitsubishi e540 inverter. PLC doesn't have any modules, VFD has CC-LINK module. I need to set the VFD output frequency from PLC program and check VFD for errors in order to restart it in case of fail. Frequency has to differ in time. There is an encoder on line driven by this VFD, I use it's output in PLC to start some actions.

I wonder which variant to control VFD is better:

1) Buy analog output module for s7-200 and connect it to VFD's potentiometer input to set frequency, then configure PID on s7-200 (there is my own routine to calculate speed from encoder signals (HSC0)) so PLC program will set setpoint for PID, PID output is analog module's output voltage and read variable is internal VD**** with current speed (program calculates it every 100ms), no problem if PID will adjust speed once a second.

2) The same as in 1) but also configure VFD's PID so PLC will convert current line speed into current on second output of analog module, and in the same time PLC's PID routine will output voltage for VFD PID's setpoint input, in this case both analog outputs of PLC analog module will be used and two PIDs (as of PLC and VFD) will work simultaneously.

3) VFD supports cc-link, devicenet and it's own uart protocol, as I didn't manage to find any s7-200 module for devicenet or cc-link communication, the only option is to implement VFD's uart protocol connecting PLC and VFD through their builtin rs485 ports.

So what do you think will be correct and the easiest solution to control speed of VFD?