Lenze variable frequency drives upgrade

Question:
We have several obsolete German dc motors on Lenze variable frequency drives we are going to upgrade. Some of these motors have encoders on them and they are all on a Siemens Simatic S5 PLC.
We are going to go with ac motors and newer variable frequency drives. Management is wanting to keep the Simatic S5 PLC. If we keep this plc do I need to have any programming changes done to the plc to recognize/communicate with the new VFDs? Will the Simatic S5 PLC be compatible with newer VFDs? Finally would it just be wiser to upgrade the plc? We are not upgrading the whole production line just the palletizing section of this production line. This production line makes paper bags.

Answer:
Management always wants to keep the old. But the reality is that he S5 has been out of production for almost 2 decades now. I do not know how much development you are doing but we used to have special PC's capable to run windows 98 to be able to keep the development environment. If you need to replace hardware you will pay an arm and a leg for Spare unless you raid EBAY for parts abandoned by others.

As far as your question it is difficult to give a good answer without really understanding how the interface between the S5 and the variable frequency drives are done. If they use any kind of communication like Profibus, Modbus or other, the likelihood to be compatible is near 0. Your only chance is if you have a high end VFD that you could program to make it understand the S5. One of the options would be to ask Lenze for a drive compatible with their old standard. But then you are at their mercy. Overall this might be on the surface cheaper. But now you will be stuck with the old S5 and its costs. If the machine life expectancy is still long, then you will need to upgrade the S5. Now you are paying for the development twice.
If the interface is hardware then it is more likely to be doable. But then again a good study, case by case would be required.