Stop trying to reinvent the wheel and go out and buy a Woodward GCP30 series generator controller or something similar. The GCP30 is really quite cheap for what it does - tell it what to do and it does it when properly tuned.
Do not use prox switches or mag pick ups into the PLC to control speed either. PLC controlled overspeed has been a disaster wherever I have seen it used. I use the generator controller for overspeed and a separate overspeed relay as well. Nothing like seeing bits bust out of the side of the engine if you stuff up I can assure you. Damnned expensive too.
These companies invest millions of dollars developing their products and everyone wants to reinvent the wheel to save a bit. No way Jose.
I also get the manufacturer to site to tune the controller. They can normally do in a day what takes me 2-3 days as they are doing it all the time. Get the job commissioned and get on to the next job and make some money. Time is your most expensive item usually at commissioning as there is a cast of thousands hanging around waiting for practical completion so they can all get paid. Not only time wasted on this job but putting you behind on the next job.
We have all tried full PLC control for speed control, Var contol, no export control and those that make good money have given that nonsense away years ago.
The best generator controller I have seen is an Ozzie product but it is expensive (ouch). They tune these things really aggressively though - I have seen a diesel up to speed and synchronised in way under 10 seconds regularly from cold start. Have also seen a set synchronised with other sets or the mains for sometimes up to minutes at a time without going out of synch. Very good tuning - I cannot do that and have been doing generator systems for over 15 years including base load power stations running at 11kV.
PID is normally used for all the tuning functions. Diesel sets are normally set up without any "D" at all. Gas sets use heaps of "D" as they are as sluggish as get out.
The Ozz controller uses multiple PIDs - one for starting and acceleration, on for idle speed, one for running, one for synchronised with other sets and another for synchronised with the council - really optimum control. I have seen on a job I put together 3 sets synched together on a common bus with no load sharing 5-10 kW and 5-10 kVar. The sets varied from an old 1.1 mW heap of garbage to a 4.1 mW Ruston and the 3rd set was a 2 mW high performance Wartzilla. They all responded differently, were of different capacity, different metal mass, different AVR response and all worked extremely well together, despite the differences, after a 13 hour commissioning period by the manufacturers representantive. I would have been there for a month and I am very experienced with these things. Just going through my bragging sheet the other day and I have done over 350 generator jobs now including several very complex base load power stations and some of them included using and having to control the treatment of crude oil as fuel - couple of drops on the pavement go hard in minutes - really nasty stuff.
I repeat stop trying to reinvent the wheel and go out and by a good generator controller (digital) that will do the job and get the manufacturer in to tune the darn thing!
