PLC program

Hello, attached is a program i designed to control my simple power system. Please kindly go through it and help me out.

I have a busbar onto which 3 loads, 2 generators and a utility line are connected. i want to set my generation (utility power)to say 50MW when all the loads are on and the generators off. I want to increase the load (i used a counter) and calculate the frequency from
generation - demand= change in demand;
change in demand/14.0= change in frequency;
frequency= 50+change in frequency;

when the frequency goes below 49.5, generator 1 comes on and the generation increases by 7MW and the frequency settles. when gen 1 is on and the frequency gets below 49.5, gen 2 comes on and the generation increases by 7MW. if the same continues, the loads 1 and 2 go off. the reverse should happen incase the frequency gets above 50.5.

this is a kind of automatic load shedding depending on frequency only that i will have to load shed after having all my generator on.

Please guys, try and look through my failed program and help me for adjustments.

what could be the best way of increasing demand and also for generation?

if anyone has done something similar, feel free to share it with me. i am sure it will be of great help.

I see you use MW1 several times, MW2, MW3, MD0, MD1, MD2 and MD3. For that reason I'm fairly sure you're not aware of the following facts:

• there is such thing as a "double coil syndrome" in PLCs;
• multiple use of memory bytes has a similar effect as double coil syndrome on single bits;
• MW1 is made up of MB1 and MB2;
• MW2 is made up of MB2 and MB3;
• MW3 is made up of MB3 and MB4;
• MD0 is made up of MB0, MB1, MB2 and MB3;
• MD1 is made up of MB1, MB2, MB3 and MB4;
• MD2 is made up of MB2, MB3, MB4 and MB5;
• MD3 is made up of MB3, MB4, MB5 and MB6.

If you were aware of these facts, I'm fairly sure your program would look somewhat different than it does now. Therefore I would strongly suggest that you start reading about the memory organisation of S7. It's all in the on-line help files.

Kind regards,

Can someone help tell me how i can achieve this best. I will be glad.