PIDE and SRTP RSLogix 5000

[dabatman99]

I have an application that I was wondering if these function blocks could help me out. I work at a hydro-dam (less than 4 MWatts), and we control our headpond level by how much we open our intake gates to our turbines (there are 3 main gates). We are currently controlling level by using setpoint differential from the desired headpond level. This causes the level to always oscillate up and down by a few inches. I would like to see us have a more consistent level (the environment guys would love us to keep the fishways operating at a more consistent rate). I was thinking of adapting the PIDE and SRTP function blocks as we monitor our headpond via a pressure transducer and we pulse our gates open and close depending upon how far it is from the setpoint. Does anybody have any experience working with such an application? I know the SRTP function block is to be used for a temperature heating/cooling cycle, but why couldn't it be used for this application? Let me know what you guys are thinking. Thanks

 

[dabatman99]

anybody?

 

[Peter Nachtwey]

I have an application that I was wondering if these function blocks could help me out. I work at a hydro-dam (less than 4 MWatts), and we control our headpond level by how much we open our intake gates to our turbines (there are 3 main gates).

You can't control two things at once. You have a choice, control the level or control the water to the generators to meet demand. If the generator power varies then obviously the flow required will vary and that will vary the level of the pond.

There are ways of minimizing a cost function.
That means there will be a compromise between pond level and generator power output.

 

[dabatman99]

We actually have to maintain the pond level because we need a constant flow in our fishway ladder. Essentially maintaining headpond level is what we are doing now, but its by predetermined levels. For example, if headpond level goes up by 2 inches, then we open the gates by a certain amount. If level continues to rise up another few inches, then the gates will open another amount. It will continue to do this until the level decreases below the setpoint by a few inches...therefore the gates will pulse close a bit. This inability to maintain constant level changes the flows in the units and the fishway. Its actually more important for us to keep the fishway constant than our units. Im just looking for a better way to control our headpond to satisfy the dept of fisheries and help the fishies so they can get upstream and do what it is they do. Lol. Any ideas or suggestions would be greatly appreciated.

 

[Peter Nachtwey]

OK, so controlling the pond level is most important.
A trend would be nice.
It would seem to me that if the gates were at the pond level and excess water would flow between the fish ladder and the gates without any control so the trick is to lower the gates just a little as the level starts to increase. I wouldn't use a PID or PI. I would use a P only with a bias. The bias should move the gate to a position that is the normal pond level-offset to get the desired flow. The error is the difference between the current pond level and the normal pond level.

In short, don't use the integrator. Use P only with a bias. I think the integrator is winding up and down causing your problems.

 

[dabatman99]

Thank you for the advice. I was thinking the same way you are. Ive used the pid function before in rslogix but not with the srtp function. Im going to setup a mockup and try to simulate conditions and see what the outcome is. Thanks again