Need help with configuration of feedforward control in the CU universal controller. Do not understand how it is ca
C.CU feedforward application - DTB pin functionality
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I'm not familiar with the controller you are using but the basic principle of feedforward is quite simple.
Feedforward isnt "calculated" inside the PID. The feed forward value is simply added to the output of the controller after the PID algorith is executed. So if the PID Algorithm output is 50% and the Feed Forward Value is -10% then the PID block output is 50%-10% = 40%
Some PID Blocks will apply a Feedforward Gain. The FFwd value is multilied by the gain before adding to the output.
If you need any compensation for deadtime or different process response time constants then typically you need to program these outside the PID block. The simplest way is a DeadTime + Lead/Lag block.
In order for Feedforward to work you MUST know accurately the process gains, deadtimes and time constants of both the PID controled process AND the Disturbance that you are compensating for. This is required to accurately model the effect of the disturbance on the process. Otherwise you can easily end up making things worse, not better. You cant just throw some guesswork tuning values at a feedforward loop - you need to tune it properly.