How to make voltage control loop via PI or PID controller ?

Hello,

I've got a problem when i try to make a control loop with PID and PI controller.

The problem is that i've got variable voltage signal that i want to regulate on some point. The specific here is that to regulate it i need to change the cos fi ( power factor ) of the system.

So in the original way we have one signal and a control loop with error and PID so the PID control the actual siignal. but here i cant touche the signal but if i change the cos fi, the signal will change automaticlly.

On the picture below im, show what i really what. U can see one the 1st plot, i want whenevery i got the signal above 0 to put the cos fi eaquals to that cos fi that the signal will stay at zero until the signal goes down itself. In other words i want to cut all other above with moveing cosfi up and down until my signal go down itself.

Anyone can give a hang on this example will be great!

Thanks in advance!