How to predict value of a variable which depends on difference between other two variables.

Dear Matlab Experts,

I have a system (controller and plant) in Simulink which has three variables. let's say, x,y, and z. I want to identify the correct value of x. The system is such that, by changing the value of x, the difference between y and z changes(positive or negative difference).

case:

I start my system with a certain value of x (e.g 0.3) then the difference between y and z is eg. 30. This difference is because the actual value of x in the plant model is different(e.g 0.25). This value I cannot know because it's a variable of a physical system in Simscape.

Now, when I change the value of x from 0.3 to 0.25 the difference between y and z becomes 0. In this case, I know the correct value of x is 0.25. Therefore, I want to develop such an algorithm which will change the value of x to make the difference between y and z 0. And thus, the algorithm should give me the exact value of x.

All the three variables are accessible to me. Also, I tried using a PID controller, but because of other influencing PID controller in the system, this controller has not been helpful.

Thank you in advance for your time and support.

Kind regards

Onkar