In a standard feedback control system, you have a set point, a controller, a plant, and a sensor to enable feedback. The sensor measures the process variable (or in other words, the argument you are actually trying to control).
Now, I want to add a feedforward component. Referring to this MATLAB example, when implementing feedforward component, you require an additional disturbance model and a feedforward controller.
This is where I need some clarification. When adding a feedforward component, do I have to measure the disturbance separately from the process variable? Or is disturbance equal to my process variable itself? If the prior, in my system, I only have a sensor to measure to the process variable and I have no way of measuring the disturbance. Is it possible to implement a feedforward component into my control system?