What are linear and non-linear systems?

Before discussing linear and non-linear system, you need to know about term Homogeneity. It is a term defined for those systems, in which, if the input is multiplied with a constant then the output will also be multiplied with the same constant.

Linear Control Systems

In a linear control system, we get a linear voltage and current characteristics. In this, all the unwanted effects are ignored (which is possible only in theories) and it is assumed an ideal behavior of each element in the network. The linear control system follows the principle of Homogeneity and additivity. In this, the output is proportional to the input.

Non-linear Control Systems

A nonlinear control system is defined as a system that does not follow the principle of homogeneity. In this system, the output is not proportional to the input. All the control systems in real life are nonlinear control systems.