Controllers
Controllers are inserted in the control loop between the control error and the system. The input quantity is always the control error e = w − y; the output quantity varies depending on the system. Usually the controller drives the actuator in the system. Whatever the actuator’s input quantity is, it is the output quantity of the controller. The goals of the control loop can only be achieved by cleverly selecting the right type of controller and then setting the right parameters. This chapter introduces various types of controller.
Parameter A combines the behaviours of controller, actuator and plant. Actuator and plant form the system to be controlled. Via the controller, we influence the behaviour of A and thus the behaviour of the entire controlled system.
Types of controller
The simplest controllers have only one behaviour. There are, for example, P controllers, which only have P behaviour. On such a controller, the control engineer can only adjust one parameter: kPR. A pure I controller can also be used. Then only kIR can be varied. We use the subscript “R” to identify a parameter of the controller.
Control loops with more than one parameter are complicated to calculate. That is why controllers with only one parameter are used for a basic understanding of the behaviour of a controlled system. In practice, more complex controllers are used, in which several parameters can be set at the same time. Their behaviour is generally simulated and no longer calculated.
The following types of controller are discussed in this chapter:
1. Controllers with one parameter
2. PID controllers
3. On-off (two-position) controllers
At the end of the chapter, heuristic (experimental) methods for setting the parameters of a PID controller are covered.