Digital Control

1 Introduction The revolutionary advances in computer technology today have made it possible to replace conventional controllers with digital computers. Digital control thus refers to the control scheme in which the controller is a digital device, practically a digital computer. This means that we can make use of a much more advanced control logic and versatility than those made possible with conventional analog controllers. On the other hand, we also need an interface that connects a computer with real plants. In particular, • measurement is made at discrete time instants, and • such data must also be spatially discretized to allow digital data handling. In other words, digital controllers can handle data that are discretized both in time and space. The former discretization is usually referred to as sampling and the latter quantization. These two features place digital control systems outside the scope of the usual linear, time-invariant control systems. (There is also the problem of saturation effect when controllers have a fixed word length. But this problem is much less studied in the context of digital control.)