In the following some analytical design methods will be discussed, which will lead directly to the design solution in a strongly systematic way. In contrary to these direct design methods, the methods hitherto discussed, e.g. the design method using frequency-domain characteristics or the root-locus method, are indirect methods based more on systematic trial and error techniques iterating through some design steps. The success depends strongly on the experience and skill of the designer. The starting point was always the open loop, which was modified iteratively by adding lead and lag elements until the closed loop shows the desired behaviour.
Whereas in the direct design methods one will always start from the behaviour of the closed loop. Mostly a desired transfer function is given. In general this follows from the specification of some performance indices, which, for example are required for the step response . For a series of appropriate transfer functions a table of numerator and denominator polynomials of the associated transfer function and its distribution of zeros and poles to yield a specific response are given. Then for a known plant behaviour the required controller can be directly calculated.
The controllers designed in this way are not always optimal. They guarantee the compliance of the desired specification, e.g. maximum overshoot and settling time. A drawback of theses methods is that they cannot be applied directly to systems with dead time.