Decoupling techniques in multiloop control systems

The stability and accuracy of a control system consisting of two interwoven loops are affected by interaction among all transfer functions and all inputs. This is undesirable, since the design of each transfer function must be compromised to account for the interaction effects. In some cases, the two loops can be decoupled by the addition of an appropriate feedback path. This paper describes the application of this technique to a radar angle tracking loop. The technique described has the following advantages: 1. The required matching takes place within the loop so that the effect of any mismatch is attenuated by the open loop gain. 2. For the example used, the output angular rate accuracy becomes independent of aircraft motion. 3. Subject to the rather minor restriction implied by item 1, the two loops become independent as far as stability is concerned. Decoupling, which is described in this paper by illustrating its application to a particular system, is applicable to any complex control system. However, to the author's knowledge, no formal procedure for general application is available.