In this paper, by dividing a multivariable system into single inputoutput systems by a decoupling technique and adding feedback control loops to each single input-output system, the author has tried to design an automatic control system to satisfy our specifications for control system design, as specified in the body of the paper. A rational and clear design of a multivariable control system is proposed. The fundamental characteristics of the control system are shown analytically, and examined by computer simulation. This control system combining decoupling and PI action feedback controls shows good tracking and disturbance control ability and is effective and useful during the approach and berthing maneuvers.


Systems are generally multivariable, usually with coupling systems as shown in the top figure of Fig. 1. If the system can be divided so as to have an input-output relation of one-to-one correspondence as shown in the bottom figure of Fig. 1, it will be easier to design the control system. It is also important that the control system not only be able to perform the desired task, but that it also be able to compensate for disturbances. Ships are multivariable systems. Every input that is fed into a shipsystem has an effect on every output in the ship-system. Both functions must be factored into any control system. As an example, selecting the propeller and bow and stern thrusters as final control elements and ship speed, lateral shift displacement and heading angle as controlled variables, the author divides the multivariable system into three single input-output systems by use of a decoupling technique, and adds feedback control loops to each single input-output system. Furthermore, a rational and clear design method of the control system that satisfies our specifications for control system design is proposed.

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