DYNAMIC POSITIONING OF SHIPS USING DISTURBANCE OBSERVER BASED CONTROL

Abstract

A dynamic positioning (DP) system controls the position and heading of the vessel exclusively by means of its own propulsion system. DP systems are also being extensively used during slow speed movement and manoeuvring marine crafts and sea going vessels at high seas while carrying out very specific tasks which require high level of precision and accuracy. It is important to note that environmental disturbances in the form of wind, waves and ocean currents are present and continually varying thus by the act of which the vessel deviates from the desired track / position thereby hampering the maritime operations. Therefore, to overcome the above-mentioned obstacles, a suitable control technique is required to maintain heading and orientation of marine crafts and sea going vessels. It is a well known fact that PID controllers have a very strong presence in almost all domains of control application simply because of its modest structure, compatibility with analogue and digital applications and insurmountable record of success. However, in the application of Dynamic Positioning system, it is challenging to establish a decent tuning procedure for PID based controllers. In this report, three different type of controllers will be used for DP system in presence of low disturbance and high disturbance. The performance will be analysed first without the use of disturbance observer and then with the use of disturbance observer. Being the most widely used, first PID controller will be used and then to overcome the limitations of above controller Classical Sliding Mode Controller (SMC) will be used. The classical SMC has the problem of chattering and thus Higher Order Sliding Mode (HOSM) controller will be used for DP system.