IEEE Proof Web Version IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY 1 Multi-Operational Controller Structure for Station Keeping and Transit Operations of Marine Vessels Trong Dong Nguyen, Asgeir J. Sørensen, Member, IEEE, and Ser Tong Quek Abstract—In this brief, a novel control system structure for in- tegrated dynamic positioning, maneuvering, and transit operation of marine vessels is proposed. The proposed structure is based on supervisory switching control (SSC) using switching logics in con- junction with operator initiated commands. The SSC is a hybrid system consisting of continuous state multi-controllers and discrete state logics that allow switching among the various controllers for the particular operations. The switching between appropriately designed controllers facilitates operations from normal conditions to extreme situations such as severe seas and possible failure situ- ations. Through this, it will be possible to extend the vessel oper- ability under harsh environments, and increase the safety and per- formance in marine operations with greater fault-tolerance. One demonstrating example of the integrated marine control system verified by experiments is demonstrated. Index Terms—Extreme conditions, hybrid system, station keeping, supervisory switching control (SSC), transit. I. INTRODUCTION M ARINE business covers three main clusters including shipping, offshore exploration and exploitation of hy- drocarbons, and aquaculture and fisheries. Marine vessels are the major element within these clusters. Nowadays, the marine vessels are required to operate in wider range of environmental conditions and different speed regimes with acceptable perfor- mance and safety. All-year marine operations are important for oil companies and contractors to conduct safe and cost effec- tive explorations and exploitations of hydrocarbons. In partic- ular, when conducting marine operations in deep water, the op- erations are more time consuming, and hence more sensitive to changes in the sea states. Therefore, marine control systems must be designed such that the marine vessel can operate under many different operational and environmental conditions with adequate reliability and economy. This motivates nonlinear controller design since the dynamics of the process, the constraints and the control objectives vary Manuscript received June 2, 2006; revised November 24, 2006. Manuscript received in final form May 23, 2007. Recommended by Associate Editor R. Rajamani. This work was supported by the Centre for Offshore Research & En- gineering at NUS in cooperation with the Centre for Ships and Ocean Structures (CeSOS) at Norwegian University of Science and Technology (NTNU). T. D. Nguyen is with the Center for Ships and Ocean Structures (CeSOS), Norwegian University of Science and Technology (NTNU), NO-7491 Trond- heim, Norway (e-mail: trong.d.nguyen@ntnu.no). A. J. Sørensen is with the Department of Marine Technology, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway (e-mail: asgeir.sorensen@ntnu.no). S. T. Quek is with the Department of Civil Engineering, National University of Singapore, Singapore 117576 (e-mail: cveqst@nus.edu.sg). Color versions of one or more of the figures in this brief are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TCST.2007.906309 subject to the different operational conditions. There are two major solutions for this nonlinear control strategy: either the de- sign of a unique nonlinear controller or the integration of sev- eral simpler controllers. The single nonlinear controller may be complicated or even impossible to design for the applications in which the dynamics of the process changes significantly. In addition, it is difficult to satisfy the different control objectives within only one single controller. In the second solution, several controllers are integrated into a system, and the switching is performed among the controllers by some automatic mechanisms. The design of controllers is based on the well-formulated linear and/or nonlinear models which are simplified from the process dynamics dependent on oper- ational regimes. In addition, it is easier to satisfy the different control objectives with a multi-operational controller structure. Although the drawback could be a bundle of controllers with chattering problem, this control strategy has been already im- plemented widely in many industrial applications using ad hoc solutions. In the literature, similar approaches have been used, e.g., gain scheduling in flight control [25], and in land-based vehicle control [11], and hybrid power/torque thruster control [17]. The switching between the various controllers may lead to instability. This can be prevented by the supervisory switching control (SSC) proposed by [8] and [9]. This control strategy makes it possible to switch either between linear or nonlinear controllers according to the prevailing operational conditions. The switching is done by a certain discrete logic to guarantee the stability of the whole system, therefore associated with the switched system. Readers can find examples of switching logics: scale-independent hysteresis switching logic (SIHSL) and hi- erarchical hysteresis switching logic (HHSL) in [10]. The SSC also associates with the hybrid system since it consists of contin- uous state multi-controllers and discrete state logics that allow switching among the various controllers. The SSC is more ad- vantageous than adaptive control [2] in terms of rapid adapta- tion, flexibility and modularity, and decoupling between the su- pervision and control. One of the applications of SSC was illus- trated by [4] on multi-model proportional–integral–differential (PID) controller for a nonlinear pH neutralization process. Reference [7] proposed an SSC system for disassembling and reassembling with fault-tolerance consideration of the mobile offshore bases (MOB). Reference [13] proposed a SSC system to handle dynamic positioning (DP) operation in calm to ex- treme environmental conditions. In this brief, the SSC concept of [13] is extended to include the different speed assignments and the various control modes as well. Instead of having sev- eral separated controllers with inconvenient manual transfer and switching, the controllers can be integrated into one control system. 1063-6536/$25.00 © 2008 IEEE