An Integrated Positioning Thruster Control System

ABSTRACT Honeywell has integrated its dual redundant Automatic Station-Keeping (ASK?) System with a new thruster control system (TCS). The ASK System provides high-quality, high-reliability dynamic positioning performance, while the primary function of the TCS is to enable an operator to control each propulsion element individually. In this system, the TCS also provides automatic, coordinated steering and control of the propulsion system during transit (cruise) operation and during short-distance maneuvering, when three-axis control (TAC) is required. The new system is called a positioning/ thruster control system (PTCS). Final testing is in progress, and the first system will be installed on the SEDCO 710 semi submersible in the summer of 1982 Salient features of the new system are microprocessor- based electronics for growth and flexibility, color CRT displays, Kalman filtering of position and heading data, and a generalized thruster-allocation algorithm. The thruster allocation is composed of a fixed pointing-angle, minimum energy allocation for all thrusters, blended with an allocation that commands both thrust level and azimuth angle to all steer able thrusters. It includes power limiting and cutback algorithms to avoid vessel blackout. This paper gives an overview of the PTCS, including the design philosophy and the hardware and software architecture. The thruster allocation logic is discussed in some depth, paying particular attention to its operational flexibility and ability to perform efficiently in both light and heavy weather INTRODUCTION Deep-water drilling and related operations from Semi submersible vessels present many complex control problems. Traditional vessel control systems used for these applications employ both a dynamic-positioning (DP) system and a thruster control system (TCS). The thruster control system gives the operator manual control of each element of the propulsion system, e.g., rudder, steer able thruster, fixed-axis thruster, or main screw. The DP system automatically controls the propulsion elements to keep the ship on location and is the only source of coordinated automatic control of the vessel propulsion system. In January 1981, under contract from SEDCO, Honeywell Marine Systems Operations began developing an integrated DP and thruster control system, based on requirements dictated by SEDCO, the industry's most experienced DP operator. This new system, called a positioning/thruster control system (PTCS) retains the advantages of independent thruster control and DP systems, and also incorporates some of the conveniences of a computer-controlled automatic system into the TCS. The system uses modern microprocessor technology and advanced sensor processing techniques. The capability of former thruster control strategies was expanded and incorporated into both the TCS and DP system. The PTCS is now undergoing final system tests and will begin sea trials in the fall of 1982. This paper outlines briefly the PTCS system's functional design, hardware design, and software design. Special emphasis is placed on the new capabilities in the thruster allocation logic. FUNCTIONAL DESCRIPTION Design Requirements The new equipment was designed for the SEDCO 710, a large semi submersible with eight steer able thrusters for propulsion. Some important design objectives for the integrated PTCS were