| With the rapid development of economy, the problem of the energy and resource’s shortages is becoming more and more obvious. Hence more attention and exploration should be paid to the resources of ocean before new energy becomes popular, more offshore drilling platform will be used and its key technology is the research of ship’s dynamic positioning system. At present the main researches of general interest on dynamic positioning systems are:how to establish the outside load model of ship/platform on the basis of winds, waves, flows, thrusts and water power; how to make the higher accurate ship dynamical model; hybrid intelligent control algorithm with higher precision and fused with multiple intelligent method; fast compensation of second order wave drift force estimating technology; wind feedforward technology and Doppler Measurement base on the wind direction and speed; study more higher accurate dynamic positioning location reference system based on multi-sensor fusion technology; control systems redundancy with heat backup; green dynamic positioning with the optimal thrust allocation method based on the thrusters’ power characteristic curve.In this paper we take the ship on the sea as object, using the method of nonlinear control theory to research the following problems:modeling of ship’s dynamic positioning system, propeller’s thrust estimation, indoor position measurements of ship model, observer design, and study on control of ship course and surge motion as well as ship’s dynamic positioning. The main contents and achievement in this paper are as follow:(1) Considering the complexity of the sea conditions, environmental disturbances model (wind, wave and current) are discussed. Then, according to the limit of Global Position System (GPS) signal indoor for dynamic positioning ship model, a high accurate indoor location scheme based on ultrasonic has been presented. Weighted least squares method is adopted to establish the model of system location algorithm, the solving processes of the equation are given. After that, aiming at the difficulties in the propeller’s dynamics modeling and dynamic characteristics, a thrust estimation scheme on the basis of Chebyshev fitting for marine propellers in four-quadrant operations is proposed. To calculate the thrust and torque coefficients of screw propeller in four-quadrant, a Chebyshev fit expression of the propeller properties in four-quadrant for surface vessel is given, and then it is changed into an ordinary polynomial expression. Finally the thrust is estimated according to the dynamical models of propeller in four-quadrant operations. The effectiveness of the proposed ultrasonic indoor positioning system and thrust estimation scheme are validated by experimental results derived from a 2.8 meter ship model, which scale 1:26 of a supply vessel. Finally, the ship’s moving dynamic characteristics and its water dynamic characters are discussed in view of dynamics, and the dynamic equation of ship is established.(2) A nonlinear observer is proposed to avert linear ship motion equation caused by Kalman filtering in Dynamic Positioning (DP) System. Considering the system noises, measuring noises and unmodeled dynamics, the proposed observer produces noise-free estimates by wave filtering techniques and separates the measured values into low frequency and wave frequency, the state value of vessel unmeasured is also estimated. The nonlinear observer plays an important role in filtering and estimating. The stability proof ISS is based on Lyapunov stability theory. Simulation results show the proposed nonlinear observer has excellent robustness and anti-interference ability.(3) Considering the ship’s maneuverability, the problem of ship’s course control and surge motion control are discussed. Considering the nonlinear ship course control with uncertain parameters and disturbance, a nonlinear adaptive backstepping control algorithm with integrator is proposed. Firstly, the control algorithm realizes the tracking control of nonlinear ship course with the known perturbation bounds, and obtained the control effects of global exponential stability. Taking the influence of the random marine environment to the ship into account, the other control algorithm realizes the tracking control of nonlinear ship course with the unknown perturbation bounds, and proves that the control algorithm meets L2 control standards and has the control effect of global stability make use of Lyapunov stability theory. On the basis of the course stable, control the surge motion to achieved the ship’s positioning or tracking. Considering the influence of wind, wave, current, working environment (sailing speed, operational model), navigational conditions and other uncertainties, it’s hard to describe the ship’s surge motion by an accurate model, so an adaptive fuzzy controller is designed, and its stability is proved by Lyapunov stability theory. Simulation results show the effectiveness of the design method.(4) In allusion to the dynamic positioning nonlinear model, dynamic positioning control algorithms are studied. Considering the problems of the nonlinear Dynamic Positioning Systems (DPS) with uncertain disturbance, a nonlinear adaptive backstepping controller using vectorial observer based on the simplified DPS model is proposed. First, a nonlinear observer was derived; the proposed observer includes an estimation of both the position and velocity of the ship from noisy position measurements. Then use the filtered position signal, an adaptive backstepping controller with observer is designed for the nonlinear ship. To improve the performance of the ship which has unknown parameters and uncertain dynamic disturbances, Integral action is included into backstepping controller. Global asymptotic stability is proven by applying Lyapunov stability theory. Considering the influence of wave frequency and environmental disturbances, a parallel distribution compensation control algorithm to the ship dynamic positioning is presented. First, the approximation of the nonlinear DPS model using T-S fuzzy model, then the model-based fuzzy PDC controller for DPS using the LMI method is designed. Simulation results verify the effectiveness of the above control algorithm.This research subject roots in the cooperative project with MCA ELECTRIC CO.,LTD., which is supported by key project of science and technology department of Panyu District of Guangzhou and 211 engineering characteristics as well as sub-project of Guangdong university of technology, faculty of automation. |
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