基于Bech模型的船舶航向离散变结构控制

Discrete Variable Structure Control of Ship Autopilots Based on Bech's Equation

采用带不确定项的 Bech模型可以更好地反映船舶运动的非线性特性以及不确定因素对船舶运动的影响。在 Bech模型中增加不确定项 ,采用离散变结构控制理论设计船舶航向控制器。针对传统设计方法稳态抖振的缺点 ,提出一种新型的离散趋近律 ,可以消除传统趋近律自身参数导致的抖振。设计扰动估计器 ,能够自适应估计不确定因素对系统的影响 ,只要不确定因素的变化率有界 ,即可保证闭环系统的鲁棒稳定性 ,特别是对于慢变不确定性 ,具有很高的估计精度。仿真结果表明 ,所设计的离散变结构控制器可以快速准确地跟踪设定航向 。

In ship autopilot design, the non linear behaviour of ship motion and the influences of uncertain factors can be more exactly characterized if the Bech's equation with uncertain terms is used. This paper presents a new approach for the ship steering autopilot design based on the Bech's equation and the discrete variable structure control theory. Firstly, a new discrete reaching law, which is stable at the origin and can eliminate the chattering caused by conventional discrete reaching law parameters, is proposed. Subsequently, an algorithm for uncertainty estimation is developed. The estimator can adaptively compensate the influence of system uncertainties and has high precision, especially for slowly varying uncertainties. Robust stability of closed loop system can be ensured if the changing rate of system uncertainties is bounded. Simulation results show that the dicrete variable structure controller designed here can track a desired course well and exhibits good performance robustness.