Smooth Variable Structure Research Articles

A Novel Calibration Algorithm of SINS/USBL Navigation System Based on Smooth Variable Structure

Aiming at the problem that the USBL installation error is difficult to accurately calibrate in the complex underwater environment. In this paper, based on smooth variable structure and unscented Kalman filter, a novel USBL installation error calibration algorithm is proposed. Firstly, the nonlinear system model of USBL installation error based on the filter estimation principle is analyzed. On this basis, the USBL installation error calibration algorithm based on the principle of unscented Kalman filter is given. Secondly, in view of the shortcomings of the UKF calibration algorithm, smooth variable structure is introduced, and a novel algorithm combining smooth variable structure and UKF is proposed. Finally, the effectiveness of the algorithm proposed in this paper is verified by simulation and river test. The results show that the algorithm proposed in this paper can accurately and stably estimate the USBL installation error parameters when the underwater acoustic signal is disturbed.

INVARIANT SLIDING SECTOR FOR VARIABLE STRUCTURE CONTROL

A sliding sector has been defined as a subset of the state space, inside which a norm of state decreases with zero control input [1]. In this paper, an invariant sliding sector is defined to be such a kind of sliding sector inside which with a suitable control law, the norm keeps decreasing and the system state stays there since then after entering the sector, i.e. the sector defined in the paper is an invariant subset of the state space. Design algorithms of the invariant sliding sector and the Variable Structure (VS) controller with the sector are given. The proposed VS controller with the invariant sliding sector ensures that the system state moves from the outside to the inside of the sector in a finite time and stays inside it forever after being moved into it, and that the norm of state keeps decreasing in the state space. The resulted VS control system is quadratically stable with a smooth VS control law. The experimental results with the inverted pendulum show the invariance of the sector and the robustness of the proposed VS control system with the invariant sliding sector.