Path following of underactuated USV based on modified integral line-of-sight guidance strategies

Path following control is one of the key technologies for unmanned surface vehicle (USV) to complete its mission, which is widely concerned by the field of motion control at home and abroad. In order to improve the accuracy and robustness of USV's path following control under the disturbance of the external environment such as wind, wave and flow, path following control problem of the asymmetry underactuated USV under external disturbances such as current is discussed, and two modified integral line-of-sight(ILOS) guidance strategies are proposed. Based on the modified guidance strategies and feedback control theory, path following of the USV at horizontal level is realized. Compared to the conventional ILOS guidance strategy, the first modified strategy with time-varying integral gain can avoid integral windup and overshoot phenomenon; on the basis of the first modified strategy, the lookahead distance is designed as a time-varying element in the second modified strategy, making the USV control more flexible. In the modified strategies, integral gain and lookahead distance are all computed as different functions of cross-track error, which can conduce the USV to converge to desired path in an elegant and fast manner. Based on the cascaded system theory, the control system proposed is proved to be global k-exponential stable (GKES) when the target tasks are all achieved. The theoretical analysis and simulations show effectiveness and advancement of the proposed method.