This brief addresses the dynamic positioning (DP) control problem of surface vessels with input saturation and external disturbances, and a simple DP control law is proposed. First, a saturation handling model and a dynamic compensation system are designed to deal with input saturation. Then, an exponentially convergent disturbance observer is constructed to approximate the external disturbances. Moreover, to guarantee the asymptotic stability of the DP closed-loop system and reduce the design complexity of the DP control law, a simple auxiliary control law is designed by combining the hyperbolic tangent function. Notably, combined with LaSalle’s invariance principle, a DP system stability analysis strategy is constructed, which ensures that the DP system can be asymptotically stable, even if the derivative of the scalar function proving the stability of the DP system is semi-negative definite. Finally, the numerical simulation results demonstrate the effectiveness of the proposed DP control law.

In this paper, a variable gain prescribed performance control law is proposed for dynamic positioning (DP) of ships with positioning error constraints, input saturation and unknown external disturbances. The error performance index functions are designed to preset the prescribed performance bounds and the error mapping functions are constructed to incorporate the prescribed performance bounds into the DP control design. The variable gain technique is used to limit the output amplitude of the control law to avoid input saturation of the system by dynamically adjusting the control gain of the DP control law according to the positioning errors, and the error mapping function replaces the positioning error as a recursive sliding-mode surface to realize the prescribed performance control of the system and guarantee the stability of the closed-loop system with variable control gains. It has been proved that the proposed DP control law can make the uniformly ultimately boundedness of all signals in the DP closed-loop control system. The numerical simulation results illustrate that the proposed control law can make the ship’s position and heading maintain at the desired value with positioning error constraints, enhance the non-fragility of the DP control law to the perturbation of system’s parameters and improve the system’s rejection ability to external disturbances.

In order to accurately determine the growth of greenhouse crops, the system based on AVR Single Chip microcontroller and wireless sensor networks is developed, it transfers data through the wireless transceiver devices without setting up electric wiring, the system structure is simple. The monitoring and management center can control the temperature and humidity of the greenhouse, measure the carbon dioxide content, and collect the information about intensity of illumination, and so on. In addition, the system adopts multilevel energy memory. It combines energy management with energy transfer, which makes the energy collected by solar energy batteries be used reasonably. Therefore, the self-managing energy supply system is established. The system has advantages of low power consumption, low cost, good robustness, extended flexible. An effective tool is provided for monitoring and analysis decision-making of the greenhouse environment.