Design of Ship Course-Keeping Autopilot using a Sine Function-Based Nonlinear Feedback Technique

Abstract

Course keeping for ships is the core of automatic navigation in sea transportation. Much work has concentrated on developing novel control strategies for closed loop systems. We have turned our attention the other way to improve the control performance of marine autopilots in this work by "modulating" the control error using a sine function while the construction of the controller is not changed. The nonlinear feedback signal thus obtained is sent to the controller to replace the control error itself, which used to be the deviation between the output response and the reference input of the system. Such a control scheme is called "nonlinear feedback control" hereafter. Theoretical analysis by using a describing function and robust control theory shows that the same control quality is guaranteed with minor control actions for the nonlinear feedback scheme. Simulation experiments were carried out for the ship Yulong of Dalian Maritime University. It is shown that the method postulated in this paper has advantages of safety and energy saving in navigation; the maximum initial rudder angle is reduced by 31·2% with satisfactory control effect.2. Closed-loop gain shaping. 3. Course keeping. 4. Nonlinear feedback. 5. Sine function.6. Describing function.

Pressure Control of Insulation Space for Liquefied Natural Gas Carrier with Nonlinear Feedback Technique

“…The energy conservation problem was discussed for the first time. The technique was applied to the control of a ship course-keeping autopilot and achieved good results [16][17][18]. Chen et al [19] designed an adaptive neural fuzzy interference system (ANFIS) course-keeping controller with the technique in [15] to make the parameters easy to adjust.…”

“…There is less discussion about the pressure control of insulation spaces for LNG carriers and the nitrogen saving problem with this technique. Based on previous research [15][16][17][18][19][20][21], this paper applied the nonlinear control technique to the pressure control of insulation space. The controller in this paper is designed with nonlinear feedback based on a closed-loop gain shaping algorithm (CGSA).…”

“…The demonstration process of mathematical derivation is presented in reference [16]. As there is no extra effect on the steady state and dynamic performance of the system, sine driven function is suitable for the nonlinear feedback system, and it can also save the energy of the system.…”

“…From Figure 1, the describing function of f (ω(r − y)) can be written as F(u). According to reference [16], the influence on the steady state for a closed loop system with input of step signal can be expressed in Equation (1).…”

“…Here f (ω(r − y)) takes sin(ωe). So, Equation (11) can be achieved using the nonlinear feedback technology with sine function in [15,16]. The value of error input can be controlled within ± 1 with sine function.…”