Abstract-This paper addresses the idea of improving transient behavior by internal state resetting of dynamic controllers, such as controllers with integral action or adaptation. The concept presented here assumes that for a given closed loop system with a dynamic controller, improved transient performance is achieved when reset of controller states gives negative jumps in the Lyapunov function value. The Lyapunov function constitutes a part of the controller algorithm. By combining this with existing stability theory for switched systems, the stability analysis of the overall system follows directly. The framework assumes that a Lyapunov function is given, and that full state measurement is available for feedback. Moreover, an estimator is needed to give a coarse estimate of the system equilibrium point.An anti-spin feature in local thruster speed control on ships with electric propulsion is in this paper presented as an application for the given framework. Transients arise when the ship operates in extreme seas, where disturbances such as ventilation and in-and-out of water effects may give rise to loss in propeller thrust. A Lyapunov function is used to decide appropriate reset of the integrator state of a standard PI-controller. The method is illustrated with experimental results.

Multiple model adaptive control (MMAC) is a well established approach for implementing adaptive systems with fast transient response. This paper considers a recently developed MMAC method based on adaptive nonlinear backstepping control where the parameter estimate may be instantaneously reset based on a criterion that requires a negative jump in the associated control Lyapunov function. Particular attention is paid to transient effects due to data filtering, which must be introduced in any practical implementation of the MMAC algorithm in order to reduce the sensitivity to noise, disturbances and model uncertainty. The main contribution of this paper is insight into the robust behavior of the adaptive system resulting from the filtering, and an investigation into the trade-offs between high transient performance and robustness to uncertainty.We also suggest data filter tuning guidelines and illustrate the results using a simulation example.

Abstract-PI controllers are often tuned such that the overall performance is a trade-off between performance in steady state and transient regimes. By introducing reset of the integrator value in these controllers, the performance in transient regimes may be increased without influencing the performance in steady state. An advantage of this strategy is that it can be integrated into an already existing controller as a separate module. This will only affect the performance in the transient regimes, by speeding up the controller response only when large control errors are measured. We will in this paper show how integrator reset can be used for anti-spin in local thruster speed control on ships with electric propulsion. Transient regimes arise when the ship is in extreme seas, where ventilation and in-and-out of water effects may give rise to loss in propeller thrust. In this paper, a Lyapunov function is used to decide when a reset of the integrator value is appropriate. The method is illustrated with experimental results. I. INTRODUCTIONElectrically driven thrusters are becoming the standard in advanced ship propulsion for offshore vessels, cruise vessels, navy ships and some advanced tankers. In these systems, thrusters are electrically driven taking the power from power buses, where the power is supplied by generators driven by diesel engines or gas turbines. The control hierarchy consists of a high-level controller giving commands to a thrust allocation scheme, which in turn gives commanded thrust set-points to the different local thruster controllers (LTC), see [1]. Examples of high-level controllers are dynamic positioning (DP) systems, joysticks and autopilots. In many cases the LTC is a conventional PI-controller, controlling the propeller shaft speed. The PI-controller may be tuned such that the performance is acceptable in both steady-state and transient regimes. The faster the PI-controller is tuned, the better the controller will perform in transient regimes. This will in turn increase the sensitivity to noise and increase variations in torque, power and mechanical load, and hence decrease the performance while in steady-state.In normal operation, there may be no need for high transient performance. When the ship is in extreme seas, however, the propeller may start to spin due to ventilation and in-and-out-of water effects. This, in turn, may lead to wear and tear of the ship's propulsion equipment and undesired transients on the power bus that may increase the risk of blackouts due to overloading of the generator sets, see [2].To handle these phenomena, an anti-spin controller is developed in [3], which utilizes an estimate of the torque loss to detect ventilation incidents. The anti-spin controller in [3] is based on a combined power/torque controller which in order takes control of the propeller shaft speed. A similar approach is considered here, but instead the anti-spin controller is based on a standard shaft speed PI-controller,

Abstract:In this paper a nonlinear thrust controller for a fixed pitch marine propeller with torque loss estimation and an anti-spin strategy is presented. The controller, designed to work in the four-quadrant plane composed by the shaft speed and the vessel speed, is a combination of a thrust controller designed for calm sea conditions and an anti-spin strategy to reduce power peaks and wear-and-tear in extreme sea conditions. The anti-spin algorithm avoid large increase of the shaft speed once high torque losses due to ventilation are detected and set the shaft speed to normal when the loss situation is considered over. The ventilation incident is detected by monitoring the torque losses, estimated with a nonlinear observer. The performances of the proposed controller are validated by experiments carried out in a towing tank.

Transient regimes arise when the propeller of a ship is operating in extreme seas, where ventilation and in-and-out of water effects results in loss of propeller thrust. By introducing Lyapunov based controller state reset, the performance in transient regimes may be increased without influencing the performance in calm seas. Improvements have been presented previously for dynamically positioned (DP) vessels. Transit operations, however, introduces additional losses due to variations in the propeller advance velocity. The controller in this paper combines an existing shaft speed reference generator that uses an estimate of the propeller torque losses with a PI shaft speed control law with integrator reset. Moreover, an anti-spin strategy is included to be able to operate also in extreme seas. The method is experimentally validated in a towing tank.