Øyvind N. Smogeli

A Four-Quadrant Thrust Estimation Scheme for Marine Propellers: Theory and Experiments

A thrust estimation scheme for marine propellers that can operate in the full four-quadrant range of the propeller shaft speed and the vessel speed has been developed. The scheme is formed by a nonlinear observer to estimate the propeller torque and the propeller shaft speed and by a mapping to compute the thrust from the observer estimates. The mapping includes the estimation of the propeller advance ratio. The advance speed is assumed to be unknown, and only measurements of shaft speed and motor torque have been used. The robustness of the scheme is demonstrated by Lyapunov theory. The proposed method is experimentally tested on an electrically driven fixed pitch propeller in open-water conditions, in waves and with a wake screen that scales the local flow down in order to simulate one of the effects of the interaction between the propeller and the vessel hull.

Lyapunov-Based Integrator Resetting With Application to Marine Thruster Control

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.

Nonlinear Thrust Controller for Marine Propellers in Four-Quadrant Operations

In this paper a nonlinear thrust controller for a marine propeller in four-quadrant operations is presented. It is a shaft speed controller where the desired velocity is computed based on the desired propeller thrust and on the torque losses, estimated with a nonlinear observer. Experimental results are provided to demonstrate the effectiveness of the controller. The proposed scheme shows improved performance in thrust production when compared to traditional shaft speed and torque control.

Modeling, identification, and adaptive maneuvering of CyberShip II: A complete design with experiments

Abstract Good nonlinear maneuvering models, including numerical values, for control of ships are hard to find. This paper presents a complete modeling, identification, and control design for maneuvering a ship along a desired path. A variety of references have been applied to describe the ship model, its difficulties, limitations, and possible simplifications for the purpose of automatic control design. The numerical values of the parameters in the model are identified in towing tests and adaptive maneuvering experiments for a scaled model ship in a marine control laboratory.

Experimental validation of power and torque thruster control

Results from laboratory experiments with an electrically driven propeller controlled by three different control systems are presented, showing the advantages of torque and power thruster control over shaft speed control. For fixed pitch propellers, the industrial standard today is shaft speed control based on a static mapping from desired thrust force to desired shaft speed. When the operating conditions change due to vessel motion, waves and current, the propeller loading changes. The results are fluctuating thrust production and load torque, which lead to mechanical wear and tear and unpredictable power consumption. This may lead to severe deterioration of the performance of a vessel; the power fluctuations force the operators to have more generators running than necessary, and the mechanical wear and tear lead to vessel down-time due to repairs. Alternatives to shaft speed control are torque and power control, based on static mappings from desired thrust to desired torque and power respectively. This paper demonstrates by experimental results that significant performance improvements can be achieved by changing to torque or power thruster control

Anti-spin control for marine propulsion systems

An anti-spin controller for marine propulsion systems in rough seas is developed. From measurements of motor torque and propeller shaft speed, an observer providing an accurate estimate of the propeller load torque is used to calculate an estimate of the torque loss. A monitoring algorithm utilizing the estimated torque loss detects ventilation incidents, and activates the anti-spin control action. When a ventilation situation is detected, the anti-spin control action will reduce the propeller shaft speed to some optimal value, using a combined power/torque controller. The ultimate goal is to minimize the effect of ventilation, and hence increase the thrust production, limit the transients in the power system and reduce the mechanical wear and tear of the propulsion system components. Simulations are provided to validate the performance of the control scheme.

Anti-Spin Thruster Control in Extreme Seas

Abstract A hybrid control scheme for thruster control in moderate and extreme seas is proposed. Two operational regimes are defined: 1) Normal thruster control for handling of low and moderate thrust losses. 2) Anti-spin thruster control for handling of high thrust losses. Alternative thruster control schemes are possible: Conventional speed control, torque control, power control or combinations of these. When high thrust losses are detected, a switch to an anti-spin controller which counteracts the engine racing is proposed. The control system is shown to give increased performance in extreme seas in terms of reduced power system transients, increased station-keeping capability and reduced mechanical wear and tear on the propulsion system

Improved Transient Performance by Lyapunov-based Integrator Reset of PI Thruster Control in Extreme Seas

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

Marine Propeller Thrust Estimation in Four-Quadrant Operations

This paper proposes a scheme for thrust estimation of a marine propeller over the full four-quadrant range of propeller shaft speed and vessel speed. Based on shaft speed and motor torque measurements, the scheme involves a nonlinear observer for the propeller torque that shows stability and robustness for hounded modeling and measurement errors. The propeller thrust is computed as a static function of the propeller torque. The performance has been demonstrated in experimental tests

Antispin Thruster Control for Ships

This paper considers the control of thrusters and propellers on ships in extreme operating conditions. In normal operating conditions, recent results have demonstrated that torque and power thruster control will lead to reduced mechanical wear and tear of the propulsion unit, more accurate thrust production, and more predictable power consumption when compared to conventional shaft speed control. In high seas, however, when the propeller may be subject to large thrust losses due to ventilation and in-and-out-of-water effects, torque and power thruster control will lead to propeller racing. This may cause structural damage to the propeller, increase mechanical wear and tear, and give excessive power peaks. To facilitate the use of torque and power control in extreme conditions as well as in normal conditions, an antispin thruster controller is developed, analyzed, and experimentally tested on a model-scale propeller.