Abstract-A dynamic positioning (DP) system on a dieselelectric ship applies electric power to keep the positioning and heading of the ship subject to dynamic disturbances due to the winds, waves and other external forces using electric thrusters. Vice versa, position and heading errors can be allowed in order to implement energy storage in the kinetic and potential energy of the ship motion using the DP control system to convert between mechanical and electrical power. New simple formulas are derived in order to relate the dynamic energy storage capacity to the maximum allowed ship position deviation, as a function of the frequency of the requested dynamic energy storage. The benefits of DP dynamic energy storage are found to be reduced diesel-generator maintenance need, reduced fuel consumption and emissions, reduced risk for blackout, and increased operational flexibility allowing power-consuming operations such as drilling and lifting to be safely prioritized over DP for short periods of time.

Abstract-Modern ships and offshore units built for dynamic positioning are often powered by an electric power plant consisting of two or more diesel-electric generators. Actuation in any desired direction is achieved by placing electrical thrusters at suitable points on the hull. Such ships usually also have other large electrical loads. Operations in the naturally unpredictable marine environment often necessitate large variations in power consumption, both by the thrusters and by the other consumers. This wears down the power plant, and increases the fuel consumption and pollution. This paper introduces a thrust allocation algorithm that facilitates more stable loading on the power plant. This algorithm modulates the power consumption by coordinating the thrusters to introduce load variations that counteract the load variations from the other consumers on the ship. To reduce load variations without increasing overall power consumption it is necessary to deviate from the thrust command given by the dynamic positioning system. The resulting deviations in position and velocity of the vessel are tightly controlled, and the results show that small deviations are sufficient to fulfill the objective of reducing the load variations. The effectiveness of the proposed algorithm has been demonstrated on a simulated vessel with a diesel-electric power plant. A model for simulation of a marine power plant for control design purposes has been developed.

a b s t r a c tDiesel-electric power and propulsion systems with electric thrusters are the industry standard for vessels with dynamic positioning (DP) systems. Diesel engines are paired with generators in generator sets and are used to produce electric power used by thrusters and main propellers during stationkeeping and transit, and other consumers such as hotel load, drilling drives, cranes, and heave compensators. Consequence analysis is used to verify the safety of a DP operation. It is used to check whether there is sufficient running power and thruster capacity available to retain sufficient thrust to maintain vessel position after a worst single failure. Recently, extensions of class rules enable standby generators to be considered in this analysis. This provides a more efficient configuration as relatively fewer generator sets may be running. However, DP performance is degraded during the transition from the fault occurrence until the plant is completely recovered. It is important to determine if this degradation leads to a loss of position during the transition. This study presents a simulation-based dynamic consequence analysis method that can be used to dynamically simulate fault scenarios such that the dynamics of the transient recovery can be analyzed. This analysis can be used for decision-support to configure marine electric power plants in DP. Results from the simulation study show that the currently used static consequence analysis method may provide non-conservative results under certain configurations.

Modern marine electric propulsion vessels have many systems. These interactions and integration aspects are essential when studying a system and subsystem behavior. This is especially important when considering fault scenarios, harsh weather, and complex marine operations. However, many simulators, including a selection presented here, study the positioning system and the power system separately. This paper proposes a simulator combining the two systems, as an extension to the marine systems simulator MATLAB/Simulink library. The intended use cases and the according design choices are presented. New subsystem models include a power-based electrical bus model and a simplified diesel engine model. Both are validated through the simulation against established models. In addition, established models for generators, electrical storage devices, thrusters, and a mean-value diesel engine model are summarized with rich references. Three case studies illustrate the multi-domain use of the simulator: 1) a semi-submersible drilling rig performing station keeping under environmental disturbances; 2) the same vessel subject to an electrical bus reconfiguration; and 3) a supply vessel with a hybrid power plant.INDEX TERMS Marine technology, marine vehicles, power system simulation, dynamic positioning.

For vessels with dynamic positioning system, diesel-electric propulsion is often used. At all time the vessel should be able to withstand any single point failure without loss of position. This paper studies the use of simulation of worst-case failure to decide which configurations of the power plant are sufficient for the current operation. The loss of position due to reduced power to the thrusters is simulated and compared with the safety requirements. This method gives both a practical approach to implement the safety requirement and information which can be used as a decision support system or for automatic start and stop of generator sets. The operational cost is also optimized by using the results from the simulations.