Torstein Ingebrigtsen Bø

Marine Vessel and Power Plant System Simulator

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,s 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.

Dynamic Positioning System as Dynamic Energy Storage on Diesel-Electric Ships

A dynamic positioning (DP) system on a diesel-electric 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.

Battery Power Smoothing Control in a Marine Electric Power Plant Using Nonlinear Model Predictive Control

This brief presents a power variation smoothing method using batteries on a weak ship grid. For some marine vessels, power fluctuations on the ac grid are large. This results in the large variations in the electrical frequency of the grid and excessive wear and tear of the power producers. Adding batteries connected to a dc/ac drive to smooth out the power fluctuations has been suggested. However, due to the large amount of fluctuation, batteries can overheat. Therefore, we suggest using a bandpass filter with the cutoff frequency parameters optimized by a model predictive control based on a power spectral density estimate of power consumption for disturbance prediction.

Dynamic Safety Constraints by Scenario Based Economic Model Predictive Control

This paper studies scenario-based model predictive control (MPC) for dynamic safety constraints. For marine electric power plant with direct current distribution and variable speed generator set, the speed of the generator sets should be as low as possible to increase the efficiency of the diesel engines. However, a safety margin toward underspeed is necessary. In this paper, a dynamical safety constraint is achieved by including a fault scenario in the MPC formulation. This is done using a nominal trajectory of the predicted states for the fault-free operation, and adding fault trajectories starting from the samples of the nominal trajectory. The fault trajectories simulate the fault scenario and dynamically constrain the nominal trajectory. The controller is shown to be effective using closed-loop simulations of a marine electric power plant.

REAL-TIME MARINE VESSEL AND POWER PLANT SIMULATION

In this paper, we present a system simulator of a marine vessel and power plant which contains the mechanical system with diesel engines, propellers, steering gear, and thrusters; the electrical system with generators, switchboards, breakers, and motors; and the plant level controllers with dynamic positioning controller, thrust control, and power management system. Interconnections are possible to simulate by using a multi domain simulator. This is important when evaluating system performance and fault handling. The simulator is implemented in Simulink and is modular, configurable and scalable. It can be extended to run on National Instruments’ cRIO embedded control and acquisition system, for real-time simulation.Copyright

Unit Commitment of Generator Sets During Dynamic Positioning Operation Based on Consequence Simulation

Abstract 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.

Dynamic Safety Constraints by Scenario-Based Economic Model Predictive Control of Marine Electric Power Plants

This paper studies scenario-based model predictive control (MPC) for dynamic safety constraints. For marine electric power plant with direct current distribution and variable speed generator set, the speed of the generator sets should be as low as possible to increase the efficiency of the diesel engines. However, a safety margin toward underspeed is necessary. In this paper, a dynamical safety constraint is achieved by including a fault scenario in the MPC formulation. This is done using a nominal trajectory of the predicted states for the fault-free operation, and adding fault trajectories starting from the samples of the nominal trajectory. The fault trajectories simulate the fault scenario and dynamically constrain the nominal trajectory. The controller is shown to be effective using closed-loop simulations of a marine electric power plant.

Toward Safer, Smarter, and Greener Ships: Using Hybrid Marine Power Plants

Electrical power plants with dieselgenerator sets segregated (i.e., the diesel generator sets are divided into different power buses and physical stations on ships and rigs) on several power buses have become the preferred solution for ships with various operational profiles and corresponding power demands. Examples of such ships are dynamically positioned (DP) vessels with electric power plants in the range of 10-80 MW used in the offshore oil and gas industry for service, drilling, intervention, and production operations (Figure 1). The operations are characterized as safety critical and take place year-round, with large variations in the environmental loads acting on the ship, e.g., wind, waves, ocean currents, and sea ice. Electrical power plants have also become the preferred solution for cruise ships, ferries, navy ships, liquefied natural gas tankers, and icebreakers. The electric energy production may be powered by a hybrid marine power plant consisting of diesel or gas engines and integrated energy storage devices (ESDs) such as banks of batteries. Proper design and control systems can deliver significant fuel savings to make the ships greener and safer.

Investigation of drivetrain losses of a DP vessel

Traditionally the efficiency of the drivetrain of a marine vessel is evaluated at rated power and speed. However, the thrust and power consumption of the thrusters are low during DP operation. In this study, the loss energy during one month is investigated. The distribution of the loss energy is shown as a function of speed and power. The results show that considerable losses are occurring at low speed and power. This motivates the need to optimize drivetrain for operational profiles, instead of optimizing them for full load operation.

Models and Methods for Efficiency Estimation of a Marine Electric Power Grid

Diesel electric propulsion has become industry standard for many marine applications. Typically, a significant part of the operations of vessels with diesel electric propulsion is done with low loads on the motors and generators. However, the efficiency of a drive train is typically only calculated for full load conditions. This underestimates the losses during low load conditions. This article presents modeling methods for the electric drive train, which can be used to estimate the efficiencies, also at low load. The models are established with limited parameter sets, as detailed information about of the components are seldom available. This article compares the estimated efficiency of the generator and motor with the given data from datasheets.