A distributed object-oriented simulator framework for marine power plants with weak power grids

In this work, we discuss and demonstrate how multi-engine marine power plants with weak power grids efficiently can be set up and simulated in a distributed co-simulation framework. To facilitate configuration switching such as starting and stopping, connecting and disconnecting arbitrary gensets online, the generator models are modelled as hybrid causality component models. This implementation enables seamless and energy conservative model switching. Also, the proposed simulator framework is scalable such that the number of gensets in the power plant can be set by a single parameter, which automatically scales the power management system and the tailored simulator master algorithm accordingly. To control the number of active gensets being connected to the power grid while running the simulation, a simple mixed integer linear programming formulation is proposed. A simulation case study including a marine power plant configuration with four equal-sized gensets is conducted in the end to demonstrate the features of the proposed simulator framework, which also can be applied to, e.g. a small wind farm, or an isolated number of islands with interconnected power generators.publishedVersio

Improving pre-turbine SCR systems in marine two stroke diesel engines using hybrid turbocharging: a numerical study of SCR operation range and system fuel efficiency

In this article, a performance evaluation of a novel system solution combining a hybrid turbocharger and a pre-turbine selective catalytic NOx reduction system is carried out. Pre-turbine selective catalytic system are used with marine two-stroke diesel engines to comply with International Maritime Organization Tier III. The system solution focuses on expanding the selective catalytic reduction operation range which is limited by fuel sulphur content by increasing exhaust temperature at low engine loads. The extended operation range is to be achieved while minimizing any fuel consumption penalties. Increasing the operation range brings improvements to emission levels during manoeuvring operations which are often carried out close to populated areas. It also provides flexibility by enabling emission reduction during slow steaming operations in which mitigating fuel consumption penalties is paramount. In addition to system evaluation in still water conditions, furthermore evaluations have been carried out taking into consideration the effect of waves on the system performance. Investigating the effect of operating in waves bring additional insight that is relevant for predicting performance in operational conditions. Analysis of the system solution found that improvements in selective catalytic reduction operation range can be achieved while also improving fuel consumption. Fuel consumption is significantly improved in the high load range. Effect of realistic operation conditions where found to affect performance; however, significant effects are only found for harsh sea states in the load range below the design point.submittedVersio

On the numerical stability in dynamical distributed simulations

This work takes aim at studying numerical stability in distributed simulations through dynamic stabilityand stability criteria for explicit solvers. This is done by studying outer stability limits, for example stabilityconditions when handling unstable subsystems or marginally stable solvers. To conclude global stability of adistributed system simulation both dynamic stability and solver stability must hold, and this work combinesthese stability criteria into one unified criterion for distributed linear dynamical systems. Some examples aregiven in order to both highlight numerical stability issues and to prove stability in different case studies. Thederived stability criterion is also extended to include distributed systems containing non-linear dynamics.acceptedVersio

Data-Driven Methodology for the Analysis of Operational Profile and the Quantification of Electrical Power Variability on Marine Vessels

Measurements from the on-board systems of marine vessels are increasingly available for data analysis and are growing in importance as the ship industry enters a phase of digitalization. The purposes of the data analysis from vessels in operation include the verification of the power system design in general and improvement of the electrical power load analysis in particular. In this paper, we show how to extract valuable information from the data-driven operational profile analysis, which reveals the real power demand, and how the vessel was operated. Using the real power range analysis, we emphasize the significance of rarely occurring high power demands, which are critical for power system design and optimization. We propose a methodology for the quantification of variability in the generated power, which explains the tails of probability distributions of a power signal based on signal decomposition. The proposed methodology makes use of the data and it can facilitate the selection of the optimal size, number, and configuration of generators or batteries when designing new power systems. Measurements from a data collection system are used to demonstrate the methodology for dynamic positioning (DP) mode of the operation of a platform supply vessel (PSV).acceptedVersion© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Data-Driven Methodology for the Analysis of Operational Profile and the Quantification of Electrical Power Variability on Marine Vessels

Measurements from the on-board systems of marine vessels are increasingly available for data analysis and are growing in importance as the ship industry enters a phase of digitalization. The purposes of the data analysis from vessels in operation include the verification of the power system design in general and improvement of the electrical power load analysis in particular. In this paper, we show how to extract valuable information from the data-driven operational profile analysis, which reveals the real power demand, and how the vessel was operated. Using the real power range analysis, we emphasize the significance of rarely occurring high power demands, which are critical for power system design and optimization. We propose a methodology for the quantification of variability in the generated power, which explains the tails of probability distributions of a power signal based on signal decomposition. The proposed methodology makes use of the data and it can facilitate the selection of the optimal size, number, and configuration of generators or batteries when designing new power systems. Measurements from a data collection system are used to demonstrate the methodology for dynamic positioning (DP) mode of the operation of a platform supply vessel (PSV)

A real-time simulator framework for marine power plants with weak power grids

This work takes aim at presenting a generic real-time simulation framework for marine power plants with weak power grids, containing transient functionalities such as starting and stopping of arbitrary generators, and phase synchronization. The generator models used in the power plant are hybrid causality models, meaning that they have the ability to switch between causality orientations, between voltage and current. These models facilitate real-time simulations as long as they are solved properly, as will be discussed in this article. Much is devoted to numerical stability, model robustness and power plant control, e.g. rms voltage control, engine speed control, active- and reactive power sharing control and phase synchronization control. Some focus is also given to overall power plant control structure. A case study of a marine power plant including two generators and a fluctuating- and noisy power consumption is presented and analysed, and illustrates the advantages of the proposed framework as well as giving a good foundation for future works

Non-angular MPC-based Thrust Allocation Algorithm for Marine Vessels - A Study of Optimal Thruster Commands

In this paper, a thrust allocation algorithm for marine vessels based on model predictive control (MPC) theory and a nonangular vector formulation is presented and studied. The main objective in this paper is to highlight the potentials of using an optimal thrust allocation algorithm including a time horizon to reduce the power consumption as well as reducing the environmental disturbances in the thruster commands. The proposed thrust allocation algorithm is compared with a one-step optimization algorithm in a benchmarking test. A one-step thrust allocation algorithm is an optimization algorithm with a time horizon that includes only one sample. When using a longer time horizon in the proposed algorithm, the thrust allocation has the potential of optimizing rate limited states in the long run, e.g., whether it would be beneficial to rotate a thruster or to increase or decrease the commanded thrust when thruster biasing is considered as an option. Preliminary case studies are presented where different cost function weights and horizon lengths are compared. The finite time horizon in the MPC thrust allocation algorithm also makes it possible to affect the dynamics of the optimized thruster signals since it can use the entire time horizon to reach its objective. This is very important when considering reducing the thrust rates when controlling a marine vessel in dynamic positioning operations since wave filters never succeed in filtering out all oscillatory environmental effects. Thus, an optimal thrust allocation algorithm with well-chosen cost function weights, along with thruster biasing, would reduce the magnified oscillations in the produced thrust, while keeping the power consumption at a minimum, which has been devoted the main focus of this paper.acceptedVersion© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

The Theory of Bond Graphs in Distributed Systems and Simulations

The bond graph theory provides a firm and complete strategy for making mathematical models and are used in this work to obtain a good relation between connectivity, causality and model fidelity in distributed systems. By distributing a system more computational power is available which makes it possible to increase the model fidelity in large systems without increasing the time to solve the total system. Also, more complex models with causality switching properties may be used for simplifying the connectivity problem between distributed models and for representing changing dynamics that also affects the model causality. Stability of distributed systems are dependent on both solver stability and dynamical stability, when neglecting the stability results based on cascaded systems with certain passivity properties. For linear distributed systems solver with fixed step size solvers a stability criterion involving the system dynamics, local solver time step and global synchronization time step can be formulated. In this work a stability criterion for linear distributed systems solved with the Euler integration method will be derived and a hybrid causality model, representing a small power plant, will be used to test the stability criterion

On the numerical stability in dynamical distributed simulations

This work takes aim at studying numerical stability in distributed simulations through dynamic stabilityand stability criteria for explicit solvers. This is done by studying outer stability limits, for example stabilityconditions when handling unstable subsystems or marginally stable solvers. To conclude global stability of adistributed system simulation both dynamic stability and solver stability must hold, and this work combinesthese stability criteria into one unified criterion for distributed linear dynamical systems. Some examples aregiven in order to both highlight numerical stability issues and to prove stability in different case studies. Thederived stability criterion is also extended to include distributed systems containing non-linear dynamics