Shipboard Power System Research Articles

Wavelet-based convolutional neural network for non-intrusive load monitoring of next generation shipboard Power Systems

In this study, a non-intrusive load monitoring (NILM) framework is developed for next generation shipboard power systems (SPS) based on a discrete wavelet transform signal processing and a convolutional neural network (CNN). We have applied the developed NILM method to a four-zone medium voltage direct current (MVDC) SPS to evaluate the effectiveness of the proposed method. Each zone of the MVDC SPS consists of multiple components, such as propulsion load, pulsed load, high ramp rate load, cooling load, and hotel load. The current signals from the main generators are the main inputs to the NILM model. The current signals are first processed through a discrete wavelet transform to create a coefficient vector that reflects the status of all the components in each zone. Then, a multi-class classification problem is formulated and solved using a CNN architecture model to monitor the load statuses in real time. The results of case studies show that the developed NILM model in comparison with benchmark methods can (i) accurately monitor the status of all components with a total accuracy of over 98%, (ii) identify unique pulsed loads with a total accuracy of over 99%, and (iii) sustain the functionality of load monitoring under extreme events such as cyber/physical attacks, load uncertainty, and noisy inputs.

A Novel Reinforcement-Learning-Based Compensation Strategy for DMPC-Based Day-Ahead Energy Management of Shipboard Power Systems

A Novel Reinforcement-Learning-Based Compensation Strategy for DMPC-Based Day-Ahead Energy Management of Shipboard Power Systems

Non-intrusive fault detection in shipboard power systems using wavelet graph neural networks

Naval shipboard power systems (SPS) are rapidly embracing electrification, resulting in loads that generate pulsation currents and encounter substantial transients. However, conventional time-based features alone are inadequate for effectively monitoring and safeguarding these loads against faults. This highlights the critical requirement for advanced machine learning based methods to discern and differentiate between the various transient stages within the load profile. In this paper, we propose a Wavelet Graph Neural Network (WGNN) model for non-intrusive fault detection in SPS. The fault detection system leverages the dynamic model of the SPS to train and test performance with varying fault scenarios. The underlying structure and the interdependence among component states in the SPS network are effectively captured using the WGNN model, resulting in accuracies over 99% for intrusive fault detection and 97% for non-intrusive fault detection. The developed WGNN model has also shown to be robust in the presence of pulse loads and noise, achieving an accuracy of over 95%. At the end, a real-time simulation of the proposed method is validated on a hardware-in-the-loop system, guaranteeing the high fidelity and low latency of the proposed approach. These findings validate the effectiveness of the proposed WGNN model for fault detection and real-world applications in SPS.

Model-Predictive-Based Power Management for Pulsed Power Load Fed With Multizonal Shipboard Power System

Model-Predictive-Based Power Management for Pulsed Power Load Fed With Multizonal Shipboard Power System

A prediction and load shed-based approach of controlling a medium voltage AC/DC testbed

Shipboard power systems have previously relied on oversized generators with minimal monitoring of the output, preventing the implementation of many real-time controls. Redundant generation is implemented instead of controls, resulting in uncontrolled load sheds when capacity is exceeded, or generators fail. The naval power system community is extensively studying the advantages of distributed zonal power system architectures that allow for the buffering of multiple generation sources and loads using energy storage and regulating power electronics. Extensive sensing and controls are necessary for successful operation of a distributed power system, and they must be evaluated adjoint to representative hardware topologies. The University of Texas at Arlington (UTA) is utilising a medium voltage (MV) AC/DC testbed to examine predictive high ramp rate (PHRR) and advanced load shed (ALS) control algorithms developed and modelled by Clarkson University (CU). A single zone of a zonal power system is being emulated using UTA’s testbed. Experimental results collected after integrating the CU control strategies into the UTA testbed will be discussed here.

Generator Scheduling Methods for Improving Fuel Efficiency in Electric Shipboard Power System Using Load Forecasting

Generator Scheduling Methods for Improving Fuel Efficiency in Electric Shipboard Power System Using Load Forecasting

Stability Analysis in a Direct-Current Shipboard Power System with Parallel Permanent Magnet Synchronous Generators and Supercapacitor Integration

This paper investigates the small-signal stability of a DC shipboard power system (SPS) with the integration of a supercapacitor. As an efficient energy storage solution, supercapacitors can not only provide rapid energy response to sudden power demand spikes, effectively mitigating load fluctuations, but also enhance the system’s resilience to disturbances. In the context of the parallel operation of two Permanent Magnet Synchronous Generators (PMSGs), the inclusion of supercapacitors may alter the system’s dynamic behaviors, thereby affecting its small-signal stability. This paper develops the small-signal model of SPS and explores the small-signal model under various power distribution strategies in the parallel operation of diesel generator sets. Through the calculation of eigenvalues and influence factors, the system’s oscillation modes are analyzed, and key parameters affecting the stability of the DC distribution system are identified. Furthermore, this paper meticulously examines the specific impacts of electrical and control parameter variations on the system’s small-signal stability. Simulation experiments validate the accuracy of the small-signal stability analysis after supercapacitor integration into SPS.

Identification of Intermittent Ground Fault Lines in Medium Voltage Shipboard Power Systems

To locate increasingly frequent intermittent ground faults in medium-voltage shipboard power systems, this study proposes a fault branch selection method using wavelet analysis. By analyzing transient fault current characteristics in ship medium-voltage grids, this method utilizes wavelet analysis tools to extract features and obtain modulus maxima of branch currents. Based on a dual threshold detection strategy, the fault branch is then identified. The feasibility and validity of the proposed method are verified through simulations on the Matlab/Simulink platform. The simulation results demonstrate the capability of the wavelet analysis approach to accurately locate intermittent ground faults in ship medium-voltage power systems. This research provides an effective solution for fault branch selection of intermittent grounding faults in ship medium-voltage grids.

Decentralized Power Sharing with Frequency Decoupling for a Fuel Cell-Battery DC Shipboard Power System

The maritime industry is under increasing pressure to reduce its carbon footprint by adopting new energy generation and storage technologies in shipboard power systems (SPS). Fuel cells (FCs) show great potential as primary power sources when hybridized with energy storage systems (ESS). Integrating different technologies in future SPS requires the coordination of power generation and storage modules, which can be facilitated by DC technology with power electronics interfaces. However, studies on FC integration have primarily focused on small-scale applications with centralized control architectures. There has been little research on the modular control of multiple FC and battery modules in SPS. This study proposes a decentralized droop-based power sharing approach with load frequency decoupling to efficiently utilize power system modules based on their dynamic capabilities. The proposed strategy further incorporates decentralized voltage regulation and state-of-charge (SoC) management functions. The methodology was applied to a short-sea cargo vessel with an FC-battery DC power system. The results indicate that the mission load profile can be satisfied while limiting fluctuations in the FC output power. Moreover, the proposed strategy achieves the same voltage regulation performance as a centralized proportional-integral (PI) controller and can be easily tuned to achieve load frequency decoupling with the desired time constant. Finally, a comparative analysis shows how the trade-off between the dynamic operation of the FC and the discharge depth of the ESS is affected by the choice of time constant.

A Model Predictive Control-Based Energy Management Strategy for Secure Operations in Shipboard Power Systems

A Model Predictive Control-Based Energy Management Strategy for Secure Operations in Shipboard Power Systems

A Decentralized Model-Based Fault Detection and Isolation Scheme for MVDC Shipboard Power Systems

A Decentralized Model-Based Fault Detection and Isolation Scheme for MVDC Shipboard Power Systems

Fault Diagnosis of Shipboard Medium‐Voltage Alternating Current Power System with Fault Recording Data‐Driven SE‐ResNet18‐1 Model

The electrification trend of marine vessels has led to the rapid development of all‐electric ships. Yet the unique topology and harsh working environment of shipboard power system have posed significant challenges to its fault diagnosis. This paper addresses the research gap in fault diagnosis for shipboard medium‐voltage alternating current (MVAC) power systems and proposes a machine learning‐based fault diagnosis scheme. Signals from fault recorders before relay triggering are used as input for the neural network model. By combining the residual neural network (ResNet) with Squeeze‐and‐Excitation (SE) Block, the feature extraction capability of the network model is maximized. Utilizing the fault transient information, the proposed scheme can realize real‐time diagnosis of any large disturbance to the power system. The data set for scheme verification is established through simulation experiments on PSCAD/EMTDC platform, while model training is completed under the PyTorch framework. The experimental results show that the proposed fault diagnosis scheme can effectively discriminate all types of faults from non‐fault conditions in shipboard MVAC power system. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Optimal Operation Schedule Strategy of High-power Pulsed Loads in Shipboard Power System

Optimal Operation Schedule Strategy of High-power Pulsed Loads in Shipboard Power System

Modeling Shipboard Power Systems for Endurance and Annual Fuel Calculations

_ Endurance fuel calculations are used to determine the required volume of fuel tanks; annual fuel calculations are used to estimate the fuel consumed during a year of ship operations, primarily to estimate the projected cost of fuel as part of the life cycle cost estimate. These calculations depend on the fuel rates (kg/h) for different electrical and propulsion system configurations. The fuel rates in turn depend on factors, such as equipment efficiency, prime mover-specific fuel consumption curves, electrical loads, ambient temperature, propulsion loads, and the manner in which the power and propulsion systems, are operated. This paper details how to perform endurance fuel and annual fuel calculations, provides guidance for modeling system components based on data typically provided in data sheets, and provides guidance on the manner in which the power and propulsion systems are operated. Four examples are provided to illustrate the methods using the Smart Ship System Design modeling and simulation tool along with supporting spreadsheets. Keywords Marine design for ships and offshore structures; endurance; fuel efficiency; electrical efficiency; electrical system; performance prediction

The optimal allocation of H-SFCL in MVDC SPS

Medium voltage direct current shipboard power system (MVDC SPS) is the development trend of navy in the future. At present, one of the bottlenecks restricting the development of MVDC SPS is that the short fault. There is a lack of effective means to limit short fault current to protect MVDC SPS. This paper presents a method of applying a hybrid type superconducting fault current limiter (H-SFCL) to MVDC SPS protection. The architecture and system modeling of MVDC SPS are introduced, and the mechanism of bipolar DC short fault is analyzed. The topology and working principle of H-SFCL are introduced. The small-scale prototype experiment is done, the current limiting effect of H-SFCL is compared with resistive type superconducting fault current limiter (R-SFCL) and flux-coupling type superconducting fault current limiter (FC-SFCL) in the prototype test, so as to verify the superiority of H-SFCL. A dual objective hierarchical optimization configuration method is proposed, and the number and position of H-SFCLs are verified on a four-terminal system, as well as multi-objective optimization for H-SFCLs. A fault isolation and H-SFCL optimal allocation evaluation model is proposed; An improved method suitable for fault isolation and multi-objective optimal allocation of H-SFCLs is proposed to address the issue of breaking timing between internal switches in H-SFCLs and external circuit breakers in the optimization process. The research results indicate that the proposed optimal allocation method can optimize the inductance, resistance, and switch breaking time inside the current limiter, and can match the timing with the external circuit breaker; The proposed multi-objective optimization configuration method has a maximum effective individual ratio of 88% in the first 20 generations of improvement, and the improved iteration speed has significantly increased. In the 5th generation, the effective individual ratio can reach 100%.

Optimal output‐constrained control of medium‐voltage DC shipboard power systems for pulsed power load accommodation

AbstractFor pulsed power load (PPL) accommodation in a medium‐voltage DC (MVDC) shipboard power system (SPS), the charging control of energy storage systems (ESSs) and the generation control of distributed generators (DGs) need to be properly coordinated. Targeting the important but not well‐studied problem, an optimal output‐constrained control algorithm for the offline PPL accommodation strategy is presented. Three control objectives including realising the generation and charging control references, maintaining the DC bus and supercapacitor voltages within the safe operating ranges, and minimising the total generation cost of DGs, are fulfilled concurrently. First, an SPS model with multiple DGs, a supercapacitor ESS, and regular loads is developed. By restricting the DC bus and supercapacitor voltages within pre‐defined constraints, both the transient‐ and steady‐state performances of the SPS are guaranteed. Furthermore, by incorporating the cost minimisation objective into designed virtual control signals, the third control objective on energy efficiency is realised. The stability of the presented algorithm is rigorously proven based on the Lyapunov method. Finally, detailed case studies are conducted to validate the performance of the designed algorithm.

Joint Optimal Energy Management and Voyage Scheduling for Economic and Resilient Operation of All-Electric Ships Considering Safe Return

Marine power systems are isolated from external grids, making them more vulnerable than land-based power systems. When ships are sailing on the ocean, complicated maritime environment and electrical component failure pose a crucial challenge to a safe and resilient shipboard power system. Different from fixed terrestrial microgrids, all-electric ships (AES) are mobile transportation vessels, complying with the navigation regulation of safe return to port. Thus, the economic and resilient operation needs to be considered from both energy and transportation aspects. In this regard, this study proposes a two-stage coordinated optimization framework for an AES, taking into account the impact of navigation. In the first stage, the normal operation mode follows the pre-voyage plan, which jointly optimizes voyage and energy management to reduce the whole voyage operation costs and greenhouse gas emissions simultaneously. In the second stage, a resilience-oriented optimization is developed to defend against emergencies by rescheduling navigation speed and generation. Furthermore, resistance during the whole AES navigation is also considered. Numerical results demonstrate the necessity of resistance impact on the voyage and the efficiency of the proposed operation scheme in economic and resilient operation for AESs.

An investigation into the robustness of a double-ended wideband impedance-based fault location technique

The double-ended impedance-based fault location technique (DEFLT) uses the wideband frequency content of the transient generated by the fault to determine the impedance from the point of measurement to the fault. This paper evaluates and develops the DEFLT experimentally for a Shipboard Power System (SPS) to determine its robustness to source impedance, the presence of interconnected loads (“tapped” loads) and tapped lines. Results demonstrate that the estimated impedance (and therefore distance to the fault) is influenced by the presence of tapped loads when the source impedance is large, or when the tapped load is comparable to the rated load of the system. Therefore, a scheme is proposed that compensates for any tapped load without requiring any additional measurements. Using the proposed scheme, the maximum error is significantly reduced from 92 to 13%. Simulation and experimental results show that a high accuracy for the estimated fault location can be achieved.

Optimal Power Generation and Voyage Scheduling in Shipboard Power Systems Considering Load Characteristics-Based Operating Reserve Management

Optimal Power Generation and Voyage Scheduling in Shipboard Power Systems Considering Load Characteristics-Based Operating Reserve Management

High Efficiency Isolated 5-Level Dual Active DC–DC Converter Using Wide Band Gap Devices

In this paper a bidirectional isolated dc-dc converter is proposed for application in shipboard power systems. In this topology, an active 5-level T-type converter is used on the primary and secondary sides of a high-frequency transformer. The operation of the proposed converter is optimized based on minimizing power losses. For the optimization, the transformer core loss, reactive power, and rms current are considered. Wide band gap devices are used for minimization of semiconductor switching losses. A control method based on the Fourier series and decomposition theorem is proposed. The proposed converter features higher efficiency, fault tolerant capability and smaller filter size compared to the common dual active bridge dc-dc converters. To reduce voltage overshoot, a laminated dc-link is designed and a two-level turn-off method is used for operating frequencies around 75 kHz. Finally, the step-up and step-down operations of the proposed structure are verified through experiments.