A five-level single-phase inverter topology suitable for distributed power sources is experimentally verified and compared to a conventional inverter topology. The basic unit of the inverter comprises a voltage-level generator and a classical H-bridge inverter. The voltage-level generator generates positive voltage levels while the H-bridge is used to generate the zero and negative voltage levels. The utilization of the phase opposition disposition (POD) and the alternative phase opposition disposition (APOD) PWM techniques on the five-level single-phase inverter is also presented. Suitable inverter switching gate signals are derived to generate the desired five-level output waveforms. The five-level operation presented in this paper can be extended to an n-level inverter. The functionality of the proposed topology is verified via MATLAB/Simulink simulations and tested experimentally using DC power supplies as the DC voltage inputs. Finally, the circuit was also tested using photovoltaic (PV) modules as the DC voltage inputs. The proposed topology produced lower THD values as compared to the conventional topology discussed.

A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.

Posture-based plant pre-alignment is the preparation and configuration of naval power systems to tailor its performance based on multiple projections of anticipated system loading. Pre-alignment differs from alignment because it prepares power and energy systems for success in the near future, rather than just optimizing for current conditions. This method leverages the operator's intuition or foreknowledge of upcoming mission segments to enable more effective operation of a ship electrical power plant and should improve responsiveness to challenging loads, including pulsed mission systems, when the method is applied in a Navy Power and Energy System (NPES) tactical energy management controller. As with conditions of readiness for crew members, the NPES posture and alignment can proactively change to establish readiness for potential power demands based on the requirements of the mission for the current mode of operation. Preliminary experimental results of posture-based alignment, as integrated with digital twin technology, are provided and discussed. Future impact of posture-based pre-alignment on Naval applications include reduced load shedding and integration of power and energy systems to include propulsive loads and mission critical loads.

A real-time digital twin of a DC-DC boost converter is developed and verified experimentally using various load scenarios. The developed DT can be used to provide a comprehensive understanding of the system s behavior and support improved decision-making and predictive maintenance. Moreover, this digital twin can be integrated into a larger digital twin system that represents the entire power system hardware. By connecting these digital twins together, a complete digital model of the power system can be created. Results confirm the capability of the developed digital twin and its hardware to reflect the electrical behaviors of the physical twin in real-time. The maximum deviation between the digital twin and the physical twin was ±2%.

The current-carrying capacity of electric power cables has a significant effect on the total power transmitted from generation bus to the load bus. The capacity decreases as the cable temperature increases. The physics involves a positive feedback effect in which the resistance of the conductor increases as the temperature increases. Observing and predicting the thermal profile of power cables on shipboards will contribute to an efficient, reliable, and robust shipboard power system. An electro-thermal Digital Twin (DT) for predicting and observing the thermal profile of power cables is developed. The developed DT can be used to study the effect of cable temperature on power transmission. The objective of the DT will be to keep the cable temperature below its thermal rating at which deleterious effects occur. The maximum deviation between the physical and digital twin was ±0.7 °C and is well within a reasonable margin of error. Experimental results verify the capabilities of this DT which is ready for integration into larger power system digital twins.

Integrating pulsed loads to power systems requires the use of energy storage due to slow generator ramp rates. The derived challenge for these integrated systems is the control mechanism for power sharing in pulsed, transient conditions. Improvement in the system response to pulsed loads is enabled by the introduced control method, Extended Droop Control, a frequency-based load allocation technique. A rapid simulation method for Extended Droop Control is presented and used to validate load sharing in the time and frequency domains. Then, a system with pulsed and base loads with Extended Droop Control is experimentally evaluated for a naval DC power system application, and trade-offs between higher and lower cutoff frequencies of the load filter are evaluated. Simulated and experimental results of applying Extended Droop Control to this system are compared, and Extended Droop Control is found to be a suitable way to integrate energy storage and pulsed loads into a power system.

Understanding the thermal response of lithium-ion batteries is imperative to their safe operation. With investigating cooling methods in mind, an electro-thermo hardware-in-the-loop battery emulator is being developed. The emulator will reproduce both the electrical and thermal outputs of a lithium-ion battery. The coupled electrical model is developed from an electric circuit representation of lithium-ion batteries. To run this model, look up tables have been assembled from experiments to select parameters based off a battery s temperature and state of charge. For the coupled electro-thermo model, an isothermal reduced-order model has been modified to account for liquid cooling and convection. It is important to note that the current work neglects the side reactions and mixing terms of the equation as they require in-depth knowledge of the battery s specific materials and concentrations; as such, this approach is only valid for low C-rates (1C or less). The model is compared to experimental data of a Samsung 30Q 18650 battery Results show a good agreement between modeled and experimental results for the battery s electrical and thermal response. Temporal electrical and thermal response for charging and discharging are presented and discussed.

In this paper, a step-by-step solution procedure used to estimate the single-diode model parameters is proposed. The procedure is a combination of least-squares, Newtonian, and quasi- Newtonian numerical methods. Current and voltage measurements are acquired from a conventional 36-cell photovoltaic (PV) module manufactured by AMERESCO Solar. The single-diode equation was then fit to the acquired data in the least-squares sense. The developed least-squares equation is solved by two different numerical methods, the Newton-Raphson (NR) method, and Broyden’s method. Since there are five different parameters to be determined, a system of five nonlinear equations was developed and solved. The main distinction between the NR and Broyden’s algorithms is the way they handle the Jacobian matrix. The NR algorithm requires the computation of a new Jacobian matrix at every iteration. Broyden’s algorithm only requires an initial Jacobian, and then the Jacobian is updated iteratively by means of a correction formula. The functionality of the two algorithms is compared, and the five parameters extracted from each algorithm are used to simulate a 36-cell PV module. The simulation results are compared to experimental data to provide validation and to determine how accurate each procedure was in estimating the model parameters.

Current optimization methods for medium-frequency transformers (MFTs) within power electronic converters yield unrealistic results in the multiphysics framework. Comparing the optimal design to an experimental setup for a 3.5-kW MFT, the core loss is underestimated by 28%, which results in the experimental steady-state temperatures being 10 °C greater than the analytically optimized model. To counteract these disadvantages, an optimization procedure, using the aggressive space mapping (ASM) technique, is experimentally verified and compared with the previous state-of-the-art (SOA) method. It is shown that the ASM design produces more realistic and feasible experimental outcomes than the SOA design. The core losses are accurately predicted to within 10%, which, in turn, vastly improves the thermal modeling accuracy. The ASM method accurately predicts the core hot spot temperature and the average core temperature. This work also introduces a robust optimization method to the MFT design process to handle variations from both converter-level attributes and manufacturing tolerances to create a potential design region, which contains 97.725% of possible design outcomes. This method replaces the nominal design optimization that is used to produce the optimized MFTs in the SOA and ASM methods.

This paper summarizes, compares, and contrasts various modeling techniques which can be used in the notional digital twins which are under development for naval shipboard power and energy systems. The models can range from fully predetermined analytical models to fully data-driven empirical models, along with many hybrid approaches which fall between the two extremes. Hybrid approaches are of particular interest for digital twin applications as they can share benefits of both rigid analytical models and empirical models. One hybrid approach is proposed and discussed in detail as a particularly effective modeling solution. Drawbacks of the proposed approach are presented, along with further improvements which can mitigate those shortcomings.