Rob Hovsapian

Cross-platform validation of notional baseline architecture models of naval electric ship power systems

To support efforts in assessing the relative merit of alternative power system architectures for future naval combatants, the Electric Ship Research and Development Consortium (ESRDC) has developed notional baseline models for each of the primary candidate architectures currently considered, medium-voltage DC (MVDC), conventional 60 Hz medium-voltage (MVAC), and high-frequency medium-voltage (HFAC). Initial efforts have focused on the development of a consistent set of component models, of which the system models can be comprised, and the basic definition of the system models. The broader objectives of the consortium, however, go beyond the definition of the baseline models. The focus is on the process by which the models are implemented in software and validated, the process by which the performance of the disparate system models are objectively and quantitatively assessed and compared, and, ultimately, the process by which the relative merits of the architectures may be assessed. This paper focuses specifically on cross-platform component validation.

Notional all-electric ship thermal simulation and visualization

The impact of unpredicted or unplanned thermal disturbances on any future all-electric ship may well lead to unexpected and untimely failure of mechanical-electrical systems (e.g., power electronics, high power sensors, and pulsed weapons) to the detriment of the ships combat mission. The high power, rapid transients, and harsh environment expected to be imposed on both the electrical and thermal systems may well be unique to this class of ship. In order to develop the thermal analysis, a comprehensive visualization tool to display the temperature and heat dissipation distributions in the entire ship has been developed. This tool includes a simplified physical model, which combines principles of classical thermodynamics and heat transfer, resulting in a system of three-dimensional differential equations which are discretized in space using a three-dimensional cell centered finite volume scheme. Therefore, the combination of the proposed simplified physical model with the adopted finite volume scheme for the numerical discretization of the differential equations is called a volume element model (VEM). In this work, a 3D simulation is performed in order to determine the temperature distribution inside the ship for six different operating conditions. Visit visualization tool is used to plot the results.

Notional all-electric ship systems integration thermal simulation and visualization

This work presents a simplified mathematical model for fast visualization and thermal simulation of complex and integrated energy systems that is capable of providing quick responses during system design. The tool allows for the determination of the resulting whole system temperature and relative humidity distribution. For that, the simplified physical model combines principles of classical thermodynamics and heat transfer, resulting in a system of three-dimensional (3D) differential equations that are discretized in space using a 3D cell-centered finite volume scheme. As an example of a complex and integrated system analysis, 3D simulations are performed in order to determine the temperature and relative humidity distributions inside an all-electric ship for a baseline medium voltage direct current power system architecture, under different operating conditions. A relatively coarse mesh was used (9410 volume elements) to obtain converged results for a large computational domain (185m×24m×34m) containing diverse equipment. The largest computational time required for obtaining results was 560 s, that is, less than 10 min. Therefore, after experimental validation for a particular system, it is reasonable to state that the model could be used as an efficient tool for complex and integrated systems thermal design, control and optimization.

Temperature and Pressure Drop Model for Gaseous Helium Cooled Superconducting DC Cables

The need to transfer large amounts of power in applications where cabling weight and space are a major issue has increased the interest in superconducting cables. Gaseous helium and neon are being considered as possible coolants due to their suitability for the expected operating temperature ranges. Gaseous helium is preferred due to its higher thermal conductivity and relatively lower cost than neon. This paper enhances a previously presented mathematical model of a superconducting cable contained in a flexible cryostat by including flow pressure drops. In this way, the model is capable of properly sizing and minimizing fan power, and allows the prediction of system response to localized heating events (e.g., quenching). A volume element model approach was used to develop a physics model, based on fundamental correlations, and principles of classical thermodynamics, mass and heat transfer, which resulted in a system of ordinary differential equations with time as the independent variable. The spatial dependence of the model is accounted for through the three-dimensional distribution of the volume elements in the computational domain. The model numerically obtains the temperature distribution under different environmental conditions. Pressure drop calculations are based on realistic correlations that account for the wavy nature of the coolant channels. Converged solutions were obtained within the imposed numerical accuracy even with coarse meshes.

Thermal Modeling of Helium Cooled High-Temperature Superconducting DC Transmission Cable

The recent increase in distributed power generation is highlighting the demand to investigate and implement better and more efficient power distribution grids. High-temperature superconducting (HTS) DC transmission cables have the potential to address the need for more efficient transmission and their usage is expected to increase in the future. Thermal modeling of HTS DC cables is a critical tool to have in order to better understand and characterize the operation of such transmission lines. This paper introduces a general computational model for a HTS DC cable. A physical model, based on fundamental correlations and principles of classical thermodynamics, mass and heat transfer, was developed and the resulting differential equations were discretized in space. Therefore, the combination of the physical model with the finite volume scheme for the discretization of the differential equations is referenced as Volume Element Model, (VEM). The model accounts for heat transfer by conduction, convection and radiation obtaining numerically the temperature distribution of superconductive cables operating under different environmental, operational and design conditions. As a result, the model is expected to be a useful tool for simulation, design, and optimization of HTS DC transmission cables.

Modeling and Simulation of the Thermal and Psychrometric Transient Response of All-Electric Ships, Internal Compartments and Cabinets

We introduce a general computational model for all-electric ships and internal compartments (open and closed domains) that contain heat sources and sinks. A simplified physical model, which combines principles of classical thermodynamics and heat transfer, is developed and the resulting three-dimensional (3D) differential equations are discretized in space using a 3D cell-centered volume element scheme. The combination of the proposed simplified physical model with the adopted finite volume scheme for the numerical discretization of the differential equations is therefore called a volume element model (VEM). Two case studies are presented: a simulation of a whole ship at sea, and one of the ships internal compartments (or cabinet). The proposed model was utilized to simulate numerically the steady-state responses of the systems in both cases. Of particular interest in the first case is the possibility of predicting the ships thermal signature at sea. Mesh refinements were conducted to ensure the convergence of the numerical results. The converged mesh in both cases was relatively coarse (175 and 320 cells) and therefore the solutions were obtained with low computational time. Since accuracy and low computational time are combined, the model is shown to be efficient and could be used as a tool for simulation, design and optimization of thermal management of all-electric ships, internal compartments and cabinets. Finally, experiments are conducted in a test-bed facility to demonstrate, from simulated sea conditions, how to quantify the electric motors transient heat rejection to cooling water and the environment in a notional all-electric ship, with the objective of serving as known heat generation inputs to the mathematical model to simulate the transient thermal response of the entire ship and its compartments.

Dynamic modeling of adjustable-speed pumped storage hydropower plant

Hydropower is the largest producer of renewable energy in the U.S. More than 60% of the total renewable generation comes from hydropower. There is also approximately 22 GW of pumped storage hydropower (PSH). Conventional PSH uses a synchronous generator, and thus the rotational speed is constant at synchronous speed. This work details a hydrodynamic model and generator/power converter dynamic model. The optimization of the hydrodynamic model is executed by the hydro-turbine controller, and the electrical output real/reactive power is controlled by the power converter. All essential controllers to perform grid-interface functions and provide ancillary services are included in the model.

Real time optimal control of supercapacitor operation for frequency response

Supercapacitors are finding wider applications in modern power systems due to a controllable fast dynamic response. Use of power electronically interfaced supercapacitors for frequency support is a proven technique. In practical applications the heat generated from the Equivalent Series Resistance (ESR) can significantly reduce the life of supercapacitor. Hence thermal issues must be addressed for optimal operation. It is infeasible to use traditional optimization control methods to mitigate the impacts of frequent cycling due to the lack of active thermal management. This paper proposes a Front End Controller (FEC) using Generalized Predictive Control based on real time receding optimization. The constraints in the optimization are based on thermal management to enhance the efficiency of utilization life of the supercapacitors. A rigorous mathematical derivation is provided and supporting simulation results are obtained using Real Time Digital Simulator to demonstrate the effectiveness of the proposed technique.

Potential for Plug-In Electric Vehicles to provide grid support services

Since the introduction of Plug-in Electric Vehicles (PEVs), scientists have proposed leveraging PEV battery packs as distributed energy resources for the electric grid. PEV charging can be controlled not only to provide energy for transportation but also to provide grid services and to facilitate the integration of renewable energy generation. With renewable generation increasing at an unprecedented rate, most of which is non-dispatchable and intermittent, the concept of using PEVs as controllable loads is appealing to electric utilities. If incentivized suitably, this could serve as an additional driver for PEV adoption. It has been widely proposed that PEVs can provide valuable grid services, such as load shifting to provide voltage and frequency regulation. The objective this work is to address the degree to which PEVs can provide grid services and mutually benefit the electric utilities, PEV owners, and auto manufacturers.

Synchronous generator stabilization by thyristor controlled supercapacitor energy storage system

A thyristor-controlled supercapacitor energy storage (SES) system is proposed in this work to improve the transient stability of a synchronous generator located in a power network. To check how effective the proposed SES in augmenting the transient stability of the generator is, its performance is compared to that of a thyristor-controlled superconductive magnetic energy storage (SMES) system. Both symmetrical and unsymmetrical faults are considered in the power network. Simulation results demonstrate the effectiveness and validity of the proposed method in enhancing the transient stability of the synchronous generator. Moreover, the performance of proposed SES is found to be better than that of SMES. Overall, it can be inferred that the proposed thyristor-controlled SES technique provides a simple and effective means of transient stability improvement of synchronous generator.