Angelo L. Gattozzi

A DC Arc Model for Series Faults in Low Voltage Microgrids

This paper presents a dc arc model to simplify the study of a critical issue in dc microgrids: series faults. The model is derived from a hyperbolic approximation of observed arc voltage and current patterns, which permit analyzing the arc in terms of its resistance, power, energy, and quenching condition. Recent faults staged by the authors on a dc microgrid yielded enough data to develop an arc model for three fault types: constant-gap speed, fixed-gap distance, and accelerated gap. The results in this paper compare experimental and simulation results for the three fault types. It is concluded that because the instantaneous voltage, current, power, and energy waveforms produced by the model agree well with experimental results, the model is suitable for transient simulations.

Operational characteristics of a flux pump

The mechanism of switching that is taking place in a moving flux spot in a superconducting foil has been investigated in details. The structure of the current, temperature and magnetic field in the leading edge of the spot has been derived theoretically. The resulting distributions for these field variables have then been used to estimate the effective inductance and resistance of the spot. These parameters allow the determination of an equivalent electric circuit for the flux pump as an electric generator. The ratio of the inductance to the resistance of the spot decreases with the inverse square of the velocity for small velocities. On the other hand, the external current generated by the flux pump first increases with the velocity, it then reaches a maximum and eventually decreases inversely with the velocity. Design parameters, such as efficiency and dependence of the output current on the velocity for the pump, have been evaluated. These theoretical predictions were found to be verified by experimental observations which are also presented in this paper.

Flexible test bed for MVDC and HFAC electric ship power system architectures for Navy ships

Several power architectures have been considered for Navy ships and significant effort has been focused on simulation of the various power system topologies. The University of Texas at Austin Center for Electromechanics (UT-CEM) has taken a step forward by assembling a microgrid capable of operating at MW power levels to experimentally validate key elements of these system models. The present system is an MVDC architecture but can easily be reconfigured as an HFAC network. This paper describes the UT-CEM microgrid and plans to demonstrate critical technical issues in naval power systems and enable model validation. The intent is for the microgrid to be a flexible test bed for investigation of naval power systems and to become a useful bridge from theoretical and computer studies to a realistic experimental platform.

A 2-MW Motor And ARCP Drive for High-Speed Flywheel

A high-speed induction motor and soft-switching electronic drive are selected to transfer energy between a flywheel and the other power components of a prototype hybrid locomotive power system. The motor-generator operates in direct coupling at 15,000 RPM with the composite flywheel. The motor drive rating is 2MW (2600HP) over the operating frequency range of 125 to 250 Hz. The power-frequency range and harmonic heating considerations have led to an auxiliary resonant commutated pole (ARCP) soft-switching design. The drive and motor have been tested to nearly the full speed range. Unique requirements of energy storage and transfer are also presented.

Applications of an Auxiliary Resonant Commutated Pole Converter

The Auxiliary Resonant Commutated Pole Converter (ARCP) utilizes an auxiliary resonance circuit to enable zero voltage turn on in the main circuit and maintain zero current turn off in the auxiliary circuit. The ARCP converter can therefore be designed with snubbers that are undersized for the power rating of the switches. Another advantage of the ARCP converter is that it can be driven by a PWM control source. This paper discusses some concepts that need consideration in order to operate an ARCP converter with undersized snubber circuits and standard PWM sources. It also discusses the need to coordinate the voltage supply and the load current for successful commutation. Test data is presented related to these issues.

Large scale simulations of a ship power system with energy storage and multiple directed energy loads

A large scale Simulink simulation model of the electrical power system of a ship is described. The model includes the major systems onboard, from prime movers to the actual loads, and incorporates several intermittent duty loads along with continuous duty loads. Three types of energy storage systems have been modeled: flywheels, batteries, and capacitors. Therefore, critical issues like stability, reconfigurability, fault management, and minimum rating of energy storage units can be studied. The presence of energy storage has also allowed the study of how these systems can be used to improve the overall performance of the ship. Typical functions, for example, would include load leveling of the power bus, an uninterruptible power supply function for sections of the ship, and the potential for fuel efficiency improvement by reducing the number of turbines being run at fractional loads to fewer being run closer to their optimal specific fuel efficiency point. Typical outputs of the simulations are presented and discussed. In addition, several challenges presented by the scale of the simulations, the software platform used, and the underlying modeling philosophy are discussed with an outlook toward future improvements both in the computing hardware and in the programming methods.

Challenges in the design of a 100 kw induction motor for a PHEV application

This paper summarizes some design challenges encountered in the development of a high speed induction motor/generator for a plug-in hybrid electric vehicle (PHEV). The traction system motor/generator was developed for integration into a high performance full-sized passenger car being developed by a major automotive manufacturer. The paper summarizes the traction motor performance requirements and presents the electromagnetic, mechanical and thermal design issues of the high speed 100 kW peak power induction machine.

Power system and energy storage models for laser integration on naval platforms

High power solid state laser systems are being developed for advanced weapons and sensors for a variety of Department of Defense applications including naval surface combatants. The transient power and cooling requirements of these emerging technologies present significant challenges to the electric power distribution and thermal management systems, particularly for applications requiring back fit of the new systems onto existing platforms with limited electric power generation and cooling capacities. The University of Texas Center for Electromechanics (UT-CEM) and the Naval Postgraduate School (NPS) have collaborated in the development of simulation models of ship power systems to evaluate and help guide the integration of pulsed laser loads onto existing ship platforms. Key to the success of these efforts is the definition of a suitable energy storage system to handle the effect of the transient load. This paper reports on the progress of detailed MatLab/Simulink models of a destroyer class ship service electric power distribution system that have been developed to evaluate the performance of battery, flywheel, and capacitor energy storage in support of laser weapons. The models allow the user to develop comparative studies of the three energy storage systems in regard to several relevant metrics that can be used for their discrimination. Examples of some of these results based on the simulations are given.

Analysis of the Power Quality Impact of Multiple Directed Energy Loads on an Electric Ship Power System

The electrical power system of an all-electric ship has been modeled in Simulink for the case of a ship supporting several high power directed energy loads, among which are a Free Electron Laser (FEL), an Active Denial System (ADS), and a Laser Weapon System (LaWS). Starting from a load centered approach, and a physical description of the components of the various loads, individual models of each load plus a combined model for a system supporting simultaneously one instance of all loads have been developed. Sample case studies are presented corresponding to expected operational scenarios for a US Navy ship and to potential emergency conditions. The models have been designed to be interactive, allowing the operator to change key settings dynamically while the simulation is running, thus mimicking an actual operation of the power system on a ship in real time. A preliminary graphical user interface has also been developed to demonstrate the ability of these models to be converted into top-level training tools for Navy personnel supported by a realistic representation of the ship power system.

Experimental results and design guidelines derived from the testing of a 2 MW, 250 Hz, auxiliary resonant commutated pole bi-directional converter

An auxiliary resonant commutated pole (ARCP) converter, rated for an output of 2 MW at 250 Hz, has been built and has undergone preliminary tests at the University of Texas at Austin Center for Electromechanics (UT-CEM). Experimental results are reported on its testing as the bi-directional link between a power DC bus and a flywheel energy storage system. Design issues encountered in the course of development of the converter and the system are discussed and some considerations are made regarding the application of soft-switching ARCP-type converters versus their hard-switched counterpart.