Experimental Test bed to De-Risk the Navy Advanced Development Model

This paper presents a reduced scale demonstration test-bed at the University of Texas’ Center for Electromechanics (UT-CEM) which is well equipped to support the development and assessment of the anticipated Navy Advanced Development Model (ADM). The subscale ADM test bed builds on collaborative power management experiments conducted as part of the Swampworks Program under the US/UK Project Arrangement as well as non-military applications. The system includes the required variety of sources, loads, and controllers as well as an Opal-RT digital simulator. The test bed architecture is described and the range of investigations that can be carried out on it is highlighted; results of preliminary system simulations and some initial tests are also provided. Subscale ADM experiments conducted on the UT-CEM microgrid can be an important step in the realization of a full-voltage, full-power ADM three-zone demonstrator, providing a test-bed for components, subsystems, controls, and the overall performance of the Medium Voltage Direct Current (MVDC) ship architecture.Center for Electromechanic

A novel backup protection scheme for hybrid AC/DC power systems

This thesis presents and demonstrates (both via simulation and hardware-based tests) a new protection scheme designed to safeguard hybrid AC/DC distribution networks against DC faults that are not cleared by the main MVDC (Medium Voltage DC) link protection. The protection scheme relies on the apparent impedance measured at the AC "side" of the MVDC link to detect faults on the DC system. It can be readily implemented on existing distance protection relays with no changes to existing measuring equipment. An overview of the literature in this area is presented and it is shown that the protection of MVDC links is only considered at a converter station level. There appears to be no consideration of protecting the MVDC system from the wider AC power system via backup - as would be the case for standard AC distribution network assets, where the failure of main protection would require a (usually remote) backup protection system to operate to clear the fault. Very little literature considers remote backup protection of MVDC links.;To address this issue, the research presented in this thesis characterises the apparent impedance as measured in the neighbouring AC system under various DC fault conditions on an adjacent MVDC link. Initial studies, based on simulations, show that a highly inductive characteristic, in terms of the calculations from the measured AC voltages and currents, is apparent on all three phases in the neighbouring AC system during DC-side pole-to-pole and pole-poleground faults. This response is confirmed via a series of experiments conducted at low voltage in a laboratory environment using scaled down electrical components. From this classification, a fast-acting backup protection methodology, which can detect pole-to-pole and pole-poleground faults within 40 ms, is proposed and trialled through simulation. The solution can be deployed on distance protection relays using a typically unused zone (e.g. zone 4).;New relays could, of course, incorporate this functionality as standard in the future. To maximise confidence and demonstrate the compatibility of the solution, the protection scheme is deployed under a real-time hardware-in-the-loop environment using a commercially available distance protection relay. Suggestions to improve the stability of the proposed solution are discussed and demonstrated. Future areas of work are identified and described. As an appendix, early stage work pertaining to the potential application and benefits of MVDC is presented for two Scottish distribution networks. The findings from this are presented as supplementary material at the end of the thesis.This thesis presents and demonstrates (both via simulation and hardware-based tests) a new protection scheme designed to safeguard hybrid AC/DC distribution networks against DC faults that are not cleared by the main MVDC (Medium Voltage DC) link protection. The protection scheme relies on the apparent impedance measured at the AC "side" of the MVDC link to detect faults on the DC system. It can be readily implemented on existing distance protection relays with no changes to existing measuring equipment. An overview of the literature in this area is presented and it is shown that the protection of MVDC links is only considered at a converter station level. There appears to be no consideration of protecting the MVDC system from the wider AC power system via backup - as would be the case for standard AC distribution network assets, where the failure of main protection would require a (usually remote) backup protection system to operate to clear the fault. Very little literature considers remote backup protection of MVDC links.;To address this issue, the research presented in this thesis characterises the apparent impedance as measured in the neighbouring AC system under various DC fault conditions on an adjacent MVDC link. Initial studies, based on simulations, show that a highly inductive characteristic, in terms of the calculations from the measured AC voltages and currents, is apparent on all three phases in the neighbouring AC system during DC-side pole-to-pole and pole-poleground faults. This response is confirmed via a series of experiments conducted at low voltage in a laboratory environment using scaled down electrical components. From this classification, a fast-acting backup protection methodology, which can detect pole-to-pole and pole-poleground faults within 40 ms, is proposed and trialled through simulation. The solution can be deployed on distance protection relays using a typically unused zone (e.g. zone 4).;New relays could, of course, incorporate this functionality as standard in the future. To maximise confidence and demonstrate the compatibility of the solution, the protection scheme is deployed under a real-time hardware-in-the-loop environment using a commercially available distance protection relay. Suggestions to improve the stability of the proposed solution are discussed and demonstrated. Future areas of work are identified and described. As an appendix, early stage work pertaining to the potential application and benefits of MVDC is presented for two Scottish distribution networks. The findings from this are presented as supplementary material at the end of the thesis

Comparisons of MVAC and MVDC systems in dynamic operation, fault protection and post-fault restoration

One of the most significant obstacles preventing the large-scale application of direct-current (DC) technology in medium voltage (MV) distribution networks is their fault protection. The existing AC relay protection needs to be changed or redesigned to protect the future overlay MVAC and MVDC distribution networks. Therefore, a comprehensive understanding of the dynamic and fault behavior and post-fault restoration strategies of MVAC and MVDC systems are critically important. Moreover, a comparison of MVAC and MVDC systems during a fault will also contribute to designing the protection systems of hybrid MV AC/DC systems. In this paper, the challenges of protecting DC faults of MVDC systems and possible solutions are first introduced. Then, the fault characteristics and post-fault restoration of MVDC and MVAC distribution systems are compared and investigated through case studies. Time-domain simulations have been conducted in PSCAD/EMTDC. The work in this paper will be valuable for the protection design for future hybrid MV AC/DC systems

Protection and Disturbance Mitigation of Next Generation Shipboard Power Systems

Today, thanks to modern advances mainly in the power electronics field, megawatt-level electric drives and magnetic levitation are being integrated into the marine power grids. These technologies operate based on Direct Current (DC) power which require Alternating Current (AC) to DC conversion within the current grid. Medium-voltage Direct Current (MVDC) and Flywheel Energy Storage Systems (FESS) are the next state-of-the-art technologies that researchers are leaning on to produce, convert, store, and distribute power with improved power quality, reliability, and flexibility. On the other hand, with the extensive integration of high-frequency power electronic converters, system stability analysis and the true system dynamic behaviors assessment following grid disturbances have become a serious concern for system control designs and protection. This dissertation first explores emerging shipboard power distribution topologies such as MVDC networks and FESS operation with charge and discharge dynamics. Furthermore, the important topic of how these systems perform in dynamic conditions with pulsed power load, faults, arc fault and system protection are studied. Secondly, a communication-based fault detection and isolation system controller that improves upon a directional AC overcurrent relay protection system is proposed offering additional protection discrimination between faults and pulsed-power Load (PPL) in MVDC systems. The controller is designed to segregate between system dynamic short-circuit fault and bus current disturbances due to a PPL. Finally, to validate the effectiveness of the proposed protection controller, different bus current disturbances are simulated within a time-domain electromagnetic transient simulation of a shipboard power system including a PPL system operating with different ramp rate profiles, pulse widths, peak powers, and fault locations. This overarching goal of this work is to address some of the critical issues facing the US Navy as warfighter mission requirements increase exponentially and move towards advanced and sophisticated pulsed power load devices such as high energy weapon systems, high energy sensor and radar systems. The analyses and proposed solutions in this dissertation support current shipbuilding industry priorities to improve shipboard power system reliability and de-risk the integration of new power system technologies for next generation naval vessels

Control and Optimization of Energy Storage in AC and DC Power Grids

Energy storage attracts attention nowadays due to the critical role it will play in the power generation and transportation sectors. Electric vehicles, as moving energy storage, are going to play a key role in the terrestrial transportation sector and help reduce greenhouse emissions. Bulk hybrid energy storage will play another critical role for feeding the new types of pulsed loads on ship power systems. However, to ensure the successful adoption of energy storage, there is a need to control and optimize the charging/discharging process, taking into consideration the customer preferences and the technical aspects. In this dissertation, novel control and optimization algorithms are developed and presented to address the various challenges that arise with the adoption of energy storage in the electricity and transportation sectors. Different decentralized control algorithms are proposed to manage the charging of a mass number of electric vehicles connected to different points of charging in the power distribution system. The different algorithms successfully satisfy the preferences of the customers without negatively impacting the technical constraints of the power grid. The developed algorithms were experimentally verified at the Energy Systems Research Laboratory at FIU. In addition to the charge control of electric vehicles, the optimal allocation and sizing of commercial parking lots are considered. A bi-layer Pareto multi-objective optimization problem is formulated to optimally allocate and size a commercial parking lot. The optimization formulation tries to maximize the profits of the parking lot investor, as well as minimize the losses and voltage deviations for the distribution system operator. Sensitivity analysis to show the effect of the different objectives on the selection of the optimal size and location is also performed. Furthermore, in this dissertation, energy management strategies of the onboard hybrid energy storage for a medium voltage direct current (MVDC) ship power system are developed. The objectives of the management strategies were to maintain the voltage of the MVDC bus, ensure proper power sharing, and ensure proper use of resources, where supercapacitors are used during the transient periods and batteries are used during the steady state periods. The management strategies were successfully validated through hardware in the loop simulation

A review of power electronics equipment for all-electric ship MVDC power systems

Medium Voltage DC (MVDC) distribution Power Systems for all-electric ships (AES) can be regarded as functionally composed of three subsystems, namely the power sources, the load centers and the distribution network. Extensive use of power electronics is required for connecting power sources and load centers to the MVDC bus and for protecting the MVDC power system through properly placed DC circuit breakers. In this paper, an overview is given of the power electronics equipment found in the literature and on the market that could be suitable for use in future AES MVDC power systems. Some industrial experiences regarding DC generator systems, energy storage apparatus and solid-state DC circuit breaker prototypes are reported in the paper as examples of state-of-the-art realizations. Different DC/DC converters, which can be employed as solid-state transformers, are also discussed and a structure obtained by combining them is proposed

Resistive Solid State Protective Device

Abstract: This thesis describes and explains different fault to characterize fault specifically for DC distribution systems and DC Microgrids fed by synchronous generators. This will result in a testbed for static and intermittent line-to-line faults, and in future work, various types of ground faults. Automaton allows for repeated testing at various voltage levels and precise control over intermittent fault generation. The fault generator is implemented with an IGBT H-bridge topology. Its physical implementation and benefits are described. Experimental results are shown for static line-to-line fault. This testbed will be used to help develop closed-form expressions. Once fault currents are characterized and closed-form expressions are made, adequate protection systems can be designed. finally, this paper will include the simulation and experimental results of line-to-line fault characterization with a DC smoothing capacitor, and intermittent faults of various times

Next-Generation Shipboard DC Power System: Introduction Smart Grid and dc Microgrid Technologies into Maritime Electrical Networks

In recent years, evidence has suggested that the global energy system is on the verge of a drastic revolution. The evolutionary development in power electronic technologies, the emergence of high-performance energy storage devices, and the ever-increasing penetration of renewable energy sources (RESs) are commonly recognized as the major driving forces of the revolution. The explosion in consumer electronics is also powering this change. In this context, dc power distribution technologies have made a comeback and keep gaining a commendable increase in research interest and industrial applications. In addition, the concept of flexible and smart distribution has also been proposed, which tends to exploit distributed generation and pack together the distributed RESs and local electrical loads as an independent and self-sustainable entity, namely a microgrid. At present, research in the area of dc microgrids has investigated and developed a series of advanced methods in control, management, and objective-oriented optimization that would establish the technical interface enabling future applications in multiple industrial areas, such as smart buildings, electric vehicles, aerospace/aircraft power systems, and maritime power systems