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Sustainable Grid Integration of Distributed and Renewable Resources

1.  Design of Multiple-input Converters for Integration of Diverse Distributed Generation SourcesProf. Alexis Kwasinski

One of the main barriers for increased use of renewable energy sources is their variability and low availability (e.g., in the extreme ideal case of a place where clouds do not form, solar power is available on average 50 % of the time).  One identified approach that mitigates individual renewable energy source variability in order to provide a more continuous power supply is by diversifying energy sources through hybrid systems that combine two or more types of sources.  However, in these hybrid systems there is always a tradeoff between higher power electronic interface availability—achieved through modular redundant configurations—and lower cost—achieved through a single center converter.  The PI has shown that multiple-input converters can achieve availabilities equivalent to those obtained from modular single input converters, but at a cost in between that found in center converters and in modular single-input converters.  Multiple-input converters are built from their single-input version by multiplying their input stage and sharing the output stage.  Multiple-input converters provide not only high availability, but they also provide a more effective way of integrating renewable sources. For example, multiple-input converters allow for individual maximum power point tracking in each photovoltaic module, which otherwise would be limited to the output of the solar panel by the array component with the worst performance.  Therefore, the goal of this project is to study multiple-input dc-dc converters, with special focus on integrating energy storage and improving efficiency.

2.  Data Collection Framework for Home Energy Management SystemsProf. Alexis Kwasinski, Prof. Robert Hebner

One of the envisioned advantages of smart grid technology development is the creation of a more customer-oriented electric power environment.  Arguably, the critical component within this customer centric environment that allows more effective interactions between the power supply (i.e., utility) side and the power point-of-use (i.e., user loads) side is the Home Energy Management System (HEMS).  The HEMS acts as a communication portal and electric management interface between the distribution side of the smart grid and the user’s home or business power installation.  Thus, the HEMS collects and processes data both from the utility, such as pricing information, and from local electric devices at the user premises, such as local energy storage levels, or expected consumption needs from loads, such as smart air conditioners or electric vehicles.  The goal of this research project is to explore HEMS data collection needs on the customer side of a smart grid by identifying which data to collect, how to collect it and where to measure it.  For example, one of the questions to be addressed is what is the optimal sampling rate?  Another relevant question to be investigated is can fewer points be measured and can that information be used to infer behavior for the rest of the system? This project is intended to support standards development and evaluation as part of the Pecan Street Project.

3.  Dynamic Availability Estimator for Smart Grid Systems with Energy StorageProf. Alexis Kwasinski

Some of the expected advantages of smart grids include higher power availability, higher penetration of distributed renewable energy generation sources, and an increased electrification of the transportation sector.  Energy storage devices, and in particular batteries, have been identified as an important enabling technology necessary to achieve the benefits of smart grids.  However, high costs have impeded penetration of energy storage, particularly at the consumer level, in homes, and in electric vehicles (EVs).  One of the factors that create high costs of energy storage (especially batteries) is their relatively short life, which depends on both their operation (e.g., cycling frequency and depth of discharge) and on environmental conditions (e.g., temperature).  The goal of this research project is to develop a dynamic availability estimator (DAE) that could be integrated within a home energy management system (HEMS) or an EV controller.  The DAE collects operational and environmental data that is used to adjust failure and repair rates in a system availability model embedded within the DAE.  This availability model is used for real-time evaluation of a home or EV energy system availability.  The availability information yielded by the DAE can then be used by the HEMS or the EV controller in order to operate its energy system in a way that maximizes the life of energy storage devices.  It is expected that a DAE can reduce energy storage life cycle cost as much as 10 to 20 percent.

4.  Direct Current Power Architectures for Residential and Commercial Smart Grid ApplicationsProf. Alexis Kwasinski, Prof. Ross Baldick, Prof. Robert Hebner

This research work aims at studying power quality, efficiency, stability, and control issues in dc distribution power architectures for homes or commercial facilities.  Direct current supplied by relatively low-power generators to loads located nearby was the technology chosen in the first power distribution systems in the early part of the 20th century.  Yet, dc-based power distribution architectures were soon overshadowed by ac systems.  Some of the fundamental reasons why ac prevailed over dc for power distribution systems were that ac power supply was better suited for feeding induction motors, and that voltage transformation was significantly simpler with ac, so that longer distance transmission necessitated ac.  As a result of these advantages, ac power has been the standard for power transmission and distribution for the last 120 years.  However, the advent of power electronics interfaces used to convert dc power has altered the ac paradigm for distribution.  Presently, dc power distribution architectures are more suitable to integrate alternative and renewable distributed generation (DG) technologies, such as fuel cells and photovoltaic (PV) modules, with more efficient loads, such as LED lights and motors with variable-speed drives (VSD).  Dc distribution can be a suitable choice in many applications, particularly because modern electronic loads are inherently dc.  One such application is in residences.  Use of dc distribution in houses allows using more efficient dc lighting fixtures and more efficient air conditioning systems driven with variable speed drives and is possibly a simpler interface for plug-in electric vehicles. Moreover, operation of dc power architectures became transparent to the grid as a dc home will interface with a grid through a rectifier/inverter.  Since the interface between the utility side and the customer side of a dc power architecture is controllable, both the grid and its connected inherent dc systems can benefit from the flexibility provided by the independent control at the grid tie point.  However, questions persist in terms of stability issues caused by constant-power loads and power quality/harmonic control properties of dc power architectures. The goal of this research is to address these issues.

5.  Grid Interaction and ControlProf. Surya. Santoso

Short-term and long term voltage variations, including voltage fluctuations caused by the intermittent nature of wind and PV generators, are projected to increase substantially over the next decade and beyond.  The PI will quantify the magnitudes and temporal profiles of voltage variations and their impacts on sensitive loads.  These variations will be dependent on the amount of load and generation, the architecture of the microgrid, voltage regulation apparatus (including capacitor banks), and the control of intermittent generators.   A novel voltage regulation coordination scheme specific to a microgrid with a high penetration of renewable energy sources will be developed.  This system will coordinate local and remote bus voltage regulation using both generator and microgrid control mechanisms.  Current practices lack this coordination and often lead to situations in which controllers’ actions conflict with each other.  The research will consider optimum placement for line regulators and capacitor banks to enable control of local and remote bus voltages, as well as reactive power support.  Algorithms for microgrids and generators will be developed and coordinated with and without direct communication links.  The frequency of microgrid short-circuits is expected to experience a significant diurnal variation that scales with the total amount of energy produced.  Unpredictable variability in short-circuit levels poses serious challenges for coordination of overcurrent protection .  Bidirectional power flows complicate utility protection and coordination processes, such as fault-clearing and reclosing.  We will address this problem by developing algorithms that estimate the short-circuit contribution of distributed generation units directly connected to the grid.  The interaction of various sources, switches, and loads within a microgrid will be explored via modeling and simulation of these complex systems and validated using microgrid test facilities at UT-Austin, as well as infrastructure set up by the Pecan Street Project.

6.  Distribution System Design and ControlProf. Mack Grady

In the electric power distribution systems of the future, customers will no longer operate as passive loads, but will instead utilize controllers that perform day-ahead energy planning to minimize net kWh or net electricity purchase costs. The customer will receive new forms of information, such as solar radiation, weather forecasts, projected hourly kWh price curves, and occasional distress signals from the utility to reduce load.   Distribution systems will have to contend with this two-way power flow and be able to adapt their planning, operation, and optimization of the system.  With the proliferation of electronic metering, there will be hundreds of monitoring points on each feeder capable of reporting voltage levels and power usage. Once customers can inject power onto the feeder on a regular basis, the complexity of operating distribution feeders will increase greatly.  The intermittent nature of PV generation caused by cloud movement presents a particularly serious voltage flicker threat.  In part because UT-Austin maintains the solar radiation data base for NREL and Austin Energy, the Electric Power Research Institute (EPRI) is beginning a study at UT-Austin with the PI to assess the impact of high penetration levels of PV on distribution and transmission systems, including the potential significance of voltage flicker.

7.  Advanced Energy Storage SystemsProf. Arumugam Manthiram, Prof. Jeremy Meyers

Electrochemical energy storage devices, such as batteries and electrochemical capacitors, are the leading EES technologies, but current EES technologies cannot meet the full set of requirements for commercial, residential, and transportation applications. Substantial increases in energy and power densities, reduction in system cost, and improvement in durability and reliability are needed to realize the full potential of EES technologies for these applications. The difficulties are largely associated with severe materials challenges and complex system issues. A fundamental understanding of the complex atomic and molecular processes that govern performance and durability will enable the design and development of new materials, cell designs, and system concepts that can meet future energy storage requirements. The energy storage team has diverse expertise ranging from materials development to system design/integration to implementation in vehicles or grids. The team also has the capability to fabricate an EES system with the new materials developed and then to demonstrate the EES system in a vehicle or stationary power unit.

8.  Lithium Ion Batteries – Prof. Arumugam Manthiram, Prof. Jeremy Meyers, Prof. Buddie Mullins

Building on UT-Austin’s existing strength and leadership in the lithium-ion battery area, our approach will be to develop new materials and novel system designs that can increase energy and power, improve safety and durability, and lower the cost so that the lithium-ion technology will be viable for transportation and stationary applications.  We will focus on the design, chemical synthesis, advanced characterization, and electrochemical evaluation of new low-cost, better-performing cathode and anode materials.  Specifically, high capacity layered oxides, high-voltage spinel oxides, nanostructured olivine phosphates as well as nanocomposites of layered spinel oxide offer a combination of high energy and power and will be pursued as cathode hosts. Nanostructured alloys and oxides as well as their nanocomposites will be pursued as anode hosts.  Selected properties such as Li+ ion transport and capacity of novel transition metal carbides will be screened and their feasibility as next generation anode hosts will be assessed. The causes of degraded performance will be examined in terms of material and composite layer characterization at the beginning and end of battery life (>105 charge/discharge cycles). By quantifying the sources of degraded performance and developing mitigation strategies, the range and utility of the batteries may be extended closer to their theoretical limits (full capacity or energy).

9.  Flow BatteriesProf. Jeremy. Meyers, Prof. Arumugam Manthiram

Rechargeable batteries offer a simple and efficient way to store electricity, but battery development to date has largely focused on smaller scale systems for portable power or intermittent backup power. Metrics related to size and volume, such as energy and power densities, are less critical for grid storage than in portable or transportation applications. Batteries for large-scale grid storage instead require durability for large numbers of charge/discharge cycles as well as calendar life, high round-trip efficiency, an ability to respond rapidly to changes in load or input, and reasonable capital costs.  Battery technologies are under development for such large-scale storage devices such as high-temperature batteries and redox flow batteries of various chemistries. Flow batteries are particularly promising for stationary power applications because there is no solid-phase electrode reaction.  Reactants can be carried to and from the site of charge-transfer rapidly, and convective pumping can be employed to replenish the interface for charge transfer.  Further, because the electrode does not participate in the reaction other than as a source or sink for electrons, morphological changes and degradation are not expected with repeated cycles. The electrolyte also can be stored separately from the cell, which allows for energy and power to be selected independently for specific applications.   Researchers will identify inexpensive, reversible electrochemical couples that offer sufficiently large cell voltage. They will also focus on understanding electrolyte/membrane interactions, designing new, low-cost membranes, optimizing electrode utilization, and minimizing external pumping and control requirements.

10.  Electrochemical CapacitorsProf. Rod Ruoff

While the energy density of ECs is lower than that of batteries, they provide an important advantage of fast charge-discharge rates with higher power density and longer cycle life compared to batteries. As hybrid devices in combination with batteries or fuel cells, they offer great potential for transportation and stationary applications.  We will evaluate chemically modified graphene (CMG), which are 1-atom thick sheets of carbon functionalized with other elements as needed, as electrode materials for ECs.  Graphene has a remarkably high theoretical surface area of 2630 m2/g, which is several-fold higher than that of the currently used activated carbons. The physical and chemical versatility of graphene-based systems is appealing to increase energy density. The system does not depend on the distribution of pores in a solid support; every chemically modified graphene sheet can “move” physically to adjust to the different types of electrolytes (their sizes, their spatial distribution), while still maintaining an overall high electrical conductivity for such a network of individual CMG’s.

11.  Rates and PricingProf. Ross Baldick, Prof. James Dyer, Prof. David Adelman, Prof. John Butler

We will research how different rate structures, including possible time-of-use pricing, would affect the sustainability of the traditional utilities as distributed renewable penetration increases and evaluate the regulatory constraints on such rate structures and the effects of other regulations (e.g., Renewable Portfolio Standards) on utility business models.  Electric utilities operate in the shadow of an elaborate web of environmental and commercial regulations that shapes business incentives and strategies.  Business models therefore cannot be properly evaluated in the absence of a detailed understanding of the regulatory environment, and regulations can either ameliorate or aggravate the economic tensions between traditional utilities and renewable sources of power.  Utility regulation and business models will have to change as levels of distributed generation become substantial. In particular, capital planning for new generation, transmission, and distribution will need to adapt economically to the net demand of customers (i.e., demand minus distributed generation).  The projected change in net demand characteristics is, for example, likely to shift investment towards peak generation capacity (i.e., gas-powered) and possibly towards storage.  Concomitant with increased levels of distributed renewable resources, many more “demand-side” resources may be available to compensate for intermittency of renewable generation.  Billing structures, and by implication rate-setting regulations, must change to enable such participation because a customer will only cede control of appliances in return for some kind of compensation.  The control of customer resources to help with grid-management objectives is likely to be in conflict with the private objectives of individual consumers and widespread concerns about privacy and data security.  In return for either variable pricing that provides incentives for cooperation or direct compensation, the boundary of control will shift “behind the meter,” which will require evaluating potential incentive schemes for consumers and sophisticated models of consumer behavior.

12.  Fleet Evolution, Fleet Use, and Fleet Charging/Storage in the Smart Grid – Prof. Kara Kockelman, Prof. Ross Baldick

In order to quantify electrical demand, we will estimate how many plug-in electric vehicles (including PHEVs, battery-electric vehicles [BEVs], and extended-range EVs) are likely to be used in Austin in the next 20 years and their likely spatial and temporal charging patterns, which range from regular overnight charging of individual vehicles at  residences, to regular daily charging of clusters of vehicles in parking lots at work, to random opportunistic charging at public charging stations.  Model frameworks include a continuous cycling of vehicle holdings and use patterns with attention to power-demand profiles and correlation with the availability of residence, work, and public charging stations. First-hand data collection of vehicle owner and traveler preferences will be used in a simulation model, along with mining of existing household travel surveys and other data sets to determine vehicle-use profiles across owners. The effect of time-differentiated and spatially-differentiated electricity rates will be investigated.

13.  Simulation Test Bed for the Sustainable Distribution GridProf. Surya Santoso, Prof. Mack Grady

Sustainable distribution grids consist of distributed generation, energy storage systems, controllable and uncontrollable loads, power apparatus, power quality monitoring, and utility communication /control devices.  Developing a simulation-based test bed incorporating those devices is critical in designing, evaluating, and simulating how digital technologies can be deployed to control and operate a grid.  We have developed various distribution grid simulation models for power quality and harmonic studies.  These models will be combined to develop a test-bed based on the Pecan Street Project distribution grids.  A time-domain simulation software package (PSCAD/EMTDC) along with MATLAB will be integrated allowing holistic analysis of the grid’s electrical, mechanical, communication, and sensing/control behaviors. Distributed generation (including PV modules, fuel cell, and wind turbines), energy storage systems, loads, digital controllers, sensors, and communication channels described above will also be incorporated into the simulation. The test bed will allow faculty and students to design and evaluate specific generation and storage technologies, controllers, and sensing devices prior to actual deployment as part of the Pecan Street Project. Smart grid operating scenarios such as self-healing and self-reconstruction, maximum renewable energy penetration, energy storage control and dispatch, and real-time price impacts can be studied and evaluated using the test bed.

14.  Use of Synchrophasor Measurements for Large-scale Wind Power Integration – Prof. Mack Grady

The greatest technical impediment to large-scale wind generation is the capacity of an electric grid to accommodate huge wind farms and still maintain stability. Texas is the power generation leader in wind, and the Texas State grid (ERCOT) has the highest penetration of wind generation, which accounts for as much as 15% of total power. Wind curtailments occur almost every day due to transmission constraints, and larger wind penetration levels will destabilize the grid because the large wind farms are 300 - 500 miles away from major load centers.   UT has the only independent (i.e., non-utility owned) synchrophasor measurement network in the U.S.  This new technology employs GPS time stamping so that, for the first time, voltage phase angles can be known. Power flow is proportional to phase angle differences, and phase angle is thus very sensitive to power oscillations and can give a “heads up” when the grid is approaching unstable levels. With advance notice, grid operators can take corrective actions such as re-dispatch before a serious threat to the grid develops.  The capability that this system affords to observe system responses to sudden events (which occur frequently) will allow us to tune-up stability modeling data by matching simulations with measurements and also to determine the types of responses that are “normal” or “abnormal” for a grid.  Synchrophasors are not yet widely deployed and few guidelines exist on how to best use them. Our first task will be to monitor and understand the synchrophasor information we collect—for example, what is “normal” and “abnormal” in ERCOT.  The second task will be to use major grid events, which occur every week, to determine if generator and other component models used by electric utilities to assess grid stability are suitable, and if not suitable, to refine those models.

15.  Enterprise Integration, Control and SecurityProf. Suzanne Barber

UT will investigate the enterprise engineering enabling energy systems to integrate, control, and secure the disparate components of energy systems. Enterprise energy systems components will include (1) energy technology components, (2) hardware components, (3) software components, and (4) telecommunications/networking components.  Research focusing on enterprise integration must be grounded on fundamental investigations exploring:   Enterprise requirements engineering – the components of the integrated system must satisfy the numerous, often conflicting, and evolving stakeholder needs; Architectures – the components and their infrastructure must be accurately selected and configured to meet the identified needs; and Verification/validation – the system components must be tested to assure that enterprise requirements were met by the integrated whole. This research must also consider the challenges presented by emerging technologies in an immature marketplace.  Enterprise security has also become increasingly important and is a pervasive challenge for energy providers. As energy systems become more digitally connected, both the software architecture and the data it stewards must be trusted and secured. Every node and every customer must be protected by system capabilities that anticipate and defeat malicious threats and misuses.  Students performing research in these areas must deliver unprecedented advances in system engineering, and will be required to leverage an integrated knowledge set of energy systems, software engineering, computer engineering, and telecommunications.

16.  Building Integrated SolarProf. Matt Fajkus, Prof. Ulrich Dangel, Prof. Alexandre da Silva, Prof. Atila Novoselac

The goal of designing homes that are energy efficient enough to be net zero energy homes with the addition of on-site energy generation requires collaboration with architectural engineers (air quality, comfort, numerical simulation of thermal performance, lighting and ventilation), and architects (comfort requirements, systems integration, construction, functional aspects, construction, aesthetics).  Climate-related building design is one of the most effective and efficient ways to reduce daily energy demands.  The positioning, orientation, sizing, and construction of each window must be done in such a way that the right amount of fresh air and daylight can enter a building without excessive cooling demands in summer or heating demands in winter.  Passive design strategies necessarily include the design of an optimal building envelope, including highly insulating building envelopes for the minimization of heat transfer. Very often, comfort- and energy related issues are neglected during the initial stages of the design process and considered only at a later point through active control systems for the indoor environment.  The tremendous potential of passive technologies permits minimization of the energy demand for heating, cooling and lighting.  Solar water heating eliminates the need to use electricity from the grid or natural gas to heat water.  A typical single family home with 4 occupants can save 2,323 kwh and 3,215 pounds of CO2 annually by using solar water heating.  There is a critical need for the analysis of the introduction of various components such as vacuum-tube and flat-plate collectors into the building skin as well as the integration of these systems in the building HVAC system.   Solar absorption cooling can effectively reduce cooling energy use especially in a city like Austin.  Options for solar-assisted cooling will be examined to determine the feasibility of widespread use. The various technological options, their technical potential and the strategies to integrate these alternative technical solutions in the design and building process will be analyzed.

17.  High Thermal Conductivity MaterialsProf. Rod Ruoff

Thermal management systems are now being developed alongside electrical systems as a way to improve overall energy efficiency.  Harvesting and using the excess heat from power producing machines reduces total energy losses in the total energy system.  However, thermal systems experience efficiency problems just as electrical systems do.  Heat losses during transport from the source to the site of use can be minimized, though, by using conduits made of highly thermally anisotropic materials. Graphene and hexagonal boron nitride layered films have exhibited thermal conductivity on the order of 3,000 Wm-1k-1 within plane yet have low thermal conductivity between the layers, i.e., orthogonal to the plane of a typical film.  The use of these materials in the production of thermal management devices could greatly improve their efficiency. The nature of the transport processes in these materials will be explored, considering both chemical and structural influences.

18.  Integration of Passive Desiccant Systems into Building MaterialsProf. Atila Novoselac

It is well known that approximately 40% of the energy consumption in the United States is attributed to the operation of buildings.  However, it is less known that significant fraction of this energy relates to dehumidification which is considered a key feature of heating ventilation air-conditioning (HVAC). Passive desiccant systems designed to introduce “moisture capacitance” into a building’s performance, the way that thermal capacitance, or thermal mass, is now used ubiquitously.  In commercial buildings latent cooling loads are generated by occupants and occupants related activity; they are often cyclical, as they increase during the day when workers are present, and decrease dramatically at night when workers leave the building and outdoor humidity subsides.  This suggests an opportunity for the introduction of “night-dehumidification” strategies in conjunction with passive or integrated moisture collection systems such as desiccant-laced ceiling panels or wall coverings, analogous to night-cooling strategies used to reduce sensible loads.  The goal of this research project is to develop building finishing materials and control systems capable to manage moisture transport in a way that is favorable for building energy performance. The conceivable impacts of such a system include a cut in the amount of electric energy needed to dehumidify air, reduction of peak electric energy demand, shifting of dehumidification energy demand to night time, and reduction of the incidence of mold and its associated health problems.

19.  Building HVAC Control for Dynamic Energy Pricing - Prof. Atila Novoselac and Prof. Tom Edgar

Keeping thermal comfort and indoor air quality parameters at desired level, is the primary purpose of the heating, ventilation, and air-conditioning (HVAC) control system. More sophisticated HVAC control systems have an additional task to minimize energy consumption. Beside sensors inside and outside of the building, most of these control systems use predictive daily and seasonal cycles such as: outdoor temperature, occupancy schedule, and on- and off-peak electric energy pricing schedule. For example, the benefit from thermal storage systems relies heavily on fixed daily energy pricing schedule. However, with the dynamic energy pricing, where electricity rate is provided by the utility company only a short period of time ahead, there is a new challenge for designers of HVAC control systems. To exploit the benefit of dynamics pricing, the control systems should be analyzed in greater details. These systems should use control strategies that take into account stochastic change of electric price beside the dynamics of cooling/heating loads and building components.  To define demands for these new systems, we plan to use building energy simulations where building models (such as EnergyPlus, and TRNSYS) are coupled with control models (such as Matlab).  The modeling of various building types, HVAC systems and control strategies should identify building systems and controls that can use advantage of dynamic pricing.  Furthermore, we plan to use our test rooms (the environmental chamber and the facade thermal lab) that have reconfigurable HVAC systems and the-state-of-the-art control systems for testing of the most promising control methods.