5. TECHNOLOGIES RELATED TO HYBRID ELECTRIC VEHICLES WITH SPECIAL EMPHASIS ON PLUG-IN HYBRIDS

 

Hybrid electric vehicles (HEVs) and plug-in hybrids (PHEVs) require advanced technology in the areas of energy storage technology (batteries and/or electrochemical capacitors), motors and capacitors.  These technology areas represent some of the most critical barriers to the development and marketing of cost-competitive HEVs and PHEVs. The Office of Energy Efficiency and Renewable Energy is interested in identifying and developing innovative concepts for advanced technologies to improve the performance, extend the life, and significantly reduce the cost of hybrid electric vehicles.

 

HEVs require energy storage devices that can deliver high power pulses.  PHEVs will require devices that both store significant energy and can deliver high power pulses.  All of these devices must be able to accept high power recharging pulses from regenerative braking.  For HEV applications, the goal is to develop cells that provide peak power of 1200 W/kg or greater, have a cycle life of at least 300,000 shallow cycles, and have a calendar life of 15 years.  PHEVs will require batteries that can deliver significant energy (several kWh) for several thousand discharge cycles from an almost full charge to a low state of charge.  It has been suggested that a PHEV battery would operate in a charge depleting hybrid mode from about 90% of full charge to about 25% of full charge.  Once the battery reaches this lower state of charge, it will function in a manner similar to the battery in an HEV and must be able to sustain 200,000 – 300,000 shallow cycles with a 15 year calendar life.  For all systems, materials to be utilized should be plentiful, have low cost (< $10/kg), be environmentally benign, and be easily recycled.  Evaluation of the technology with regard to the above criteria should be performed in accordance with applicable U.S. Advanced Battery Consortium test procedures or Society of Automotive Engineers recommended practices (see references that follow).

 

Advances in materials and designs for advanced electric motors, power electronics, and packaging are opening a variety of opportunities to significantly improve the performance, reliability, and economics of efficient energy use in transportation, buildings, industry, and renewable energy.  These include new applications for the conversion of power from electrical to mechanical or mechanical to electrical forms; power electronics that can operate reliably at higher temperatures.

 

Grant applications must show how the proposed innovations would result in significant advances in performance and/or cost reduction over state-of-the-art technologies.  Successful proposals will clearly demonstrate the ability of the applicants to proceed to more advanced stages of development; for motors and power electronics, these stages include hardware development, fabrication, testing, and manufacture of components and devices.

 

Grant applications are sought only in the following subtopics:

 

a. New Materials to Improve the Performance of Lithium-Ion Batteries in HEV and PHEV Applications—Advances in battery performance often come in two stages:  first there is the development of new materials for use in an electrochemical cell; then there is the optimization of how the cell is fabricated.  In this model, new materials must come first.  Most of the active materials now being used in advanced rechargeable batteries, such as the family of lithium-ion systems, have been known for some time.  Many of the recent improvements in performance have come from relatively small adjustments in the chemical formulation or physical form of known materials.  Some members of the technical community believe that new materials will be required to meet the cycling profiles of advanced HEVs and PHEVs while also meeting the goals for cost, calendar life, and other properties. 

 

Grant applications are sought to identify, synthesize, and characterize novel materials for use as the active materials in advanced batteries for HEVs and/or PHEVs.  Proposals in response to this subtopic may focus on materials associated with the positive electrode, negative electrode, and/or electrolyte.  Existing materials may be used for components that are not under development.  The new materials may fit within a current family of batteries, such as lithium-ion, or may represent a novel electrochemical system.  Successful applications must clearly explain why the proposed materials are truly novel and discuss why the materials are expected to be able to meet the requirements of a vehicular battery.  Materials that clearly can not meet vehicular requirements, such as those that require very expensive starting materials, are not appropriate.  Preference will be given to applications that propose “out-of-the-box” materials and support that proposal with appropriate theory or available data.  During Phase I, the new materials must be prepared and demonstrated by cycling in laboratory cells.  In Phase II the material’s properties should be refined, synthesized in repeatable batches, and characterized in cells of at least 200 mAh in size. 

 

Questions - contact James Barnes (james.barnes@hq.doe.gov)   
 

b. Improved Lower Cost Electrode Materials for Electrochemical Capacitors—The most common electrochemical capacitors, also known as “super” or “ultra” capacitors, use a form of carbon as the active material in both electrodes.  The carbons which perform well (good capacitance, long cycle life, long calendar life, relatively little self discharge, etc.) tend to be quite expensive, costing over $50/kg.  Carbons which cost less than $25/kg tend to exhibit one or more performance problems.  The high cost of the materials that perform well is one of the limiting factors in the development and potential adoption of capacitors for vehicular applications.  Novel grant applications are sought that will address the cost of electrode materials in either symmetric (both electrodes are of the same material) or asymmetric (electrodes with different materials) capacitors.  Replacement materials that result in reduced performance relative to the state-of-the-art (in areas such as power capability, energy stored, operating temperature, useful life, or cost) are not of interest.  All proposals must provide a clear discussion, based upon available data and theory, to support an assertion that the materials to be developed will offer acceptable performance at a lower cost.  Grant applications must include a demonstration of the materials’ performance in laboratory cells by the end of Phase I and in capacitors suitable for use in a vehicle by the end of Phase II.

 

Questions - contact Susan Rogers (susan.rogers@hq.doe.gov)   
 

c. Technologies to Address Problems Associated with Internal Heating in Capacitors—Capacitors suitable for harsh automotive environments must suffer extreme environmental conditions.  Film capacitors present an option for use as high voltage bus capacitors.  However, they must accommodate high ripple currents, in a high temperature environment.  There is a need for higher density lower resistivity foils to allow more ripple current capability with less heating.  If a capacitor is going to be exposed to under-hood temperatures of up to 150oC it is necessary for the capacitor to be capable of handling high current without the need for external cooling.  The present design package of most film capacitors presents a heat dissipation problem in that the foil is wrapped so that the heat is dissipated more quickly in the axial direction.  When internal heating is increased due to an increase in ripple current the capacitor could fail if that heat isn’t removed quickly enough.  New materials and designs that allow better heat transfer out of the capacitor to reduce internal heating problems and increase life expectancy.

 

Questions - contact Susan Rogers (susan.rogers@hq.doe.gov)   
 

d. Technologies Associated with Advanced Motors—High-temperature, high-strength, lower-cost permanent magnets (PMs) are needed for traction motors for HEVs and PHEVs.  The trend for higher-temperature electric machines requires higher-temperature PMs.  The strength of the current NeFeB PMs is weakened significantly as temperature rises.  Grant applications are sought to develop new magnetic materials to allow low cost, easily manufacturable permanent magnets with energy products comparable to what is commercially available today with sintered magnets at temperatures up to 240oC.

 

Grant applications are sought to produce stator and rotor core as well as magnet material with increased resistivity to improve electric motor efficiency by reducing eddy currents and to reduce fabrication costs, even for complex shapes.  The calculation of efficiency involves loss from windage, bearing friction, Joule heating in the copper wires, hysteresis in the core and stator, and eddy currents in the core, stator, and magnets.  Eddy current losses are significant and reducing them will increase the efficiency of a motor.  In all synchronous motors, the rotation of the magnetic field, which is produced by the stator windings and is in sync with the rotor, generates eddy currents in the stator core.  Furthermore, the magnetic field pulses generated as the rotor magnets pass the openings between the stator teeth, generate eddy currents in the magnets.  Eddy current density is inversely proportional to the resistivity of the core material and magnets.  Power loss is proportional to the product of resistivity and the square of the eddy current density, which causes the eddy current power losses to be inversely proportional to the resistivity. Insulated laminated core material has conventionally been used to increase resistivity normal to the laminates in the stator and, more recently, an epoxy coating on magnetic particles, which are formed into "bonded" magnets, is being used to increase the resistivity of the magnets.  The difficulty with conventional laminated materials is that many sheets must be punched and assembled to produce the final stator or core.  The difficulty with the bonded magnets is that their remanence is lower than that of sintered magnets.  Grant applications are sought to economically produce core material and magnet material with high resistivity that would improve motor efficiency and reduce fabrication costs.  Such research could look for ways to coat particles, possibly nano-particles, with thin high resistance ceramic materials that do not break down during sintering.  Particles could be structural as well as magnetic.  Coated structural particles might be injection molded to complex shapes and sintered to achieve final strength in place of laminates in the stator and core.  Thin ceramic coatings on magnetic particles instead of epoxy coatings could increase the remanence while retaining low resistivity. 

 

Questions - contact Susan Rogers (susan.rogers@hq.doe.gov)   
 

References:

 

Subtopic a:  New Materials to Improve the Performance of Lithium-Ion Batteries in HEV and PHEV Applications

 

1.      Links to the following Manuals are available at:  http://avt.inl.gov/energy_storage_lib.shtml.  These documents provide a good general basis for understanding the performance requirements for electric and hybrid electric vehicle energy storage devices.
· FreedomCAR 42V Battery Test Manual
· FreedomCAR Battery Test Manual for Power Assist Hybrid Electric Vehicles
· PNGV Battery Test Manual, Revision 3
· Electric Vehicle Capacitor Test Procedures
· USABC Electric Vehicle Battery Test Procedure Manual, Revision 2

 

2.      The internet site for the Batteries for Advanced Transportation Technologies (BATT) program at http://berc.lbl.gov/BATT/BATT.html includes quarterly and annual reports. This program addresses many long-term issues related to lithium batteries, including new materials.

 

3.      This site contains multiple references that summarize work supported by the FreedomCAR and Vehicle Technologies Program related to energy storage.  Prior to 2002, there are separate publications for the Energy Storage Effort and for Advanced Technology Development.  In more recent years, there is a combined report for Energy Storage.  These reports include information about cell chemistries that have proven to be useful model systems for these applications along with discussions of issues related to abuse tolerance and cell life.  (URL:  http://www1.eere.energy.gov/vehiclesandfuels/.  On menu at left, click on “Energy Storage”.)

 

4.      Information about requirements for vehicular batteries, separators for lithium-ion batteries, and abuse testing can all be found at the USABC section of the USCAR internet site.  Go to http://www.uscar.org/; on menu at left, click on “Teams”; under the USCAR Consortia section, click on “United States Advanced Battery Consortium (USABC)”. This site provides a second source for many of the documents found at reference 1.

 

Subtopic b:  Improved Lower Cost Electrode Materials for Electrochemical Capacitors and Subtopic c:  Technologies to Address Problems Associated with Internal Heating in Capacitors

 

5.   Efford, T., et al., "Development of Aluminum Electrolytic Capacitors for EV Inverter Applications," presented at the IEEE Industry Applications Society Annual Meeting, New Orleans, LA, October 5-9, 1997. http://ieeexplore.ieee.org/xpl/conferences.jsp 

 

Subtopic d:  Technologies Associated with Advanced Motors

 

6.      Otaduy, P. J., et al., “The Role of Reluctance in PM Motors,” Oak Ridge National Laboratory, June 2005.  (Report No. ORNL/TM-2005-86) (Full text available at:  http://www.ornl.gov/~webworks/cppr/y2001/rpt/123193.pdf)

 

7.      “Design of PM-Assisted Synchronous Reluctance Motors, Design Analysis, and Control of Interior PM Synchronous Machines,” IEEE Industry Applications Society Tutorial Course Notes, October 4, 2004.

 

8.      Hsu, J. S., et al., “Report on Toyota/Prius Motor Design and Manufacturing Assessment,” Oak Ridge National Laboratory, July 2004.  (Report No. ORNL/TM-2004-137) (Full text available at:  http://www.ornl.gov/~webworks/cppr/y2001/rpt/120761.pdf.)

 

9.      Lawler, J. S., et al., “Minimum Current Magnitude Control of Surface PM Synchronous Machines During Constant Power Operation,” IEEE Power Electronics Letters, 3(2), June 2005.  (ISSN 1540-7985)

 

10.  Hendershot, J. R., Jr., and Miller, T. J. “Design of Brushless Permanent Magnet Motors,” Chapter 16, Oxford:  Magna Physics Publishing and Clarendon Press, 1994.  This chapter contains a good discussion of eddy current and hysteresis core losses.  (ISBN: 1-881855-03-1)

 

11.  Russell, R. L., and Norsworthy, K. H., “Eddy Currents and Wall Losses in Screened Rotor Induction Motors,” Paper No. 2525U, The Institution of Electrical Engineers, April 1958.  This paper shows how eddy currents are generated by a varying magnetic field in a conducting surface using Maxwell's equations.

 

12.  Slemon, G. R. and Xian, L., “Core Losses in Permanent Magnet Motors,” IEEE Transactions on Magnets, 26: 1653-1655, September 1990.  A classic early paper on calculation of core losses.

 

13.  Mi, C., et al., “Modeling of Iron Losses of Permanent-Magnet Synchronous Motors,” IEEE Transactions on Industry Applications, 39(3), May/June 2003.  The latest paper on core loss used during design of the 6 kW fractional slot PM motor with concentrated windings built at the University of Wisconsin, Madison in 2005.

 

 

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