RSS_Auto_Poster
Well-known member
Written by Steven Ashley
Inside everyplug-in vehicle there"s a black box the size of a six-pack cooler that connectsthe battery to the electric motor. It"s called the power inverter. Thiscrucial, but often overlooked component converts the battery pack"s high-voltage direct current (DC) into alternating current (AC) pulses that control the traction motor. A DC-to-AC inverter,basically a fast-acting silicon semiconductor switch, functions something likean Engine Management System does in a internal-combustion power plant. It feeds the driver"s commands to the traction motor in the form of pulse-width-modulated drive signals at frequencies that can range from 10 Hz to 10 kHz. Becauseall electric traction power passes through the inverter, any efficiency lossesthat occur within cut directly into a plug-in vehicle"s battery-only drivingrange. In fact, more efficient inverter technology ranks second in importance onlyto more power-dense batteries for extending battery-only range innext-generation plug-ins. Improvedelectric and hybrid vehicles are not alone in their need for better inverters.High-efficiency inverter technology would also greatly benefit industrial motors,consumer electronics, appliances and data centers as well as photovoltaic andwind energy systems. It"s no surprisethen that electronics and materials researchers worldwide are working todevelop improved semiconductors that could deliver inverter performance that is superior to conventional silicon including fewer switching losses, greater thermalefficiency and importantly, reduced system costs. Even Google is working on thisissue, having established last year a prize competition The Little Box Challenge that will award $1 million tothe developer of the best inverter design for "green energy" applications; see The Little Box Challenge, an open competition to build a smaller power inverter. The goal of thisresearch is to develop what are called wide bandgap (WBG) semiconductors. To physicists,WBG materials exhibit a relatively large quantum energy range in which noelectron states can exist a bigger electron energy gap compared to silicon between the top ofthe valence band and the bottom of the conduction band. In practice, it refers to the amount of energy that is needed to release electrons from a particular semiconductormaterial for conduction. Semiconductorswith wider bandgaps can, for example, withstand higher applied electric fields,or voltages, as well as operate at higher temperatures, power densitiesand frequencies. In theautomotive sector, the U.S. Department of Energy recently awarded research grantsto General Motors ($3.99 million) and Delphi ($2.46 million) to support three-year,cost-shared projects to develop high-efficiency, cost-competitiveintegrated power inverter modules based on WGB semiconductors for plug-invehicles. Automotive Engineering previously reported on Toyota"s continuing research efforts to develop more efficient automotive power electronics modules using silicon carbide; see Efficient power electronics for hybrids and EVs - SAE International. Smaller, lighterinverters Inverters in currentplug-ins rely on silicon-based power transistor technology that was developed forindustrial applications over the last 25 years, said Pete Savagian, GM"s GeneralDirector for Electric Drives and Systems Engineering and a veteran of thecompany"s pioneering EV-1 program. These insulated-gatebipolar transistors (IGBTs), often tuned for automotive use, combine goodefficiency and fast switching, he explained, but expanding plug-ins" battery-onlydriving range means moving beyond silicon. Two emerging WBGsemiconductors, silicon carbide and gallium nitride, are expected to fill thatrole, Savagian continued, because they "can bring three to ten times better energyefficiency when they"re turned on and especially, when they"re turned off. And when you"reswitching at rates of 10,000 Hz, reducing losses becomes important." Wide-bandgapinverter technology "plays upon the ability of the transistor material to run at highertemperature and with fewer losses than silicon-based power electronics," explained A.J.Lasley, Director of Electronic Controls Advanced Engineering at Delphi inIndianapolis. "The improved efficiency can directly translate into longer range." He noted that wide-bandgapmaterials, particularly silicon carbide semiconductors, have been trying topush into industry for many years, with the recent DoE-supportedprojects aiming to "push the limit" in plug-in inverter technology. "The newmaterials offer great potential for allowing us to reduce the size of invertersby as much as 30% and cut energy losses by 20% to 30%," Lasley said. According to GM"s Savagian, the new WBG semiconductors would allow "using less semiconductor material ininverters than we do now. The resulting smaller footprint means that everythingelse can shrink as well, including all the support equipment electricalconnectors, cooling system, heat exchanger, and the housing and chassisstructures." Suchphysical and operational downsizing should in addition yield significantlycheaper power inverter units, Savagian predicted. He noted that the inverter typicallyaccounts for about 40% of the total cost of an electric drive train, whichincludes an electric motor and a gear reduction system. Both Savagianand Lasley stressed that one of the principal benefits of WBG semiconductors toplug-in vehicles is that they would enable engineers to integrate powerinverters directly into the transmission systems. "Their smaller size meansthat the mounting and packaging can be more rigid and robust," Savagian observed. "It also would enable engineers to incorporate the devices into the transmission units, saving space and weight. You could, for instance, get rid of the electrical cables, whichmakes assembly easier." Beyond silicon Experts note that gallium nitridehas similar bandgap characteristics to silicon carbide, which is a more mature technology. But silicon carbide chip fabrication "is very expensive, whilegallium nitride offers the possibility of lower-cost manufacturing because ofit is more compatible with the underlying substrate materials," said Jayant Baliga, Director of the Power SemiconductorResearch Center at North Carolina State University. Baliga, a pioneer in powerelectronics, invented and commercialized IGBT devices when he worked at GeneralElectric. Baliga"s NCSUcenter is taking the lead in the Power America program, also known as the Next Generation PowerElectronics National Manufacturing Innovation Institute. This is a five-year,$140-million R&D effort established in January 2015 by the DoE "to drive WBG semiconductor costs to make them more competitive with siliconmaterials." In the case of silicon carbide, the researchers are attempting to adaptexisting silicon chip foundries to silicon carbide chip fabrication, Baliga noted. Anant Agarwal, the senior WBGexpert at the DoE"s Advanced Manufacturing Office, has said heexpects that highly efficient power electronic devices using the newsemiconductors will be able to achieve price parity with traditionalsilicon-based devices within about five years. Power America"s memberscomprise a dozen companies as well as seven universities and laboratories,including ABB, Arkansas Power Electronics International, Cree, Delphi, JohnDeere, Monolith Semiconductor, Qorvo, Toshiba, Transphorm, United SiliconCarbide, VACON and X-FAB. Besides NCSU, the program"s academic and lab partnersare Arizona State University, Florida State University, the National RenewableEnergy Laboratory, the U.S. Naval Research Laboratory, the University ofCalifornia, Santa Barbara and Virginia Polytechnic Institute and StateUniversity.
Date: 28-Dec-2015 09:30 EST
More of this article on the SAE International website
ID: 1451
Inside everyplug-in vehicle there"s a black box the size of a six-pack cooler that connectsthe battery to the electric motor. It"s called the power inverter. Thiscrucial, but often overlooked component converts the battery pack"s high-voltage direct current (DC) into alternating current (AC) pulses that control the traction motor. A DC-to-AC inverter,basically a fast-acting silicon semiconductor switch, functions something likean Engine Management System does in a internal-combustion power plant. It feeds the driver"s commands to the traction motor in the form of pulse-width-modulated drive signals at frequencies that can range from 10 Hz to 10 kHz. Becauseall electric traction power passes through the inverter, any efficiency lossesthat occur within cut directly into a plug-in vehicle"s battery-only drivingrange. In fact, more efficient inverter technology ranks second in importance onlyto more power-dense batteries for extending battery-only range innext-generation plug-ins. Improvedelectric and hybrid vehicles are not alone in their need for better inverters.High-efficiency inverter technology would also greatly benefit industrial motors,consumer electronics, appliances and data centers as well as photovoltaic andwind energy systems. It"s no surprisethen that electronics and materials researchers worldwide are working todevelop improved semiconductors that could deliver inverter performance that is superior to conventional silicon including fewer switching losses, greater thermalefficiency and importantly, reduced system costs. Even Google is working on thisissue, having established last year a prize competition The Little Box Challenge that will award $1 million tothe developer of the best inverter design for "green energy" applications; see The Little Box Challenge, an open competition to build a smaller power inverter. The goal of thisresearch is to develop what are called wide bandgap (WBG) semiconductors. To physicists,WBG materials exhibit a relatively large quantum energy range in which noelectron states can exist a bigger electron energy gap compared to silicon between the top ofthe valence band and the bottom of the conduction band. In practice, it refers to the amount of energy that is needed to release electrons from a particular semiconductormaterial for conduction. Semiconductorswith wider bandgaps can, for example, withstand higher applied electric fields,or voltages, as well as operate at higher temperatures, power densitiesand frequencies. In theautomotive sector, the U.S. Department of Energy recently awarded research grantsto General Motors ($3.99 million) and Delphi ($2.46 million) to support three-year,cost-shared projects to develop high-efficiency, cost-competitiveintegrated power inverter modules based on WGB semiconductors for plug-invehicles. Automotive Engineering previously reported on Toyota"s continuing research efforts to develop more efficient automotive power electronics modules using silicon carbide; see Efficient power electronics for hybrids and EVs - SAE International. Smaller, lighterinverters Inverters in currentplug-ins rely on silicon-based power transistor technology that was developed forindustrial applications over the last 25 years, said Pete Savagian, GM"s GeneralDirector for Electric Drives and Systems Engineering and a veteran of thecompany"s pioneering EV-1 program. These insulated-gatebipolar transistors (IGBTs), often tuned for automotive use, combine goodefficiency and fast switching, he explained, but expanding plug-ins" battery-onlydriving range means moving beyond silicon. Two emerging WBGsemiconductors, silicon carbide and gallium nitride, are expected to fill thatrole, Savagian continued, because they "can bring three to ten times better energyefficiency when they"re turned on and especially, when they"re turned off. And when you"reswitching at rates of 10,000 Hz, reducing losses becomes important." Wide-bandgapinverter technology "plays upon the ability of the transistor material to run at highertemperature and with fewer losses than silicon-based power electronics," explained A.J.Lasley, Director of Electronic Controls Advanced Engineering at Delphi inIndianapolis. "The improved efficiency can directly translate into longer range." He noted that wide-bandgapmaterials, particularly silicon carbide semiconductors, have been trying topush into industry for many years, with the recent DoE-supportedprojects aiming to "push the limit" in plug-in inverter technology. "The newmaterials offer great potential for allowing us to reduce the size of invertersby as much as 30% and cut energy losses by 20% to 30%," Lasley said. According to GM"s Savagian, the new WBG semiconductors would allow "using less semiconductor material ininverters than we do now. The resulting smaller footprint means that everythingelse can shrink as well, including all the support equipment electricalconnectors, cooling system, heat exchanger, and the housing and chassisstructures." Suchphysical and operational downsizing should in addition yield significantlycheaper power inverter units, Savagian predicted. He noted that the inverter typicallyaccounts for about 40% of the total cost of an electric drive train, whichincludes an electric motor and a gear reduction system. Both Savagianand Lasley stressed that one of the principal benefits of WBG semiconductors toplug-in vehicles is that they would enable engineers to integrate powerinverters directly into the transmission systems. "Their smaller size meansthat the mounting and packaging can be more rigid and robust," Savagian observed. "It also would enable engineers to incorporate the devices into the transmission units, saving space and weight. You could, for instance, get rid of the electrical cables, whichmakes assembly easier." Beyond silicon Experts note that gallium nitridehas similar bandgap characteristics to silicon carbide, which is a more mature technology. But silicon carbide chip fabrication "is very expensive, whilegallium nitride offers the possibility of lower-cost manufacturing because ofit is more compatible with the underlying substrate materials," said Jayant Baliga, Director of the Power SemiconductorResearch Center at North Carolina State University. Baliga, a pioneer in powerelectronics, invented and commercialized IGBT devices when he worked at GeneralElectric. Baliga"s NCSUcenter is taking the lead in the Power America program, also known as the Next Generation PowerElectronics National Manufacturing Innovation Institute. This is a five-year,$140-million R&D effort established in January 2015 by the DoE "to drive WBG semiconductor costs to make them more competitive with siliconmaterials." In the case of silicon carbide, the researchers are attempting to adaptexisting silicon chip foundries to silicon carbide chip fabrication, Baliga noted. Anant Agarwal, the senior WBGexpert at the DoE"s Advanced Manufacturing Office, has said heexpects that highly efficient power electronic devices using the newsemiconductors will be able to achieve price parity with traditionalsilicon-based devices within about five years. Power America"s memberscomprise a dozen companies as well as seven universities and laboratories,including ABB, Arkansas Power Electronics International, Cree, Delphi, JohnDeere, Monolith Semiconductor, Qorvo, Toshiba, Transphorm, United SiliconCarbide, VACON and X-FAB. Besides NCSU, the program"s academic and lab partnersare Arizona State University, Florida State University, the National RenewableEnergy Laboratory, the U.S. Naval Research Laboratory, the University ofCalifornia, Santa Barbara and Virginia Polytechnic Institute and StateUniversity.
Date: 28-Dec-2015 09:30 EST
More of this article on the SAE International website
ID: 1451
