A 55-kW Three-Phase Inverter With Si IGBTs and SiC Schottky Diodes

278 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 1, JANUARY/FEBRUARY 2009 A 55-kW Three-Phase Inverter With Si IGBTs and SiC Schottky Diodes Burak Ozpineci, Senior Member, IEEE, Madhu Sudhan Chinthavali, Leon M. Tolbert, Senior Member, IEEE, Avinash S. Kashyap, Student Member, IEEE, and H. Alan Mantooth, Senior Member, IEEE Abstract Silicon carbide (SiC) power devices are expected to have an impact on power converter efficiency, weight, volume, and reliability. Currently, only SiC Schottky diodes are commercially available at relatively low current ratings. Oak Ridge National Laboratory has collaborated with Cree and Semikron to build a Si insulated-gate bipolar transistor SiC Schottky diode hybrid 55-kW inverter by replacing the Si p-n diodes in Semikron s automotive inverter with Cree s made-to-order higher current SiC Schottky diodes. This paper presents the developed models of these diodes for circuit simulators, shows inverter test results, and compares the results with those of a similar all-si inverter. Index Terms DC AC conversion, hybrid electric vehicle, insulated-gate bipolar transistors (IGBTs), inverter, Schottky diode, silicon carbide (SiC). I. INTRODUCTION THERE IS a growing demand for more efficient, higher power density, and higher temperature operation of the power converters in transportation applications. In spite of the advanced technology, silicon (Si) power devices cannot meet some transportation requirements. Silicon carbide (SiC) has been identified as a material with the potential to replace Si devices in the near term because of its superior material advantages, such as wider bandgap, higher thermal conductivity, and higher critical breakdown field strength. SiC devices are capable of operating at high voltages, high frequencies, and at higher junction temperatures. Significant reduction in the weight and size of SiC power converters with an increase in the efficiency is projected [1] [5]. SiC unipolar devices, such as Schottky diodes, vertical-junction field-effect transistors, MOSFETs, etc., have much higher breakdown voltages compared with their Si counterparts, which makes them suitable for Paper IPCSD-08-002, presented at the 2006 IEEE Applied Power Electronics Conference and Exposition, Dallas, TX, March 19 23, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Power and Electronics Devices and Components Committee of the IEEE Industry Applications Society. Manuscript submitted for review November 3, 2006 and released for publication April 9, 2008. Current version published January 21, 2009. B. Ozpineci and M. S. Chinthavali are with the Power Electronics and Electric Machinery Research Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6472 USA (e-mail: ozpinecib@ornl.gov; chinthavalim@ornl.gov). L. M. Tolbert is with the Oak Ridge National Laboratory, Oak Ridge, TN 37831-6472 USA, and also with The University of Tennessee, Knoxville, TN 37996-2100 USA (e-mail: tolbert@utk.edu). A. S. Kashyap and H. A. Mantooth are with the Department of Electrical Engineering, University of Arkansas, Fayetteville, AR 72701 USA (e-mail: akashya@uark.edu; mantooth@uark.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIA.2008.2009501 use in traction drives replacing Si p-n diodes and insulated-gate bipolar transistors (IGBTs) [6] [14]. Presently, SiC Schottky diodes are the most mature and the only commercially marketed SiC devices available. These diodes are commercially available up to 1200 V/50 A or 600 V/20 A. SiC Schottky diodes have been proven to have better performance characteristics when compared with their equivalent Si p-n diodes [1], [15], particularly with respect to the switching characteristics. SiC devices can also operate at higher temperatures and thereby results in reduced heatsink volume. It is expected that the first impact of SiC power devices on automotive traction drives will be observed when SiC Schottky diodes replace Si p-n diodes in inverters [16]. Oak Ridge National Laboratory (ORNL) has collaborated with Cree and Semikron to build a Si IGBT SiC Schottky diode hybrid 55-kW inverter by replacing the Si p-n diodes in Semikron s automotive inverter with Cree s SiC Schottky diodes. This paper shows the results obtained from testing this inverter and comparing it with a similar all-si inverter. II. SIC SCHOTTKY DIODES Semikron has built 55-kW automotive integrated power modules (AIPMs) for the U.S. Department of Energy s Freedom- CAR Program s hybrid electric vehicle traction drives. These modules contain three-phase inverters with 600-V/600-A Si IGBTs and p-n diodes. For an ORNL project, Cree has developed 600-V/75-A SiC Schottky diodes, as shown in Fig. 1. Semikron has replaced each 150-A Si p-n diode in their AIPM with two of these 75-A SiC Schottky diodes. A. Static Characteristics After extensive testing, the I V characteristics of these diodes were obtained at different temperatures in the 50 C 175 C ambient temperature range (Fig. 2). Considering the piecewise linear (PWL) model of a diode, which includes a dc voltage drop V D and a series resistor R D, the diode I V curves can be approximated with the following: V d = V D + R D I d (1) where V d and I d are the diode forward voltage and current, respectively, and V D and R D are the diode PWL model parameters. 0093-9994/$25.00 2009 IEEE

OZPINECI et al.: THREE-PHASE INVERTER WITH Si IGBTs AND SiC SCHOTTKY DIODES 279 Fig. 1. The 600-V/75-A SiC Schottky diodes on a wafer next to a quarter. Fig. 4. (Solid) Measured and (dotted) simulated ON-state waveforms of the SiC Schottky diode at different temperatures. TABLE I SiC POWER DIODE MODEL PARAMETERS AND EXTRACTION CHARACTERISTICS FOR CREE 75-A DIODE Fig. 2. Experimental I V curves of the 75-A SiC Schottky diode. that these devices can be paralleled easily. The following show the temperature dependence of the SiC Schottky diode PWL model parameters: V D = 0.001 T +0.94 (2) R D =8.9 10 5 T +0.013 (3) Fig. 3. R D and V D obtained from the experimental data in Fig. 2. Fig. 3 shows R D and V D values of the 600-V/75-A SiC Schottky diodes with respect to temperature. As shown in Fig. 3, V D decreases with temperature, and R D increases with temperature. An increase in R D is a sign of the positive temperature coefficient the SiC Schottky diodes have, which implies where T is the temperature in degree Celsius. Another model of this SiC diode has also been developed for use in circuit simulators. The model, which was constructed in MAST hardware description language and simulated in the Saber simulator, was based on a diode model [17] developed at the University of Arkansas. Fig. 4 shows how the static characteristics of the model fit the experimental results. The percentage error is approximately 0.3% 0.4% in the 100 C and 150 C curves and approximately 2% 3% in the 25 C curve. Table I contains the values of the modeling parameters for this diode.

280 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 1, JANUARY/FEBRUARY 2009 Fig. 5. Reverse-Recovery current waveforms of the SiC Schottky diode for different forward current values. Fig. 7. Static characteristics of the packaged 600-V/450-A SiC Schottky and Si p-n diodes at room temperature. Fig. 6. (Solid) Measured and (dotted) simulated reverse-recovery waveforms of the SiC Schottky diode. Fig. 8. Reverse-recovery current waveforms of the Si p-n diode for different forward current values. B. Dynamic Characteristics The SiC Schottky diode was also tested in a chopper circuit to observe its dynamic properties. The chopper was switched at 1 khz with a 40% duty cycle. The reverse-recovery current waveforms obtained for different forward currents are shown in Fig. 5, where the reverse-recovery current does not change with the forward current. Note that, theoretically, Schottky diodes do not display a reverse-recovery phenomenon. Required junction capacitance for the diode model listed in Table I is obtained from the experimental reverse-recovery current waveforms. The corresponding fit of the model to the experimental waveform is shown in Fig. 6 for a forward current of 3 A. Note that the reverse-recovery current is larger in this plot compared with the ones in Fig. 5. This is because the forward current is selected to be much smaller to observe the fit in detail. Fig. 9. Experimental turnoff energy losses of a 75-A SiC Schottky diode and a 150-A Si p-n diode at room temperature.

OZPINECI et al.: THREE-PHASE INVERTER WITH Si IGBTs AND SiC SCHOTTKY DIODES 281 Fig. 10. Inverter output voltage and current during the inductive load test for two different conditions. (a) V dc = 325 V; i a,peak = 80 A; and f o = 50 Hz. (b) V dc = 325 V; i a,peak = 60 A; and f o = 100 Hz. C. Comparison With Si P-N Diode The automotive inverter used in this paper has 600-V/450-A diodes. For this reason, six 75-A SiC Schottky diodes are used to replace three 150-A Si p-n diodes. The static characteristics of the packaged 600-V/450-A SiC Schottky and Si p-n diodes at room temperature are shown in Fig. 7, where both diodes have similar characteristics. At low currents, the Si p-n diode has a lower voltage drop, while at higher currents, the SiC Schottky diode has a lower voltage drop; therefore, for higher power operations, the SiC Schottky diodes will have lower conduction losses. Switching losses of the 75-A SiC Schottky diode have been shown in Fig. 5. Similar tests have been done on the 150-A Si p-n diodes. The results of these tests are shown in Fig. 8. It can be observed that the peak reverse-recovery current of the Si p-n diode is much higher than that of the SiC Schottky diode at the same forward current and increases further with increasing forward current. This corresponds to high reverserecovery losses that increase with the forward current [18]. Fig. 9 shows the comparison of the energy losses per turnoff of a 75-A SiC Schottky diode and a 150-V Si p-n diode. As the diode forward current increases, the energy losses of the Si p-n diode increase exponentially, while those of the SiC Schottky diode are negligible. As a summary, the static characteristics of both of the tested diodes are similar; however, the dynamic characteristics are much different. The Si p-n diode has high peak reverse-recovery currents that result in high diode switching losses and extra IGBT losses since the reverse current has to go through a main switch. Consequently, it is expected the Si IGBT SiC Schottky diode inverter will perform better than the similar all-si inverter. III. INDUCTIVE LOAD TEST Both the Si SiC hybrid and the all-si inverters were tested with an inductive load and a dynamometer set with the same procedure and the same conditions. Fig. 11. R L load test efficiency curves for various load conditions. For the inductive load test, the output leads of the inverter are connected to a three-phase wye-connected variable resistor bank with a three-phase inductor in series. The dc inputs are connected to a voltage source capable of supplying the maximum rated operating voltage and current levels for the inverter. The dc link voltage was varied from the minimum operating voltage of 200 V to the maximum bus voltage of 450 V. The load resistance was set to the minimum value, and the output current was varied. The inverter operates with a 20 C coolant at a flow rate of 9.46 L/min. The open-loop frequency of operation and the PWM frequency (10 khz) were fixed, and the current command was varied for a particular dc-link voltage. For each value of the current command and open-loop frequency, the dc-link voltage, dc-link current, input/output power, efficiency, and output line currents and voltages were

282 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 1, JANUARY/FEBRUARY 2009 Fig. 12. Inverter output voltage and current during the dyn test for two different conditions. (a) One-thousand revolutions per minute and 50 N m. (b) One-thousand revolutions per minute and 150 N m. recorded. The three-phase power was measured using the twowattmeter method. The command current was increased in steps of 10 A without exceeding the power rating of the inverter or the power rating of the load. The procedure was repeated by increasing the openloop frequency in steps of 25 Hz. The coolant temperature was changed to 70 C and the aforementioned procedure was repeated to observe the operation at higher temperatures. The operating waveforms for two specific operating conditions of the Si SiC hybrid inverter are shown in Fig. 10. The data obtained for both of the inverters were analyzed, and the corresponding efficiencies were calculated. The efficiency versus output power plots for several operating conditions are shown in Fig. 11. The average loss reduction resulting from using SiC Schottky diodes instead of Si p-n diodes was calculated as %loss reduction = P loss Si P loss SiC Ploss Si 100. (4) The Si SiC hybrid inverter losses are up to 33.6% less than the all-si inverter. Fig. 13. Dynamometer test. Motoring mode efficiency plots with 70 C coolant and (a) 100-N m, (b) 150-N m, and (c) 200-N m load torques. IV. DYNAMOMETER TEST The inverters were connected individually to an induction machine set up in a dynamometer test cell to test them for their dynamic performance in the motoring and regeneration modes. The induction motor used was a four-pole induction motor with a base speed of 2500 r/min, and the dynamometer had a 100-hp capacity. The tests were performed with the inverter being supplied with 70 C coolant and a flow rate of 9.46 L/min.

OZPINECI et al.: THREE-PHASE INVERTER WITH Si IGBTs AND SiC SCHOTTKY DIODES 283 Fig. 14. Inverter output voltage and current during the regeneration test for two different conditions. (a) One-thousand revolutions per minute and 50 N m. (b) One-thousand revolutions per minute and 150 N m. A. Motoring Mode In this mode, the speed set point, the magnetizing current, the direction of rotation, and the current limit were the parameters that could be adjusted. The dc voltage input to the inverter was set at the nominal battery operating voltage (325 V dc). The closed-loop speed controller gains were adjusted for a given magnetizing current value and current limit to achieve a stable operation of the system for a wide range of speeds. The direction of rotation was set to forward, and the motor speed was increased from 750 r/min to the rated base speed for a specific continuous load torque. The load torque was varied gradually from zero to the required torque and then decreased to zero. The data were obtained for a wide range of speed and torque values by changing the load torque (100, 150, and 200 N m) using the dynamometer controller. The following information was recorded at each speed increment: motor shaft speed, motor torque, input and output voltages, and currents. The operation waveforms for two different load conditions are shown in Fig. 12. The efficiency plots for various speeds and Fig. 15. Dynamometer test. Regeneration mode efficiency plots with 70 C coolant and (a) 100-N m, (b) 150-N m, and (c) 200-N m load torques. load torques are shown in Fig. 13. The average loss reduction was obtained as described in the previous section. In this case, up to 10.7% reduction in the losses is observed. B. Regeneration Mode In this mode, the torque limit and the operating current can be adjusted. The dc voltage input to the inverter was set at the nominal battery operating voltage. The direction of rotation was set to be forward. The dynamometer controller was adjusted

284 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 1, JANUARY/FEBRUARY 2009 to control the speed, while the inverter controller controlled the current. Data had been collected for the 100-, 150-, and 200-N m torque produced by the drive. The procedure was repeated to obtain the data for a wide range of speed and torque values. The following information at each speed increment was recorded: motor shaft speed, motor torque, input and output voltages, and currents. The operating waveforms for the regeneration mode are shown at two different speeds in Fig. 14. The curves comparing the efficiency of the inverters with the 70 C coolant are shown in Fig. 15. In this mode, the reduction in the losses is comparable to the motoring case. V. CONCLUSION The testing of both the Si SiC hybrid and all-si inverters was completed successfully. The inverters were able to operate at peak power levels with efficiencies greater than 90%. The inverters were tested for a peak power of 47 kw and continuous rating of up to 35 kw. The test results show that, by merely replacing Si p-n diodes with their SiC Schottky diode counterparts, the losses of an inverter decrease considerably. As the device tests showed, the main reason for this is the high reverse-recovery losses of Si p-n diodes, which are negligible for SiC Schottky diodes. Note that both inverters were tested in the exact same conditions with the same controller. Since SiC Schottky diodes have a negligible reverse recovery, they do not stress the main switches as much as Si p-n diodes. Therefore, it is possible for the Si SiC hybrid inverter to operate at higher switching frequencies than the one used in these tests. ACKNOWLEDGMENT The authors would like to thank Dr. A. Agarwal and Dr. S.-H. Ryu of Cree and Dr. J. Mookken of Semikron for their part in building the hybrid inverter. Prepared by the Oak Ridge National Laboratory, Oak Ridge, TN 37831, managed by UT-Battelle for the U.S. Department of Energy under Contract DE-AC05-00OR22725. This paper has been authored by a contractor of the U.S. Government under Contract DE-AC05-00OR22725. Accordingly, the U.S. Government retains a nonexclusive royalty-free license to publish from the contribution, or allow others to do so, for U.S. Government purposes. REFERENCES [1] B. Ozpineci, L. M. Tolbert, S. K. Islam, and F. Z. Peng, Testing, characterization, and modeling of SiC diodes for transportation applications, in Proc. IEEE Power Electron. Spec. Conf., Cairns, Australia, Jun. 23 27, 2002, pp. 1673 1678. [2] L. M. Tolbert, B. Ozpineci, S. K. Islam, and F. Z. Peng, Impact of SiC power electronic devices for hybrid electric vehicles, presented at the Future Car Congr., Arlington, VA, Jun. 3 5, 2002, SAE paper 2002 01 1904. [3] S. Hodge, SiC Schottky diodes in power factor correction, Power Electron. Technol. 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Hefner, R. Singh, J. Lai, D. W. Berning, S. Bouche, and C. Chapuy, SiC power diodes provide breakthrough performance for a wide range of applications, IEEE Trans. Power Electron., vol. 16, no. 2, pp. 273 280, Mar. 2001. [10] B. Allebrand and H. Nee, On the possibility to use SiC JFETs in power electronic circuits, in Proc. Eur. Conf. Power Electron. Appl., Graz, Austria, 2001. [11] M. Ruff, H. Mitlehner, and R. Helbig, SiC devices: Physics and numerical simulation, IEEE Trans. Electron Devices, vol. 41, no. 6, pp. 1040 1054, Jun. 1994. [12] D. Peters, H. Mitlehner, R. Elpelt, R. Schorner, and D. Stephani, State of the art technological challenges of SiC power MOSFETs designed for high blocking voltages, in Proc. Eur. Conf. Power Electron. Appl., Toulouse, France, Sep. 2 4, 2003. [13] S. H. Ryu, A. Agarwal, J. Richmond, J. Palmour, N. Saks, and J. Williams, 10 A, 2.4 kv power DiMOSFETs in 4H-SiC, IEEE Electron Device Lett., vol. 23, no. 6, pp. 321 323, Jun. 2002. [14] S. H. Ryu, S. Krishnaswami, M. Das, J. Richmond, A. Agarwal, J. Palmour, and J. Scofield, 4H-SiC DMOSFETs for high speed switching applications, in Proc. 5th Eur. Conf. Silicon Carbide Related Mater., Aug. 31 Sep. 4, 2004, pp. 797 800. [15] S. Kyungmin, M. Kamaga, Y. Tanaka, and H. Ohashi, Optimum combination of SiC-diodes and Si-switching devices in high power application, in Proc. 37th IEEE Power Electron. Spec. Conf., Jun. 18 22, 2006, pp. 1 6. [16] W. Wright, J. Carter, P. Alexandrov, M. Pan, M. Weiner, and J. H. Zhao, Comparison of Si and SiC diodes during operation in three-phase inverter driving AC induction motor, Electron. Lett., vol. 37, no. 12, pp. 787 788, Jun. 2001. [17] T. R. McNutt, Modeling and characterization of silicon carbide power devices, Ph.D. dissertation, Dept. Elect. Eng., Univ. Arkansas, Fayetteville, AR, 2004. [18] N. Y. A. Shammas, M. T. Rahimo, and P. T. Hoban, Effects of external operating conditions on the reverse recovery behaviour of fast power diodes, EPE J., vol. 8, no. 1/2, pp. 11 18, Jun. 1999. Burak Ozpineci (S 92 M 02 SM 05) received the B.S. degree in electrical engineering from the Middle East Technical University, Ankara, Turkey, in 1994, and the M.S. and Ph.D. degrees in electrical engineering from the University of Tennessee, Knoxville, in 1998 and 2002, respectively. He is with the Power Electronics and Electric Machinery Research Center, Oak Ridge National Laboratory (ORNL), Knoxville, TN, first with the Postmasters Program in 2001, then as a Full-Time Research and Development Staff Member in 2002, and then as a Technical Program Manager in 2006. Currently, he is also an Adjunct Faculty with the University of Arkansas, Fayetteville. He is doing research on the system-level impact of SiC power devices, multilevel inverters, power converters for distributed energy resources and hybrid electric vehicles, and intelligent control applications for power converters. Dr. Ozpineci was the Chair of the IEEE Power Electronics Society Rectifiers and Inverters Technical Committee and was the Transactions Review Chairman of the IEEE Industry Applications Society Industrial Power Converter Committee. He was the recipient of the 2006 IEEE Industry Applications Society Outstanding Young Member Award; the 2001 IEEE International Conference on Systems, Man, and Cybernetics Best Student Paper Award; and the 2005 UT-Battelle (ORNL) Early Career Award for Engineering Accomplishment.

OZPINECI et al.: THREE-PHASE INVERTER WITH Si IGBTs AND SiC SCHOTTKY DIODES 285 Madhu Sudhan Chinthavali received the B.E. degree in electrical engineering from Bharathidasan University, Tiruchirapalli, India, in 2000, and the M.S. degree in electrical engineering from The University of Tennessee, Knoxville, in December 2003. He is currently with the Power Electronics and Electric Machinery Research Center, Oak Ridge National Laboratory, Oak Ridge, TN. His areas of interest include wide bandgap semiconductor power electronics, power system applications, and very large scale integration. Leon M. Tolbert (S 89 M 91 SM 98) received the B.E.E., M.S., and Ph.D. degrees in electrical engineering from Georgia Institute of Technology, Atlanta, in 1989, 1991, and 1999, respectively. He was with Oak Ridge National Laboratory (ORNL), Oak Ridge, TN, in 1991 and worked on several electrical distribution projects at the three U.S. Department of Energy plants in Oak Ridge, TN. In 1997, he was a Research Engineer with the Power Electronics and Electric Machinery Research Center, ORNL. Currently, he is an Associate Professor with the Department of Electrical and Computer Engineering, University of Tennessee, Knoxville, where he has worked since 1999. He is also currently an Adjunct Participant with ORNL and conducts joint research at the National Transportation Research Center. He does research in the areas of electric power conversion for distributed energy sources, motor drives, multilevel converters, hybrid electric vehicles, and application of SiC power electronics. Dr. Tolbert is a registered Professional Engineer in the state of Tennessee. He was the coordinator of Special Activities for the Industrial Power Converter Committee of the Industry Applications Society (IAS) from 2003 to 2006. He was the recipient of the 2001 IAS Outstanding Young Member Award. He was the Chair of the Education Activities Committee of the IEEE Power Electronics Society from 2003 to 2007. He was an Associate Editor of the IEEE POWER ELECTRONICS LETTERS from 2003 to 2006. He is currently an Associate Editor of the IEEE TRANSACTIONS ON POWER ELECTRONICS. Avinash S. Kashyap (S 03) received the B. Tech. degree in electrical and electronics engineering from the University of Calicut, Kerala, India, in 2001, and the M.S. degree in electrical engineering from the University of Arkansas, Fayetteville, in 2005, where he is currently working toward the Ph.D. degree in the Department of Electrical Engineering. His research is primarily focused on modeling (compact and Technology Computer Aided Design), characterization, and study of various semiconductor devices in extreme environments. He was an Intern with the Wide Bandgap Research Group, Oak Ridge National Laboratory, Knoxville, TN, and also with the SPICE Modeling Group, National Semiconductor, Santa Clara, CA. Mr. Kashyap is the recipient of the Sam Walton Doctoral Academy Fellowship and the William E. Clark Endowed Doctoral Fellowship. H. Alan Mantooth (S 83 M 90 SM 97) received the B.S. (summa cum laude) and M.S. degrees in electrical engineering from the University of Arkansas (UA), Fayetteville, in 1985 and 1987, respectively, and the Ph.D. degree from the Georgia Institute of Technology, Atlanta, in 1990. He was with Analogy in 1990, where he focused on semiconductor device modeling and the research and development of hardware-description-language (HDL)-based modeling tools and techniques. Aside from HDL-based modeling, his research interests include analog and mixed-signal IC designs. In 1998, he was a member of the faculty of the Department of Electrical Engineering, UA, as an Associate Professor, where he has received teaching, service, and/or research awards every year since his return and has been a Full Professor since 2002. In 2003, he cofounded Lynguent, an electronic design automation company focused on modeling and simulation tools. He has published over 100 refereed articles on modeling and IC design. He holds patents on software architecture and algorithms for modeling tools and has others pending. He is the coauthor of the book Modeling with an Analog Hardware Description Language (Norwell, MA; Kluwer, 1994). Dr. Mantooth is a member of Tau Beta Pi and Eta Kappa Nu and is a registered Professional Engineer in Arkansas. He was the Technical Program Chair for the IEEE International Workshop on Behavioral Modeling and Simulation in 2000 and was the General Chair in 2001. He served as the Guest Editor for a Special Issue on Behavioral Modeling and Simulation for the IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN in February 2003 and as an IEEE Circuits and Systems Society Distinguished Lecturer in 2003 2004. He is currently serving the profession in the following roles: IEEE Circuits and Systems Society (CAS) representative on the IEEE Council on Electronic Design Automation and member of the Power Electronics Society Advisory Committee as Chair of the Society s Standards Committee. In 1996, he was named Distinguished Member of Technical Staff at Analogy (now owned by Synopsys). He was also selected to the Georgia Tech Council of Outstanding Young Engineering Alumni in 2002 and to the Arkansas Academy of Electrical Engineers in 2006. He helped establish the National Center for Reliable Electric Power Transmission, UA in 2005, for which he serves as the Director. In 2006, he was selected as the Inaugural Holder of the 21st Century Chair in Mixed- Signal IC Design and Computer-Aided Design, an endowed chair position. He has served on several technical program committees for IEEE conferences.