ICEMS 2021

Biography

Jih-Sheng (Jason) Lai received M.S. and Ph.D. degrees in electrical engineering from the University of Tennessee, Knoxville, in 1985 and 1989, respectively. In 1989, he joined the Electric Power Research Institute (EPRI). From 1993, he worked with the Oak Ridge National Laboratory as the Power Electronics Lead Scientist. He joined Virginia Tech in 1996. Currently he is James. S. Tucker Endowed Chair Professor and the Director of Future Energy Electronics Center (FEEC). He has published more than 490 refereed technical papers and holds 30 U.S. patents in the area of high power electronics and their applications. He received Technical Achievement Award in Lockheed Martin Award Night and 12 Best Paper Awards from IEEE conferences and journals. His student teams won Grand Prizes in TI Analog Design Competition in 2011 and International Future Energy Challenge in 2013. He also won the Top Three Finalist Award from Google Little Box Challenge in 2016 and a Finalist in American Made Solar Prize Challenge in 2020.

Lecture Summary

With fast development of wide bandgap (WBG) semiconductor devices and their promising features, ultrahigh-efficiency power electronics design can be realized. The WBG device Figure of Merit (FOM) measured by conduction and switching loss reduction is orders of magnitude improvement over the traditional silicon devices. Major impacts with WBG devices in electric vehicles (EV) traction drives are energy efficiency, size and weight reduction, and cooling system reduction that lead to the system cost reduction. However, there are some challenges associated with parasitic components and the fast di/dt and dv/dt slew rates. For a conventional voltage source inverter, the parasitic inductance in the phase leg can introduce a large voltage spike that false-triggers the opposite side or other phase leg switches. This phenomenon is well known with traditional silicon devices but is much more severe with WBG devices. Packaging and thermal management technologies are quite challenging as WBG devices tend to have a lot smaller chip areas to process the same power. Even with the silicon carbide having more than 3 times thermal conductivity than that of silicon, the thermal interface material is an obstacle that blocks the heat transfer path. Advanced packaging and thermal management technologies are needed to fully explore the capabilities of WBG devices. Overall, while WBG devices are showing promises, how to overcome all the underlying issues remains challenging.

Biography

Ronghai Qu, Fellow IEEE, received his B.E. and M.S. degrees from Tsinghua University, Beijing, China, in 1993 and 1996, respectively, and the Ph.D. degree in electrical engineering from University of Wisconsin-Madison in 2002. He had been with the General Electric (GE) Global Research Center, Niskayuna, NY as a Senior Electrical Engineer with the Electrical Machines and Drives Laboratory from 2003 to 2010. He was the recipient of more than 11 GE GRC awards including EPST Technical Achievement Award, Outstanding Teamwork and Management Award. In 2010 he joined Huazhong University of Science & Technology, Wuhan, China as a titled professor. He is currently the member of academic degrees committee, director of State and Province Joint Engineering Research Center of Novel Electrical Machines, director of Center for Advanced Electrical Machines and Drives (CAEMD), and deputy director of State Key Laboratory of Advanced Electromagnetic Engineering and Technology. From 2012 to 2016, he served as deputy dean of school of Electrical & Electronic Engineering. He is currently a member of ICEM NPO AdCom and the chair of IEEE Industry Application Society (IAS) Wuhan Chapter. His research interests include Design and Drive of Electrical Machines. He has published over 400 technical papers including 12 IEEE award papers and holds over 170 patents. Dr. Qu is the IAS Distinguished Lecturer for 2019-2021, and one of the winners of IAS Outstanding Member Awards in 2019.

Lecture Summary

Maximizing the torque density of electrical machines is always desired to save cost, volume and mass. Benefited from the Flux Modulation principle, the machine torque density now can be much improved by using two or more working airgap flux harmonics. One of examples is the permanent magnet vernier machines (PMVM), which can deliver up to 50% more torque than regular PM machines under natural cooling condition. And the torque density improvement is still going on as new topologies is discovered. What is the maximum torque density a machine could offer without knowing the machine topologies first? Or, how to design a machine to achieve the maximum torque density before knowing the winding topology? This presentation will try to look for an answer to that question.
This presentation will explore the upper limit of torque capability of a PM machine using an airgap flux design method named Airgap Flux Editing. With the specific PM rotor structure and major machine structure parameters, this method analyzes the working permeance harmonics at each position circumferentially along the airgap, and establishes the relationship between the working permeance harmonics and torque. After the optimal permeance value for the maximum torque is obtained at each point, the desired permeance values are combined point by point to form the optimized overall permeance distribution which leads to the desired stator structure. This presentation will firstly give a review of PMVMs which contains flux modulation principle, topology evolution and can also illustrate the bottlenecks of torque production. Airgap Flux Editing will then be introduced, the process of constructing optimal airgap permeance distribution based on Discrete Permeance Harmonic model to achieve maximal torque. At the end, several machine examples designed using the proposed method will be analyzed and presented.