With the application of wide bandgap power electronics in electric machine drive systems, engineers and researchers are concerned that the higher dv/dt rate will accelerate the degradation of the insulation system in variable speed drives. It is not well understood which part of the machine insulation should be strengthened and which part could be reduced. Thus, high precision modeling, simulation and test methods are needed to predict voltage stress and current distribution in machine windings to reach an optimal design to ensure the reliability within reasonable design margins.
This seminar will discuss the finite element modeling, mathematical modeling and experimental testing of the voltage stress and current distribution inside electric machine windings driven by PWM voltage excitations. Both the stranded random-wound windings and bar-wound windings will be used in the teaching demonstration. The voltage stress considered includes the voltage across individual turns, the voltage between any two turns, and the voltage between any turn and the stator ground wall during power electronics switching transients and steady state. The current distribution includes the currents in parallel wires and the current distribution within each conductor for the bar-wound winding case.
Julia Zhang has been an Assistant Professor with the Center for High Performance Power Electronics (CHPPE) at The Ohio State University since 2017. From 2012 to 2017, she was an Assistant Professor with Oregon State University. From 2010 to 2012, she was a control engineering with Ford Motor Company, Dearborn, MI. She received her Ph.D. in Electrical Engineering from The Ohio State University in 2010. Her research interests are electric machines, power electronics, high voltage engineering and robotics.
Yanyan Xie is a Senior Electromagnetic Design Engineer with Rivian. She received her Ph.D. degree in Electrical Engineering from The Ohio State University in 2020. From 2016 to 2017, she was a Ph.D. student at Oregon State University. From 2012 to 2015, she worked as an electrical engineer with China Southern Power Grid. She received her B.S. and M.S degrees in Electrical Engineering from Xi'an Jiaotong University in 2009 and 2012, respectively. Her research interests are electric machines, power electronics and power system engineering.
Franco Leonardi (M’96) received the Degree and the Doctorate degree in electrical engineering from the Università degli Studi di Padova, Padova, Italy, in 1991 and 1995, respectively. From 1994 to 1996, he was a Research Associate at the University of Wisconsin, Madison, where his research focused on Doubly Salient PM machines. Since 1999, he has been with the Ford Research Laboratories, Ford Motor Company, Dearborn, MI, where he has been involved in the development of hybrid electric vehicles. He is currently the supervisor of the Power Electronics and Electric Machines Research team. He has authored 19 U.S. patents and 30 international publications that have received over 1600 citations.
Figure 1. Cross-sectional view of random-wound windings
Figure 2. Capacitances between individual conductors and stator ground wall
Figure 3. First 3-phase winding prototype used in lab for voltage stress measurement
Figure 4. Production motor on hybrid electric vehicle product used for voltage stress measurement
Figure 5. Voltage stress at machine end winding