An official website of the United States government
Electric vehicles (EVs) rely on robust inverter-to-motor connections to ensure high-efficiency operation under the challenging conditions imposed by wide-bandgap (WBG) semiconductors. High switching frequencies and steep voltage rise times in WBG inverters lead to repetitive transient overvoltages, causing insulation degradation and premature motor winding failure. This study proposes a wideband (WB) model of EV cables, developed in EMTP-RV, to improve transient voltage prediction accuracy compared to the traditional constant parameter (CP) model. Using a commercially available EV-dedicated cable, the WB model incorporates frequency-dependent parasitic effects calculated through the vector fitting technique. The motor design is supported by COMSOL Multiphysics and MATLAB 2023 simulations, leveraging the multi-conductor transmission line (MCTL) model for validation. Using practical data from the Toyota Prius 2010 model, including cable length, motor specifications, and power ratings, transient overvoltages generated by high-frequency inverters are studied. The proposed model demonstrates improved alignment with real-world scenarios, providing valuable insights into optimizing insulation systems for EV applications.
more »
« less
Precise Evaluation of Repetitive Transient Overvoltages in Motor Windings in Wide-Bandgap Drive Systems
The increasing interest in employing wide-bandgap (WBG) drive systems has brought about very high power, high-frequency inverters enjoying switching frequencies up to hundreds of kilohertz. However, voltage surges with steep fronts, caused by turning semiconductor switches on/off in inverters, travel through the cable and are reflected at interfaces due to impedance mismatches, giving rise to overvoltages at motor terminals and in motor windings. The phenomena typically associated with these repetitive overvoltages are partial discharges and heating in the insulation system, both of which contribute to insulation system degradation and may lead to premature failures. In this article, taking the mentioned challenges into account, the repetitive transient overvoltage phenomenon in WBG drive systems is evaluated at motor terminals and in motor windings by implementing a precise multiconductor transmission line (MCTL) model in the time domain considering skin and proximity effects. In this regard, first, a finite element method (FEM) analysis is conducted in COMSOL Multiphysics to calculate parasitic elements of the motor; next, the vector fitting approach is employed to properly account for the frequency dependency of calculated elements, and, finally, the model is developed in EMTP-RV to assess the transient overvoltages at motor terminals and in motor windings. As shown, the harshest situation occurs in turns closer to motor terminals and/or turns closer to the neutral point depending on whether the neutral point is grounded or floating, how different phases are connected, and how motor phases are excited by pulse width modulation (PWM) voltages.
more »
« less
- Award ID(s):
- 2306093
- PAR ID:
- 10383379
- Date Published:
- Journal Name:
- Vehicles
- Volume:
- 4
- Issue:
- 3
- ISSN:
- 2624-8921
- Page Range / eLocation ID:
- 697 to 726
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
This study examines how fast rise times, which are common in modern power electronics and drive systems, affect the aging of electric machine windings. It focuses on how to ensure these windings can last longer and work reliably in electrical systems. A twisted pair magnet wire with insulation commonly used in wound machines was used to get experimental data to understand how different voltage waveforms can influence endurance testing of motor insulation systems powered by inverters. Unlike past studies that looked at comparatively slower rise times and fewer repetitions, this research specifically addresses the challenges posed by next-generation wide bandgap (WBG)-based conversion systems. These systems operate at very high speeds, up to 100 kV/μs, and switch frequencies up to 500 kHz, where both frequency and rise time are crucial factors affecting insulation aging over time.more » « less
-
High-performance switching devices like SiC MOSFETs introduce high-frequency ringing and overvoltage transients at motor terminals, leading to uneven voltage distribution across windings. In SiC-driven motors, the first coil and initial turns experience significant overvoltage stress, increasing the risk of insulation degradation and inter-turn faults. This study proposes an analog circuit to mitigate overvoltage stress. The circuit detects high dv/dt in the first coil and adaptively inserts a ceramic capacitor via a GaN switch, forming a low-impedance path for high-frequency currents. This diverts part of the transient energy to the second coil, reducing stress on the first coil and promoting uniform voltage distribution. The GaN switch remains closed to sustain the high-frequency current path through the capacitor, adapting to different operating conditions and cable lengths. The circuit was prototyped and experimentally validated on a 2hp induction motor driven by a SiC inverter, demonstrating its effectiveness in mitigating overvoltage stress. This compact solution enhances the reliability of SiC-driven motor systems by addressing uneven high-frequency voltage distribution.more » « less
-
While wide bandgap (WBG) switches have revolutionized power electronics and motor-drive systems, the high dv/dt associated with these fast-switching semiconductors can easily induce reflected high-frequency overvoltage spikes on motor stator terminals. The shorter rise time of the voltage pulses confines the cable length between the inverter and the motor in practice to avoid overvoltage across the motor stator windings. Even with shorter cables, voltage spikes from variable-speed drives can still cause premature insulation failure and reduce the remaining useful lifetime of the motors. While effective, conventional methods such as dv/dt passive filters or active gate drivers are usually bulky and/or inefficient. To address this problem, an overvoltage mitigation solution, named “Smart Coil,” is introduced in this article. The smart coil circuit is installed in parallel with the first coil of each motor phase, which typically experiences the highest reflected overvoltage. Upon detection of overvoltage, the proposed ultracompact smart coil circuit, located at the motor junction box, is activated to limit voltage stress across the coils. Since the smart coil is connected in parallel with the first coil, it only needs to process very low pulsed power during the overvoltage transients. Therefore, it has high efficiency and an ultracompact footprint while effectively mitigating voltage spikes. The proposed smart coil circuit can be easily scaled for various motor-drive systems regardless of the cable length or rise time of the switching devices. Simulation and experimental test results are provided to verify the effectiveness of the proposed method.more » « less
-
Emerging power electronic drives and converters, especially wide bandgap (WBG) technology-based devices, are expected to operate at high voltages and switching frequencies, potentially reaching up to several hundred kHz. These operating conditions pose significant challenges to the reliability of insulation systems in motor windings, which are critical to the longevity and safe operation of electrical machines. This study investigates the impact of high-frequency square wave voltage pulses on the lifetime of motor winding insulation by conducting lifetime tests on twisted pair magnet wire commonly used in electrical machines. The experiments were conducted in the frequency range of 100 kHz to 300 kHz, with rise times of 50 ns and 400 ns (slew rate ranging from 2.4kV/μ s to 19.2kV/μs), to simulate the conditions typical in modern power electronics and inverter-driven systems. The results show that fast rise times and high switching frequencies influence turn-to-turn insulation's aging and breakdown characteristics. The findings highlight the importance of switching frequency and rise time in determining the reliability of insulation systems, offering critical data to enhance the design and performance of electrical machines in the context of high-frequency operation.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/vehicles4030040
