Date of Award


Publication Type


Degree Name



Electrical and Computer Engineering


Capacitor, Condition Monitoring, DC-Link, Lifetime Extension, PWM


Narayan Kar


Lakshmi Varaha Iyer



Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.


Electric vehicles offer the benefit of eliminating tailpipe emissions, which emit greenhouse gases (GHG) into the atmosphere, lead to diminished air quality, and contribute to global warming. Therefore, plenty of research has gone into the development and improvement of EV technologies to create more effective and reliable vehicles in comparison to traditional internal combustion engine (ICE) vehicles. The electric traction drive, or powertrain, is the fundamental system responsible for controlling the output response of the electric motor within an EV. High efficiency and reliability are extremely desirable traits for the electric drive to extend the range of the EV to reduce driver anxiety, as well as to extend the vehicle’s lifetime for a more cost-effective product. Condition monitoring of fragile components allows for the prediction of device failure before it occurs so that catastrophic failure can be avoided, system downtime is reduced, and system reliability can be enhanced. This thesis aims to develop an existing condition monitoring strategy for the most fragile electrical component within the drive, the DC-Link capacitor. The functionality of the DC-Link capacitor is discussed and power loss modelling for the device is presented. A DC-Link capacitor condition monitoring scheme that employs two state-of-health (SOH) determination strategies is presented for improved reliability of the DC-Link capacitor, and overall motor drive system. This scheme features an online degradation calculation method and a quasi-online parameter estimation method for determining the SOH of the device. An analysis of the impact of sensor tolerance, sampling frequency and ambient temperature on parameter estimation accuracy is also performed, and the minimal sampling frequency required for reliable condition monitoring is identified as 50 kHz through simulation and experimental results. This thesis also proposes a novel LUT based PWM selection strategy with the aim of prolonging the lifetime of the DC-Link capacitor without significantly sacrificing the performance of the permanent magnet synchronous machine (PMSM) drive compared to conventional control methods. The total capacitance degradation over a drive-cycle based analysis is compared under the proposed PWM selection strategy and under conventional space vector PWM control in order to validate the ability of the proposed strategy to extend the lifetime of the DC-Link capacitor. In the simulation study, over a nine load point load profile the degradation of the dc-link capacitor was reduced by 3.994% under the proposed strategy, validating the ability to extend the lifetime of the dc-link capacitor.

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