Reliability-Oriented Design of Inverter-Fed Low-Voltage Electrical Machines: Potential Solutions

Abstract

Transportation electrification has kept pushing low-voltage inverter-fed electrical machines to reach a higher power density while guaranteeing appropriate reliability levels. Methods commonly adopted to boost power density (i.e., higher current density, faster switching frequency for high speed, and higher DC link voltage) will unavoidably increase the stress to the insulation system which leads to a decrease in reliability. Thus, a trade-off is required between power density and reliability during the machine design. Currently, it is a challenging task to evaluate reliability during the design stage and the over-engineering approach is applied. To solve this problem, physics of failure (POF) is introduced and its feasibility for electrical machine (EM) design is discussed through reviewing past work on insulation investigation. Then the special focus is given to partial discharge (PD) whose occurrence means the end-of-life of low-voltage EMs. The PD-free design methodology based on understanding the physics of PD is presented to substitute the over-engineering approach. Finally, a comprehensive reliability-oriented design (ROD) approach adopting POF and PD-free design strategy is given as a potential solution for reliable and high-performance inverter-fed low-voltage EM design.

The Insulation Resilience of Inverter-Fed Low Voltage Traction Machines: Review, Challenges, and Opportunities

“…In this regard, it is a kind of renaissance of the phenomenon compared to the introduction of the insulated gate bipolar transistor (IGBT) devices [3]- [5]. However, the electrical stress is further increased by the two factors mentioned and the reliability decreases significantly if no countermeasures or fundamental system changes are made, which increases electrical resilience [6]. In addition to the electrical stress, the electric machine is exposed to further multifactorial interacting influences during operation -the so-called TEAM factors (thermal, electrical, ambient, mechanical).…”

“…High safety margins or alternative materials are simply too expensive or not suitable for BEVs. Hence, a profound understanding is required, for designing the insulation system to the edge, avoiding cost-intensive over-engineering, as is still the practice at the moment [6]. Unfortunately, those required insights are currently not at hand, which will be outlined throughout this paper.…”