Traction Inverter Highly Accelerated Life Testing With High-Temperature Stress

Highly accelerated life testing (HALT) is one of the most popular step-stress testing methodologies for identifying the weaknesses and increasing product reliability in a fast and cost-efficient way. The traction inverter plays a critical role in EV/HEV power train systems, and the requirements on its reliability at the harsh environment operation are becoming more demanding. In this article, to evaluate the weak links and various components performance and ascertain the effect of high temperature on the traction inverter, the traction inverter HALT was carried out with high-temperature stress between 190 °C-220 °C taking the IGBT on-die temperature as the benchmark. Nine traction inverters were tested, which were divided into four groups with respect to the designed step-stress test profile. The changes in electrical and thermal indicators were observed online using the proposed monitoring system. At the end of each test, the effects of different conditions on the overall testing time, failure modes, and damage were examined, and the damages were listed systematically and discussed. Furthermore, the characteristics of the dc-link capacitor at different temperatures and the related degradation were observed online. The results show that the inverter can operate hundreds of hours with the IGBT on-die temperature of 200 °C, and the gate driver board chip of 127 °C. The findings in this study could help to the improvement design of the traction inverter, as well as to keep the design life prediction never be overestimated.

I. Introduction

Developing electric vehicles (EVs) and hybrid EVs (HEVs) have the potential to reduce fossil energy dependence and alleviate global air pollution due to their lower levels of carbon dioxide and pollutant emissions than conventional fuel vehicles. In recent years, EVs/HEVs have obtained significant market penetration and stimulated a great number of research works both in industry and academia [1], [2]. Automakers, in particular, are making great efforts to develop different types of EVs/HEVs with strong support from worldwide governments and energy organizations. However, the growth of EVs/HEVs brings not only many opportunities but also a series of challenges in terms of the power, efficiency, weight, volume, cost, reliability, and lifetime of these vehicles. Among these, reliability is a critical issue because they are essential requirements for vehicle safety given a harsh environment [3], [4]. To make EV/HEV technology commercially viable, current trends in the automotive electronics industry will integrate the motor-drive cooling system and engine-coolant system, which leads to IGBT switching devices operating at a junction temperature of 200 °C [5]–[7]. Apart from the integrated IGBT power modules, the traction inverter also assembles the filter capacitors, bus-bar connections, low-voltage auxiliary power supplies, current and temperature sensors, control and gate drive boards, mechanical parts, and so on. [8]. These components’ temperatures also increase with environment temperature, which affects their performance and reliability.