Reliability Study of the Motor Controller of Pure Electric Vans

The market of electric vehicles (EVs) is rapidly growing across the world attributed to their unique feature of zero carbon emission. Take the Chinese market as an example, 984,000 pure electric vehicles were sold in China in 2018, which is an increase of 50.8% over the same period of the previous year. This means there will be more and more electric vehicles will run on the road in the future. However, the reliability of these electric vehicles is still an open issue remaining to resolve today. In particular, the reliability of the motor controller in electric vehicles is receiving more concern than ever before. On the one hand, this is because it is well known that power electronic components in the controller are much less reliable than the mechanical components in other EV subassemblies. One the other hand, it is because the failure of motor controller may lead to dangerous accidents on the road. Previously, much effort has been made to try to predict the reliability of motor controller, however detailed investigation of its reliability issues has never been done before. In view of this, a detailed reliability study of the motor controller in pure electric vans will be conducted in this paper, with the consideration of the fact that more than 90% of sold commercial electric vehicles are pure electric vans. In the research, the detailed root causes of the reliability issues in the motor controller will be investigated first and then based on which the failure rates of individual components (e.g. control module, driver module, communication module, and discharging module) in the controller will be estimated with the aid of fault tree analysis and the international standards IEC TR62308-2004, MIL-HDBH-217E and the technical standards for the Chinese electric vehicle industry. Finally, the tendency of the unreliability index of the entire motor controller against the service life of the electric vehicle is estimated based on the fault tree analysis results in order to obtain a more reliable understanding of the reliability performance of the motor controller over time. From such detailed reliability research, it has been found that the reliability performance of the motor controller will degrade gradually over time; and among the four functional modules of the controller the control module is most vulnerable, followed by driver module. This could be due to the application of more electronic components and thinner printed lines on the modules.