Evaluation of Hitachi Electric Vehicle Combined Battery System Lifespan in India (Related with "Development of a Combined Battery System for Electric Vehicles with Battery Lifespan Enhancements" )

Paper #:
  • 2018-01-0447

Published:
  • 2018-04-03
Abstract:
We have developed a drive cycle (DC) to test Hitachi’s combined battery system (CBS) for electric vehicles (EVs) having battery lifespan enhancements. Low cost EVs popularly called as Neighbourhood Electric Vehicle or Low-Speed-Electric-Vehicle are spreading in developing countries. Conventionally their batteries consist of high energy density cells, and we call them as capacity type battery (CTB). A major issue with the EVs is high operational costs mainly due to short lifespan of the CTBs. The CBS almost doubles the CTB lifespan and thus overall battery system lifespan, with a marginal additional cost, as per the evaluation over Worldwide harmonized Light vehicles Test Procedure (WLTP) based method. We want to test the CBS under Indian conditions which has predominantly hot weather, uneven and traffic jam scenarios. The battery deterioration and thus its lifespan is sensitive to the traffic conditions and ambient temperature. Hence, it was needed to evaluate the CBS over an Indian drive cycle (DC) and use 40°C as ambient temperature. However, it was difficult to carry out the tests as there is no standard Indian DC for small / light weight four wheelers. Hence, we decided to synthesize a DC and collected over 1.5 million OBD data samples from four cars driven along different routes within Bangalore city. The synthesized DC, for accuracy should resemble the original data in terms of speed and acceleration. We proposed a novel method to synthesize a DC. We evaluate our method through statistical (such as average/max. speed, acceleration, etc.) and frequency based similarity of the synthesized DC from the OBD data. Finally, using the synthesized DC it was recognized that the battery lifespan could be enhanced by a factor of 2 through CBS over CTB alone, for Indian conditions also. However, lifespan under the Indian conditions is reduced by a factor of 0.72 of the corresponding WLTP based lifespan estimates.
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