Energy management and sizing of a dual energy storage system for electric vehicles

Abstract

Ambitions of emission reductions have been pushing increasing electrification of the automotive industry. Currently, battery powered electric vehicles (EVs) typically use a Li-ion battery-only energy storage system for propulsion. However, one single energy storage technology is not optimal for all demands of power density, energy density, lifetime and cost. In contrast, dual energy storage system (DESS) paring two energy storage components can decouple EV propulsion demands to each energy storage component. This work focuses on the optimisation of DESS in EV applications with five inter-related questions: (1) How to model DESS operations with EV propulsion so that the performance metrics of DESS can be simulated. (2) How to control the DESS in real-time so that the DESS can support EV propulsion adaptively and optimally. (3) How to determine the size of DESS so that the DESS can be configured with best-case parameters in long-term usage. (4) What the most critical factor is in controlling and sizing the DESS and how to optimise the factor. (5) Whether the emerging Al-ion battery technologies can replace the conventional Li-ion batteries and supercapacitors in the DESS with better performances. Consequently, five research problems of DESS are divided in terms of modelling, energy management, sizing, battery degradation and Al-ion DESS, and seven performance metrics are adopted as power capability, energy capacity, mass, volume, initial cost, battery degradation and electricity consumption. With the research problems and performances metrics, this work provides the following deliverables: (1) Hierarchical modelling approaches of EV with DESS. (2) Systematic design flow of the adaptive, optimal energy management strategy. (3) Joint energy management-sizing optimisation framework and general sizing guides. (4) Widely applicable benchmarks to optimise battery degradation. (5) Comparison of Al-ion batteries, Li-ion batteries and supercapacitors for the future development of DESS. By the investigations presented in this work, it is expected to offer optimisation methods and guides to enable the DESS to be robust, compact, economical and long life in EV applications.

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ORCID for Richard Wills: orcid.org/0000-0002-4805-7589

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