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Minimum-time optimal control for battery electric vehicles with four wheel-independent drives considering electrical overloading

This paper analyses the performance benefit due to electrical overloading of battery pack and electric motors in battery electric vehicles with four wheel-independent drives. The performance enhancement is quantified by relative lap time improvements which are computed using minimum-time optimal control. Additionally, a concurrent optimisation is performed which provides the optimal gear ratios for the front and rear reduction gears as well as the optimal performance distribution between the front and rear motors under the specification of a fixed total motor performance. We characterise the motor performance by the maximum torque, the maximum speed and the overload capability of the electric machines. The essential dynamics are represented using a nonlinear two-track vehicle model and a Thevenin battery model. We propose a simplified modelling approach for electrical overloading using power loss maps and energy reservoirs. This way, we keep the number of additional states low which is advantageous for optimal control problems. Direct optimal control and Hermite-Simpson collocation is used to solve the optimisation problem numerically.