Range extension via electrothermal recuperation

Abstract

One of the decisive reasons for the slow market penetration of electric vehicles is their short driving range, especially in cold temperatures. The goal of this paper was to increase the driving range in cold temperatures. Electric vehicles recover kinetic energy by recuperation and storage in the battery. However, if the battery is fully charged or cold, the option of recuperation is severely limited. Braking energy is dissipated into the environment via the mechanical brake, and the range thus decreases. Electrothermal recuperation (ETR) enables the braking power to be used in heater systems and thus saves energy in the overall system. In this paper, ETR was investigated with a highly responsive serial layer heater. An overall model consisting of the electric powertrain, the heating circuit, and the vehicle interior was developed and validated. The limitations of recuperation capability were determined from driving tests. The factors state of charge and battery temperature were varied in the conducted simulations in order to quantify the range increase through ETR. The results showed that the range could be increased via electrothermal recuperation by up to 8% at-10 °C in a real driving cycle, using a serial heater. A control strategy of the heating circuit enabled the coolant circuit to function as buffer storage. The interior temperature-and consequently user comfort-remained unchanged.