Abstract
As the only power source of pure electric vehicles, lithium-ion batteries play an important role in vehicle powertrain systems. However, lithium-ion batteries have a significant reduction in capacity and power capability at low temperatures, which results in a greatly shortened driving range and poor acceleration of the vehicle. In this study, a rule-based battery external heating control strategy was developed to heat the battery during driving. The electrothermal film was affixed to the surface of each cell as an external heating material and powered by the battery. An equivalent circuit model combined with a thermal model was established to simulate the electrical and thermal dynamics of the system with sufficiently high accuracy and the control rules were developed based on the model. The optimal solution was obtained by adopting the dynamic programming algorithm to optimize the trade-off between temperature rise and energy consumption and maximize the total driving range under different conditions. Hardware-in-the-loop simulation results show that the vehicle with the proposed control algorithm can increase the total driving range by 18.6% to 220% for different driving conditions at cold to extremely cold temperatures compared with the vehicle without external heating. Furthermore, the rule-based control also shows a 1.1% to 4.4% improvement compared with the maximum (constant) power heating method.
Highlights
As environmental issues and the energy crisis continue to intensify in recent years, electric vehicles (EVs) have become a promising mobility that greatly reduces emissions and fossil fuel consumption
Instead of shortening the preheating time before driving, this study focuses on recovering the battery capacity and increasing the driving range by employing onboard heating control during driving
A battery external heating system by using electrothermal film and rule-based heating control strategy for electric vehicle driving at low temperature was developed in this study, based on an equivalent circuit model and thermal model, which were proven to have high fidelity through experimental and real-world driving tests
Summary
As environmental issues and the energy crisis continue to intensify in recent years, electric vehicles (EVs) have become a promising mobility that greatly reduces emissions and fossil fuel consumption. Under the requirements of vehicle performance, lithium-ion batteries have become increasingly widely used as traction batteries in EVs owing to their advantages of high energy density, low self-discharge, and long cycle life [2][3]. There is a nonnegligible drawback of lithium-ion batteries, in that the performance is greatly reduced at low temperatures. This is mainly due to poor electrolyte conductivity, poor lithium intercalation kinetics at the electrode surfaces, and poor ionic diffusion in the electrode bulk [4]. Because the traction battery is the only power source of pure electric vehicles, the reduced performance has a significant impact on the vehicle performance, including the shortened range, poor acceleration and loss of regenerative braking energy. A battery heating system and strategy in cold weather conditions are urgently needed to guarantee satisfactory vehicle performance
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