Battery Sizing for Mild P2 HEVs Considering the Battery Pack Thermal Limitations

Abstract

Small capacity and passively cooled battery packs are widely used in mild hybrid electric vehicles (MHEV). In this regard, continuous usage of electric traction could cause thermal runaway of the battery, reducing its life and increasing the risk of fire incidence. Hence, thermal limitations on the battery could be implemented in a supervisory controller to avoid such risks. A vast literature on the topic shows that the problem of battery thermal runaway is solved by applying active cooling or by implementing penalty factors on electric energy utilization for large capacity battery packs. However, they do not address the problem in the case of passive cooled, small capacity battery packs. In this paper, an experimentally validated electro-thermal model of the battery pack is integrated with the hybrid electric vehicle simulator. A supervisory controller using the equivalent consumption minimization strategy with, and without, consideration of thermal limitations are discussed. The results of a simulation of an MHEV with a 0.9 kWh battery pack showed that the thermal limitations of the battery pack caused a 2–3% fuel consumption increase compared to the case without such limitations; however, the limitations led to battery temperatures as high as 180 °C. The same simulation showed that the adoption of a 1.8 kWh battery pack led to a fuel consumption reduction of 8–13% without thermal implications.

Adaptive Model Predictive Control Including Battery Thermal Limitations for Fuel Consumption Reduction in P2 Hybrid Electric Vehicles

“…The constituents of the backward model are addressed in the following sections, and the parameters of the vehicle model are defined in Table 1. The detailed description of the backward model and its experimental validation for the case with conventional powertrain (Mazda CX9 2016) is illustrated in [17]. Furthermore, the experimental validation of the battery electro-thermal model described here is also illustrated in [17].…”

“…The detailed description of the backward model and its experimental validation for the case with conventional powertrain (Mazda CX9 2016) is illustrated in [17]. Furthermore, the experimental validation of the battery electro-thermal model described here is also illustrated in [17]. However, here the models of the main subsystems are presented for the sake of completeness.…”

“…The electro-thermal model of the lithium cell was developed and validated experimentally at an ambient environmental temperature in [17]. The equivalent circuit of the electric model according to [47] is shown in Figure 5.…”

“…The consequence is increased ageing and thermal runaway. The effect of battery temperature on fuel economy and battery ageing is discussed in [15][16][17][18].…”

“…Notwithstanding the benefits of ECMS, the results are not globally optimum [27]. By defining an equivalent fuel cost for the battery energy, the ECMS strategy is developed to be solved at each instant rather than over the driving range [15,17,28]. Tuning the ECMS can be a complex task since the weighting parameters are determined heuristically.…”