Regression Analysis of Factors Affecting Round-Trip Regenerative Braking Efficiency Using Real-World Data

Regenerative braking is an effective way of improving the overall efficiency of electrified road vehicles. When driving, as well as optimising the strategy, it is important to understand the main factors affecting the energy recuperated in the real-world, both positively and negatively. A series of over 60 drives in both directions between Swieqi, Malta, and the Faculty of Engineering at the University of Malta were performed, on different days, in different conditions, on a 2017 Nissan LEAF AZE-0. A multiple linear regression study with threefold validation was performed for each direction, taking the round-trip regenerative braking efficiency as the dependent variable. When eliminating outliers, a model with an absolute mean error of less than 5 per cent was achieved. The trip between Swieqi and the Faculty of Engineering is predominantly downhill, while the return is predominantly uphill. It was found that downhill, the main factors influencing the round-trip regenerative efficiency were brake pressure and vehicle speed. Uphill, however, the regenerative braking efficiency was mostly influenced by the torque. It was therefore concluded that the independent variables of brake pressure, vehicle speed, and motor torque can capture the regenerative braking efficiency successfully for such routes. Considering input and output motor torque, the average round-trip regenerative braking efficiency was found to be 50.1 per cent.