Reducing the energy consumption of electric buses with design choices and predictive driving

Abstract

Transportation electrification is increasing and recently more focus has been directed on heavy vehicles and especially on city buses. Battery electric buses are inherently more energy efficient than diesel buses and the efficiency can be further increased by different methods. This paper evaluates the energy consumption reductions that are achievable with an aluminum chassis, low-drag body, low-rolling-resistance class C tires, heat pump, and predictive driving. A simulation model of a generic electric bus was developed in the Simulink software. Simulations were carried out on various types of driving cycles in cold (-10 °C) and warm conditions (20 °C). A novel nonlinear model predictive control problem formulation was created for minimizing the energy consumption of an electric bus. Using a heat pump instead of an electric heater provided the highest energy savings in the cold conditions with an average consumption reduction of 12.7 %. The results indicated that a heat pump is particularly effective on low-speed bus routes. However, the class C tires and aluminum chassis provided higher energy savings than the heat pump in the warm conditions. The low-rolling-resistance tires achieved the most robust energy savings. The aluminum chassis reduced the energy consumption more than the class C tires, but the benefit of the lighter chassis was shown to also correlate strongly with the aggressiveness of the driving. The results showed that a low-drag body is a potential method for consumption reduction on high-speed bus routes. Predictive driving was found to reduce the average consumption by 9.5 % at -10 °C when using 10-second prediction and control horizons.