Energy analysis of an electric minibus in real conditions

The objective of this study has been to analyze the energy flows and evaluate the overall performance under real conditions of the system " electric minibus", with particular reference to an application case of public transport. The analyzed vehicle is 5,3 m length of and 2,1 m width and it can carry 28 passengers maximum. The traction is guaranteed by a Direct Current (DC) electric motor with a power of 25 kW at 72 V, with a maximum torque of 235 Nm. The energy required by the engine is provided by two nickel-cadmium battery packs connected in series and having 125 Ah total capacity, with a nominal overall voltage of 72 V. The power output is modulated by the chopper, which controls the energy flow between the batteries and the motor. To perform the energy analysis, together with the on-board electronic diagnostic and monitoring systems installed by the vehicle manufacturer, an additional measurement chain has been used. The preliminary tests have been carried out on the vehicle to monitor the characteristic parameters: current and voltage of the batteries, vehicle speed. Through the study of the obtained values, the vehicle energy performance has been analyzed in dynamic and real conditions, with particular reference to the following quantities: energy consumption per km in urban areas, overall efficiency of the system, maximum speed, charging time. The first four variables have been evaluated under different load conditions (people that get on the bus and increasing the total vehicle mass) and routes (slopes), so that energy consumption of the vehicle can be evaluated in real drive cycles.