Effects of battery degradation on a hybrid electric propulsive system management

Amongst the most concerning issues regarding hybrid electric propulsive systems (HEPS), together with sizing and control, is that of energy management strategy (EMS). EMS is crucial for the optimal usage of the system itself and is generally aimed at the minimisation of fuel consumption while keeping under control the battery state of charge, especially if the electric path of the HEPS is also used to ensure power availability in the case of engine failure. However, the battery is prone to fast degradation during its useful life. Therefore, it is particularly important to include battery aging effects in the energy management strategy. The present study compares two different approaches in the energy management strategy of a rotorcraft for urban air mobility, age-dependent and age-independent, on a given mission. The parallel HEPS includes a turboshaft engine, two electric motors, and a lithium battery whose degradation is analysed in terms of capacity, internal resistance, and Peukert coefficient. The results show that the age-dependent strategy determines a more conservative usage of the battery with the consequence of achieving a higher degree of safety at the expense of slightly higher fuel consumption.