Structural and energy storage retrofit of an electric bus for high-power flash recharge

The activity here presented describes the retrofit performed on a small-size electric urban bus, which has been transformed in a laboratory vehicle for flash charge functionality using energy transfer between supercapacitors. The existing motor and driveline has been maintained, while the energy storage, originally based on lead batteries, has been modified reducing battery capacity and installing high voltage supercapacitors; such hybrid energy storage system is able to accept high recharge power (approximately about 150kW-peak in the used configuration), while smoothing power load on battery during traction. The system is therefore also able to extend the life of aged batteries. The so-called flash charge occurs through a pantograph connection to the infrastructure, typically in case of bus stops, during ascent and descent of passengers. The structure of the vehicle used for the transformation, which is still widely used worldwide, is constituted by as a glass fiber bodywork installed on a steel frame; since the body was not designed for the support of a significant mass as the one of the pantograph, it has been necessary to install an additional frame anchored to the main vehicle frame; such auxiliary frame has been designed also to substitute the internal fittings of the vehicle, in order to be used as stanchions for the standing passengers. In parallel, the battery compartment has been redesigned in order to install the supercapacitors and the new power converters needed. The contents of the article include the description of the mechanical components installed for the retrofit, the definition of the main power management strategy for the new powertrain and the results of preliminary testing activities.