Hybrid buses: defining the power flow management strategy and energy storage system needs

The following article will analyze the benefits of retrofitting a diesel-electric bus by hybridizing its drive train with a supercapacitor based energy storage system (ESS). Several power flow management strategies will be proposed and compared; and their respective ESSs will be sized and designed accordingly. The energy savings achieved range between 32 % and 40%, due to braking energy recovery and an improved ICE efficiency, and show the importance of the power flow strategy. Results are obtained by means of a quasi-static ‘backwards/forward looking’ simulation program, developed for this purpose, which includes a dynamic model of the ICE. Performance of the conventional bus and the hybrid bus is also compared.