Modelling and Control of a Hybrid Urban Bus

This paper describes the development and on-vehicle validation testing of next generation parallel hybrid electric powertrain technology for use in urban buses. A forward-facing MATLAB/Simulink powertrain model was used to develop a rule-based deterministic control system for a post-transmission parallel hybrid urban bus. The control strategy targeted areas where conventional powertrains are typically less efficient, focused on improving fuel economy and emissions without boosting vehicle performance. Stored electrical energy is deployed to assist the IC engine system leading to an overall reduction in fuel consumption while maintaining vehicle performance at a level comparable with baseline conventional IC engine operation. Regenerative braking is integrated with the existing braking systems on the vehicle, and the control system tailored to maximise the amount of energy recuperated during deceleration events and accelerator pedal lift off without adversely impacting on the normal behaviour of the vehicle. The control system was implemented on both prototype single (Streetlite) and double-deck (Streetdeck) vehicle configurations for real vehicle testing with partner Wrightbus. The hybridisation has reduced equivalent CO₂ emissions by 34% (single-deck)/ 35% (double-deck) over the conventional Euro VI diesel vehicle on the Low Carbon Vehicle Partnership UK bus cycle (based on London Bus Route 159). These results compare favourably with alternative powertrain technologies currently available with similar certification. Moreover, the next generation hybrid urban bus has several distinct advantages as it is less restricted by infrastructure, range, or terrain issues, and has a comparatively lower purchase price point. Hybrid bus technologies offer the option of maintaining existing service levels without significant modifications to operations or budgets while achieving significant reductions in average fleet emissions.