Propulsion and Energy Recuperation
Hybrid bus propulsion systems are generally formed using one of two types of systems – parallel and series hybrid systems.
In a parallel hybrid bus, the internal combustion engine (ICE) and the electric motor are connected to the transmission independently. In this case, the electric motor is designed to provide power during stop-and-go traffic while at higher speeds the vehicle will be powered by the ICE solely. During acceleration, both the electric motor and the ICE can power the transmission. A process called regenerative braking is typically employed to recover energy lost during the braking period to charge the electrical system. In this case the electrical system is comprised of a bank of ultracapacitor modules that are discharged during acceleration and recharged during braking.
Similarly, in the series hybrid bus, it too has an electrical system comprised of a bank of ultracapacitor modules. However, in this configuration, the bus is exclusively propelled by the electric motor, and the ICE is used to drive a generator which will charge the electrical system in conjunction with the charging provided by the regenerative braking system.
Whether the bus system uses a series or parallel configuration, the ultracapacitor module plays an integral role in the total system and helps bus manufacturers reach their government mandated pollution reduction, and increased fuel economy goals.