A gatekeeper energy management strategy for ECVT hybrid vehicle propulsion utilising ultracapacitors

Since their introduction in 1995, power split electronic continuously variable transmissions (eCVT's) have evolved rapidly and found wide acceptance in hybrids. The eCVT exhibits smooth and seamless speed transitions by virtue of its lack of clutch and step ratio gear change transmission. There are increased demands on the vehicle energy storage system (ESS) in the form of higher power cycling and thermal dissipation. Energy management strategies (EMS) have become very prominent in the need to manage the multiple power sources via efficiency optimizing control of engine output, floating bus voltage level on the generator and motor, electronically controlled brakes, and converter buffering of the traction battery. This paper discusses a novel gatekeeper EMS that relies on the ultracapacitor as the power cache focal point for all ESS energy transactions. It is found that controlled power circulation to replenish the battery significantly reduces battery cycling and provides state of charge (SOC) control that facilitates battery size reduction. Hybrid electric vehicle energy management strategies have become very important in the optimization of economy and performance. For the majority of drivers however a more efficient electrical architecture coupled with enhanced EMS control will result in hybrids delivering on expectations on economy. Using an ultracapacitor and battery combination ESS has the potential to substantially improve battery life and economy. The ultracapacitor is more efficient at energy cycling than batteries and is not subject to the wear out mechanisms that batteries are.