Frameworks for Power and Systems Management in Hybrid Vehicles: Challenges and Prospects

Pi Technology has been working on hybrid propulsion systems for its various customers for several years, including the Ford Fuel Cell Focus and Hybrid Escape. The systems we have worked on cover a wide range of technologies, from fuel cell/battery and engine/battery systems to hydraulic based systems. As a result we are only too aware of the multitude of issues that need to be addressed. Each of the systems when viewed in isolation appears to be completely different to each of the others; however, we have found this not to be the case, in that common architectural challenges have emerged from each system. In this paper we review the issues we encountered on two early hybrid projects and discuss our experimental efforts at creating a unified control strategy framework for combining different components, in a way that provides a consistency of view between the individual subsystems and the system as a whole. We then go on to examine how we applied this experience to a hydraulic hybrid vehicle, and to some of the novel issues that such systems possess.