Development of a BISG Micro-Hybrid System

Hybrid electric powertrain can be a promising and cost-effective technology to meet forthcoming emissions regulations. However, the hybridization of a conventional powertrain remains a complex task. According to their functions, hybrid powertrains can be classified into full-hybrid, mild-hybrid and micro-hybrid, of which micro-hybrid system is regarded as the most cost-effective solution for current regulations. Although a micro-hybrid system employs relatively simple new functions, such as stop/start and regenerative braking, to achieve the target fuel economy with reasonable cost, the engineer must consider many practical aspects in order to deliver a solution which is robust, effective and easy to understand for customers. In this paper the development of a belt-driven integrated starter generator (BISG) micro-hybrid system for a light-duty commercial vehicle application is presented. The system consists of a BISG machine, a power inverter, a DC/DC converter, an ultracapacitor package and an improved 12V lead-acid battery with battery monitoring system. The control system is implemented in a highly integrated vehicle control network via both CAN and LIN communications. Several practical aspects, such as system robustness, functional safety and control software development are discussed.