Extending the low-speed operation range of PM generator in automotive applications using novel AC-DC converter control

This paper outlines a case study on an integrated starter-generator-torque-booster (ISGtB) for a hybrid propulsion system, with a particular focus on the generator operation in the low-speed range. The propulsion system consists of an internal combustion (IC) engine and a brushless dc machine and is intended to drive a street scooter. The complex functionality of the ISGtB, some outstanding characteristics of modern IC engines, stringent demands on the generated supply voltage, and operational principle of the selected electrical machine are the reasons for our research on the generator operation. An ac-dc converter and its control are proposed. By utilizing MOSFET transistor reverse conduction characteristics, the idea of synchronous rectification, and the principle of boost switching conversion, several improvements in the generator characteristics are accomplished. The proposed solution, enabling each of the three-phase converter legs to operate as an autonomous boost converter with synchronously driven upper transistors instead of using body diodes, extends the generator operation range below the nominal rotational speed and offers simple yet efficient energy flow control.