Technology Considerations for Belt Alternator Starter Systems

Technology Considerations for Belt Alternator Starter Systems

ABSTRACT

Due to the need for improving fuel economy, reducing tailpipe emissions and the trend towards increasing electrical content in automobiles, hybrid drivetrains are being considered by the automotive industry. In the foreseeable future, in order to address the drive towards hybridization, vehicle manufacturers will begin to use a 42 volt-based architecture in conjunction with an integrated starter and generator system. Depending on the desired power level and allowable changes to the vehicle drivetrain, either an Integrated Starter Generator which mounts between the engine and the transmission or a Belt Alternator Starter (BAS) system which mounts on the accessory belt can be used.

This paper will examine the impact of choosing either a Permanent Magnet (PM) machine or an Induction machine for a BAS application. The impact of the technology on the electric machine design process, power stage implementation, control strategy and overall system design philosophy will be discussed. Test data for both Induction and PM machines will be presented to help underscore the differences.

INTRODUCTION

A Belt Alternator Starter system is comprised of an electric machine, power electronics, controller, and battery and acts to increase vehicle fuel economy and reduce tail pipe emissions. Improvements of over 10% in fuel economy for city drive cycles have been achieved in vehicles using BAS systems [1], [2]. Figure 1 shows a high level functional diagram of a BAS system. A BAS system takes the place of the traditional generator and starter and is located in place of the generator. Such systems provide the ability to perform engine stop/start, electromechanical launch assist, regenerative braking, high power generation, and other functionality without requiring large changes to the vehicle. These systems can be implemented with several different types of electric machine technologies. The choice of machine technology will determine the required inverter stage of the power electronics, its associated protection circuitry, as well as the machine control strategy. The machine technology will also dictate the achievable system performance in terms of motor/generating efficiency and output power capability.

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