Developments in voltage regulation of variable-speed PM synchronous alternators in automotive electric systems

This paper evaluates the performance of a voltage regulator for a high-efficiency, high-energy density alternator system that comprises of a PM synchronous generator and a swithced-mode rectifier. A closed-loop control system is designed to regulate the output dc voltage of the alternator system operated under varying engine speeds, electrical loads, and battery state-of-charge conditions. The open-loop transfer function of the overall power system has been derived by combining the transfer functions of the alternator, switched-mode rectifier, battery, and system loads. The variation of pole-zero locations of the open-loop transfer function with the battery state-of-charge level has been investigated. It is shown that the dominant pole effecting the stability of the voltage regulation is determined by the battery transfer function.