Design of dual-output alternators with switched-mode rectification

Abstract

Electrification of many automotive functions and the desire to introduce many new features are dramatically increasing the electrical power requirements of vehicles. The increasing power demands are becoming very challenging within the context of the present 14V electrical system and have sparked investigation of a higher-voltage electrical system. The introduction of a 42V electrical system for future automobiles is therefore gaining widespread industry acceptance. The large number of electrical subsystems in today's 14 Volt vehicles make it extremely challenging for manufacturers to make a direct transition to a single 42 V electrical system, therefore dual-voltage (42V/14V) automotive electrical systems are attracting considerable interest. This push to introduce dual-voltage (42V/14V) automotive electrical systems necessitates power generation solutions that are capable of supplying power to both 14V and 42V electrical loads. A number of approaches for implementing dual-voltage electrical systems have been proposed, but most suffer from severe cost or performance limitations. This thesis explores the design of alternators incorporating dual-output switched-mode rectifiers. The approach enables the full load-matched power capability of the alternator machine to be achieved, with power delivered to the two outputs in any desired combination. Switched mode rectifier topologies for this application are introduced. The design guidelines for alternators with switched mode rectifiers are established, and appropriate control laws derived. A prototype dual-output alternator incorporating a switched-mode rectifier is designed and built. Simulation and experimental results that demonstrate the feasibility and high performance of the approach are presented.