為了因應車用電子裝置的增加，現行的14V汽車供電系統將提昇輸出電壓準位到42V。傳統爪極式同步發電機具有控制簡單與低成本等優點，但因為定子繞組與場繞組上的功率損失，導致此型發電機效率較低。另外，傳統爪極式同步發電機三相電源轉換為直流電源的部分，因使用了無法控制的二極體整流器，這將使得於42V系統下，發電機於低速時會有無法提供輸出功率的問題。因此，如何改善引擎在怠速，亦即發電機於低速操作下的輸出功率，是近幾年來重要的研究議題。
本論文主要探討一有別於上述之傳統汽車發電系統的新型架構，利用具有功率密度高、維修保養容易且效率高之內藏式永磁同步發電機與可控制的半橋式開關型整流器，藉由功率元件開關的控制，達到有效提升發電機低速操作下之輸出功率。本研究透過位置感測器回授轉子位置資訊決定切換的正確時序，經由微處理器送出不同策略的功率開關責任週期與開關時序的控制訊號，用以討論不同的切換模式對發電機低速輸出功率之效果。

Due to the increased electrical power demands of today’s automobiles, the 14V automotive electrical systems currently used will be upgraded to 42V systems. Automotive electrical systems have long depended on the claw-pole synchronous alternator because of its low cost, simple structure, and controllability. However, the claw-pole synchronous alternator lacks efficiency due to power losses incurred during stator and field winding. In the claw pole synchronous alternator, the uncontrolled rectifier is used in such a way that the alternator does not generate power at low speeds and could not be used for a 42V system. Therefore, improving the output power of the alternator while the engine is idle (low speed) has been an issue of great concern in recent years.
This thesis investigates a new structure of 42V electrical system which consists of a controllable semi-bridge rectifier and an interior permanent-magnet synchronous alternator which have the characteristics of high power density, low maintenance and high efficiency. The power switches are controlled to improve the output power of the alternator when operating at low speed. The switching signals are determined through the feedback commutation signals of the position sensors. Thus, the control unit executes different control strategies of switching signals for each power switch, by means of investigation of the alternator output power at low speed under different control strategies.

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