Analysis and comparison of a speed-dependant and a torque-dependant mechanical device for wide constant power speed range in AFPM starter/alternators

TLDR

The paper proposes and compares two flux‑linkage regulation methods for an axial‑flux permanent‑magnet starter/alternator. The authors achieve flux‑linkage regulation with two mechanical solutions that displace the rotors to modify flux, where the speed‑dependent device behaves as a constant‑voltage source and the torque‑dependent device as a constant‑current source. Constant power generation is achieved with inexpensive devices that do not require external energy, and the devices introduce mechanical flux weakening for wide speed‑range regulation without affecting starting mode performance or the high torque density and overload capability of AFPM machines.

Abstract

In this paper, two methods for flux linkage regulation in a starter/alternator with an axial-flux permanent magnet (AFPM) machine are proposed and compared. Desired regulation is achieved by two different mechanical solutions, each of them capable of modifying the amount of flux linkage through displacement of the two rotors in the AFPM machine. Constant power generation is thus achieved with very inexpensive devices that do not require external energy sources since energy in the airgap doesn't change. The main difference between the two proposed solutions is that the speed dependant device is ideally a constant voltage source while the torque-dependant device behaves as a constant current source. Even if some improvements are still needed, both devices introduce the totally innovative concept of mechanical flux weakening for AFPM power regulation in a wide speed range. Finally, the paper demonstrates that the introduction of these devices doesn't modify machine behavior in starting mode, so that the particular features of AFPM machines in terms of high torque density and overload capability remain unaffected.