Operating-envelop-expandable control strategy for switched flux hybrid magnet memory machine

Abstract

Memory machines (MMs) equipped with hybrid permanent magnets (PMs), i.e., NdFeB and low coercive force (LCF) PMs, combine the merits of acceptable torque capability at low speeds and efficiency improvement at high speeds. Meanwhile, the PM flux linkage can be flexibly adjusted with the aid of current pulses, which is desirable for variable speed applications. To effectively extend the constant power speed range (CPSR) with minimum required flux-weakening (FW) current injected by the inverter, a new control strategy is proposed and implemented on a switched flux hybrid magnet memory machine (SF-HMMM). The configuration and operating principle of the proposed machine are introduced first, followed by the establishment of the mathematical model. Afterwards, the proposed control strategy is described accounting for a whole operating envelop. Different FW regions will be numerically identified by calculating the transition speed. In FW region I, the conventional d-axis current-based and PM demagnetization FW schemes are integrated, while only the negative d-axis current injection is employed in FW region II. The proposed control strategy combines the distinct advantages of memorable flux and negative Id FW controls, leading to an effective extension of CPSR with improved efficiency as well as low requirement of inverter current. The proposed method is verified by experiments on the prototype machine.