Hybrid-Excited Switched-Flux Hybrid Magnet Memory Machines

The memory machine concept is recently extended to switched-flux (SF) machines, forming a series of SF hybrid magnet memory machines (SF-HMMMs). They exhibit the merits of good demagnetization withstand capability and effective flux adjustability. Nevertheless, the torque density is inevitably compromised due to the geometric conflict within the stationary part. Meanwhile, the inactivated dc coil, excluding online magnetization transients, results in system redundancy. Hence, in this paper, a new hybrid-excited (HE) concept is developed and implemented in a partitioned-stator SF-HPMM (PS-SF-HMMM). Thereby, the distinct synergies of a dual-magnet memory machine and an HE machine are achieved. With slight compensated field excitation, the torque can be improved at low-speed operation. Meanwhile, the high-speed constant-power region can be further extended without sacrificing high efficiency. The stator/rotor pole numbers are optimized first. The operating mechanism and optimal stepwise HE implementation over a whole operating envelop are then addressed. In addition, a comparison between PS-SF-HMMM with hybrid-excitation and its pure HE counterpart is established. Finally, both the finite-element simulation and experiments are carried out to verify the utility of the proposed HE concept.

I. Introduction

Conventionally, flux-weakening control methods for permanent-magnet (PM) machines refer to either negative -axis current injection or advancing conduction angle [1], [2], corresponding to brushless ac and dc drives, respectively. However, they generally suffer from the inverter power-rating limitation and electronically sophisticated vector control. Recently, variable-flux PM (VFPM) machines [3]–[5] are of growing research interests. They can achieve the effective speed range extension and flux-weakening capability improvement without scarifying high efficiency. Herein, hybrid-excited (HE) machines [6]–[15], structurally derived from a combination of PM and wound field machines, were extensively investigated. They were widely recognized as a competent candidate for automotive electrification, wind power harvesting, and aerospace applications [6], [7], [13]–[15]. Nevertheless, the continuous field winding inevitably yields undesirable excited copper loss, degrading their overall efficiency. Meanwhile, a large volume of field windings is required in order to realize the flux regulation. In that case, the irreversible demagnetization risk and the torque density compromise may be caused.