Flux Hybrid Magnet Memory Machine Research Articles

A Novel Delta-Type Hybrid-Magnetic-Circuit Variable Flux Memory Machine for Electrified Vehicle Applications

This article focuses on a newly developed 30-kW hybrid-magnetic-circuit variable flux hybrid magnet memory machine (HMC-VFMM) with a delta-type magnet arrangement for automotive traction applications. The proposed HMC-VFMM can improve the torque capability with effective utilization of flux concentration due to delta-type hybrid magnet arrangement while decreasing the required magnetization current level due to the dual-layer (DL) permanent magnet (PM) design. The presence of the parallel magnetic circuit can permit a satisfactory magnetization state (MS) manipulation range. Meanwhile, the DL series-type PM configuration can maintain beneficial unintentional demagnetization withstand capability. The machine topology and operating principle are described. Furthermore, the magnetic circuit model of the proposed machine structure is developed to identify and confirm the feasibility of the electromagnetic performance enhancement. Besides, the electromagnetic characteristics of the proposed HMC-VFMM are comprehensively analyzed and compared with those of a benchmark delta-type PM machine based on the Nissan Leaf drive motor. Finally, a 30-kW prototype is manufactured and tested to verify the feasibility of the proposed HMC-VFMM design in the potential context of electric vehicle applications.

Investigation of Torque Characteristics of Switched Flux Hybrid Magnet Memory Machine by a Coupled Solution

This article investigates the torque characteristics of a switched flux hybrid magnet memory machine (SF-HMMM) by employing a coupled solution combining a quasi-linear hysteresis model (QLHM) of low coercive force (LCF) magnet and frozen-permeability method (FPM). This provides an in-depth understanding of the torque production of SF-HMMM. The QLHM is utilized to characterize the repetitive remagnetizing/demagnetizing behaviors of LCF permanent magnets (PMs), while the FPM is employed to separate and quantify the torque contributions due to two sets of PMs and armature windings. The machine topology and analysis methodology are described, respectively. The torque segregation results accounting for magnetization state variation are analyzed by the proposed coupled solution. The influence of the LCF PM property on the torque segregation result is investigated to facilitate the establishment of general design guidelines. Finally, the prototype is tested to experimentally validate the theoretical analysis.

On-load demagnetization effect of high-coercive-force PMs in switched flux hybrid magnet memory machine

In the previous researches of hybrid magnet memory motors (HMMMs), the demagnetization characteristics of low-coercive-force (LCF) magnets have been already investigated extensively. Nevertheless, the possible irreversible demagnetization of high-coercive-force (HCF) magnets remains unexplored hitherto. In this paper, the demagnetization behaviour of HCF magnets in switched flux hybrid magnet memory machines (SF-HMMMs) accounting for the high-level current pulse is revealed and investigated. A simplified magnetic circuit model is built to illustrate when and how the DC current pulse poses the risk of irreversible demagnetization to the HCF magnets. Furthermore, the influences of temperature, DC current amplitude and HCF magnet thickness on the irreversible demagnetization effect of HCF magnets in the investigated SF-HMMM are analyzed based on finite-element (FE) analyses. The theoretical and FE results are experimentally verified by the tests on an SF-HMMM prototype.

Design Considerations of Switched Flux Memory Machine with Partitioned Stators

This paper presents general design considerations of a partitioned stator switched flux hybrid magnet memory machine (PS-SF-HMMM). The armature windings and permanent magnets (PMs) are placed on two separate stators, respectively, in the PS-SF-HMMM, and thus both high torque density and wide flux regulation capability can be obtained. The topology and working principle of the machine are introduced briefly first, and then different magnet arrangements and stator/rotor pole combinations are investigated. In addition, various design parameters are optimized based on finite element (FE) methods. Finally, a prototype is fabricated to experimentally validate the FE results.

Influence of Design Parameters on On-Load Demagnetization Characteristics of Switched Flux Hybrid Magnet Memory Machine

In this paper, the influences of design parameters on the on-load demagnetization behavior of a switched flux hybrid magnet memory machine (SF-HMMM) are evaluated, which aims to provide a useful design guideline to avoid this performance degradation. The machine topology and on-load demagnetization phenomenon are described, respectively. Furthermore, some key design parameters are selected to optimize to elevate the operating point of the low coercive force (LCF) permanent magnets (PMs). Then, some geometric modifications are suggested to alleviate the on-load demagnetization effects. Finally, an SF-HMMM prototype is fabricated and tested to experimentally verify the finite-element analysis.

Analysis of On-Load Magnetization Characteristics in a Novel Partitioned Stator Hybrid Magnet Memory Machine

The on-load magnetization characteristics of a newly developed partitioned stator switched flux hybrid magnet memory machine are comprehensively analyzed in this paper. First, the open-circuit and on-load permanent magnet magnetization performances are evaluated and compared. The mismatch of the required demagnetizing currents between open-circuit and on-load cases is identified. Then, the on-load demagnetization behavior of low coercive force (LCF) magnet is disclosed by the frozen permeability method. Besides, a numerical solution for the refinement of LCF magnet sizing is presented by a proposed virtual linear hysteresis model so as to effectively prevent the undesired on-load demagnetization. Finally, an optimized prototype is tested to verify the theoretical analyses.

Flux-Concentrated External-Rotor Switched Flux Memory Machines for Direct-Drive Applications

In this paper, an external-rotor switched flux hybrid magnet memory machine with a flux-concentration design is developed. Due to the external-rotor configuration, the stator design space is enlarged to alleviate the stator geometric conflictions existed in the internal rotor machine. Meanwhile, the spoke-type permanent magnet (PM) structure is designed to cope with the reduced armature slot area in its original “U”-shaped PM counterpart. In addition, the high-efficiency operation within a wide range of speeds and loads can be achieved. The topology, flux-adjusting principle and distinct features are introduced. Thereafter, the key design parameters including the stator/rotor pole combination, PM hybridizing ratio, and LCF PM thickness are optimized. Finally, the electromagnetic characteristics of the proposed machine are investigated and quantitatively compared with that of its“U”-shaped PM counterpart, which confirms the advantages of the proposed design.

Design of external rotor switched flux memory machine with hybrid magnets

Purpose– The purpose of this paper is to propose the design concepts of external rotor switched flux hybrid magnet memory machine (SFHMMM) to further increase the torque capability while keeping the merits of internal rotor SFHMMM, such as adjustable back-EMF, and good flux weakening performance, etc.Design/methodology/approach– The torque enhancing principle of external rotor SFHMMM, and the design considerations such as feasible stator and rotor pole numbers (Ns/Nr) are discussed by equations. Then, the performances such as back-EMF, dq-axis inductances, torque and flux weakening performances are calculated and compared with the aid of finite element analysis software.Findings– The external rotor SFHMMMs have obviously larger torque capabilities compared with the internal rotor ones under the same copper loss and machine size. The main reason is that the external SFHMMs could fully utilize the inner space of stator, which offers higher slot area, larger split ratio and consequently the higher average torque. For the external rotor machines with larger rotor pole numberNr, the back-EMF adjust ratio as well as the maxim torque are better. However, leakage flux and losses also increase with Nr due to limited machine size and higher operation frequency. Considering torque capability and flux weakening performance (efficiency map), the external SFHMMM withNr=2Ns+1, e.g. 6/13Ns/Nrstator/rotor pole machine, is the optimal choice.Originality/value– This paper introduces the design concept and design considerations of external SFHMMM for the first time. The proposed machine could be a competent candidate for direct-drive electric vehicle applications.

Switched flux hybrid magnet memory machine

A novel switched flux permanent magnet machine (SFPMM) with both normal NdFeB and low coercive force (LCF) magnets has been developed in this paper. Outside a conventional SFPMM, the LCF magnets are mounted on the back of every U-shaped stator lamination segment with parallel magnetisation direction and alternative polarities. A lamination ring yoke is placed around all the LCF magnets, while extra magnetisation coils are wound on each of them. By injecting different directions of current pulses into the magnetisation coils, the polarities of the LCF magnets can be rewritten in order to enhance or weaken the field generated by normal NdFeB magnets. Therefore the back EMF and torque capability could be adjusted in a wide range. In this paper, the operation principle and machine topology are introduced firstly. Then the stator/rotor pole combinations and design considerations of the machine have been discussed. With the help of two-dimensional finite element software, a 6/5 stator/rotor pole machine has been globally optimised as an example to show the machine performances such as open-circuit field and back EMF, dq -axis inductances, torque capabilities and magnetisation. Finally, a prototype with the same dimensions has been manufactured and tested to validate the analysis results.