Jingang Bai

Investigation of a Novel Radial Magnetic-Field-Modulated Brushless Double-Rotor Machine Used for HEVs

A novel brushless compound-structure permanent-magnet synchronous machine (CS-PMSM) with six different topologies is proposed based on the magnetic field modulation principle. As the key part of the brushless CS-PMSM, the radial magnetic-field-modulated brushless double-rotor machine (MFM-BDRM) is investigated on the speed and torque relations of the first-stator magnetic field, the first-PM rotor and the modulating ring rotor by analytical method. Besides, on the basis of analyses of magnetic field distribution in the inner and outer air gap, the back electromagnetic force and torque performance of the radial MFM-BDRM are further studied by finite-element method (FEM). The results indicate that the low power factor is a major problem of the radial MFM-BDRM. Therefore, the influence of parameters, such as combinations of magnetic block number and PM pole pair number, the span ratio and radial thickness of magnetic blocks, and the length of air gap, on the power factor is analyzed. Additionally, to investigate the distribution law of core loss in the radial MFM-BDRM, amplitudes and frequencies of the magnetic fields in each part of the machine are analyzed. Furthermore, considering the weak mechanical strength of modulating ring rotor employing DW310 laminations, an attempt to use iron instead of DW310 in modulating ring rotor is investigated.

Characteristic Analysis and Verification of the Magnetic-Field-Modulated Brushless Double-Rotor Machine

The magnetic-field-modulated brushless double-rotor machine (MFM-BDRM), composed of the stator, the modulating ring rotor, and the permanent-magnet (PM) rotor, is a new power-split device for hybrid electric vehicles (HEVs). Compared with traditional double-rotor machines (DRMs), the MFM-BDRM shows more complicated electromechanical energy conversion relations, due to its special operating principle-the magnetic field modulation principle. To analyze the speed relation in the MFM-BDRM, a diagrammatized method is proposed. It shows that the speeds of stator magnetic field, modulating ring rotor, and PM rotor present a collinear speed characteristic. On this basis, the torque relations of stator, modulating ring rotor, and PM rotor are investigated from the view of a conservative lossless system. Then, a lever-balanced torque map is proposed to analyze their torque characteristic. It shows that the torques of stator, modulating ring rotor, and PM rotor can be calculated by the lever balance principle. The power flow map is further proposed to analyze the power flow characteristic among three ports. In addition, comparison of the MFM-BDRM and the planetary gear shows that the MFM-BDRM can be totally equivalent to an electrical machine and a planetary gear, making it gain a great advantage particularly when the MFM-BDRM is used in HEVs. The electromagnetic performance of MFM-BDRM is investigated by a finite-element method, which shows that the MFM-BDRM has advantages of fine sinusoidal back electromotive force and low torque fluctuation. Finally, the speed and torque analysis and FE results are verified by experiment.

A Brushless Claw-Pole Double-Rotor Machine for Power-Split Hybrid Electric Vehicles

This paper investigates a claw-pole double-rotor machine (DRM) for power-split hybrid electric vehicles (HEVs). Based on the mathematical analysis of the machine, the boundary speed-torque characteristic required by the hybrid electric system is studied. To achieve high power density with acceptable torque ripple for automotive applications, the back electromotive force (EMF) and torque performance of the DRM are investigated with respect to the configurations of permanent-magnet rotor, claw-pole dimensions, and air-gap length. Based on the optimized model, characteristics of the claw-pole DRM, such as flux density, inductance, torque, core losses, and efficiency, are investigated by finite-element method. A downsized prototype machine is manufactured and tested. The experimental EMF, inductance, and torque performance agree well with simulation data. A drive cycle containing various working modes of the DRM is carried out, and the feasibility of using the machine as a power-split device for HEVs is validated.

Electromagnetic Design and Control Strategy of an Axially Magnetized Permanent-Magnet Linear Alternator for Free-Piston Stirling Engines

A 1-kW axially magnetized permanent-magnet linear alternator and the control strategy are investigated for free-piston Stirling engines (FPSEs). To meet the requirement of FPSE applications, the power densities of axially magnetized and radially magnetized structures are compared, and the shape of the stator end tooth is studied to reduce thrust fluctuation. Moreover, the thermal field of the proposed alternator is investigated for the appropriate selection of insulation class. The equivalent method is used to simplify the thermal modeling of slot coils. Due to the complex control of the FPSE, the stroke control strategy is investigated. Energy storage devices are employed to provide transient power supply and reduce voltage ripple. The hardware structure and voltage control scheme are discussed and validated by Matlab/Simulink. The prototype alternator and controller were designed and tested, and satisfactory experimental results were obtained.

Optimization of an 80 kW Radial-Radial Flux Compound-Structure Permanent-Magnet Synchronous Machine Used for HEVs

Compound-structure permanent-magnet synchronous machine (CS-PMSM), which is composed of a stator machine (SM) and a double-rotor machine (DRM), is a new power-split concept for hybrid electric vehicles (HEVs). To compare the CS-PMSM system with Toyota Prius based on the planetary gear unit, an 80 kW radial-radial flux prototype machine is designed. Fractional slots are employed for SM and DRM and the slot openings and pole-arc embraces of the two machines are optimized to decrease torque fluctuation. As the outer rotor is the structural and magnetic common part of SM and DRM, the magnetic circuits of the two machines are coupled. To obtain the thinner outer rotor and to decrease magnetic saturation of the outer rotor during machine design, the influences of the thickness and pole-arc embraces of permanent magnets on magnetic coupling are investigated by finite-element method. The magnetic field in the outer rotor may reach saturation, due to the impact of armature reaction on the flux distribution in the outer rotor. Under the condition of armature reaction, the flux distribution and electromagnetic torque are analyzed.

Topology Comparison of Compound-Structure Permanent-Magnet Synchronous Machines

A compound-structure permanent-magnet synchronous machine (CS-PMSM) system is a hybrid-electric-vehicle power-train concept. Six typical topologies of CS-PMSMs are proposed. The characteristics of different CS-PMSMs are compared and evaluated from the aspects of torque density, manufacturability, heat-dissipating capability, and magnetic coupling. The selecting principle of different topologies is proposed for practical application.

A novel single-phase flux-switching permanent magnet linear generator used for free-piston Stirling engine

This paper investigates a novel single-phase flux-switching permanent-magnet (PM) linear machine used for free-piston Stirling engines. The machine topology and operating principle are studied. A flux-switching PM linear machine is designed based on the quasi-sinusoidal speed characteristic of the resonant piston. Considering the performance of back electromotive force and thrust capability, some leading structural parameters, including the air gap length, the PM thickness, the ratio of the outer radius of mover to that of stator, the mover tooth width, the stator tooth width, etc., are optimized by finite element analysis. Compared with conventional three-phase moving-magnet linear machine, the proposed single-phase flux-switching topology shows advantages in less PM use, lighter mover, and higher volume power density.

Magnetic System Study of a Compound-Structure Permanent-Magnet Synchronous Machine for HEVs

The magnetic coupling problem is discussed for the six topologies of compound-structure permanent-magnet (PM) synchronous machine (CS-PMSM), and the radial-radial flux CS-PMSM is investigated as example. Taking Toyota Prius hybrid system as reference, a radial-radial flux CS-PMSM is designed. Owing to mechanical reason, the thicknesses of the PMs on the outer and inner sides of the outer rotor are quite different, which induces more coupling problem. The magnetic system of CS-PMSM is researched in two aspects: the combination of thicknesses of PM and outer rotor yoke and the effect due to armature reaction. It is concluded that the magnetic coupling problem can be solved by designing an appropriate outer rotor thickness. In order to evaluate the magnetic structure, a downsized radial-radial flux CS-PMSM prototype was designed and manufactured. Back electromotive force (BEMF), relations between torque and current, and efficiency of the prototype were measured, and the experimental results are in good accordance with the calculated results.

Research on electromagnetic performance of a novel radial magnetic-field-modulated brushless double-rotor machine

A novel radial magnetic-field-modulated brushless double-rotor machine (MFM-BDRM), which is the key part of compound-structure permanent-magnet synchronous motor (CS-PMSM), is proposed in this paper. The speed and torque relations of the first-stator magnetic field, the first PM rotor and the modulating ring rotor are investigated by analytical method. The harmonic components of magnetic field in the inner and outer air gap are analyzed by finite-element method (FEM), when the PM magnetic field and armature field work independently. Furthermore, electromagnetic performances of two typical schemes are analyzed, which shows that torque ripples are the major problem of the radial MFM-BDRM. Some methods are proposed to reduce the torque ripples and validated by FEM.

Investigation of a 7-pole/6-slot Halbach-magnetized permanent-magnet linear alternator used for free-piston stirling engines

This paper investigates a 7-pole/6-slot Halbach-magnetized permanent-magnet linear alternator used for free piston Stirling engines (FPSEs). Taking the advantages of Halbach array, a 1 kW prototype alternator is designed. Considering the rms value of electromotive force (EMF) and harmonic distortion, the optimal length ratio of the axial- and radial-magnetized permanent magnets and thicknesses of the permanent magnets are optimized by 2D finite element method. The alternator detent force, which is an important factor for smooth operation of FPSEs, is studied by optimizing slot tip and end tooth. The load and thermal performances of the final design are simulated. A prototype alternator was designed, built and tested. Experimental data indicated satisfactory design.