Luming Cheng

Analysis and Optimization of a Novel Tubular Staggered-Tooth Transverse-Flux PM Linear Machine

A novel tubular staggered-tooth transverse-flux permanent magnet linear synchronous machine is proposed. The machine is characterized by simple structure and low flux leakage. First, the structure and the operational principle are introduced. Second, the 3-D equivalent magnetic circuit model of the machine is built, and the analytical expression of the electromagnetic force is derived. Last, the force density and the force ripple are optimized with respect to three key dimensional ratios by the 3-D finite-element method. An optimized scheme with the high force density of 2.697 × 105 N/m3 and the low force ripple of 2.78% is achieved. In addition, the characteristics of the proposed machine are compared with other topologies of linear machines.

Investigation of Magnetically Isolated Multiphase Modular Permanent-Magnet Synchronous Machinery Series for Wheel-Driving Electric Vehicles

This paper presents a novel multiphase permanent-magnet (PM) synchronous machinery series adopting two adjacent coils per phase and modular stator. Machine design principles, including modular stator design, segmental interior PM-assisted rotor design, and winding factor improvement, are investigated. Moreover, analytical modeling of winding inductance is developed to provide insights into the magnetic circuit of this type of machine. The proposed machinery series is suitable for wheel-driving electric vehicles attributing to their high magnetic isolation feature, good flux-weakening capability, and feasibility of modular fabrication.

Influence of Third Harmonic Back EMF on Modeling and Remediation of Winding Short Circuit in a Multiphase PM Machine With FSCWs

For multiphase open-winding permanent-magnet (PM) machines, both back electromotive force (EMF) and short-circuit current (SCC) contain third harmonic components that interact with each other and produce even-harmonic torque pulsation. This paper investigates the impact of the third harmonic component on SCC prediction, torque pulsation and postfault remediation method in case of a winding short-circuit fault. Analytical modeling of SCC is developed, which shows that the third harmonic SCC increases the maximum value of SCC. It is found that the transient SCC is heavily influenced by the initial phase angle of winding axis and exciting current when the fault is incepted. The braking torque due to the negative q-axis SCC component is investigated, which peaks at low speed as winding inductive impedance goes down. The comparison of two postfault remediation methods for single-phase short-circuit faults shows the importance of considering the third harmonics of SCC and back EMF in terms of torque performance. Finally, the theoretical results of SCC, braking torque, and remediation methods are verified and evaluated with experimental results.

A New Magnetic-Field-Modulated Brushless Double-Rotor Machine

In this paper, a new magnetic-field-modulated brushless double-rotor machine (MFM-BDRM) is proposed, solving the contradictory problem of the electromagnetic performance and the mechanical strength of an MFM rotor in the traditional MFM-BDRMs. The operating principle of the proposed MFM-BDRM, including the speed and torque relations of the stator, the MFM rotor, and the permanent magnet (PM) rotor, is investigated by an analytical method. The magnetic field distribution law in the air gap, the back electromotive force, and the torque performance of the proposed MFM-BDRM are investigated. To obtain the maximum torque density, the influence of some key parameters, such as PM pole-arc coefficient, span ratio, and thickness of magnetic units, on the maximum torque is investigated. Besides, due to the rich magnetic-field harmonics with high rotating speed in the air gap, the distribution law of iron loss in the proposed MFM-BDRM is investigated. The PM-split method along the circumferential direction is employed to reduce the PM loss. Finally, the overall performance of this new MFM-BDRM is evaluated, including loss, efficiency, power density, and so on.

Design and optimization of five-phase fault-tolerant in-wheel permanent machine with low mutual-inductance

In safety-critical applications, five-phase fault-tolerant permanent machines are attracting more and more attentions. In this paper, the synthesis of magnetomotive force (MMF) produced by the windings in five-phase machine is analyzed firstly. A method to eliminate the mutual-inductance in fault-tolerant machines is proposed and an approach of the pole-slot combination selection of the five-phase fault-tolerant machine with low-mutual inductance is given. Then a five-phase fault-tolerant in-wheel permanent machine is designed according to the requirements of the electric vehicle application. The basic dimensions of the machine are derived from the analytic machine design method. Finally, the finite-element model of the designed machine is built, and a method of machine parameter optimization is proposed with the help of the finite-element model. The waveform of the no-load back EMF, output torque and the fault-tolerant capacity have been taken into account in the optimization, which improves the performance of the machine.

Research on a tubular yokeless PM linear machine

Free-piston energy converter, which has great potential in applications of space and electric vehicles (EVs), has drawn wide interests in recent years. Free-piston energy converter consists of a free-piston Stiring engine and a linear machine. Tubular permanent-magnet (PM) linear machines are widely adopted due to the salient characteristics like high power density and high efficiency. Radially-magnetized, axially-magnetized, and quasi-Halbach PM linear machines are developed [1-3]. However, the common demerit of the developed machines is the low utilization of space, which provides potential for the improvement of power density. Hence, a novel yokeless PM linear machine is reported in this paper. Compared with conventional PM linear machines, the proposed machine has advantages of higher power density, higher efficiency, and higher utilization of space.

Magnetic circuit analysis and performance improvement of a tubular staggered-tooth transverse-flux linear machine for free-piston energy converter

A free-piston energy converter (FPEC) integrated by a combustion engine and a linear electric machine is suitable for series HEV or other applications stand-alone generators . The transverse-flux machine (TFM) is considered advantageous for such application because of its high specific power and force density. The finite element method (FEM) is widely used in the machine analysis, which is time-consuming . The equivalent magnetic circuit analysis is a time-effective method compared with FEM. In this paper, a tubular staggered-tooth transverse-flux permanent magnet (PM) linear synchronous machine (STTF-PMLSM) is proposed, which is used for FPEC. The machine is characterized by a relative high power factor due to the low flux leakage. An equivalent magnetic circuit model of the machine has been proposed . The magnetic circuit analysis results are validated by the results of 3-D FEM simulation. The influence of leading design parameters, mainly containing PM magnetization length (hm), pole pitch (p) and length of the stator core (ls), on the performance of machine is analyzed in detail.

A novel five-phase fault-tolerant modular in-wheel permanent-magnet synchronous machine for electric vehicles

This paper describes a five-phase fault-tolerant modular in-wheel permanent-magnet synchronous machine (PMSM) for electric vehicles. By adopting both the analytical and finite-element methods, the magnetic isolation abilities of some typical slot/pole combinations are analyzed, and a new fractional-slot concentrated winding topology that features hybrid single/double-layer concentrated windings and modular stator structure is developed. For the proposed hybrid single/double-layer concentrated windings, feasible slot/pole combinations are studied for three-, four-, and five-phase PMSMs. A five-phase in-wheel PMSM that adopts the proposed winding topology is designed and compared with the conventional PMSM, and the proposed machine shows advantages of large output torque, zero mutual inductances, low short-circuit current, and high magnetic isolation ability. Some of the analysis results are verified by experiments.

Design of a novel electromagnetic planetary gear used for hybrid electric vehicles

A new electromagnetic planetary gear (EPG), which is the key part of compound-structure permanent-magnet synchronous machine (CS-PMSM) for hybrid electric vehicles (HEVs), is designed in this paper. To obtain the optimal electromagnetic performance of the EPG, the distribution law of permanent-magnet (PM) magnetic field and armature field are investigated, respectively. Furthermore, the influence of some key parameters, like span and thickness of magnetic block, and PM pole-arc coefficient on the PM magnetic field and armature field are investigated. On that basis, the electromagnetic performances of no-load and load working conditions are analyzed. The influence of magnetic blocks and PMs on fundamental back EMF, voltage distortion rate, electromagnetic torque and torque ripple are further investigated. Finally, a optimal scheme of EPG with a high torque and a low torque ripple is designed.

A Novel Variable-Flux Permanent-Magnet Synchronous Machine With Quasi-Series Magnet Configuration and Passive Flux Barrier

Variable flux permanent magnet synchronous machine (VF-PMSMs) has drawn considerable attention due to the capability of operating in a wide speed range with overall high efficiency. The conceptual machine firstly proposed employs AlNiCo magnets characterized by low Hc and (BH)max as sole magnetomotive force (MMF) source [1]. Various topologies have been further developed to enhance the torque density by employing both low coercive-force PMs (AlNiCo) and high coercive-force PMs (NdFeB) [2], [3]. The magnet configuration could be classified to parallel configuration and series configuration, as shown in Fig. 1 (a) and (b). In parallel configuration, part of MMF generated by NdFeB magnets exerts on AlNiCo magnets, which leads to low working point and even unintentional demagnetization of AlNiCo magnets under on-load operation. Preceding defects could be avoided in series configuration due to the support of NdFeB magnets to AlNiCo magnets, but several times of demagnetizing current are required to fulfill the demagnetization process and the magnetization state variation range is usually limited. In this paper, a topology of VF-PMSM with quasi-series magnet configuration and passive flux barrier is proposed, which exhibits both advantages of high torque density of series configuration and easily achievable demagnetizing current of parallel configuration.