Dheeraj Bobba

A Novel 6/4 Flux-Switching Permanent Magnet Machine Designed for High-Speed Operations

The purpose of this paper is to investigate a novel flux-switching permanent magnet (FSPM) machine that is amenable for high-speed operation. The low-pole topology of high-speed machine is favorable to minimize fundamental frequency requirement. The lowest possible three-phase topology of the FSPM machine, with six stator slots and four rotor poles (6/4), has unacceptably large second-order harmonic distortion in the flux linkage and severe cogging torque in its conventional single-stator-single-rotor form. To resolve these challenges, a novel dual-stator structure is proposed that eliminates the even-order harmonics in the flux linkage. Harmonic distortion and cogging torque are notably reduced in the proposed machine. The principles of operation and design methods are described in this paper. The properties of the proposed dual-stator 6/4 FSPM machine are compared with a conventional 6/4 FSPM machine and a conventional 12/10 FSPM machine for a 5 kW, 15 000 r/min design. Comparison results gathered from 3-D finite-element analysis demonstrate that the proposed dual-stator 6/4 FSPM machine achieves significantly better flux linkage, back EMF, and cogging torque than the conventional 6/4 design and better efficiency than the conventional 12/10 FSPM machine.

Design and Performance Characterization of a Novel Low-Pole Dual-Stator Flux-Switching Permanent Magnet Machine for Traction Application

The purpose of this paper is to characterize the performance of a novel dual-stator six-slot four-pole (6/4) flux-switching permanent magnet (FSPM) machine. The proposed dual-stator 6/4 FSPM machine topology eliminates even-order harmonics in the flux linkage and back-electromotive force, which exist in the conventional single-stator single-rotor topology. The resulting back-electromotive forces of the proposed dual-stator machine are balanced and sinusoidal waveforms. Design principles including sizing equations for the machine are studied based on the flux linkage harmonic contents and generalized sizing laws. The performance characterization is studied for two possible topology variations of the dual-stator structure. A design for a 30-kW traction application is investigated to demonstrate good constant power operation capability. The low fundamental frequency requirement of the dual-stator 6/4 FSPM machine is beneficial to the reduction of iron loss at high-speed conditions. High efficiency is achieved for the majority of the speed range, particularly at the high-speed regions.

A novel dual-stator flux switching permanent magnet machine with six stator slots and four rotor poles configuration

The purpose of this paper is to introduce a novel dual-stator six stator slots four rotor poles flux switching permanent magnet machine that is viable for operation. The conventional six slots four poles topology suffers from asymmetrical flux linkage and severely unbalanced back-EMF, which makes it unfeasible. The proposed dual-stator structure utilizes windings in the second stator to produce a corresponding flux linkage that cancels the even order harmonic components in the first stator winding. The resulting flux linkage, back-EMF have no even order harmonics and are almost sinusoidal waveforms. The performance of the proposed machine is validated by analytical and finite element analysis.

Concept of Integration of Axial-Flow Compression Into Electric Machine Design

The purpose of this paper is to propose a novel concept of a high-speed electric machine system with integrated airfoil-shaped rotor designed to perform axial-flow compression for vehicle applications. The proposed high-speed machine is both a motor for electromagnetic (EM) energy conversion and an axial flow compressor for thermodynamic energy conversion. Conventional designs usually have a separate motor and compressor that are connected through a common shaft with or without a gearbox. The proposed design simplifies the high-speed machine and compressor system by eliminating the components that connect the motor and the compressor. The integrated motor-compressor design can achieve a more compact system. The flux-switching permanent magnet (FSPM) machine is chosen out of several possible electric machine topologies with salient rotor pole features for the integrated motor design. The feasibility of this integrated motor-compressor design is discussed from both the EM and thermodynamic perspectives in this paper. The selection of slot/pole combination and EM sizing equations for the integrated FSPM motor-compressor are discussed. Mean-line design equations for the axial flow compressor are studied for the proposed integrated motor-compressor. The EM torque production capability of the proposed integrated motor-compressor is verified for one possible design in this paper by finite element analysis (FEA). The effects of two different attack angles of the rotor blades are studied compared to the conventional FSPM machine. The FEA results show that the proposed integrated motor-compressor achieves the expected output performances.

A novel flux-switching permanent magnet motor-compressor with integrated airfoil-shaped rotor design

The purpose of this paper is to propose a novel flux-switching permanent magnet motor with an integrated airfoil-shaped rotor. Some of the conventional axial-flow compressor systems need an electric motor to provide mechanical energy input to the compressor. The proposed novel flux-switching motor-compressor can integrate both an electric motor and an axial-flow compressor into a single entity and perform axial-flow compression using the airfoil-shaped rotor. This integrated motor-compressor design eliminates the connection between the electric motor and compressor and makes the entire system more compact. Due to the high-speed nature of the integrated motor, no gearbox is needed in the proposed design so that reliability is improved. The principle of design for the proposed integrated motor-compressor is discussed. Analytical studies for the thermodynamics and electromagnetics are elaborated in this paper. A case study design is done to investigate the effect of rotor airfoil curvature to the torque production capability, and the results are demonstrated by finite element analysis.

Method to eliminate even harmonics in flux-switching permanent magnet machines

This paper presents an analytical method to realize even order harmonic elimination in flux-switching permanent magnet machines. The proposed method enables the calculation of total offset angle of flux linkages, taking into account an offset angle of stator slot and rotor poles. The 6-slot, 12-slot, and dual structure flux-switching permanent magnet machines are analyzed using the proposed method which is verified by finite element analysis. The advantage of the proposed method is that it clearly explains the reason for different winding configurations of even and odd number of rotor poles flux-switching permanent magnet machines.

A low-pole split magnet flux switching permanent magnet machine with minimized harmonic distortion in flux linkage for high speed operation

Flux switching permanent magnet machines provide many advantages. Due to their superior behavior associated with sinusoidal Back-EMF and low torque ripple, topologies featuring 12 stator teeth and 10 rotor poles (12/10) are favored. However, this follows that for a given mechanical rotor speed, the required electric fundamental frequency is ten times to that of a conventional two pole PM machine imposing challenging requirements are set on the power electronics. In this paper, a 6/4 FSPM machine design is investigated since it has the lowest feasible slot-pole combination. The conventional 6/4 FSPM machine design is not a viable design due to the presence of dominant second order harmonic component of flux linkage and high torque ripple. Thus, a split magnet design is introduced which allows achieving better performance by significantly reducing the second harmonic component. A multi-objective optimization scenario is carried out utilizing an evolutionary algorithm and performing massively distributed finite element simulations on a computer cluster. The selected machine design and its particular torque characteristics are analyzed. The achieved results reveal that by considering split magnet topologies, the low slot-pole FSPM machine configurations can unlock their potential for high-speed operation.

Fault index current estimation and analysis for fault diagnostics in IPMSM under inter-turn short circuits

This paper proposes an analysis of a fault index signal for internal permanent magnet synchronous machines (IPMSM) under inter-turn short circuits (ISC). Research has proven that the dynamic model of an electrical motor under ISC can be modeled as a healthy machine affected by a disturbance current representing the effect of the ISC. This current is equal to the product of the shorted turns ratio and the current flowing in the failure path. This signal has been used extensively for fault diagnostics. Having an understanding of how this fault index current affects the model of the IPMSM allows generating observer-based techniques to extract information of the fault index current and flux linkage estimation. A dynamic model for an IPMSM under ISC in combination with a fault index current observer is implemented in Matlab/Simulink; this model is validated with finite element analysis. The fault index current and sequence components analysis is studied to match previous work from other research. This work aims to accomplish two goals. The first is to show the observer-based estimation being effective in estimating ISC condition for several phases simultaneously and improve torque performance. The second, provide insight into the fault index current for diagnostics and show it as a generalized version of sequence component analysis. These goals produce better diagnostics and improve the control of the motor under ISC.

Novel permanent magnet machines with integrated fluid dynamic design for compression applications

The goal of this paper is to propose a novel concept of permanent magnet machine with integrated airfoil-shaped rotor that can perform compression action. Electrically driven conventional compressor systems need electric machines as prime movers to provide mechanical energy to rotate the compressor. The proposed novel integrated permanent magnet machine system synthesizes both an electric machine and an axial-flow compressor into a single device to convert electrical power to mechanical rotational power of the rotor, which simultaneously compresses the gas. This novel integrated design simplifies the compressor system by eliminating the connection between the electric machine and compressor. Weight, volume, and cost savings are expected. The feasibility of the proposed concept is demonstrated by combining the principle knowledge in electric machine design and compressor design. The operating principles of this novel integrated machine are described in the paper. Analytical design methods are used to study the proposed integrated machine and compressor. Possible topology variations of the proposed concept are discussed.

Design optimization for reducing harmonic distortion of flux linkage in low pole flux-switching permanent magnet machines

High-speed machines are gaining interest, especially in traction applications because of their ability to produce high power density with a reduced size. Flux-switching permanent magnet (FSPM) machines are ideal for such applications since they have a simple rotor structure that can operate at very high speeds and utilize PM in the stator to achieve high power density. It is also desirable to keep the operating frequency at a minimum possible value to reduce core losses and cost of power electronics. A 6-stator slot, 4-rotor pole (6/4) FSPM machine has the lowest operating frequency for a three-phase FSPM configuration. This research aims at exploring design modifications to minimize the even order harmonic content and cogging torque to make the 6/4 configuration practical for highspeed applications. The analysis and methods proposed in this paper will be useful in tackling harmonic content of FSPM machines in general. An alternative structure with dual-stator configuration is provided to minimize harmonic distortion of the 6/4 FSPM machine in the paper.