Vipulkumar I. Patel

Fractional-Slot Permanent Magnet Brushless Machines with Low Space Harmonic Contents

The paper is concerned with new winding configurations and associated pole-slot combinations for permanent magnet (PM) machines that lead to improved performance and facilitate cost reduction. Compared to the current state of the art, the salient feature of the proposed designs is elimination and/or reduction of undesirable space harmonics which result from the existing fractional-slot per phase per pole permanent magnet machines with concentric windings. This will bring the benefits of significant reduction of the eddy current loss in the rotor permanent magnets, short end-winding and hence reduced copper loss and copper usage, increased power/torque density, reduction in manufacturing cost, and improved energy efficiency. Although the proposed technique is primarily aimed for brushless permanent magnet machines, it is also applicable to synchronous reluctance machines, induction machines and synchronous wound field machines. The proposed technique is applied to the design of an interior mounted permanent magnet machine for electric vehicle traction applications, and demonstrated by the measurements on a prototype machine.

Demagnetization Assessment of Fractional-Slot and Distributed Wound 6-Phase Permanent Magnet Machines

A 6-phase fractional-slot-per-pole-per-phase interior permanent magnet (IPM) machine having a novel topology of 18-slot, 8-pole and a 6-phase, 48-slot, 8-pole IPM with distributed windings, both designed for a segment-A electric vehicle, are assessed for the risk of partial irreversible demagnetization under various fault conditions. This paper describes a more accurate approach of demagnetization assessment based on 2-D transient finite-element analysis. It is shown that due to the presence of low-order space harmonics in the fractional-slot IPM machine, the demagnetization risks across all pole pairs are different. Compared with the distributed wound machine, the fraction-slot machine is less vulnerable to demagnetization due to relatively high winding inductance, although its demagnetized regions are not uniform in each pole. It is also shown that although the demagnetizing current of one 3-phase short-circuit (SC) is greater than that of 6-phase SC, the resultant demagnetization risk is lower than that of 6-phase SC in the fractional-slotmachine.

Six-Phase Fractional-Slot-per-Pole-per-Phase Permanent-Magnet Machines With Low Space Harmonics for Electric Vehicle Application

This paper discusses the development of new winding configuration for six-phase permanent-magnet (PM) machines with 18 slots and 8 poles, which eliminates and/or reduces undesirable space harmonics in the stator magnetomotive force. The proposed configuration improves power/torque density and efficiency with a reduction in eddy-current losses in the rotor permanent magnets and copper losses in end windings. To improve drive train availability for applications in electric vehicles (EVs), this paper proposes the design of a six-phase PM machine as two independent three-phase windings. A number of possible phase shifts between two sets of three-phase windings due to their slot-pole combination and winding configuration are investigated, and the optimum phase shift is selected by analyzing the harmonic distributions and their effect on machine performance, including the rotor eddy-current losses. The machine design is optimized for a given set of specifications for EVs, under electrical, thermal and volumetric constraints, and demonstrated by the experimental measurements on a prototype machine.

Enhanced Availability of Drivetrain Through Novel Multiphase Permanent-Magnet Machine Drive

This paper deals with a novel multiphase permanent-magnet (PM) machine drive to enhance drivetrain availability in electric traction applications. It describes the development of new winding configurations for six-phase PM brushless machines with 18 slots and eight poles, which eliminate and/or reduce undesirable space harmonics in the stator magnetomotive force. In addition to improved power/torque density and efficiency with a reduction in eddy current loss in rotor PMs and copper loss in end-windings, the developed winding configuration also enhances availability of drivetrain, in a variety of applications requiring a degree of fault tolerance, by employing it as two independent three-phase windings in a six-phase interior-PM machine, which is designed and optimized for a given set of specifications for an electric vehicle, under thermal, electrical, and volumetric constraints. This paper also describes the design and development of a six-phase inverter with independent control for both sets of three-phase windings. The designs of the motor and the inverter are validated by a series of preliminary tests on the prototype machine drive.

Analysis and design of 6-phase fractional slot per pole per phase permanent magnet machines with low space harmonics

The paper is concerned with new winding configurations for 6-phase permanent magnet (PM) machines with 18-slot, 8-pole, that eliminates and/or reduces undesirable space harmonics in the stator mmf. The proposed configuration improves power/torque density and efficiency with a reduction in eddy current losses in the rotor permanent magnets and copper losses in end windings. To improve drive train availability for applications in electric vehicles, the paper proposes the design of 6-phase permanent magnet machine as two independent 3-phase windings. A number of possible phase shifts between two sets of 3-phase windings due to their slot-pole combination and winding configuration is investigated and the optimum phase shift is selected by analyzing the harmonic distributions and their effect on machine performance including the rotor eddy current losses. The machine design is optimized for a given set of specifications for electric vehicle (EV), under electrical, thermal and volumetric constraints.

Post-Demagnetization Performance Assessment for Interior Permanent Magnet AC Machines

This paper assesses the post-demagnetization performance of interior permanent magnet (IPM) ac machines by employing the more accurate recoil line approach based on a 2-D transient finite-element analysis (FEA). The method predicts continuous demagnetization of each magnet element undergoing partial demagnetization and evaluates the machine behavior after an event of short-circuit faults across its terminals. Along with the short-circuit faults, a failure in a drive controller or a position sensor, which may lead to a reverse voltage across the machine terminals that can eventually be more fatal and can cause significant reduction in the performance due to high levels of demagnetization, is analyzed as the worst case scenario. The FE predicted post-demagnetization performance is validated by experimental measurements in which a six-phase IPM machine designed for electric vehicle traction is allowed to lose its synchronization with the inverter when forced to operate on a torque-speed envelope, which is way beyond the drive voltage setting.

A Generic Approach to Reduction of Magnetomotive Force Harmonics in Permanent-Magnet Machines With Concentrated Multiple Three-Phase Windings

This paper proposes a generic approach to reduction of magnetomotive force (MMF) harmonics in permanent-magnet machines with multiple three-phase concentrated windings. Analytical equations for the MMF distributions of the proposed multiple three-phase concentrated windings are derived, and the principle for harmonic cancellation is established and validated by finite-element analysis. A new 18-slot 14-pole nine-phase winding machine in which all sub-MMF harmonics are eliminated is presented based on the proposed generic approach. The proposed approach is also applicable to other slot-pole combinations with concentrated windings except for slot number being equal to 1.5 times the pole number. Retaining all the advantages of the concentrated windings, the new technique improves the fundamental winding factor, enhances the fault tolerance capability, and reduces the detrimental effects of lower and higher order MMF harmonics on the machine, such as high rotor eddy-current and iron losses, less reluctance torque, acoustic noise, and vibration.

A Nine-Phase 18-Slot 14-Pole Interior Permanent Magnet Machine With Low Space Harmonics for Electric Vehicle Applications

One of the key challenges of utilizing concentrated winding in interior permanent magnet machines (IPMs) is the high rotor eddy current losses in both magnets and rotor iron due to the presence of a large number of lower and higher order space harmonics in the stator magnetomotive force (MMF). These MMF harmonics also result in other undesirable effects, such as localized core saturation, acoustic noise, and vibrations. This paper proposes a nine-phase 18-slot 14-pole IPM machine using the multiple three-phase winding sets to reduce MMF harmonics. All the subharmonics and some of the higher order harmonics are cancelled out, while the advantages of the concentrate windings are retained. The proposed machine exhibits a high efficiency over wide torque and speed ranges. A 10-kW machine prototype is built and tested in generator mode for the experimental validation. The experimental results indicate the effectiveness of the MMF harmonics cancellation in the proposed machine.

Assessment of 12-slot, 14-pole permanent magnet flux switching machine with hybrid excitation for electric vehicle application

Permanent Magnet Flux Switching Machines (PMFSM) with hybrid excitation having 12-slot, 14-pole topology is assessed for its suitability for a 10kW (peak) traction drive for a micro size electric vehicle with a distributed power train. The design is optimized using 2D finite element analysis (FEA) and the performance is evaluated against the rated and the peak torque operations and over the New European Driving Cycle (NEDC) using “energy center of gravity” principle. The key limitations of this machine topology for EV applications are highlighted by comparing it with 12-slot, 14-pole surface mounted permanent magnet (SPM) machine with concentric windings designed against the same thermal and volumetric constraints.

Permanent magnet generator turn fault detection using Kalman filter technique

In this paper, a stator turn fault detection strategy is developed for a permanent magnet (PM) generator system. Unlike conventional power generation systems, the output of the PM generator is directly rectified by an uncontrolled diode bridge. The only accessible signal is the DC link current/voltage. As a result, most existing detection techniques based on the phase current/voltage signals are not applicable. Instead, the 2nd and 6th harmonics of the DC link current are exploited for turn fault detection and they are extracted by a Kalman filter. It is shown that the phase unbalance caused by a turn fault gives rise to significant increase in the 2nd harmonic DC link current. Consequently, the dominant harmonic under healthy and fault conditions are of the 6th and 2nd orders, respectively. Hence, the turn fault can be detected by comparing the magnitudes of the two harmonics. The detection method is assessed by extensive simulation under various fault scenarios. It is shown that the developed Kalman filter method exhibits significant advantages in response time and computation effort than online fast Fourier transform (FFT) based techniques.