This article investigates the efficient robust design optimization of a five-phase permanent magnet (PM) hub motor for electric vehicles. Besides the requirement of high-performance, like high torque ...density, low torque ripple and efficiency, fault-tolerant operation capability are also considered in the design optimization. To ensure that the motor performance is not sensitive to the variations of manufacturing tolerances, robust design optimization is employed to the investigated motor. To improve the fault tolerant capability of the motor, the motor performances under fault operation are also considered in the optimization. A Fuzzy-based sequential Taguchi robust optimization method is proposed to improve the comprehensive performance and save computing time. The proposed method is efficient because it holds the advantages of Taguchi method, fuzzy theory, and sequential optimization strategy. The motor performance is improved significantly by using the proposed method. Experimental results verify the accuracy of the model used in this study.
High-speed permanent magnet linear synchronous motor (PMLSM) is desired by high-performance electromagnetic propulsion system. A novel frequency modulation (FM) secondary proposed here to overcome ...the issues resulting from a big pole pitch of high-speed PMLSM, as well as avoid a damage to the thrust characteristics. First, the topology structure of FM secondary is designed, modeling of the main magnetic field excited by permanent magnets (PMs) is accomplished. And the impacts of FM secondary on the main magnetic field and PM eddy-current loss are presented based on the analytical method and finite-element method (FEM). The electromagnetic thrust of PMLSM with FM secondary is calculated, and the influences of FM secondary on thrust characteristics are studied by FEM simulations. Finally, a prototype of PMLSM with FM secondary is manufactured, the experiments are provided to validate the analytical results and simulation results of FM secondary.
In this paper, contributions of stator and rotor PMs in dual-permanent magnet (PM) machines with different stator/rotor pole number combinations are identified and investigated based on a ...multi-torque component decomposition method. The relationship between additive and cancellation effects of unmodulated rotor PM field component, contributions of stator and rotor PMs, and stator/rotor pole number combinations is revealed by analytical derivation and finite element analysis. It is found that the rotor PMs contribute more in torque production than the stator PMs when the rotor pole number is lower than the stator pole number due to the additive effect of unmodulated rotor PM field component, while the stator PMs contribute more in torque production than the rotor PMs when the stator pole number is lower than the rotor pole number due to the cancellation effect of unmodulated rotor PM field component. The dual-PM machines with fewer rotor pole number than stator pole number exhibit better electromagnetic performance since the torque production capability of PMs is improved by utilizing the additive effect of unmodulated rotor PM field component. A guideline for selecting stator/rotor pole number combinations to improve torque density is provided. Two prototypes are manufactured and tested to validate the conclusions.
This article proposes a robust optimization method for hybrid permanent magnet (HPM) machines, aiming to eliminate the influence of permanent magnets (PMs) asymmetric uncertainties. Exemplified by a ...12-slots/10-poles (12s10p) HPM machine, the optimization method is specifically clarified. First, uncertainties of two types of PMs are comprehensively analyzed and the worst combination of these uncertainties are estimated. Then, the design of experiments (DOEs) technique is utilized to take samples, and the corresponding performance of samples with and without consideration about uncertainties are simulated by finite element analysis (FEA), respectively. After that, a dual-level kriging surrogate model is constructed. And the difference of the two levels, as a quantitative index of robustness, is added as an additional optimization objective. Finally, a multi-objective optimization algorithm non-dominated sorting genetic algorithm (NSGA-II) is carried out. The optimization results indicate that the proposed method can effectively reduce the additional torque tipple brought from asymmetric uncertainties of PMs. In addition, a prototype is manufactured and tested to further verify the method.
Currently, surface-mounted permanent-magnet (PM) rotors are more frequently employed than interior PM rotors in high-speed PM motors. It is mainly because the mechanical strengths of sleeve materials ...can be much higher than those of silicon steels. However, at high speeds, the current harmonics caused by pulsewidth modulation (PWM) converter induce high eddy current losses in PMs and sleeves when they are conductive. Moreover, because of the existence of nonmagnetic sleeves, the surface-mounted PM motors have very poor flux weakening abilities. Interior PM motors can not only avoid sleeves, but also reduce the influence of the PWM converters. Moreover, they can provide additional reluctance torque and have better flux-weakening abilities. A major drawback of interior PM rotors is their low mechanical strengths, which limit their surface velocities. In this article, high mechanical strength amorphous metal 2605SA1 is used to increase the surface velocity of an interior PM rotor. A surface-mounted PM rotor protected by carbon-fiber sleeve is designed to perform a comparison study. Both motors are built and tested. The advantages and disadvantages of the two motors in terms of mechanical, electromagnetic, and thermal behaviors are evaluated.
Background
Fixed prosthodontic treatment (crowns, fixed dental prostheses (FDPs), complete arch prostheses) involves the use of several different materials to replace missing tooth structure. ...Traditionally full metal or metal frameworks veneered with ceramic (metal‐ceramic (MC)) have been used. In recent years several different metal‐free systems have become available to clinicians and patients. In general, metal‐free restorations should allow practitioners to better reproduce natural tooth colour, avoiding shortcomings of MC restorations. The comparative in service clinical performance of fixed prosthodontic treatments of different materials is unclear.
Objectives
To assess the effects of metal‐free materials for prosthodontic restorations compared to metal‐ceramic or other conventional all‐metal materials.
Search methods
Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (searched 3 May 2017), Cochrane Central Register of Controlled Trials (CENTRAL; 2017, Issue 4) in the Cochrane Library (searched 3 May 2017), MEDLINE Ovid (1946 to 3 May 2017), and Embase Ovid (1980 to 3 May 2017). The US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials (searched 3 May 2017). No restrictions were placed on the language or date of publication when searching the electronic databases.
Selection criteria
Randomised controlled trials (RCTs) in which the clinical performance of metal‐free fixed prosthodontic restorations was compared with metal‐ceramic (MC) or other conventional restorations in adult patients requiring prosthodontic treatment. RCTs in which the clinical performance of different kinds of metal‐free systems were compared among themselves were also considered.
Data collection and analysis
We used standard methodological procedures expected by Cochrane. Screening of eligible studies, assessment of the methodological quality of the trials and data extraction were conducted independently and in duplicate. Trial authors were contacted for missing information. Available results for the outcomes of interest of the systematic review of the studies included were tabulated as they could not be included in a formal meta‐analysis.
Main results
Nine trials involving a total of 448 participants were included. We judged two trials to be at unclear risk of bias and seven to be at high risk of bias. The majority of items of risk of bias were evaluated to be at unclear or high risk level in more than 50% of the included trials. Each trial except two was addressing a different type of intervention. All evidence was rated as being of very low quality due to problems with risk of bias and imprecision of results, the latter being due to very small sample sizes, low event rates, 95% confidence intervals including the possibility of benefit for both the test and control groups, or combinations of these problems. This means that we are very uncertain about all of the results presented in this review.
One trial compared metal‐free single crowns (full contour zirconia) to cast gold single crowns in 224 participants and found insufficient evidence of a difference in failure rate after one year, but after five years there was some evidence of a benefit for the gold crowns. There was insufficient evidence of a difference for crown complications at either time of assessment.
One trial compared three‐unit metal‐free FDPs (lithium disilicate) to three‐unit metal‐ceramic FDPs in 37 participants. There was insufficient evidence of a difference in bridge failure at one and six years, but some evidence of a benefit for the lithium disilicate group in terms of bridge complications at six years. One trial compared zirconia‐ceramic FDPs to metal‐ceramic FDPs in 34 participants but found insufficient evidence of a difference in bridge failures (i.e. no failures in either treatment group), bridge complications or patients' aesthetic evaluation at any time of assessment up to three years.
One trial compared metal‐free cantilevered FDPs to metal‐ceramic cantilevered FDPs in 21 participants. There was insufficient evidence of a difference for any primary outcome: bridge failures (i.e. no failures in either treatment group), bridge complications, or patients' aesthetic evaluation at any time of assessment up to three years.
One trial compared metal‐free implant‐supported screw retained single crowns (zirconia veneered with feldspathic ceramic) to metal‐ceramic implant‐supported screw‐retained single crowns in 20 participants. There was insufficient evidence of a difference for any primary outcome: crown failures (i.e. no failures in either treatment group), crown complications, or satisfaction/aesthetic evaluation at any time of assessment up to two years.
Two trials compared metal‐free implant abutments (zirconia) to metal implant abutments both supporting single crowns in 50 participants. There was insufficient evidence of a difference in abutment failure at one year.
One trial compared metal‐free implant‐supported FDPs made of two different types of zirconia ceramic in 18 participants. There was insufficient evidence of a difference in failures at any time of assessment up to 10 years (i.e. no failures in either treatment group). There was some evidence of a benefit for the zirconia‐toughened alumina group in terms of complications (chipping).
One trial compared metal‐free tooth‐supported FDPs made with two different veneering techniques (pressed versus layered) in 40 participants. There was insufficient evidence of a difference for failures (i.e. no failures in either treatment group) or complications at any time of assessment up to three years.
Authors' conclusions
There is insufficient evidence to support or refute the effectiveness of metal‐free materials for fixed prosthodontic treatment over metal‐ceramic or other type of standard restorations. The overall quality of existing evidence was very low, therefore great caution should be exercised when generalising the results of the included trials. Until more evidence becomes available clinicians should continue to base decisions on which material to use for fixed prosthodontic treatment on their own clinical experience, whilst taking into consideration the individual circumstances and preferences of their patients. There is urgent need of properly designed RCTs.
In this paper, a multimode design method is proposed for motor design under multiple operation conditions. Based on the driving cycles in electric vehicles, five typical operation conditions and the ...corresponding five driving modes are determined for the multimode design. To investigate the method conveniently, a flux controllable stator permanent magnet (SPM) memory motor is selected and taken as a design example. In the design process, by using the sensitivity analysis method, the significance of the parameters in various driving modes are evaluated effectively. Based on the motor driving demands, the whole optimization design is divided into three steps, where different optimization method is applied in each step. To verify the feasibility of the multimode design method, the operation performances of the motor in different driving modes are investigated in detail. Finally, a prototype motor is built and tested. Both the simulation and experimental results reveal that the proposed design method can offer an effective design optimization for the flux-controllable SPM memory motor, where multimode operations are indispensable.
High-frequency (HF) signal injection methods have been widely employed in the sensorless control of interior permanent magnet synchronous motor (IPMSM) drives from zero to low speed. However, the ...control performance will be deteriorated severely when the motor subjects to the disturbance. To cope with this issue, an enhanced linear active disturbance rejection control (LADRC)-based HF pulse voltage signal injection method is proposed in this paper. The cascaded extended state observer is established to guarantee relatively timely and accurate estimation of the total disturbance. The linear control law is generated to compensate for the total disturbance in a feedforward way, which reduces the plant to approximate a canonical first-order integral. The tracking performance and the stability of the enhanced LADRC are analyzed theoretically. Maximum torque per ampere control is adopted to reduce the estimation burden by making full use of the reluctance torque, which helps to further improve the tracking performance of the enhanced LADRC. Finally, the validity of the proposed sensorless control scheme is verified on a 2.2-kW IPMSM drive platform.
This study proposes an improved power density permanent magnet synchronous motor (PMSM) for more electric aircraft (MEA) and conducts a design study on aerospace motors. To improve the power density ...of PMSM, a dual permanent magnet structure using high-temperature resistant high-performance permanent magnets and high-performance soft magnetic alloy material is creatively designed. Methods of lightweight structure designed in both stator and rotor meanwhile are combined as another mean to increase power density. The optimisation models for 6-slot/8-pole and 12-slot/10-pole configurations are first established based on finite element analysis. Methods of improving the power density of PMSM are then given, including minimum core back yoke thickness and lightweight structure design. The electromagnetic characteristics of the optimised machine are analysed by finite element analysis software, including back electromotive force (back-EMF), inductance, and power loss. The configuration of 12-slot/10-pole is selected as the best design scheme for MEA, based on which a prototype is manufactured and tested. The experiment results of cogging torque and line back-EMF are in good agreement with the simulation results, which shows the rationality of the designed new machine. The design proves to be effective for improving the power density of aerospace motors.
This paper proposes a new spoke-type hybrid permanent magnet brushless (H-PMBL) motor for potential applications in electric vehicles, where the high-energy rare-earth PM and the cost-effective ...ferrite-PM are combined. In order to realize low-cost design and improve the operating points of the rare-earth PM and the ferrite-PM, the proposed motor is designed based on the calculation of PM cost and analysis on the operating points. Moreover, to fairly estimate electromagnetic performances of the H-PMBL motor, a conventional spoke-type non-rare-earth ferrite-PMBL motor with the same overall dimensions is also analyzed and compared using the finite element method. The simulation results indicate that the H-PMBL motor cannot only retain low PM cost, but also exhibit better flux-weakening ability and enhanced demagnetization withstand capability.
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