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Ear-piercing high-frequency noise from electromagnetic vibrations in motors has become unacceptable in sensitive environments, due to the application of pulse width modulation (PWM) and in consideration of switching losses. This paper proposed a synchronous periodic frequency modulation (SPFM) method based on the interleaving technique for paralleled three-phase voltage source inverters (VSIs) to eliminate PWM vibration noise. The proposed SPFM technique is able to effectively remove unpleasant high-frequency vibration noise as well as acoustic noise more effectively than the conventional periodic carrier frequency modulation (PCFM) and interleaving technique. It completely eliminates the vibration noise near odd-order carrier frequencies and reduces the PWM vibration noise near even-order carrier frequencies depending on the switching frequency variation range. Furthermore, the SPFM method is simple to implement and does not employ additional circuits in the drive system. Finally, the effectiveness of the proposed method has been confirmed by detailed experimental results. [ABSTRACT FROM AUTHOR]

Although conventional slotted limited-angle torque motors (LATMs) have a high torque density, its fatal shortcoming of non-uniform torque profile makes it difficult to apply for precise positioning systems. This paper presents a novel radial-flux slotted LATM with asymmetrical teeth for the torque performance improvement including average output torque and angular operation range. A magnetic equivalent circuit (MEC) for radial-flux slotted LATMs is first derived and implemented in the design process. Then, the finite-element analysis is utilized to validate the related analytical equations and to make the comparison of the torque performance between the radial-flux conventional and proposed LATMs. Finally, a prototype machine of the proposed LATM is accomplished, and its torque characteristic experiment is carried out to confirm the torque performance improvement. The related experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

Magnetic field sensors, such as Hall current sensors, are widely used in permanent-magnet synchronous motors drive system. For the purpose of reducing cost and volume, the phase current reconstruction method is used in the motor drive system with only one current sensor. In this paper, a novel phase current reconstruction method is introduced. By arranging the single current sensor at a novel position, the proposed method is able to sample current in two zero voltage vectors. Then, a novel dc drift error mitigation method is proposed to eliminate the dc drift error in the Hall current sensor, which can influence the motor drive performance. The Clarke coordinate transformation is modified to decouple the dc drift error in the α–β-axis current components. Then, a notch filter is adapted to estimate the dc drift component of the current sampling results, which can compensate the dc drift error in the Hall current sensor. The proposed method is validated by both simulation and experiments. [ABSTRACT FROM AUTHOR]

Field-circuit coupling method is increasingly drawing attention from researchers who engage in electric machine design. It is worth mentioning that no related field-circuit coupling methods have been presented to investigate the dynamic performance for slotted limited-angle torque motor (LATM). Hence, this paper presents a simplified field-circuit coupling method to evaluate the dynamic performance including position tracking ability and operating temperature for slotted LATM during its design optimization process. All magnetic saturation problems including nonlinear torque characteristic and inductance parameter variation with rotor position can be taken into account, which is completely consistent with the actual operation condition. The simplified field-circuit coupling method contains a thermal resistance network (TRN) module which can be applied to estimate the slotted LATM operating temperature in accordance with the accurate winding current and copper loss information. Therefore, whether the slotted LATMs meet design requirements should be evaluated before manufacturing prototypes. Related experiments for the slotted LATM are carried out to validate the field-circuit coupling method cooperating with TRN module. [ABSTRACT FROM AUTHOR]

Three-phase permanent-magnet synchronous motors (PMSMs) are widely used in renewable energy applications such as wind power generation, tidal energy and electric vehicles owing to their merits such as high efficiency, high precision and high reliability. To reduce the cost and volume of the drive system, techniques of reconstructing three-phase current using a single current sensor have been reported for three-phase alternating current (AC) control system using the power converts. In existing studies, the reconstruction precision is largely influenced by reconstructing dead zones on the Space Vector Pulse Width Modulation (SVPWM) plane, which requires other algorithms to compensate either by modifying PWM modulation or by phase-shifting of the PWM signal. In this paper, a novel extended phase current reconstruction approach for PMSM drive is proposed. Six novel installation positions are obtained by analyzing the sampling results of the current paths between each two power switches. By arranging the single current sensor at these positions, the single current sensor is sampled during zero voltage vectors (ZVV) without modifying the PWM signals. This proposed method can reconstruct the three-phase currents without any complex algorithms and is available in the sector boundary region and low modulation region. Finally, this method is validated by experiments. [ABSTRACT FROM AUTHOR]

This paper presents a novel analysis and a design method of surface-mounted permanent magnet (SPM) machines with fractional slot concentrated windings (FSCWs) for a given constant power region ratio. The characteristics of working points in the constant power region are analyzed, and a method of quantifying important parameters, magnet flux, and synchronous inductance is proposed. According to the analysis, the design method of SPM machines with the FSCWs and notes is provided. Based on the proposed method, a double-layer 20-pole/24-slot SPM machine is taken as an example and designed. The designed machine is analyzed by the finite element method (FEM), and the constant power experiment is carried out on the prototype manufactured as design. The results validate the analysis and the design method in this paper. [ABSTRACT FROM AUTHOR]

This paper introduces the periodic carrier frequency modulation (PCFM) for permanent magnet synchronous motor (PMSM) drive systems so as to reduce the low-frequency electromagnetic interference (EMI). PMSMs are widely used in many applications and they are usually fed by pulsewidth modulation (PWM) inverters. The EMI of PMSM, which results from the switch of power device, generates undesirable effects on the control system. Therefore, it is of importance to reduce the EMI of PMSM. The common mode (CM) conducted EMI model of the PMSM drive system is constructed to investigate the CM voltage. The simulations and experiments of PMSM fed by the fixed frequency PWM (FFPWM) and PCFM are implemented to analyze the CM conducted EMI. The CM EMI spectra of PMSM fed by the FFPWM and PCFM with different spreading frequency widths are compared to explore the influence of PCFM on the CM conducted EMI. The regular patterns on PCFM in reducing the CM conducted EMI of PMSM drive systems are revealed. [ABSTRACT FROM AUTHOR]

Commutation angle is a key design criterion when brushless DC (BLDC) motors sensorlessly operate based on the detection of back electromotive force (EMF) zero-crossing and must be designed significantly less than 30 electrical degree. The paper describes a detailed investigation on the commutation angle of brushless DC motors with 120° voltage source inverter. Analytic method is applied to analyze the influence factors. The proposed design principles can provide a clear guide for the adjustment of system parameters. Then two criteria and an estimation method based on approximate anlytical solution of commutation angle are presented with experimental validation. [ABSTRACT FROM AUTHOR]

The crystallization behavior of biodegradable poly(butylene succinate) and copolyesters poly(butylene succinate‐co‐propylene succinate)s (PBSPS) was investigated by using 1H NMR, DSC and POM, respectively. Isothermal crystallization kinetics of the polyesters has been analyzed by the Avrami equation. The 2.2‐2.8 range of Avrami exponential n indicated that the crystallization mechanism was a heterogeneous nucleation with spherical growth geometry in the crystallization process of polyesters. Multiple melting peaks were observed during heating process after isothermal crystallization, and it could be explained by the melting and recrystallization model. PBSPS was identified to have the same crystal structure with that of PBS by using wide‐angle X‐ray diffraction (WAXD), suggesting that only BS unit crystallized while the PS unit was in an amorphous state. The crystal structure of polyesters was not affected by the crystallization temperatures, too. Besides the normal extinction crosses under the POM, the double‐banded extinction patterns with periodic distance along the radial direction were also observed in the spherulites of PBS and PBSPS. The morphology of spherulites strongly depended on the crystallization temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 420–428, 2007 [ABSTRACT FROM AUTHOR]

Ageing mechanism of PEEK powders at optimal powder bed temperature (Tb) and factors affecting their reusability remain unclear. This study investigated effects of gas type (air, nitrogen, and argon) and holding time (0-8 h) on physico-chemical properties of PEEK powders at optimal Tb. The hardness of sintered single-layers was measured to evaluate the quality of the parts. Results revealed that the flowability, morphology, and crystallinity of PEEK powders changed with holding time in different gases. Further, the ageing mechanism involved chain crosslinking within molecular chains in all gases but chain breakage in air. Further, laser power required for SLS decreased with the increase in holding time. However, the hardness of single-layers was stable for powders aged in argon for up to 8 h, but decreased by 7% for powders aged in nitrogen for 4 h. Severe degradation and blackening were observed for single-layers sintered in air using both virgin and aged powders. [ABSTRACT FROM AUTHOR]

This paper presents an analytical method for estimating the maximum angular operation range (MAOR) in a permanent-magnet slotted limited-angle torque motor (LATM). The operating principle of three topologies is analyzed and discussed, including a toroidal LATM, a slotted LATM with common pole/slot combination, and a slotted LATM with special pole/slot combination. The analysis indicates that no effective methods have been proposed to estimate the MAOR for a slotted LATM with special pole/slot combination. Hence, this paper is focused on solving this problem. The results obtained from the analytical method are validated by a finite-element (FE) method. The average time of the proposed method takes far less than that of an FE method, so that the design cycle of LATMs can be shortened. Finally, two prototype machines are manufactured, and their experimental results are presented and discussed. The FE and experimental results validate the accuracy of an analytical method. [ABSTRACT FROM AUTHOR]

Background: Secoisolariciresinol diglucoside (SDG) is a natural antioxidant generally extracted from flaxseed, which is one of the most important oil crops in China, the by-product of the flaxseed oil, i.e., flaxseed meal still contains a lot of lignans. However, flaxseed meal is generally treated as waste, resulting in a huge waste of resources. Objective: To establish an efficient and convenient method for extraction and purification of lignans from flaxseed meal. Methods: First, we used response surface methodology (RSM) to optimize the extraction conditions of the ultrasonic-assisted (UA) aqueous two-phase system (ATPS), and we obtained the purified extracts by macroporous resin purification (MRP). Second, the antioxidant ability of the extracts was studied in vitro. Results: The best extraction conditions obtained were as follows: 9.0% (w/w) sodium hydroxide; 30.0% (w/w) isopropanol; extraction time, 39min; liquid-to-solid ratio, 52.0mL/g; ultrasonic wave, 560W; and extraction temperature, 40°C. Under the optimal conditions, the purity of crude extracts (SDG-APTS-C) reached 21.5%. The desorption conditions of MRP were as follows: eluting 3 BV with ultrapure water, and then eluting with 25% ethanol at 2 BV (bed volume)/h to collect eluents. The purified extracts (SDG-ATPS-P) had a purity quotient of 73.9%, which was 52.4% higher than that of SDG-ATPS-C. Additionally, experiments conducted revealed that SDG-ATPS-C and SDG-ATPS-P could effectively remove DPPH (2,2-Diphenyl-1-picrylhydrazyl), ABTS (2,-Azinobis-3-ethylbenzthiazoline-6-sulphonate), and hydroxyl free radicals in vitro. Conclusions: The method was validated for extracting SDG from flaxseed meal, thus achieving the reuse of flaxseed meal. Highlights: This research provides some references for the application of UAATPS combined with MRP in natural products. [ABSTRACT FROM AUTHOR]

This paper presents a novel slotless limited-angle torque motor (LATM) for reaction wheels torque measurement system. The proposed slotless LATM has a uniform torque profile during its operating range, constant torque coefficient owing to avoiding saturation in back iron core. The slotless LATM has been designed and optimized using both magnetic circuit method and 2-D FE method. A scheme of magnetic pole spliced by three segments is proposed to improve flat width of air-gap flux density and torque performance. Finally, a prototype machine is established and its experimental results are presented and discussed. The theoretical and numerical results are validated with the experiments in the same operating conditions. [ABSTRACT FROM AUTHOR]

Plasma-arc technology was developed to dispose of chemical wastes from a chemical plant by the Institute of Mechanics, Chinese Academy of Sciences (CAS-IMECH). A pilot plant system with this technology was constructed to destroy two types of chemical wastes. The system included shredding, mixing, and feeding subsystems, a plasma-arc reactor of 150 kW, an off-gas burning subsystem, and a scrubbing subsystem. The additives (CaO, SiO2, and Fe) were added into the reactor to form vitrified slag and capture the hazardous elements. The molten slag was quickly quenched to form an amorphous glassy structure. A direct current (DC) experimental facility of 30 kW with plasma-arc technology was also set up to study the pyrolysis process in the laboratory, and the experimental results showed the cooling speed is the most important factor for good vitrified structure of the slag. According to previous tests, the destruction and removal efficiency (DRE) for these chemical wastes was more than 99.999%, and the polychlorinated biphenyls (PCBs) concentration in the solid residues was in the range of 1.28 to 12.9 mg/kg, which is far below the Chinese national emission limit for the hazardous wastes. A simplified electromagneto model for numerical simulation was developed to predict the temperature and velocity fields. This model can make satisfactory maximum temperature and velocity distributions in the arc region, as well as the results by the magneto hydrodynamic approach. [ABSTRACT FROM AUTHOR]

The purpose of this study is to compare the differences in flexural strength and compressive strength between four resin-modified luting glass ionomer cements that are commonly used in clinics. Furthermore, this study investigates the influence of curing mode on the flexural strength and compressive strength of dual-cured resin-modified glass ionomer cements. Initially, flexural strength and compressive strength test specimens were prepared for RL, NR, GCP, and GCC. The RL group and NR group were cured by the light-curing mode and chemical-curing mode. Five specimens were prepared for each test group, and the flexural strength and compressive strength of each were measured. Data were analyzed by one-way ANOVA with SPSS 13.0. Furthermore, the fracture morphology of the flexural specimens was observed by SEM. The result of the mean flexural strength of each group is as follows: the NR light-cured group > NR chemically-cured group > GCP > RL light-cured group > GCC > RL chemically-cured group. More specifically, the flexural strength of the NR light-cured group ((42.903±4.242) MPa) is significantly higher (P<0. 05) than those of the other groups, and in addition, the flexural strength of the light-curing mode is significantly higher (P<0. 05) than that of both the NR and RL chemically-cured groups. The result of the mean compressive strength of each group is as follows: GCP > NR chemically-cured group > NR light-cured group > GCC > RL light-cured group > RL chemically-cured group. Although the compressive strengths of the NR and GCP groups are higher than those of the GCC and RL groups, there are no significant differences (P>0. 05) between NR and GCP, and no significant differences between GCC and RL. Furthermore, there are no significant differences (P>0. 05) between the two curing modes on NR and RL. From the present study, it can be concluded that NR has superior flexural strength and compressive strength compared to the other three materials. Additionally, the curing mode can affect the flexural strength of dual-cured RMGIC because with the light-curing mode, the flexural strength is higher than with the chemical-curing mode. Therefore, light curing is an essential procedure when using dual-cured RMGIC in clinics. [ABSTRACT FROM AUTHOR]

The paper describes the alternative designs and performances of a single-phase moving-magnet linear oscillating actuator (LOA) which has been developed for orbital friction welding. The influences of the pole ratio on the performance of the LOAs are investigated and the optimal parameters have been identified with reference to the thrust force characteristics. It can be illustrated that a quasi-Halbach magnetized LOA, in which the magnets are assembled on a nonmagnetic mover yoke, represents the best electromagnetic performances. Finally, the predicted thrust force-current characteristic of quasi-Halbach magnetized LOA is validated by measurements on a prototype actuator. [ABSTRACT FROM AUTHOR]

Electrical error which contains amplitude error, function error and zero error has a direct impact on accuracy of resolver when resolver is used as a angle measuring device in control system. Harmonic interference existing in the output electromotive force (EMF) of signal windings is the main influencing factor of function error. Therefore, the reduction of harmonic interference will greatly weaken function error. In this paper, an axial flux variable-reluctance (AFVR) resolver with short pitch distributed winding is put forward on the basis of former variable-reluctance resolver. By the analyses of finite element method (FEM), high order harmonic of output EMF makes the distortion of EMF waveform and causes errors. Furthermore, the change regulation of high harmonics in the output EMF is got. The optimization analysis is done to rotor shape, pole-pairs and each group teeth number of this new resolver. Through FEM analysis and discussion on the optimized AFVR resolver, the analytic results show that the influence of harmonic interference is seriously weakened, and measurement accuracy is upgraded. [ABSTRACT FROM AUTHOR]