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People with difficulty walking due to a stroke or neurophysiological gait deficit require gait rehabilitation. Recent research indicates that the optimal speed range for gait rehabilitation of such patients is less than 0.4 m/s. The design of a novel low-speed gait rehabilitation device based on a single degree of freedom (DOF) geared five-bar mechanism is presented in this paper. For this purpose, a natural gait meta-trajectory is generated using the recently acquired low-speed gait data suitable for human walking. A less-bulky single-DOF geared five-bar mechanism is synthesized and adjusted by applying the accurate and robust shadow robot control (SRC) synthesis method. Therefore, a practical and easily controlled gait rehabilitation device is designed, which can be mounted on any commercial treadmill and enables the patient to walk as close as possible to a normal gait. This device applies to a wide variety of individuals with different physiologies due to the mechanism's adjustability, provided by the profile blending algorithm method. This method generates a set of continuous and speed-dependent gait trajectories for various individuals. The proposed device is inherently safe and easy to control due to the limited motion range of the single-DOF mechanisms and the use of a single actuator. Furthermore, because it only has two points of contact with the body (at the hip and the ankle), it takes less time for the user to don and doff. [ABSTRACT FROM AUTHOR]

To address the issue of serious torque pulsation and optimize the output characteristics of multi-acting cam ring motors at low speed, a sensitivity analysis was conducted on the parameters of the triangular groove at the valve plate. Firstly, a mathematical model of the flow area between the rotor hole and the valve plate hole was established. Then, a numerical simulation model was built to study the motor output characteristics. Finally, the coupling effect of the triangular groove parameters on the motor torque pulsation rate was analyzed based on the response surface methodology. The results show that the motor torque pulsation rate can be reduced by 55% when adjusting depth angle θ 1 , width angle θ 2 , and length l . The influence order of design parameters on the pulsation rate is θ 1 > l > θ 2 ; among all parameter combinations, the coupling of the triangular groove between the depth angle and the length has the most significant effect on the pulsation rate. [ABSTRACT FROM AUTHOR]

Featured Application: Moist air wind tunnels are an unknown tool to test, validate theoretical studies, and improve the design of wind turbines under different weather conditions. The present research work shows how a functional subsonic moist-air wind tunnel has been designed. Although this type of wind tunnel has never been developed to date, it is particularly interesting to develop a satisfactory design of feasibility under moist air conditions. Low-speed vertical-axis wind turbines employ different kinds of rotors, such as Savonius, Darrieus, and H-rotor. All these wind turbines present clear advantages, e.g., the horizontal-axis wind turbines are omnidirectional. This means they can work under different wind directions, need lower maintenance, and begin working under low wind speeds of 3 m/s. Recently, a new application of wind concentrators enabled the vertical-axis wind turbines to improve their performance coefficient based on new concepts like moist air phase change, which are being analysed to improve energy conversion. Thus, expectations were raised to design a suitable wind tunnel that accounts for the relative humidity of moist air. An initial prototype showed that the behaviour of open wind tunnels where the relative humidity of moist air was controlled by an adiabatic evaporative process was satisfactory. However, for such wind tunnels, certain improvements like computer control systems would need to be developed. [ABSTRACT FROM AUTHOR]

Objective : To study the early phases of osseointegration at implants installed in sites prepared with either high rotational speed with irrigation or low rotational speed without irrigation. Material and methods: After 3 months from tooth extraction, two implants were installed in one side of the mandible of twelve dogs. The osteotomies were prepared either at 60 rpm without irrigation or at 750 rpm with refrigeration. Biopsies were obtained after 4 and 8 weeks of healing, six animals each period for histological analyses. Results: After 4 weeks of healing, new bone percentage in contact with the implant surface (BIC%) was 46.6 ± 7.3% and 43.1 ± 6.8% at the low- and high-speed sites, respectively (p = 0.345). After 8 weeks of healing, the fractions increased to 60.0 ± 11.1% and 60.2 ± 6.2%, respectively (p = 0.753). Conclusions: Implants installed in sites prepared using either low-rotational drilling without irrigation or high speed with irrigation presented similar amounts of osseointegration. [ABSTRACT FROM AUTHOR]

We present a thorough experimental investigation of a simple-built low-speed water tunnel that could facilitate the study of some of the primary fluid dynamic concepts based on quantitative flow measurements using Particle Image Velocimetry (PIV). The water tunnel system is designed and built using a simple arrangement of a double reservoir tank and a centrifugal pump that drives the fluid flow at low speed into a square cross-sectional and relatively short test section. The study shows that the system reasonably and steadily generates fully developed flows inside the test section with <20% of point velocity variations. Based on the fluid-structure tests, it is also observed that the system could produce moderately consistent boundary layer separation phenomena with the variance of the area mean vorticity within 25%. With this performance, we show that the system fulfills the essential requirement to be used as a simple, easy-to-operate, and easy-to-maintain educational platform to study fluid dynamic phenomena related to the interaction of a static submerged object and fluid flow. [ABSTRACT FROM AUTHOR]

Aiming at the issue of the sliding mode observer (SMO) being sensitive to the motor model parameters at low speeds, a rotor position observation method based on resistance adaptive SMO and considering the influence of inverter dead time is designed in this paper. In this method, the online resistance identification is introduced into the conventional SMO, the resistance parameters of the SMO are modified in real-time, and the online resistance identification algorithm is designed by using the Lyapunov function. An enhanced linear dead time compensation method is proposed to improve the resistance adaptive SMO and eliminate the voltage error between the estimated and the actual motor models in order to address the impact of inverter dead time on the voltage parameters in the estimation model at low speeds. Simulation results show that the online resistance identification and dead time compensation can significantly improve the accuracy of sensorless speed control at low speeds, and the dead time compensation can also improve the accuracy of online resistance identification. [ABSTRACT FROM AUTHOR]

Electric construction machinery with zero emission and high efficiency is considered to be a main development trend. An electric motor (EM) in electric construction machinery often needs to work at low speed or even in stalling conditions with large torque value and high work efficiency. In this paper, based on vector control of the maximum torque per ampere (MTPA) of an internal permanent magnet synchronous motor (IPMSM), a voltage and current composite observation algorithm was studied to improve IPMSM control performance at low speed. By establishing the observer model, the amplitude limited compensation for the voltage flux observation method was used to observe the EM stator flux. After being combined with the current observation method and the stator current obtained by coordinate transformation, the EM parameters in real-time can be identified for MTPA. Experimental research was carried out. The results show that the algorithm improved the speed control characteristic and output torque per unit current of the EM under low-speed working conditions. [ABSTRACT FROM AUTHOR]

Copyright of Ingeniería (0121-750X) is the property of Ingenieria and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Under steady-state pure rolling conditions with low speed, the thickener fiber agglomerations can be maintained for a long time, generating a beneficial thicker film thickness. However, in industrial applications, motions with sliding or transient effects are very common for gears, rolling-element bearings or even chain drives, evaluation of the grease performance under such conditions is vital for determining the lubrication mechanism and designing new greases. In this project, optical interferometry experiments were carried out on a ball-disk test rig to study the disintegration time of the grease thickener agglomerations with the increase of the slide-to-roll ratio under steady-state and reciprocation motions. Under steady-state conditions, the thickener fiber agglomeration can exist for a while and the time becomes shorter with the increase of the slide-to-roll ratio above the critical speed. Below the critical speed, the thickener fiber can exist in the contact in the form of a quite thick film for a very long time under pure rolling conditions but that time is decreased with the increase of the slide-to-roll ratio. The introduction of the transient effect can further reduce the existence time of the thickener. [ABSTRACT FROM AUTHOR]

In this article, a rotor position tracking control (RPTC) strategy is proposed to effectively reduce the speed fluctuation for a direct-drive permanent magnet synchronous motor servo system operating at a low speed with different torque disturbances. In this article, considering the derivative relationship between the rotor position and speed, a speed command is converted to a real-time rotor position trajectory, and then a position-current two-loop control with the RPTC controller is proposed based on the internal model method to smoothly track the rotor position. In addition, the parameter design of the RPTC controller from the perspectives of robust stability and antidisturbance capability is investigated as well. The comparative simulation and experimental results demonstrate that, at a low speed, the proposed RPTC strategy has a good speed performance for both periodic and nonperiodic torque disturbances. Moreover, it enjoys a simple implementation for not requiring the precise speed feedback and specific torque disturbance information. [ABSTRACT FROM AUTHOR]

In electric motors, the use of rare-earth magnets has been increasing rapidly. A stronger magnet force of the magnet enables the motor's higher performance, resulting in the most high-performance motors generally using rare-earth magnets. However, these magnets have two crucial disadvantages: the potential restrictions on the supply of rare-earth magnetic materials and the sharp fluctuation in price. Thus, many recent researches focus on developing high-performance electric motors and reducing the use of critical rare-earth magnets. By increasing the torque density of the motor, we can reduce the use of permanent magnets. Focusing on this point, and we presented a double half permanent magnet (DHPM)-type vernier motor. This paper proposed a new saddle coil permanent magnet vernier motor with improved performance compared to its predecessor. The main feature of the proposed motor is that the permanent magnet and coil in the stator of a DHPM-type vernier motor is replaced by salient poles and saddle coils, respectively. We also investigate its characteristics through various simulations. [ABSTRACT FROM AUTHOR]

This study examines the application of the bifurcation theory to the reduced-order of longitudinal flight dynamic systems. An investigation of steady and unsteady longitudinal aerodynamic coefficients is carried out, including an extended range of pitch up and down reduced frequencies from 0 - 0.06 values. An aircraft with a general delta wing with a 1.5 aspect ratio is chosen for the present analysis. Different elevator control deflection from -28.6 to 0 degrees is used to determine the equilibrium points a and q. The unsteady aerodynamic load results increase the requirements for control power as well as thrust vectoring during pitch up than steady longitudinal one. The flow unsteadiness effect improves the vehicle stability during pitch up corresponding a loosing of it during pitch down. A positive pitch rate is required to point the nose of the fighter. This improvement in pointing will help in the close maneuvering missions. [ABSTRACT FROM AUTHOR]

In this article, a virtual cogging torque (VCT) control method to reduce the speed ripple of direct-drive permanent magnet synchronous machine servo system under low-speed conditions is proposed. Compared with other factors, at low speeds, the cogging torque is the main factor that deteriorates the drive performance, even induces speed oscillations. Especially in this article, due to volume limitation, the cogging torque is designed larger than normal one in order to remove the need of brake. Based on the model of permanent magnet synchronous motor, the cause and effect of the cogging torque are analyzed. Inspired by the characteristic of cogging torque, the VCT control method is proposed and investigated to significantly reduce the speed ripple at low speeds. The main idea of this proposed control method is to produce a proper VCT and continuously move the corresponding virtual stable equilibrium point to drive the rotor smoothly. In addition to the principle of this control method, its analysis and implementation are studied as well. Simulation and experimental results from the prototype demonstrate that the proposed control method is correct and valid, and it is simple and effective to smooth the speed at low-speed operations. [ABSTRACT FROM AUTHOR]

Despite its influence on wind energy service life, condition-based maintenance is still challenging to perform. For offshore wind farms, which are placed in harsh and remote environments, damage detection is critically important to schedule maintenance tasks and reduce operation and maintenance costs. One critical component to be monitored on a wind turbine is the pitch bearing, which can operate at low speed and high loads. Classical methods and features for general purpose bearings cannot be applied effectively to wind turbine pitch bearings owing to their specific operating conditions (high loads and non-constant very low speed with changing direction). Thus, damage detection of wind turbine pitch bearings is currently a challenge. In this study, entropy indicators are proposed as an alternative to classical bearing analysis. For this purpose, spectral and permutation entropy are combined to analyze a raw vibration signal from a low-speed bearing in several scenarios. The results indicate that entropy values change according to different types of damage on bearings, and the sensitivity of the entropy types differs among them. The study offers some important insights into the use of entropy indicators for feature extraction and it lays the foundation for future bearing prognosis methods. [ABSTRACT FROM AUTHOR]

The small-signal model of the incremental optical encoder introduced in this paper provides an insight on the impact of this sensor in the dynamics of the motion control loop of a motor drive. The model is derived and validated for the most commonly employed speed estimation methods: the pulse count and the elapsed time methods. Using the model, the reduction of the phase margin due to the encoder phase lag can be quantified at an early design stage. This model facilitates the design of control techniques to compensate for the phase margin reduction due to the associated feedback delays. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to propose a new scuffing model caused by the depletion of additives in boundary lubrication condition. Design/methodology/approach: The differential equation governing the distribution of additive content in the fluid film was used. This formula was derived from the principle of mass conservation of additives considering the consumption due to surface adsorption of wear particles. The occurrence of scuffing was determined by comparing the wear rate of the oxide layer with the oxidation rate. Findings: If the additive becomes depleted while sliding, the scuffing failure occurs even at a low-temperature condition below the critical temperature. The critical sliding distance at which scuffing failure occurred was suggested. The experimental data of the existing literature and the theoretical prediction using the proposed model are shown to be in good agreement. Originality/value: It is expected to be used in the design of oil supply grooves for sliding bearings operating under extreme conditions or in selecting the minimum initial additive concentration required to avoid scuffing failure under given contact conditions. [ABSTRACT FROM AUTHOR]

Copyright of Rigakuryoho Kagaku is the property of International Press Editing Center Incorporation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, two simple control methods are proposed for improving direct torque control (DTC) with a constant frequency torque controller (CFTC-DTC) in induction machines. The CFTC-DTC was initially introduced to reduce torque ripple and achieve constant switching frequency in inverters. However, when compared to the original DTC, the CFTC-DTC algorithm suffers from slow torque dynamic response owing to the selection of zero-voltage vectors during torque transient. In addition, when the motor operates at low speed, flux droop occurs at sector transitions, which leads to undesirable current distortions. The problem of flux droop occurs because of short-duty voltage cycles and small radial voltage components at low speeds. This paper has two main contributions—to eliminate zero-voltage vectors during torque dynamics in order to establish a fast torque response in the transient state, and to minimize the flux droop at the sector transitions by applying another triangular carrier and modifying the torque output in order to increase the duty voltage cycles at low motor speeds. A detailed analysis of the problems and proposed methods is presented. Experimental results are provided to validate the effectiveness of both proposed methods. [ABSTRACT FROM AUTHOR]

The film stiffness of dry gas seal must be sufficient to keep gas film stable at high and low speed. A generalized geometric model based on triangles is proposed to characterize spiral grooves. A mathematical model is established and solved using the finite-difference method to obtain steady performance. The optimum spiral grooves for maximum opening force and film stiffness are obtained at low speed, and their steady performance is compared with conventional spiral grooves numerically and experimentally. The pressure and flow field of optimum spiral grooves and conventional spiral grooves are simulated to reveal the mechanism of the performance difference. Results show that through-combined spiral grooves outperform the other derived spiral grooves. Their film stiffness is up to 15% larger than that of conventional spiral grooves at low speed. [ABSTRACT FROM AUTHOR]

The adsorption model for boundary lubrication was proposed considering the variations of additive content with sliding distance. With surface roughness and wear debris caused by the adhesive wear of the oxide layer, a mass conservation of additive dissolved in lubricant was established. Any rise in surface temperature due to sliding friction was ignored for this study's purposes. It was found that the additive concentration decreased rapidly with sliding distance because wear particles adsorbed and consumed the additives. This reduction of the additive concentration raised the friction coefficient by reducing the surface area protected by the adsorption layer without any temperature effect. This analysis model was verified by comparing it with the test results of existing literature. Because this model is effective at extremely low-speed conditions, these results can help explain the failure mechanism in room-temperature, lowspeed boundary lubrication. [ABSTRACT FROM AUTHOR]

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A dual three-phase machine with interior permanent magnet rotor and distributed winding has been studied and compared to a commercial automotive traction machine, the Nissan Leaf IPM machine. The performance of the two designs are compared for typical traction operating points, via high torque, low speed and low torque, high speed, and constant power field weakening operation. The dual three-phase machine is shown to have improved torque density and torque quality without compromising efficiency. [ABSTRACT FROM AUTHOR]

In order to improve the stability of brushless DC (BLDC) motors at low speed, a high-stability position-sensorless control method is proposed in this paper. Because the back electromotive force (EMF) is very small at low speed, a novel algorithm is proposed to detect the zero crossing point of back EMF accurately. First, the line-to-line back EMF is computed based on the mathematical model of BLDC motors. Then, a low-pass filter (LPF) with alterable cutoff frequency is used to reduce the disturbance of the line-to-line back EMF. Last, the commutation signal is obtained by detecting the zero crossing point (ZCP) of the line-to-line back EMF. However, the commutation signal is delayed by the LPF. For this reason, based on the three-phase back EMF, a novel compensation algorithm including an open loop and a close loop is proposed to compensate for commutation error. Moreover, the speed feedback has a big delay at low speed. According to this, a novel speed calculation algorithm is presented to decrease the delay. Both the simulation and experimental results validate the high stability and reliability of the proposed method. [ABSTRACT FROM AUTHOR]

The appropriate efficiency of a dual stator winding squirrel-cage induction motor (DSWIM) is obtained when the ratio of two frequencies feeding the machine is equal to the ratio of the number of poles. In the vector control method, the estimation of flux at low speed is difficult. To solve this problem, researchers have benefited from the free capacity of the two windings of the stator. This makes the motor deviate from its standard operating mode at low speed. The main purpose of the present study is to reduce the power losses of the inverter units in the sensorless DSWIM drive using the proposed control scheme at low speed. In this control scheme, the speed is estimated based on the modified intelligent model reference adaptive system (MIMRAS) without estimating the stator resistance at low speed. The proposed methods were simulated in MATLAB/Simulink software, and the results of simulation confirmed the assumptions. [ABSTRACT FROM AUTHOR]

A novel rotor structure with a set of compensation winding for line‐start permanent magnet synchronous motors for high capacity and low speed, which can meet the requirements of a ball mill with a high moment of inertia, is proposed to improve the motor‐starting performance. A control strategy for the compensation winding current is implemented to increase the synchronisation ability with a high‐inertia load. The compensation current and its control method are analysed using a mathematical model and verified using a time‐step finite‐element analysis. The simulation shows that the permanent magnet motor proposed in this study can successfully start at a load of 15 times rotor inertia. [ABSTRACT FROM AUTHOR]

Delta-channel modular multilevel converter (MMC) proved successful for zero/low-fundamental-frequency operation without injecting common-mode voltage. However, its application in a medium-voltage variable-speed motor drive is not verified. This paper develops a variable-speed motor drive system based on a delta-channel MMC. The converter power losses together with the compensation strategies are analyzed, and accordingly the submodule capacitor voltage controls are elaborated. The converter controls cascaded with the advanced motor control form the entire control scheme for the drive system. The system performances are tested based on a 4160-V 1-MW simulation model and 208-V 5-kW experimental setup. The results show that the delta-channel MMC along with the proposed control algorithm performs satisfactorily in a driving motor from standstill to a rated speed even under rated torque condition. [ABSTRACT FROM PUBLISHER]

Copyright of Journal of Mechanical & Electrical Engineering is the property of Mechanical & Electrical Engineering Magazine and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: The heat transfer in the turbocharger occurs due to the temperature difference between the exhaust gas and intake air, coolant, and oil. This heat transfer causes the efficiency of the compressor and turbine to be distorted, which is known to be exacerbated during low rotational speeds. Thus, this study proposes a method to mitigate the distortion of the test result data caused by heat transfer in the turbocharger. With this method, the representative compressor temperature is defined and the heat transfer rate of the compressor is calculated by considering the effect of the oil and turbine inlet temperatures at low rotation speeds, when the cold and the hot gas test are simultaneously performed. The correction of compressor efficiency, depending on the turbine inlet temperature, was performed through both hot and cold gas tests and the results showed a maximum of 16% error prior to correction and a maximum of 3% error after the correction. In addition, it shows that it is possible to correct the efficiency distortion of the turbocharger by heat transfer by correcting to the combined turbine efficiency based on the corrected compressor efficiency. [ABSTRACT FROM AUTHOR]

This paper describes the design and the construction details of a medium size subsonic low-speed wind tunnel, which has been designed to achieve 90 m/s in the working section with expected low intensity turbulence level, making it available for researching in areas such as low speed aerodynamics (flight and terrestrial vehicles), sport activities, civil engineering applications, fundamental research in Fluid Mechanics and other possibilities. To accomplish such objectives a very detailed design was carried on using theoretical analyses, CFD simulations and semi-empirical methods, all of them applied to improve the flow quality along the wind tunnel sections. A very careful attention has been focused to the design of the fan blades and the electrical engine assembly, which has been inserted in a "pusher" configuration. Flow control and stabilization also took place using screens, honeycombs and corner vanes, all of them optimized to induce low turbulence levels in the working section. The design and construction of each wind tunnel section has been presented and discussed shedding light to the most relevant technical aspects and an attempt is made here to present some design and manufacture guidance for the main components of a low subsonic wind tunnel. [ABSTRACT FROM AUTHOR]

The paper deals with control of Permanent Magnet Synchronous Motor (PMSM) without a rotor position sensor. In the low and zero speed region, the rotor saliencies are utilized to obtain the information about the rotor position. Self-sensing control techniques employ high frequency (hf) signal injection to excite the saliencies. The proposed algorithm enables tracking the saliency and allows PMSM control at zero and low speed. The theoretical assumptions were experimentally verified including the initial rotor position detection. [ABSTRACT FROM AUTHOR]

This paper deals with the feasibility of developing an external-rotor synchronous reluctance motor for a low-speed direct-drive domestic application. Here, an attempt is made to identify the rotor geometry which provides high peak, average torque, and the saliency ratio in comparison with those of equivalent external-rotor switched reluctance motor (Ex-R SRM) which has already been developed and tested for the same application. In this context, six different rotor geometries are considered for the feasibility study and their performance characteristics are predicted using finite-element analysis. These results are compared with the equivalent size of Ex-R SRM, and finally, a feasible rotor geometry is proposed for further investigation and for the prototype designing. [ABSTRACT FROM AUTHOR]

To investigate the characteristics of a cycloid gear pump which is used as the accelerating pump in the wind power, a flow mathematical model was built, the advanced modeling environment simulation (AMESim) hydraulic model of wind turbines was established, and the effectiveness of the model is verified by the experiments. Based on the AMESim model, the flow characteristics of the wind turbine under the steady and unsteady wind speeds were investigated. The results show that, at low steady speed, the pulsation rate of flow pulsation in the cycloid gear pump decreases with the increase of rotational speed; and the lower the rotating speed is, the less steady the cycloid gear pump runs. Under the unsteady wind speed, the variation trend of output flow of the cycloid gear pump is basically consistent with that of the wind speed; the fluctuation frequency of the flow is greater than that of the speed. Meanwhile, due to the flow fluctuation of the cycloid gear pump, the mechanical energy with sudden change can be converted into the soft hydraulic energy, which is more conducive to the wind power. The research also proves that the cycloid gear pump can be used as the accelerating pump in the wind power generation system. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin University of Science & Technology is the property of Journal of Harbin University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the paper, a novel control method of a switched reluctance generator was discussed. The presented control method allows a rotor rotating at high speed to enter the continuous-conduction mode which causes an increase of generated output power. A control function of the presented method was given as well as simulation and laboratory tests. [ABSTRACT FROM AUTHOR]

Voltage model has been widely used in the field of motor control due to the advantages of the simple structure and less parameters required. A novel motor flux estimator based on phase-locked loop and proportional-integral (PI) regulator is proposed in this paper. This estimator calculates the set point of the torque component of electromotive force (EMF) through synchronous frequency and flux. Then, errors between the set point and the actual value of the EMF torque component are corrected by PI regulator to estimate the flux. This method avoids the problem of the saturation brought by the traditional integrator and the problem of the initial phase error. It also solves the magnitude and phase error problems at low speed in the flux estimator based on the low-pass filter. Finally, the simulation and the experiments are implemented on a cycloconverter-fed motor drive system to verify the effectiveness of this method. Simulation results show that this algorithm works very well at 0.2 Hz, and experimental results show that this algorithm can work well at 0.5 Hz. Meanwhile, this algorithm could detect the initial position of the rotor of separately excited synchronous motor. [ABSTRACT FROM AUTHOR]

Direct torque control is a powerful approach widely used for the control of electrical machines. However, this approach is sensitive to several problems, such as the stator flux demagnetization phenomenon and the appearance of undesirable torque ripples, especially at low-speed operation. To overcome these problems, a variable structure control approach for a direct torque control–space vector modulation system, with a constant switching frequency, is proposed in this article. The proposed sliding-mode direct torque control–space vector modulation method can (i) enhance the system robustness, (ii) reduce the torque ripples, and (iii) prevent the demagnetization problem, which penalizes the stator flux regulation. To reduce the chattering phenomenon that appeared on the control law, a second-order sliding-mode approach, which is a new second-order procedure, has been proposed. Simulation results dealing with low-speed operation of the induction motor under variable structure control direct torque control–space vector modulation strategy is presented and compared to those yielded by the direct torque control–space vector modulation strategy using hysteresis controllers. [ABSTRACT FROM AUTHOR]

This work deals with a sensorless speed control for three-phase induction motor in order to improve its operation at low speed. Initially, a direct field oriented control employing space vector pulse with modulation based on sliding mode observer (SMO) is studied and evaluated due to its high accuracy in estimating the flux at low speed. The proposed current model based on SMO provides good speed estimation under low speed and parameter or load changes. Simulations and experimental tests with diferent operational conditions at low speed are carried out in order to test the sensorless control. The results show a good perfomance and agreed with the results shown in recent papers. [ABSTRACT FROM PUBLISHER]

Copyright of Journal of Mechanical & Electrical Engineering is the property of Mechanical & Electrical Engineering Magazine and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Model reference adaptive system schemes offer simpler implementation and require less computational effort compared to other speed sensorless methods. The performance of rotor flux based model reference adaptive system schemes at low-speed operation is poor because of parameter sensitivity and presence of the integrator in the reference model. As stator resistance inevitably varies with temperature, for accurate operation at low speeds, an appropriate online identification algorithm for the stator resistance is required. In this article, a neural network based parallel stator resistance and rotor speed estimator has been proposed to simultaneously rectify the limitation of model reference adaptive system schemes,i.e., stator resistance variation and DC offset due to integrator, employing a neutral network in stator resistance estimator and modifying the reference model by adding a compensating voltage term. An indirect sensorless vector control scheme has been simulated and experimentally validated using the dSPACE DS-1104 R&D controller board (dSPACE GmbH, Paderborn, Germany) to verify the performance of drives at different operating conditions. [ABSTRACT FROM AUTHOR]

The inaccuracy and delay of speed feedback cause a vibration problem when the permanent magnet synchronous motor runs at low speed. As the low-speed smoothness is a key point of many applications of the permanent magnet synchronous motor, this article solves this problem by adding a real-time adjusted extended Kalman filter to low-precision-sensor vector control. In the mathematical model, the estimated speed of the extended kalman filter is significantly impacted by the deviations of the resistance and magnetic flux rather than other parameters. Thus, underid= 0 vector control, aRs-ψf-identifier is designed to calculate the values of the resistance and flux simultaneously with a small compensatingid. This algorithm runs on the platform in real time. Finally, the experiment results validate that when the velocity reaches as low as 1 r/min, the proposed method eliminates the vibration problem in the low-precision-sensor permanent magnet synchronous motor. [ABSTRACT FROM PUBLISHER]

This study aims to investigate the characteristic of a compact generator - hydro turbine system. The generator is of permanent magnet type and the turbine operates in a very low head. The integration of the two components is conducted in such a way that simplifies the construction of the conventional turbine generator. The method is by mounting the generator stator to the turbine casing and the permanent magnets are assembled in the perimeter of the turbine blade rotor. This simple construction is approached by making the stator from individual teeth and yoke. The permanent magnet generator (PMG) is designed to produce the nominal power of 300 Watt 50 Hz at 83 rpm of turbine shaft. All components of the integrated turbine- generator are totally immersed in the water stream. The stator has to be hermitic to avoid water entering the spool. Another issue investigated is the influence of the type of the stator inner casing material to the generator performance. The results show, the PVC material for inner casing has a good influence to the generator performance compared with the mild steel material. [ABSTRACT FROM AUTHOR]

This paper proposes a novel machine termed the axial-flux brushless doubly fed reluctance machine (AF-BDFRM) suitable for high-torque, low-speed direct drive applications. The main potential advantages of AF-BDFRM are its higher torque and power density compared with the radial-flux BDFRM. In addition, the proposed machine utilizes a bidirectional power converter of much lower rating as compared with the machine rating depending on the range of speed variation. The proposed machine axial-flux topology is composed of two stators and a reluctance iron rotor. The upper stator winding which is connected directly to the power grid, transfers active power to the grid and lower stator winding creates excitation for the machine and connects to the grid through a partially rated converter. The design principles of the proposed AF-BDFRM are studied in this paper. Furthermore, the transient 3-D finite-element analysis result of the improved design is presented. [ABSTRACT FROM AUTHOR]