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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]

The influence of excess air coefficient, ignition timing, and injection timing were investigated to examine the combustion and emission performance of a hydrogen engine operating at low speed with low loads. Comprehensive experimental research was then undertaken to evaluate the engine performance across a wide range of loads and various combinations of factors. The experimental results show a substantial improvement in brake thermal efficiency (BTE) and a noteworthy reduction in NO X emissions with an increased excess air coefficient. Although the impact of injection timing on BTE is negligible, an appropriate injection timing delay effectively reduces NO X emissions. A lean mixture and a suitable ignition timing delay exhibit high thermal efficiency at a lower engine speed and simultaneously suppress knock. The BTE reaches 33.46% at a mean effective pressure of 10.0 bar. Improving the turbocharging capability under low-speed and high-load conditions is essential for enhancing the performance of hydrogen engines. • EOI has little impact on BTE but is effective in reducing NO X emissions at low load. • Larger excess air ratio can increase BTE and reduce NO X emissions greatly. • Increasing excess air ratio can suppress knock and improve BTE at high load. • Outward-opening injectors are used to decrease hydrogen injection pressure. [ABSTRACT FROM AUTHOR]

As one of the most promising renewable energies, wind energy is abundant in the natural environment. However, it is still challenging to effectively collect wind energy because of its variable wind speed and unpredictable direction. Here, a triboelectric nanogenerator, which is inspired by ancient Chinese wind bells, has been developed to collect energy from variable‐speed and multi‐directional wind. The wind‐bell‐inspired triboelectric nanogenerator (W‐TENG) has the capability to generate electricity even at a very low wind speed of 0.5 m s−1. Furthermore, it is able to harvest wind energy effectively from all directions (0–360 degrees). The parameter‐optimized W‐TENG achieves a maximum output voltage of 9.3 V and a maximum current of 0.63 µA. Electronic devices including a digital watch and 40 light‐emitting diodes (LEDs) are successfully powered by the designed W‐TENG, demonstrating its applicability. In this study, it is believed that a novel and effective strategy is provided to harvest energy from variable‐speed and multi‐directional wind. [ABSTRACT FROM AUTHOR]

Airports strive for a greener energy transition to minimize their carbon footprint and greenhouse gas emissions. The installation of solar or wind turbines is gaining significance among stakeholders working in sustainable airports. This study focuses on developing Biratnagar airport as a completely greener airport by identifying suitable sites for installing Solar and wind farms within the premises without compromising on safety aspects, including glare occurrence and environmental and electrical safety. PVSYST V6.8.7 and HOMER V2.81 software are used to simulate the performance of PV and wind turbine power plants. Three sizes of Vertical axis wind turbines (VAWT) of EOLO 15 kW, Tree tree-shaped wind Turbine (TSWT) 58.5 kW and TSWT 585 kW have been used for the Simulation. A sensitivity analysis of various parameters, including interest rates, wind speed, and wind turbine types, has been carried out to study the cost of energy generation in grid-connected mode. According to the study, a 157 kWp solar PV power plant is sufficient for Biratnagar Airport to become Nepal's first fully green-powered airport. The project's Levelized Cost of Electricity (LCOE) equals 0.141 $/kWh if wind energy is used to supply part of the electricity with the annual wind electricity production of 23,184 kWh. The combined 15 kW wind turbine-grid scenario is superior to the grid scenario for wind speeds of more than nine m/s and interest rates of less than 10 %. These findings increase airport authorities' and stakeholders' confidence in the investment in greener airports.

To enhance the efficiency of wind power conversion systems, a DC conversion system that combines a wind turbine with a battery is introduced in this paper. The Vernier Doubly Salient Permanent Magnet (V-DSPM) generator at the center of this system, designed for low speeds and high torque, eliminates the need for troublesome gearboxes. The proposed control employs MPPT based on tip speed ratio with output as the reference current of the boost converter and a sliding mode control-based Gao’s constant plus proportional rate reaching law to track the reference current. Three tests were performed to determine the efficiency of the proposed strategy. Moreover, a comparison with a conventional PI controller was carried out. The simulations were performed using MATLAB and Simulink. The obtained results show that the system with SMC has better performance than the system with PI.

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]

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]

A low speed sensorless position control method for brushless DC motor based on pulse pulse high frequency voltage injection is proposed according to the characteristic that the brushless DC motor (BLDCM) which is produced at present makes the counter electromotive force waveform show sinusoidal waveform in view of the problem that it is difficult to accurately obtain the rotor position and speed of the brushless DC motor at zero and low speed. Its principle is to inject high frequency sinusoidal voltage signal on the estimated direct axis of the synchronous rotating coordinate system so that the motor can generate saturated salient effect, obtain the estimation error containing the rotor position information, and by detecting the output current of PI regulator of quadrature axis current loop, and then estimate the initial position of the rotor and judges the magnetic pole, realize the determination of the actual rotor position, finally, realize the non-position static low speed control of BLDCM by adding current and speed rings. According to the simulation test, it shows that this method can detect the position and speed of the motor rotor well at both zero speed and low speed.

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 θ1, width angle θ2, and length l. The influence order of design parameters on the pulsation rate is θ1>l>θ2; 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.

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.

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]

The transportation industry is increasingly focused on hydrogen based fuel as a promising alternative due to its potential for reduced emissions and enhanced performance. The purpose of this study is to improve efficiency and reduce emissions on low speed on different loads for heavy duty vehicles. This study can be impactful to train the electronic control unit (ECU) for heavy duty vehicles working on aforementioned conditions. This study investigates the effect of hydrogen ratios (0%–40 %) in HCNG, (0%–15 %) exhaust gas recirculation (EGR) ratios, and spark timing (8°-34o CA bTDC) at low and high loads (15 % & 75 %) under stoichiometric conditions at low speed (700 rpm). Performance, emissions and combustion parameters were thoroughly analysed across these conditions. Brake thermal efficiency increases by 20.7 % & 19.4 % by the addition of (0 %–40 %) hydrogen at low and high load at 14o CA bTDC running on 5 % and 0 % EGR respectively. NOx emissions reduces by 11.9 % & 17.9 % by the addition of (0 %–15 %) EGR and increases by 46.1 % & 46.4 % by increasing the amount of hydrogen in HCNG at low and high load at 14o CA bTDC at 0 % EGR respectively. Coefficient of variation reduces 13.8 % by (0 %–40 %) hydrogen addition at 11 % EGR at 16o CA bTDC. Optimized Gaussian process regression (GPR) and neural network (NN) machine learning techniques were applied to the dataset, and found GPR matern 5/2 is best one. The findings can be utilized in the development of HCNG engine. • Experiments were performed on the HCNG engine on idle conditions at low and high load. • Optimized GPR & NN applied to predict performance & emissions on low load for HCNG engine. • Performance and emissions parameters are analysed on high load in 2nd part of this study. • Combustion parameters are analysed on low and high load in 3rd part of this study. [ABSTRACT FROM AUTHOR]

During braking with ABS (Anti-Lock Brake System), low braking initial speed causes to build-up and reduce brake pressure in longer time period due to extending application time of brake pressure and response time of solenoid valve. Also, the decision about speed and acceleration variations of wheel becomes very difficult due to weak speed signals arising from low speed. This results in lower braking torque than needed on the wheels. Therefore, effects of weak wheel speed signal become more pronounced in critical road conditions due to sudden changes in wheel speed. In this study, the effects of these problems occurring in low speed were investigated on both control and braking performance of ABS under critical road conditions. For this, ABS tests were carried out for low and high speeds on four different road types, which include slippery, wet and µ-jump tests (from wet to slippery and from slippery to wet). In this way, the results were compared to both vehicle speed and road type. The test results show that the low speed worsens braking stability, control and braking performance of ABS, regardless of road conditions. For this reason, it is proposed that ABS control algorithm must be divided in two parts as low and high speed control.

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]

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]

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]

A low speed sensorless position control method for brushless DC motor based on pulse pulse high frequency voltage injection is proposed according to the characteristic that the brushless DC motor (BLDCM) which is produced at present makes the counter electromotive force waveform show sinusoidal waveform in view of the problem that it is difficult to accurately obtain the rotor position and speed of the brushless DC motor at zero and low speed. Its principle is to inject high frequency sinusoidal voltage signal on the estimated direct axis of the synchronous rotating coordinate system so that the motor can generate saturated salient effect, obtain the estimation error containing the rotor position information, and by detecting the output current of PI regulator of quadrature axis current loop, and then estimate the initial position of the rotor and judges the magnetic pole, realize the determination of the actual rotor position, finally, realize the non-position static low speed control of BLDCM by adding current and speed rings. According to the simulation test, it shows that this method can detect the position and speed of the motor rotor well at both zero speed and low speed. [ABSTRACT FROM AUTHOR]

Ni-Cr-W matrix cermet composites were prepared using powder metallurgical technology, and their microstructures, phase compositions, and mechanical properties were determined. Specifically, the tribological performances of the Ni-Cr-W composites were evaluated at a speed of 0.5 mm/s from room temperature to 800 °C, and their friction-reducing mechanism was clarified. The results showed that the NiCrW/Al 2 O 3 /Ag composite had the highest mechanical strength, with a 94.5 % increase in tensile strength compared to NiCrW/Al 2 O 3. The NiCrW/Al 2 O 3 /SrCO 3 composite exhibited the best high-temperature tribological performance because the chemical reaction on the friction surface generated new lubricating phases consisting of NiO, WO 2 , WO 3 , and Sr 2 CrO 4. These acted synergistically lubricate and anti-wear with the Al 2 O 3 , Cr 2 O 3 , and NiCr 2 O 4 , and formed a continuous glaze layer on the wear surface. Furthermore, the multiple roles of nano-alumina in the obtained composite and its service in friction were discussed. [ABSTRACT FROM AUTHOR]

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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]

It is a difficult to accurately estimate the rotor position in a surface permanent magnet synchronous motor (SPMSM), especially for low speed conditions because the back electromotive force (EMF) is almost zero. In this paper, an improved sliding mode observer (SMO) with a continuous sliding mode switching function (which could reduce the chattering effect) is proposed to estimate the real-time rotor position at a low speed. Through the introduction of an intermediate variable H, the back EMF is extended at low speed, which could improve the estimation accuracy for the rotor position. In addition, the chattering phenomenon is reduced by redesigning the sliding switching function. On the other hand, inverter nonlinearity also results in torque ripple and deteriorates the drive performance because of the harmonic components in the three-phase stator current. Here, a generalized sliding discrete Fourier transform (GSDFT) strategy is studied to extract the harmonic components, which can then be compensated with the corresponding compensation voltage calculated from the motor mathematical model. With the proposed strategy, the estimation accuracy can be apparently restricted when the rotor speed is lower than 50 rpm, while the chattering effect is also improved. With the nonlinearity compensation, the total harmonic distortion obviously decreases, which can improve the rotor estimation and the torque performance. In addition, the GSDFT algorithm executes in approximately half the time of the SDFT compensation method.

The control performance of a butterfly-shaped linear ultrasonic motor is not good when the target speed is less than 1 mm/s by traditional methods. To improve low-speed controlling characteristics of linear ultrasonic motor, a closed-loop control strategy by using both the step control and the fuzzy PID control was proposed. The controller was constructed with the function of providing a closed-loop control of the speed by adjusting the driving voltage amplitude in stepping driving mode. The corresponding step controlling parameters were determined by experiments. Comprehensive experiments on the developed control strategy were conducted under different target speeds. There was a maximum of 24.5% speed error at the target speed of 10 μm/s, meanwhile, the coefficient of variation and the response time were 16.3% and 0.11 s, respectively. With the triangular or sinusoidal waves speed tracking curves at amplitude of 1 mm/s, the maximum speed tracking error were 0.1 mm/s and 0.15 mm/s respectively. Thus, a good speed tracking performance was obtained. These results support the functional ability and potential of the proposed method as a low-speed precision control method for linear ultrasonic motors.

The requirement of high-fidelity experimental data of microscopic properties as well as the whole spray development is fundamental since they are determinant in the understanding of atomization and evaporation process in a variety of multiphase flows. The Selective Catalytic Reduction (SCR) system is one of the industrial applications where understanding the whole spray atomization and development process is essential in developing new systems to cope with stringent emission regulations. A new subsonic heated open-loop wind tunnel has been designed and manufactured specifically with a 0.25 × 0.25 m cross-section and 1.59 m long optically accessible quartz glass side panels. The purpose of the wind tunnel was to investigate Selective Catalytic Reduction (SCR) sprays using Phase Doppler Anemometry (PDA). The wind tunnel is capable of reaching a flowrate equating to 50 m/s in the test section when operating at standard room conditions (25°C and 101,325 kPa). A 145 kW heater is mounted downstream the blower to achieve air temperatures of up to 400°C with maximum air mass flow of 1200 kg/h. The diffuser, flow conditioning and contraction cone sections of the wind tunnel have been designed to minimize velocity and temperature gradients within the test section while minimizing flow disturbances. A diffuser with a cone angle of 5° and an area ratio of 3.95 and a contraction cone with a contraction ratio of 4.05 was selected. The test section has been designed to give complete visible access through top and both sides, while the bottom is made of stainless steel. The two sides are made of quartz glass to provide the best signal transmission quality for usage with any optical equipment e.g. PDA. The top of the test section has sections made of Robax glass with detachable windows for easy mounting and dismounting of any equipment subject to be tested in the flow section. The streamwise turbulence intensity in the test section was found to be less than 2% in the core with similar values for the cross-stream turbulence intensities. The complete design and construction of each section of the wind tunnel has been presented and discussed in this paper.

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.

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.

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]

The development of rolling element bearing fault diagnosis systems has attracted a great deal of attention due to bearing components having a high tendency toward unexpected failures. However, under low-speed operating conditions, the diagnosis of bearing components remains a problem. In this paper, the adaptive resilient stacked sparse autoencoder (ArSSAE) is proposed to compensate for the shortcomings of conventional fault diagnosis systems at low speed. The efficiency of the proposed ArSSAE model is initially assessed using the CWRU database. Then, the proposed model is evaluated on actual vibration analysis (VA) and acoustic emission (AE) signals measured on a bearing test rig at low operating speeds (48-480 rpm). Overall, the analysis demonstrates that the ArSSAE model is able to perform an accurate diagnosis of bearing components under low-speed conditions.

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]

This paper is about the use of BLDC motors in applications to the detriment of induction or brush motors. We have developed a software controller in Mathlab to control the BLDC motor in flow without hall sensors for low speeds and high power. By choosing small and precise speeds, both the stator flow and the rotor flow must be coordinated. [ABSTRACT FROM AUTHOR]

A dual stator winding squirrel-cage induction motor (DSWIM) is a brushless single-frame induction motor that contains a stator with two isolated three-phase windings wound with dissimilar numbers of poles. Each stator winding is fed by an independent three-phase inverter. The appropriate efficiency of this motor 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 at low speeds, flux is difficult to estimate because the voltage drop on the stator resistance is comparable with the input stator voltage, disturbing the performance of the motor drive. To solve the abovementioned 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 speeds. The main purpose of this paper is reducing the power losses of the inverter unit in the DSWIM drive at low speeds via the proposed control method and a five-leg inverter. This paper deals with two topics: 1. Using the idea of rotor flux compensation at low speeds, the motor works in its standard operating mode. Therefore, the power losses of the utilized power electronic converters are also reduced to a considerable extent; and 2. Reduction in capital cost can be achieved by utilizing a five-leg power electronic converter. The proposed methods are simulated in MATLAB/Simulink software, and the results of simulation confirm the assumptions.

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.

This paper proposes a driving method, the superimposed pulse driving method, that can make an ultrasonic motor run at a low speed. Although this method solves the periodic oscillation of speed in a traditional low-speed driving motor, it still has a small periodic fluctuation, which affects the stability of the speed. To reduce the fluctuation rate of the motor speed, the structure model and driving model of the motor are established, based on the theory of a beat traveling wave, and the motion characteristics of the particle point are analyzed in this paper. The simulation curve of the motor speed is obtained according to the stator and rotor contact model and the transfer model. The research shows that the driving method introduced in this paper causes the stator surface to generate a traveling beat wave, and the driving end of the stator generates an intermittent reciprocating vibration and drives the rotor rotation, which is the mechanism of low-speed operation when the driving method is used to drive the motor, as well as the reason for the periodic fluctuation of the motor speed. To improve the speed stability, this paper controlled the output performance of the motor by changing the two control variables—prepressure and frequency difference—and concluded that the variation trend of the average speed and speed volatility were consistent with the variation trend of the motor’s average speed determinant and the speed volatility determinant, respectively, which is verified by the velocity measurement experiment and the vibration measurement experiment. These insights lay the theoretical foundation for the velocity adjustment and stability optimization and, finally, the application of the new driving method is prospected.

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]

In this paper, a low-speed and high-efficiency permanent magnet generator (LHPM generator) for micro hydro-electrical generation system was developed, and two different low-speed generators by using silicon steel and SPCC core (Common Cold Steel Plate) were fabricated and compared. The proposed LHPM generator can have high no-load electromotive force (EMF) and high efficiency at low speed by optimizing its parameters, and shows possibility to reduce its production cost by comparing the performance with different ferromagnetic materials of iron cores. Firstly, the principle of the low-speed and high-efficiency permanent magnet generating system was introduced, and the parameter design of the LHPM generator was proposed. Then the performance with different ferromagnetic materials of cores was analyzed. Finally, various Finite Element Analysis (FEA) simulation, optimization studies and experiments were performed. The cogging torque reduction method, effect of PM's parameters, and the influence of different materials of cores were also investigated. Furthermore, as a tradeoff between the generator's performance and the production cost, so-called hybrid core type generator, of which the rotor is made of SPCC core and the stator is made of silicon steel core was proposed. The simulation and experimental results demonstrate the effectiveness of the proposed structure. • Developing a low-speed and high-efficiency direct-drive generator for micro hydro-electrical generation system. • Improving the performance of the generator by optimizing the parameters of the generator. • Shows possibility to reduce the production cost of the generator by comparing with different materials of iron cores. [ABSTRACT FROM AUTHOR]

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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]

This paper presents predictions of the added resistance of a ship in waves at a low speed according to the IMO minimum propulsion power requirement by a hybrid Taylor expansion boundary element method (TEBEM). The flow domain is divided into two parts: the inner domain and the outer domain. The first-order TEBEM with a simple Green function is used for the solution in the inner domain and the zero order TEBEM with a transient free surface Green function is used for the solution in the outer domain. The TEBEM is applied in the numerical prediction of the motions and the added resistance in waves for three new designed commercial ships. The numerical results are compared with those obtained from the seakeeping model tests. It is shown that the prediction of the ship motions and the added resistance in waves are in good agreement with the experimental results. The comparison also indicates that the accuracy of the motion estimation is crucial for the prediction of the wave added resistance. In general, the TEBEM enjoys a satisfactory accuracy and efficiency to predict the added resistance in waves at a low speed according to the IMO minimum propulsion power requirement. [ABSTRACT FROM AUTHOR]