Negative Torque Research Articles

Induced Current Reduction in Position-Sensorless SRM Drives Using Pulse Injection

This article proposes a new pulse injection scheme for low-speed position-sensorless switched reluctance motor (SRM) drives with the reduced induced current. Conventional injection methods utilize a constant injection amplitude for position estimation; however, the induced current in idle phases nonlinearly varies with the rotor position and has significant magnitude. It results in large negative torque and degrades the control performance. To mitigate this problem, an injection amplitude regulator based on terminal sliding-mode control is put forward. The amplitude of pulse voltages is adjusted online through a nonlinear control law, and the induced current can be maintained at a minimal level over the whole idle-phase period. Moreover, the adverse impacts of motor parameter uncertainties are eliminated. As a result, the proposed scheme does not require SRM's magnetic characteristics and is easy to implement. The effectiveness was experimentally validated on a three-phase 12/8 SRM setup with comparisons of the conventional method.

Aerodynamic analysis of a 2-stage elliptical-bladed Savonius wind rotor: Numerical simulation and experimental validation

ABSTRACT The Savonius rotor is a type of vertical-axis wind turbine that utilizes drag to generate power. Its design simplicity and ability to self-start at low wind speeds make it an attractive option for small-scale wind energy generation. Previous research has focused on optimizing the geometric configuration of a 1-stage, 2-bladed rotor with semicircular blade profiles to improve its performance and mitigate negative torque. However, limited research has been conducted on 2-stage, 2-bladed Savonius rotors with elliptical blade profiles. The present investigation aims to fill this research gap by evaluating the aerodynamic characteristics of a 2-stage, 2-bladed Savonius rotor with elliptical profiles. 3D unsteady simulations using the SST k-ω turbulence model in ANSYS Fluent are conducted to evaluate the performance coefficients over a range of tip speed ratios. The numerical results are validated through wind tunnel experiments. The results show that the CPmax (maximum power coefficient) for the 1-stage rotor is 0.19 and 0.12 for numerical and experimental analyses, respectively. For the 2-stage rotor, the CPmax is 0.21 and 0.17 for numerical and experimental analyses, respectively. These findings suggest that the 2-stage rotor with elliptical profiles has the potential to efficiently harness wind energy.

A novel electric differential and synchronization control method for 4WD/4WS electric vehicles based on fictitious master

Electric Vehicles (EVs) have been typically proposed to replace conventional vehicles in the near future. The use of an Electric Differential (ED) in EV has many advantages like as high efficiency, low loosing, and lightweight mechanical differentials and transmissions with electric motors directly coupled to the wheels. In this paper, a novel ED mechanism for the four–Wheel–Drive (4WD)/two–Wheel–Steering (2WS) and 4WD/four–Wheel–Steering (4WS) EVs is proposed. The proposed ED is easy-to-implement and solves the problems of previous EDs. The speed synchronization action of all wheels is achieved by using the Fictitious Master technique. Moreover, for independent control of speed and torque, the Ackerman laws are applied to the motors. Also, the currents of EV are controlled with an indirect current vector controller. For a complete assessment of the proposed control method, the EV is analyzed under two different disturbances as positive and negative torque variations. The results showed that ED ensures both reliability and good path tracking. In addition, the robustness and stability of EVs under various disturbances are validated by producing new speed references for all wheels. The considered EV could robust under disturbance conditions, at an acceptable level. Moreover, the overlaps of torque and speed in the 4WD/4WS are about 15% and 23% more than 4WD/2WS, respectively. In essence, the proposed control method shows good results for EVs with various conditions: straight movement, turning, acceleration, and deceleration.

High-Precision Finite-Time Positioning Control for an Inertial Reference Unit With Asymmetric Loads and Mover Sideslip

In this article, a finite-time controller is designed on high-precision positioning for an inertial reference unit (IRU) with asymmetric loads and mover sideslip based on a finite-time extended state observer (ESO). The asymmetric loads caused by centroid deviation from central axis are a negative factor, which results in a negative load torque for IRUs. The mover sideslip is another negative factor that brings about output forces errors between actual output forces and theoretical output forces for voice coil motors. The finite-time ESO is designed to estimate and compensate the asymmetric loads and mover sideslip. The finite-time controller is proposed with high convergence rate for the IRU. Experimental results are presented to show effectiveness of the proposed finite-time control method in high-precision positioning under asymmetric loads and mover sideslip.

Recent Advancement in Savonius Wind Turbine- A Review

In the steps to save our earth from global warming every nation focused on their own way to promote green energy among which the Savonius vertical axis wind turbine is one of the excellent viable solutions for scavenging wind energy in a downtown background, due to distinctive characteristics such as compactness, self-starting ability at light wind, minimum noise level, with relatively reasonable price and simple assembly. However, the traditional Savonius Wind Turbines with semicircular blades has a proportionately low power coefficient together with a high negative torque produced by the returning blade is a crucial disadvantage of this rotor. This work focuses on reviewing and giving an overview on the form of the wings of Savonius Vertical Axis Wind Turbine. This paper also aims to give a run through of the several augmentation approaches used in Savonius rotor over the last four decades. In this paper, a brief on all possible segments and parts of the machine is given after a brief analysis and research on each topic.

Aerodynamic Characterization of Darrieus Turbines during Self-Start at different Azimuthal Quadrants

One key technology to extract kinetic energy from wind and water is the vertical-axis turbines. However, these flows and currents often fluctuate, forcing the turbine rotors to operate in transient modes. To improve rotor performance, the transient aerodynamic characteristics across the four quadrants of the rotor sweep must be well-understood. We address this need by simulating the transient process of a 3-bladed Darrieus turbine rotor during self-start using the dedicated turbine aerodynamics software QBlade. The simulated transient evolution of the rotor compares well against the experimental and computational-fluid-dynamics data from previous studies. When the rotor self-starts within its first three cycles, its torque is contributed differently from each of the four quadrants. Respectively, its windward and upwind quadrant positively contributes by up to 43% and 326% each to the overall torque, and the leeward and downwind quadrant negatively reduces by up to -346% and -85% each from the overall torque. However, upon reaching steady state, these roles change where the positive torques are contributed by the upwind and leeward quadrants by up to 120% and 10%, respectively, while the negative torques are caused by the downwind and windward quadrants by up to -18% and -13%, respectively. Insights into these rotor dynamics can be later used to propose newer rotor designs or operations to improve the transient performance of the turbine

Numerical investigation and improvement of the aerodynamic performance of a modified elliptical-bladed Savonius-style wind turbine

<abstract> <p>The Savonius turbine has an advantage over other types of vertical axis wind turbines (VAWT), which have speeds ranging from the lowest wind speed to the highest. However, the main problem is the negative torque on the rotary blades. This paper used computational fluid dynamics to numerically investigate the two-dimensional flow analysis of a modified elliptical Savonius wind turbine. This study investigated and compared five rotor blades: Classic, elliptical, and their three modifications. The behavior of wind energy was studied explicitly by changing the angle of the axis of the elliptical blade from the concave side, which leads to a convex shape to increase the area affected by the thrust force and increase the positive torque. The ANSYS (previously known as STASYS Structural Analysis System) Fluent version 15 software solves the unstable Reynolds-Naiver-Stokes (URAN) equation. The coupling algorithm solves the pressure-based coupling pressure velocity using the ANSYS Fluent. In the simulation, the drag, lift, and moment coefficients on the Savonius turbine were calculated directly at each change in the axis angle. The test results at wind speeds of up to nine m/s showed that the modified elliptical turbine with an axis angle of 50° had the highest coefficient power (Cp) among other elliptical blade modifications. In comparison, the test results with variations in wind speeds of 4–12 m/s showed that turbines with an axis angle of 55° performed better with a higher tip speed ratio (TSR) than other models.</p> </abstract>

FLUID DYNAMIC PERFORMANCE AND PERFORMANCE ANALYSIS OF A NOVEL FLEXIBLE OSCILLATING WIND TURBINE

While the variable pitch angle design has been proven to significantly enhance the performance of vertical axis wind turbines, its implementation requires the addition of extra mechanical devices, such as a chain-and-sprocket system. These additional mechanisms not only increase system friction and produce extra vibrations but also cause vertical axis wind turbines to lose their omnidirectional characteristics. To address this issue, this study proposed a novel flexible oscillating wind turbine, wherein the function of changing the pitch angle is accomplished through the deformation of flexible blades. To reveal the internal flow field mechanism of this novel turbine, particle image velocimetry experiments were conducted. The results indicate that the flexible blade can alter its posture to form a suitable angle of attack under different azimuth angles. In the downstream region, the blades spread out to generate a substantial positive torque. In contrast, in the upstream region, the blades are in a diversion state, always maintaining a small angle of attack to avoid generating excessive negative torque. Wind tunnel experiments were carried out on the flexible oscillating wind turbine to explore the effects of wind speed and key geometric parameters on the turbine’s performance. The results show that the novel flexible oscillating wind Turbine maintains high efficiency even under low wind speed conditions.

Gradual Electronic Pole Changing Technique to Minimize the Circulating Currents During Pole/Mode Transition in Induction Motor Drive

This paper proposes a control strategy for the electronic pole changing (EPC) induction motor drive (IMD) for the transition between 3-ϕ,12-pole mode to 9-ϕ,4-pole mode. The proposed control strategy employs a gradual electronic pole changing (GEPC) technique which linearly demagnetizes the IMD winding from 3-ϕ,12-pole and magnetizes progressively to 9-ϕ,4-pole mode. The proposed GEPC technique is also compared with the instantaneous EPC technique for its performance. The proposed GEPC solution eliminates the issue of the circulating current, which exists in the instantaneous EPC technique and is responsible for negative torque generation during pole transition from 3-ϕ mode to 9-ϕ mode. Apart from eliminating the circulating current, the proposed GEPC strategy also sorts out various typical issues which exist in instantaneous EPC technique during pole/mode transition. The various issues in the instantaneous mode transition are (i) absence of interlocking between stator and rotor fields, (ii) oscillations in the flux between the 12-pole (3-ϕ) and 4-pole (9-ϕ), (iii) strengthening and weakening 4-pole formations in stator and rotor, (iv) distorted flux and pole formations, (v) dip in speed, and (vi) high oscillations/ripple content in torque and speed. Ansys simulation is done using Maxwell 2-D integrated with Twin-builder for EPC IMD for instantaneous and proposed GEPC techniques. Further, the paper presents the experimental results to validate the simulation studies.

FLUID DYNAMIC PERFORMANCE AND PERFORMANCE ANALYSIS OF A NOVEL FLEXIBLE OSCILLATING WIND TURBINE

While the variable pitch angle design has been proven to significantly enhance the performance of vertical axis wind turbines, its implementation requires the addition of extra mechanical devices, such as a chain-and-sprocket system. These additional mechanisms not only increase system friction and produce extra vibrations but also cause vertical axis wind turbines to lose their omnidirectional characteristics. To address this issue, this study proposed a novel flexible oscillating wind turbine, wherein the function of changing the pitch angle is accomplished through the deformation of flexible blades. To reveal the internal flow field mechanism of this novel turbine, particle image velocimetry experiments were conducted. The results indicate that the flexible blade can alter its posture to form a suitable angle of attack under different azimuth angles. In the downstream region, the blades spread out to generate a substantial positive torque. In contrast, in the upstream region, the blades are in a diversion state, always maintaining a small angle of attack to avoid generating excessive negative torque. Wind tunnel experiments were carried out on the flexible oscillating wind turbine to explore the effects of wind speed and key geometric parameters on the turbine’s performance. The results show that the novel flexible oscillating wind Turbine maintains high efficiency even under low wind speed conditions.

Pengaruh Overlap Ratio pada Model Turbin Savonius terhadap Karakteristik Koefisien Daya Berdasarkan Eksperimen Pada Wind Tunnel

Wind energy is a resource that is abundant, environmentally friendly, and renewable, therefore it has the potential to be developed. Savonius vertical axis type is suitable for application in low wind speed conditions. The Savonius wind turbine has good self-starting so that it is able to rotate the rotor even though the wind speed is low, besides that the torque it produces is relatively high. This study aims to determine how differences in OR affect the performance of Savonius turbines with an aspect ratio (AR) of 2. The experimental method was applied in this research to investigate the characteristic Cp of the model using the wind tunnel with different overlap ratios of 0.1, 0.15, 0.2, 0.25, and 0.3. The wind turbine model that has been made using a 3D printing process made of PLA + material. The results obtained in each OR test are the maximum Cp value for the variation OR 0.1, which is 0.121, OR 0.15, the maximum Cp value obtained is 0.213, OR 0.2, the maximum Cp value is 0.245, OR 0.25, the maximum Cp value is 0.224 and OR 0.3, the maximum Cp value is 0.210. Based on the five overlap variations, the maximum Cp ratio is obtained at OR = 0.2, namely Cp = 0.245 and TSR = 0.7. The OR value of 0.2 is able to maximize turbine power and minimize negative torque because the flow through the overlap area can maximally direct wind power to the maximum backward blade.

Numerical Simulation and PIV Experimental Investigation on Underwater Autorotating Rotor

In this work, the flow field of an autorotating rotor in a water tunnel with various pitches and shaft backward angles was investigated via particle image velocimetry (PIV). The experiments were carried out on a free-rotating two-bladed single rotor. Computational Fluid Dynamics (CFD) based on moving overset grids were developed to study the hydrodynamic characteristics of an underwater autorotating rotor. The simulation results are in good agreement with the test results. The thrust and thrust coefficient of the underwater autorotating rotor were calculated by CFD simulation under different situations. The research demonstrates that rotational speed and thrust have a significant positive correlation with water velocity, pitch, and shaft back angle. In particular, the thrust coefficient scarcely varies with the shaft backward angle. An underwater autorotation rotor with a thin airfoil, negative torque, and a suitable number of blades can increase the thrust and thrust coefficient. The investigation is of significance in enriching the autorotation theory of rotors and helping to develop underwater autorotating rotors.

Elliptical Bladed Savonius Rotor for Wind Energy: Efficacy of RANS Modeling for Flow Characteristics

Abstract Wind energy is a key contributor to renewable energy production. Vertical axis wind turbine (VAWT) of Savonius type is advantageous in places of small-scale power production and low wind speed regions. It is a VAWT of the drag-based type. The disadvantage of a Savonius rotor is its low efficiency due to the generation of negative torque on the returning blade. To reduce the negative torque, the performance parameters of a Savonius rotor need to be optimized. The shear-stress transport variant of k–ω turbulence model is used in the current study to compute 2D unsteady Reynolds-averaged Navier–Stokes calculations for an ellipse shape blade Savonius rotor to capture its aerodynamic behavior. The flow complexities, such as vortex generation and circulation, are analyzed for four different azimuthal angles 0deg, 45deg, 90deg, and 135deg for a tip speed ratio (TSR) of 0.8. A rise in CD to 1.0 at TSR equal to 0.9 indicates an adverse pressure gradient region on the forward-moving blade. The circulation studied in the present paper could be of practical importance in situations involving an array of Savonius rotors to find an optimum rotor position and rotational direction as in the case of horizontal axis wind turbine (HAWT).

Rotations of F-ATPase and V-ATPase analyzed by a torque approach

F-type ATP synthase (F-ATPase) and vacuolar ATP hydrolase (V-ATPase) are well-known biomolecular motors, which play significant catalytic roles in ATP synthesis and ATP hydrolysis reactions. Their rotational torques are important factors involved in their rotational behavior that can be measured experimentally but with considerable difficulty. To overcome this difficulty and thereby provide an in-depth understanding of their operation mechanism, we herein carry out simple and fast computer modelling to study the two proteins, using our torque approach that relies on interatomic forces and coordinates of unequilibrated configurations taken from brief molecular dynamics (MD) simulations. As predicted by the torque approach, F-ATPase is demonstrated to be a random rotor, but it prefers to rotate in clockwise direction (as seen from the membrane toward the protein) for ATP synthesis, owing to the predominantly negative angle-averaged torques. By contrast, V-ATPase tends to rotate only in counterclockwise direction for ATP hydrolysis, due to the almost uniform averaged positive torques generated by the unidirectional rotation near the three catalytic sites. The rotational behaviors of both proteins are also affected by the surrounding solvent which can promote or hinder the internal rotation. By combining the torque approach with classic force-field MD simulations, the torques of two biomolecular motors can be calculated economically, and are found to agree with previous experiments and theoretical calculations. This work demonstrates that our torque approach can be extended to the field of biology and can help gain a deeper insight into the mechanistic rotation of biomolecular motors with modest computation time. Communicated by Ramaswamy H. Sarma

Optimal Pole Ratio of Spoke-type Permanent Magnet Vernier Machines for Direct-drive Applications

Due to magnetic gearing effects, spoke-type permanent magnet vernier machines (ST-PMVMs) have the merit of high torque density, where an extra torque amplification coefficient, i.e., pole ratio (the pole-pair ratio of PMs to armature windings) is introduced. However, different from surface-mounted PMVM, the variation of torque against pole ratio in ST-PMVMs is non-linear, which is increased at first and then decreased. This article is devoted to identify the optimal pole ratio of ST-PMVMs by equivalent magnetic circuit model. It is found that except the P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> air-gap magnetomotive force (MMF) harmonic having the same pole-pair of PM, the Pa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> air-gap MMF harmonic having the same pole-pair of armature winding is also induced due to the modulation of doubly salient air-gap structure. The P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> MMF harmonic produces positive torque, while Pa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> MMF harmonic produces negative torque. With the increase of pole ratio, the proportion of Pa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> MMF harmonic as well as negative torque is increased, which reduces the advantages of high pole ratio coefficient. Further, the influence of dimension parameters on the performance of ST-PMVMs under different pole ratio are investigated. Results show that ST-PMVMs with pole ratio 2.6 have high torque density, low cogging torque and high power factor simultaneously. Finally, a prototype is manufactured to validate the analysis.

Insights into the flow dynamics and rotor performance of a Savonius turbine with dynamic venting using controllable flaps

The drag-driven vertical-axis turbines with semicircular rotor blades, commonly known as Savonius turbines, remain potentially beneficial to extract renewable energy from wind and water streams, especially in terms of their practicality to provide low-cost solutions to rural areas. However, they suffer drawbacks due to the negative torques on their returning blades. We propose a novel solution by dynamically venting out these returning blades using controllable flaps, which retained their omnidirectional capability. Results from unsteady numerical simulations showed that the vented rotor attained a maximum average power coefficient (CP) of 0.275 at the tip-speed ratio (symbolized as λ) of 0.9, which was 21.7% better than that on the unvented rotor. Furthermore, the proposed dynamically vented blades produced large improvements in the average torque coefficient (CT), with maximum gains of 38.3% on the returning blade at λ = 0.4 and 24.8% on the full rotor at λ = 1.0, relative to those on the unvented rotor. The controlled dynamic venting was beneficial because it modified the pressure distributions surrounding the returning blade and changed the flow structure downstream of the vented blade that improved the torque on the subsequent blade entering the returning side. Elucidation on the flow dynamics revealed that the flows were vented outward through the flap aperture onto the convex side of the returning blade, rather than inward into its concave side, as initially hypothesized.

A multi-functional converter based switched reluctance motor drive for electric vehicle

&lt;span&gt;Owing to the resilience and ease of control, switched reluctance motors are commonly utilized in electric vehicle drives. This paper provides a topology for a multi-functional power converter for switched reluctance motor based electric vehicle drive with driving, braking and charging potentialities. With efficient control algorithms, a single power electronic converter is used for motoring, regenerative braking, and charging of the battery bank, resulting in a cost-effective power electronic interface. The front-end voltage control and current control of the switched reluctance motor (SRM) are used to achieve open loop and closed loop speed control during driving mode. Re-generation is made possible through restricted switching of phases in negative torque region. A bridgeless rectifier converter is built in battery charging mode by combining the SRM's two-phase windings with the prevailing power devices of an integrated power converter, eliminating the need for additional inductors and charging units. Simulations are run in MATLAB/Simulink, and simulation results are used to validate the control schemes for all modes.&lt;/span&gt;

Investigation of the turbine performances in the case of dual usage of Savonius wind turbines

In this study, the turbine performances of Savonius wind turbines were investigated in the case of dual usage. While implementing the dual use of the Savonius wind turbine, a flat plate deflector was placed in front of the turbines to increase the turbine performance. The effects of design parameters such as the geometric dimensions of this flat plate placed in front of the turbines and the geometrical placement position on the turbine performance were investigated. In this direction, the flat plate prevented the negative torque that occurs during the operation of the turbines. Hence, the plate guided the wind to the turbine blade, which generated positive torque. The numerical analyses made in this study were confirmed by the previous literature study. The performance values of single, dual, and flat plate dual Savonius wind turbines were analyzed using the numerical analysis method, the accuracy of which was proven by the experimental data. It was determined that the similarity between the experimental result and the numerical result was approximately 0.3%, especially in the maximum power coefficient values. The computational fluid dynamics (CFD) program ANSYS Fluent was used for turbine performance analysis. With this design study, the maximum power coefficient ( Cp) was obtained around 0.17 with a single Savonius wind turbine, while the maximum power coefficient ( Cp) was obtained around 0.24 with a flat plate dual Savonius wind turbine. As a result, the power coefficient obtained with a single Savonius wind turbine increased by 42% in the flat plate dual Savonius turbine system when compared to the power coefficient of the single Savonius wind turbine. Thus, it was determined that the power coefficient obtained with a single Savonius wind turbine in the flat plate dual Savonius turbine system increased by 42% compared to the power coefficient of the single Savonius wind turbine.

The transitional states of a floating wind turbine during high levels of surge

With the deployment of floating offshore wind turbines, the effect of their wind- and wave-induced platform motion on the turbine’s performance and life is of concern and requires low-order models to develop appropriate control strategies. This work focusses on platform surge as one of the main additional degrees of freedom. The aerodynamic behaviour during the rotor’s transition into propeller state is explored by assessing the spanwise and rotor-integrated aerodynamic forces on the rotor of the NREL 5 MW turbine through a 3D URANS CFD simulation. The CFD findings are compared with a modified actuator disk (AD) theory and 2D Blade-Element Momentum (BEM) approach. In addition to propeller state, where both rotor torque and thrust are negative, two other states were observed with opposite signs of torque and thrust: a braking state, with negative torque but positive thrust, and the second a quasi-windmill state with thrust negative yet torque positive. The results demonstrate that BEM coupled with AD can reliably predict the transitions to these states during such high levels of platform surge and give hints to how the underpinning force balances are affected by temporal perturbations.

Physics-informed optimization of robust control system to enhance power efficiency of renewable energy: Application to wind turbine

This study mainly focused on wind turbine (WT) design in urban environments because the negative torque generated by the returning wind blade profile was the primary cause of its low power efficiency. The turbine chosen in this study was a vertical-axis wind turbine (H-VAWT). However, the physics-informed optimization of the robust control system (RCS) design of the WT was challenging because the rotor blades (NACA 0012 airfoil) had nonlinear aerodynamic characteristics. Furthermore, our proposed controller was used in this study because of its ability to suppress disturbances and ensure stability against various uncertainties. The electrical block setup used an H-type VAWT based on advanced direct vector control generators. This indicated that a low-inertia turbine was more acceptable than a high-inertia turbine because of its suitability for maximum power conversion. Overall, there was a substantial active power gain of approximately 25% greater than conventional control systems.