Torque-speed Curve Research Articles

A Proposed ANN-Based Acceleration Control Scheme for Soft Starting Induction Motor

In this article, a new soft starting control scheme based on an artificial neural network (ANN) is presented for a three-phase induction motor (IM) drive system. The main task of the control scheme is to keep the accelerating torque constant at a level based on the value of reference acceleration. This is accomplished by the proper choice of the firing angles of thyristors in the soft starter. Using the ANN approach, the complexity of the online determination of the thyristors firing angles is resolved. The IM torque-speed characteristic curves are firstly used to train the ANN model. Secondly, the IM- soft starter system is modeled using MATLAB/SIMULINK. To prove the effectiveness of the proposed ANN-based acceleration control scheme, different reference accelerations and loading conditions are applied and investigated. Finally, a laboratory prototype of 3 kW soft starter is implemented. The proposed control scheme is executed in a real-time environment using a digital signal processor (Model: TMS320F28335). The simulation and real-time results significantly confirm that the proposed controller can efficiently reduce the IM starting current and torque pulsations. This in turn ensures a smooth acceleration of the IM during the starting process. Moreover, the proposed control scheme has the superiority over several soft starting control schemes since it has a simple control circuit configuration, less required sensors, and low computational burden of the control algorithm.

A Wind Turbine Emulator Using Field-Oriented Induction Motor

This paper proposes a Wind Turbine Emulator (WTE) using an Indirect Field Oriented (IFO) Induction Motor (IM). The IM drive can be controlled as a conventional prime mover in speed mode, or a wind turbine in torque-speed mode via robust observed torque control. This paper presents key issues for establishing a high-performance IFO IM drive. Further, this study develops a wind turbine load Interior Permanent-Magnet Synchronous Generator (IPMSG) followed by a three-phase Vienna Switch-Mode Rectifier (SMR). It receives mechanical driven power from the WTE and establishes a 400V DC-link for the DC micro-grid. The good generating characteristics are achieved through proper controls of both the IPMSG and SMR. Various wind turbine torque-speed and power-speed characteristic curves under different wind speeds can be emulated by the developed WTE. The designed results are verified by simulations. The measured results indicate that the errors are within 1.5% and 1.0%, respectively, for the torque and the power compared to the designed ones. The maximum power point tracking (MPPT) function with good performance for the PMSG with Vienna SMR is achieved using the perturb and observation (P&O) approach. The dynamic and steady-state operating characteristics of the developed whole turbine emulator driven PMSG system are assessed experimentally.

Motile ghosts of the halophilic archaeon, Haloferax volcanii

Archaea swim using the archaellum (archaeal flagellum), a reversible rotary motor consisting of a torque-generating motor and a helical filament, which acts as a propeller. Unlike the bacterial flagellar motor (BFM), ATP (adenosine-5'-triphosphate) hydrolysis probably drives both motor rotation and filamentous assembly in the archaellum. However, direct evidence is still lacking due to the lack of a versatile model system. Here, we present a membrane-permeabilized ghost system that enables the manipulation of intracellular contents, analogous to the triton model in eukaryotic flagella and gliding Mycoplasma We observed high nucleotide selectivity for ATP driving motor rotation, negative cooperativity in ATP hydrolysis, and the energetic requirement for at least 12 ATP molecules to be hydrolyzed per revolution of the motor. The response regulator CheY increased motor switching from counterclockwise (CCW) to clockwise (CW) rotation. Finally, we constructed the torque-speed curve at various [ATP]s and discuss rotary models in which the archaellum has characteristics of both the BFM and F1-ATPase. Because archaea share similar cell division and chemotaxis machinery with other domains of life, our ghost model will be an important tool for the exploration of the universality, diversity, and evolution of biomolecular machinery.

Performance Investigation of Consequent-Pole PM Machines With E-core and C-core Modular Stators

This article investigates some novel modular consequent pole PM machines (CPMs) with E-core and C-core stators. Different slot-pole number combinations including 12-slot/10-pole ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ns&gt;2p</i> ) and 12-slot/14-pole ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ns&lt;2p</i> ) have been investigated. Their static and dynamic electromagnetic performances have been investigated, e.g. the phase back-EMF, on-load torque, torque-speed curves, power factor-speed curves and also efficiency maps are compared. It is found that the existence of flux gaps (FGs) can improve the average torque of the 12-slot/14-pole E-core modular CPMs while the C-core structure can be a better candidate where relatively low torque ripple is desirable. Moreover, by selecting proper FG width, the 12-slot/14-pole E-core modular CPMs can achieve better flux-weakening capability and higher efficiency while the 12-slot/10-pole C-core modular CPMs can have higher power factors over the whole speed range. The finite element simulation results have been validated by a series of experiments using 12-slot/14-pole modular CPMs with both C-core and E-core stators.

Performance Analysis of Induction-Based Reaction Spheres

Induction-based reaction spheres have been presented in many references and their performances are normally investigated through experiments or numerical simulations which are time-consuming. Here, an analytical way is presented and it enables researchers to evaluate a new design quickly. In this article, the presented performance analysis is conducted through the classical equivalent circuit approach. Involved circuit parameters are determined through the magnetic flux density distribution which is a function of design variables. Based on this, the steady-state torque–speed curve and the achievable maximum driving torque $T^\ast$ are identified. $T^\ast$ deviates from the maximum torque obtained from numerical simulations by only 3%. For validation, the presented performance analysis method is applied to an experimental case. Mean absolute percentage errors of predicted torque–speed curves are within 23% and mainly caused by end effects. The presented performance analysis method is generally applicable to induction-based spherical actuators, not only limited to reaction spheres. Additionally, since influences of design variables of the actuator have been formulated analytically through the determined circuit parameters, performance optimizations could be greatly facilitated.

Analytical Modelling of Dynamic Performance with Harmonic Current Injection for Doubly Salient SynRMs

A new analytical torque model based on dq0 -axis frame has been developed for 3-phase, 12-slot/8-pole single layer doubly salient synchronous reluctance machines. This newly developed torque model, compared to the one often based on abc -axis frame, is necessary to simplify the investigation of dynamic performance such as torque–speed curve and efficiency maps. It has been found that the third-order current harmonic injection not only improves the torque performance (increased average torque and reduced torque ripple) in constant torque region but also maintains a similar torque level as the fundamental current supply in the flux weakening region. Moreover, although the fifth- and seventh-order current harmonic injection can reduce the torque ripple of machine, their dynamic performances are compromised due to low average torque and significant voltage distortion. Finite element simulations and dynamic tests have been carried out to prove the accuracy of the developed torque model and also the efficiency of the proposed current harmonic injection method.

Development of a high-quality brushless dc electric drive systems model

When designing electric drives based on brushless DC motors with permanent magnets (BLDC), which have low level torque pulsations, the problem of modelling non-standard topological solutions appears. The known models of BLDC motors are either based on the assumptions about the symmetry of the stator pa-rameters of the electric motor and/or the ideal form of the phase back-EMF waveform, which reduce the accuracy of evaluating the effectiveness of the proposed solutions or prove unusable for modelling an operation of the electric motor with a non-standard semiconductor converter. It is necessary to develop a mathematical model of the BLDC motor-based electric drive that takes into account the structural features of the electric motor and allows for semiconductor converter configuration variability. The model is designed in the Matlab Simulink environment. The verification is carried out by comparing the modelling results with experimental data obtained previously by other researchers. The proposed method for generating phase back-EMF in the BLDC motor model provides the possibility for the user to set the EMF form templates independent for each phase. The proposed method for stator circuit simulating provides the user with access to each of the stator windings leads as well as with the possibility of asymmetric determination of each parameter of the electric motor. Upon verification, it has been shown that the difference in the control points between the simulated and experimental speed-torque curves does not exceed 3,5 %. The developed model allows analyzing the static and dynamic characteristics of operation modes of non-standard topology BLDC motor-based electric drives taking into account the stator pa-rameters asymmetry and the real phase back-EMF waveform. The specified features of the model allow exploring the operation of the designed electric drive, taking into account the BLDC motor and converter design. The model can be applied when checking atypical design decisions and when changing the set parameters of the electric drive and restrictions on working conditions and target functions to refine the control system algorithms and automate the search for optimal parameters of the motor and the semiconductor converter.

Comparative study of hybrid-PM variable-flux machines with different series PM configurations

Aiming at extending the operating speed range and increasing the machine efficiency, three series-configuration hybrid-permanent-magnet variable-flux machines (HPM-VFMs) with both low and high coercive-force magnets are proposed. The magnetization characteristics of the machine with different dimensions of the high coercive-force (HCF) magnet are investigated. Then, in order to improve the contribution rate of the HCF magnet, two improved topologies are presented. The electromagnetic characteristics of the two proposed machines, including back electromotive force (EMF), maximum torque characteristics, magnetization state (MS) variation range and magnetic field distribution, are comprehensively analyzed and compared. The influence of different types of windings on the performance of the machine is also investigated. Finally, the torque-speed curves of the machine under different MSs are given by finite element method (FEM). The results show that the HPM-VFM can operate over a wide-speed range with high efficiency.

The induction motor: neglected workhorse of classical electromagnetism

The induction motor is one of the most useful and most interesting demonstrators of Maxwellian electromagnetism in action. A fifth-order nonlinear dynamical system, it is one of the rare instances where eddy currents or induced currents actually generate motion instead of opposing or retarding it. Nonetheless, the motor attracts very little attention among physicists. In this article we consider the motor from a physicist’s viewpoint. Starting from Maxwell’s equations alone we obtain the dynamic model which is well-known in the engineering literature. In the process we clearly see how the eddy currents give rise to a torque on the motor. We then analyse the line-supplied operation of the motor and obtain its characteristic torque-speed curve.

Improving start up performance of single speed compressors by stator winding design

Some east countries have line voltage fluctuations and voltage drops which can cause cooling problems on refrigerators because compressors cannot start up at these low line voltages. That’s why not only COP, but also start up performance at low voltages is critical on single speed compressors. Torque-speed curves of single speed asynchronous motors are so critical for compressor start up performance which takes form by motor design. Depending on compressor mechanical efficiency and shaft power needed, the asynchronous motor winding design should be fine-tuned and torque speed curve should be adjusted for start up properly at low voltage values. Even when the start torque at 0 rpm and breakdown torque values are high enough to provide low voltage compressor starting, instant torque decreases along the curve negatively effects start up performance. This study analyses torque-speed curve characteristics of asynchronous motors and determines stator winding design methods to improve compressor start up performance. The findings are also validated with motor and compressor test results.

Contact Modeling and Performance Evaluation of a Radial Standing Wave Ultrasonic Motor

The focus of this paper is to propose a contact model of a radial standing wave ultrasonic motor in order to evaluate the motor performance accurately. The contact behavior between the stator and rotor is characterized by test and a continuous contact on the contact interface is confirmed. A contact model describing the continuous contact is then developed with analytical method. The stator vibration, the force transmission between the stator and rotor, and the output of the motor are analyzed. The impacts of different vibration amplitudes and structural parameters on the performances of the motor are evaluated based on the proposed model. Finally, a test platform for measuring the performance of the motor is built and torque-speed curves of the motor under different voltages are measured. The accuracy of the contact model is verified by comparison between measurement and calculation results. The proposed model not only can be used for design and optimization of the radial standing wave ultrasonic motor but also offers insight into the contact mechanics of standing wave ultrasonic motors.

A METHOD FOR CALCULATING MECHANICAL CHARACTERISTICS OF INDUCTION MOTORS WITH SQUIRREL-CAGE ROTOR

Purpose. Development of a method for calculating mechanical characteristics of induction motors, taking into consideration saturation of the magnetic path and displacement of the current in the rotor bars. Methodology . The algorithm is based on calculating the steady-state mode of induction motor operation for a set slip, described by a system of non-linear algebraic equations of electrical equilibrium, whereas the mechanical characteristic is evaluated as a set of steady-state modes using parameter continuation method. The idea of the steady-state mode calculation consists in determining vectors of currents and flux linkages of the motor circuits, using which makes it possible to evaluate the electromagnetic torque, active and reactive powers, etc. Results . The study resulted in the development of a method and algorithm for calculating static characteristics of induction motors, which allows looking into the effect of different laws of voltage regulation on the mechanical characteristics, depending on the frequency change. Originality . An algorithm for calculating mechanical characteristics of the squirrel-cage induction motor was developed based on the mathematical model of the induction motor in which electromagnetic parameters are calculated using real saturation curves for the main magnetic flux and leakage fluxes, and displacement of the current in the rotor bars is evaluated by presenting the rotor winding as a multi-layer structure. Applying the transformation of the electrical equilibrium equations into the orthogonal axes enabled a significant reduction of calculation volume without impairing the accuracy of the results. Practical value . The developed algorithm allows studying the effect of different laws of scalar regulation of the voltage on the mechanical characteristics of the induction motor in order to obtain the necessary torque-speed curves for their optimization. It can be used for programming frequency converters.

Evaluation of the Duty Ratio of the Bacterial Flagellar Motor by Dynamic Load Control

The bacterial flagellar motor is one of the most complex and sophisticated nanomachineries in nature. A duty ratio D is a fraction of time that the stator and the rotor interact and is a fundamental property to characterize the motor but remains to be determined. It is known that the stator units of the motor bind to and dissociate from the motor dynamically to control the motor torque depending on the load on the motor. At low load, at which the kinetics such as proton translocation speed limits the rotation rate, the dependency of the rotation rate on the number of stator units N implies D: the dependency becomes larger for smaller D. Contradicting observations supporting both the small and large D have been reported. A dilemma is that it is difficult to explore a broad range of N at low load because the stator units easily dissociate, and N is limited to one or two at vanishing load. Here, we develop an electrorotation method to dynamically control the load on the flagellar motor of Salmonella with a calibrated magnitude of the torque. By instantly reducing the load for keeping N high, we observed that the speed at low load depends on N, implying a small duty ratio. We recovered the torque-speed curves of individual motors and evaluated the duty ratio to be 0.14 ± 0.04 from the correlation between the torque at high load and the rotation rate at low load.

Winding Switching and Turn Switching in Permanent Magnet Vernier Machines for Wide Speed Range Operation and High Efficiency

This paper proposes to turn to switch along with winding switching for high-efficiency of permanent magnet vernier machines (PMVM) during wide speed range operation for electric vehicles application. For winding switching, the three-phase winding of the machine is divided into two sets of windings, namely, winding set A, B, C and winding set X, Y, Z. For turn switching, the number of turns for one set of winding is changed. With the different number of turns for winding set X, Y, Z, the efficiency of the machine can be significantly improved. Initially, the basic electromagnetic characteristics, such as the flux linkage, back electromotive force (EMF), torque, and phase voltages of the machine are investigated using winding switching and turn switching. Then, the output power, torque-speed curve, core losses, efficiency, and power factor of the machine are analyzed in detail using a different number of turns. In addition, the transient effects of winding switching and turn switching have been analyzed. Finally, a control strategy is proposed which combines turn switching and winding switching to ensure high-efficiency of PMVMs during wide speed range operation. A PMVM is designed and driven in accordance with the proposed control strategy (PCS) to show the characteristics of PCS. The PMVM driven with PCS is compared to a recently presented PMVM. The recently presented PMVM is driven by a different control strategy and is analyzed with two different kinds of steel laminations that are general steel (50TW470) and special steel (20JHF1300).

Improved trajectory planning of an industrial parallel mechanism by a composite polynomial consisting of Bézier curves and cubic polynomials

A new composite polynomial is generated, to be used in the trajectory planning of a 2-dof parallel mechanism; by combining cubic polynomials with Bézier curves based on quadratic Bernstein polynomials. By the cubic polynomials, a smooth trajectory is obtained in the vicinity of the starting and ending points, while a better convergence is obtained to the via points by the Bézier curves. The position, velocity, and acceleration profiles obtained using this new polynomial are compared with those obtained using the cubic polynomial spline method. The position, velocity, and acceleration profiles achieved by the new polynomial are smoother; and more, maximum speed and acceleration values are lower than those obtained by the cubic spline method. Due to these lower values, lower capacity actuators may be utilized and the life of the actuators may be extended. On the other hand, the continuous acceleration curve of the composite polynomial will prove less jerky motion, which means less vibration. It is also possible to indicate energy saving potential when considering the speed-torque characteristic curves of servomotors. Finally, a working prototype is manufactured and real-time experiments are carried out to demonstrate the validity and competency of the proposed composite polynomial approach.

Analysis on a Novel Flux Adjustable Permanent Magnet Coupler With a Double-Layer Permanent Magnet Rotor

This paper proposes a novel flux adjustable permanent magnet coupler (PMC) with a double-layer permanent magnet rotor (PMR). The PMR, as the only excited source, is divided into the inner and outer parts. The PMs in both parts are, respectively, staggered arrangement by N- and S-poles with tangentially magnetized direction. The inner part can be controlled to rotate to adjust the relative position with the outer part to offer a controllable excitation magnetic field. Therefore, the eddy current intensity and torque can also be adjustable. The structure and operation principle of the proposed PMC are illustrated in detail. Then, to analyze the field and torque at each different relative position of the two parts of PMRs, the change period of the relative position, from N–N (and S–S) to N–S state, is divided into seven steps. The distribution of magnetic field and air-gap flux density of each relative position is analyzed in static field, and the torque–speed curves are calculated in transient field by using the 2-D finite-element method. Finally, based on the torque–speed characteristics, the influences of the structural parameters on the torque are analyzed and calculated, which can provide a reference for structural optimization design of this kind of PMC.

The Second Messenger c-di-GMP Adjusts Motility and Promotes Surface Aggregation of Bacteria

Bacteria can use the second messenger c-di-GMP to adjust their motility in response to environmental cues. The protein YcgR, upon binding of c-di-GMP, interacts with the flagellar motor to affect the motor behavior. However, the full feature of the effects of c-di-GMP::YcgR on the flagellar motor remains unclear, and its interacting partners on the motor is still controversial. Here, we characterized the effects of c-di-GMP::YcgR on the torque-speed curve of the flagellar motor, one of the most important properties of the motor, finding that it affects the motor behavior throughout the full range of load conditions from zero to high loads by shifting the motor torque-speed curve downward. We also investigated the interacting partner on the motor through dynamical fluorescent studies, finding that c-di-GMP::YcgR mainly interacts with the motor-switch complex instead of the torque-generating units (stators). To directly test the behavioral consequence of elevated c-di-GMP levels, we measured the distribution of bacteria swimming near a surface, finding that elevated c-di-GMP levels promote bacterial aggregation on surfaces. The effects of c-di-GMP on bacterial motile behavior that we characterized here are consistent with the key role that c-di-GMP plays in the transition between motile and sedentary forms of bacterial life.

Analytical determination of speed-torque and speed-current curves of single-cage induction motor under supply voltage and frequency variations

PurposeAn important characteristic of most induction motors is speed- or slip-torque curve. A simplified Kloss formula is widely used for describing speed-torque characteristic because it is fairly simple. Only two parameters related to break-down torque and break-down slip are regarded as input parameters. Because this simplified formula ignores an unknown parameter that is a ratio between Thevenin’s and rotor resistances, an accurate torque curve characteristic may not be fully obtained over an entire speed range. Moreover, the conventional Kloss formula does not offer a speed-torque curve calculation when motor’s supply voltages and frequencies are deviated from rated values. Hence, the purpose of this paper is to present an extension of Kloss formula, which allows a more precise estimation of speed-torque and speed-current curves of single-cage three-phase induction motors over a wide range of speeds at different motor’s operating voltages, frequencies and rotor-circuit resistances.Design/methodology/approachThe analytical approach is mainly used for determining all key parameters in the Kloss formula using a known set of data such as rated torque, starting torque, break-down torque and rated speed, in which they can be obtained from motor’s manufacturer.FindingsThe speed-torque and speed-current curves taken from laboratory measurements are compared with those from the calculations. Good agreements between them are fully observed.Originality/valueThis analytical approach is useful in providing an accurate speed-torque and speed-current curves required for most steady-state analysis.

Eddy Current Brake With a Two-Layer Structure: Calculation and Characterization of Braking Performance

This paper presents a new method for calculating the braking force of a drum-type eddy current brake with a two-layer structure. The drum-type eddy current brake should have a structure that improves the braking force by applying a material with high conductivity inside the drum because the eddy current loss generated from the drum is used as the braking force. In addition, because the eddy current brake operates at various speeds while braking the vehicle, it is necessary to grasp the braking force according to the speed. Furthermore, because the material of the drum is composed of non-laminated iron having conductivity, the skin effect and the armature reaction phenomenon appear, and the skin depth and the air-gap flux density are different depending on the braking speed. In this paper, the value of the eddy current loss of the eddy current brake with a copper coating inside the drum is newly presented and compared with the finite-element analysis results. In addition, the change in the speed–torque curve according to the conductivity value of the drum and inner coating material are shown. Finally, an experiment was conducted to compare and verify the characteristic curve of the eddy current brake obtained from the newly derived equations.

Speed of the bacterial flagellar motor near zero load depends on the number of stator units

The bacterial flagellar motor (BFM) rotates hundreds of times per second to propel bacteria driven by an electrochemical ion gradient. The motor consists of a rotor 50 nm in diameter surrounded by up to 11 ion-conducting stator units, which exchange between motors and a membrane-bound pool. Measurements of the torque-speed relationship guide the development of models of the motor mechanism. In contrast to previous reports that speed near zero torque is independent of the number of stator units, we observe multiple speeds that we attribute to different numbers of units near zero torque in both Na+- and H+-driven motors. We measure the full torque-speed relationship of one and two H+ units in Escherichia coli by selecting the number of H+ units and controlling the number of Na+ units in hybrid motors. These experiments confirm that speed near zero torque in H+-driven motors increases with the stator number. We also measured 75 torque-speed curves for Na+-driven chimeric motors at different ion-motive force and stator number. Torque and speed were proportional to ion-motive force and number of stator units at all loads, allowing all 77 measured torque-speed curves to be collapsed onto a single curve by simple rescaling.