Slip Frequency Research Articles

A Study on Deduction of Equivalent Circuit Parameters and Verification of Control Algorithm of Thrust Force of a Small-scaled LIM for a Railway Transit

Authors conducted a deduction of some parameters using the magnetic equivalent circuit method and a verification study of the thrust force control algorithm of a rotary-typed small-scaled linear induction motor for a railway transit. In a LIM, it is possible to express the parameters of the magnetic equivalent circuit into a function of the shape of the secondary aluminium plate and the airgap between the LIM primary core and the secondary aluminium plate. It means that the LIM properties can be changed considerably by the shape of the secondary aluminium plate and the airgap between the LIM primary core and the secondary aluminium plate. So, authors analyzed a tendency of changes of the magnetic equivalent circuit parameters and the LIM characteristics by changing of the airgap of the secondary aluminium plate of a rotary-typed small-scaled LIM. And authors conducted a verification study of the indirect vector control algorithm with constant slip frequency by using the rotary-typed small-scaled LIM tester set on the basis of the calculated LIM parameters. Finally authors accomplished a research on applicability for LIM railway transit.

Modelling of a DNA packaging motor

During the assembly of many viruses, a powerful molecular motor packages the genome into a preassembled capsid. The Bacillus subtilis phage ϕ29 is an excellent model system to investigate the DNA packaging mechanism because of its highly efficient in vitro DNA packaging activity and the development of a single-molecule packaging assay. Here we make use of structural and biochemical experimental data to build a physical model of DNA packaging by the ϕ29 DNA packaging motor. Based on the model, various dynamic behaviours such as the packaging rate, pause frequency and slip frequency under different ATP concentrations, ADP concentrations, external loads as well as capsid fillings are studied by using Monte Carlo simulation. Good agreement is obtained between the simulated and available experimental results. Moreover, we make testable predictions that should guide future experiments related to motor function.

Gait and force analysis of provoked pig gait on clean and fouled concrete surfaces

Gait and force analysis have proven to be useful methods in linking claw injuries to surface material conditions. To determine the relationship between claw disorders and floor properties such as friction and surface abrasiveness, the factors controlling gait must be characterised. The effects of fouled concrete floor conditions on the gait of 10 pigs walking in a curve, using kinematics and kinetics to record gait parameters and slip frequency are described and compared with clean conditions. Pigs adapted to fouled floor conditions by reducing their walking speed and stride length, using a higher number of 3-foot support phases and by lowering diagonality. This adaption produced lower vertical forces, a twofold reduction in propulsion and outward stabilisation force and a threefold increase in braking force, without reducing the peak utilised coefficient of friction (UCOF). The UCOF values for both limbs of the curve walking pigs exceeded the recorded dynamic coefficient of friction and the corresponding UCOF values for pigs walking a straight line in fouled floor condition. As UCOF increased and available friction from the fouled floor surface decreased, this resulted in higher forward and backward slip frequencies in both limbs for pigs walking in a curve. Pigs provoked to walk in a curve can adapt to fouled floor condition, but if the floor is heavily fouled this adaption is not sufficient to ensure safe walking.

Modelling and simulation of stator and rotor fault conditions in induction machines for testing fault diagnostic techniques

AbstractOn‐line diagnostics of induction machine faults such as broken rotor bars and shorted stator windings can be accomplished by analysing the anomalies of machine stator current. Defective rotor bars result in twice slip frequency sidebands around the fundamental frequency in the stator current, while stator winding short circuits cause changes in stator current amplitude and the occurrence of negative sequence current. This paper presents an induction machine model based on the Coupled Circuit Approach to simulate both the rotor and stator faults in an induction machine and to test fault diagnostic techniques. This model is realized in Matlab/Simulink and its construction in Simulink is explained with sufficient details. Simulation results of both the rotor and stator fault conditions are presented. A novel high‐resolution spectral analysis approach and a technique based on Discrete Fourier Transform (DFT) for the detection of broken rotor bars are tested using the simulated data. The results confirm that the high‐resolution method overcomes drawbacks of DFT such as the requirement for long data windows. Copyright © 2009 John Wiley & Sons, Ltd.

Conception of optimum frequency control of an asynchronous traction electric drive

The control method of a traction electric drive with an asynchronous electric engine with a short-circuit rotor through the maintenance of the constancy of the relative angular slip frequency of the rotor is substantiated. The analytical of relationships for efficiency, cosφ, and the mechanical rigidity of the moment characteristic by determining variations in the electromagnetic time constant of the rotor are presented. The basic requirements for the optimum algorithm of the asynchronous engine control via setting the value of the phase current or the main magnetic-flux linkage and maintaining the constancy of the relative slip frequency of the rotor are formulated.

Rotor position estimator for stator flux-oriented sensorless control of slip ring induction machine

A rotor position estimation scheme for stator flux-oriented speed sensorless control of slip ring induction machine (SRIM) is presented in this paper. Position of the rotor is estimated by integrating the rotor back-electromotive force. The problem of DC drift during integration is eliminated using an error-decaying mechanism in the estimator. This estimation scheme reduces the propagation of noise in the sensed current to the estimated rotor side unit vectors. This scheme also eliminates the need for differentiating the unit vectors for estimating slip frequency. The proposed scheme is simulated and experimentally verified.

A New Model-Based Technique for the Diagnosis of Rotor Faults in RFOC Induction Motor Drives

This paper proposes a new model-based diagnostic technique, which is the so-called virtual current technique (VCT), for the diagnosis of rotor faults in direct rotor field oriented controlled (DRFOC) induction motor drives. By measuring the oscillations at twice the slip frequency found in the rotor flux of the machine, and by conjugating this information with the knowledge of some motor parameters, as well as the parameters of the flux and current controllers, it is possible to generate a virtual magnetizing current which, after normalization, allows the detection and quantification of the extension of the fault. The proposed method allows one to overcome the major difficulties usually found in the diagnosis of rotor faults in closed-loop drives by providing information about the condition of the machine in a way that is independent of the working conditions of the drive such as the load level, reference speed, and bandwidth of the control loops. Although the VCT was primarily developed for traction drives used in railway applications, it can be incorporated in any DRFOC drive at almost no additional cost. Several simulation results, obtained with different types of DRFOC drives, as well as experimental results obtained in the laboratory, demonstrate the effectiveness of this new diagnostic approach.

Active power and MRAS based rotor resistance identification of an IM drive

This paper presents a new method of estimating the rotor resistance of an induction motor. This method is based on model reference adaptive system approach. The rotor resistance changes dramatically with temperature and frequency. The rotor resistance variation has a great influence on the FOC performance of an IM since the actual slip frequency deviates from their set value by rotor resistance variations. Therefore, the compensation of the parameter variation is vital especially in FOC of an IM. Three different methods of rotor resistance estimations, namely, electromagnetic torque equation, reactive power and active power equations, are discussed in this paper. Author proposes the third technique, which is an improvement over the two strategies Although all three schemes estimate the rotor resistance effectively, the proposed technique is superior to others in providing faster estimation approach. Simulation results of all three methods will be provided in order to confirm the superiority of proposed method.

Poster 93: Inducing Slips of Action and Examining Their Relationship to Attention Failures in Daily Life

Objectives: To develop our understanding of slips in stroke patients, where task performance is often impaired, by inducing slips of action in healthy undergraduates by occasionally altering a well-learned task, by measuring slip frequency and reaction time and movement time, and, overall, to determine how these slips predict errors in daily living. Design: Pseudo-randomized controlled study. Setting: Laboratory. Participants: 30 healthy undergraduates. Interventions: Slips were induced by occasionally requiring a change in a learned sequence of movements. Participants also completed the Attention-Related Cognitive Errors (ARCES) questionnaire, a measure of attention failures in daily life, and the Sustained Attention to Response Task (SART). Main Outcome Measures: Slip frequency, reaction and movement time data, and ARCES and SART scores. Results: Numerous slips were committed and reaction and movement time data did not support a speed-accuracy trade-off account for the attention failures. Also, while SART errors were highly predictive of slips (r=.549, P=.002), the ARCES only predicted errors on trials that did not require a change in the sequence (r=.488, P=.006). Conclusions: By understanding the mechanisms through which slips are induced and how they relate to errors in everyday life we should be able to identify individuals who are prone to attention failures and equip them with strategies to protect themselves.

The Impact of Inertia on Rotor Fault Effects—Theoretical Aspects of the ViennaMonitoring Method

This paper investigates the impact of inertia on the fault signatures of squirrel cage induction machines. Rotor faults give rise to harmonic sideband currents and double slip frequency shaft torque oscillations, however. The total drive inertia thus influences the speed ripple which, again, influences the balance of the magnitudes of the lower and upper sideband current. Considering certain assumptions, the impact of the speed ripple on the current harmonics with respect to the stator and rotor fixed reference frame is investigated analytically. Additionally, the derived equations are applied to the Vienna Monitoring Method, a model-based rotor fault detection method.

Contact-less revolving stage using transverse flux induction principle

To expand the inherently limited-rotating range of existing ultra-precision stage, a revolving stage, with a magnetically suspended rotor capable of making 360° turns without contact, is suggested. The system rotates, suspends, and moves in the planar direction infinitesimally, using the vector forces by three-separate transverse flux circular induction motor (TFCIM) located at regular intervals around the circumference. This paper discusses the entire process for the successful implementation of the stage, including the modeling of the magnetic force across the air-gap and the sensing mechanism, adopting only the proximity transducer. Particularly, because thrust force and normal force of TFCIM are strongly cross-coupled with main input variables, slip frequency and ac magnitude, the novel method controlling both forces independently is suggested, using new variables through dc-biased multi-phase inputs. Finally, roundness test and rotational step test results are given to verify the system performance.

Adaptive rotor current control for wind-turbine driven DFIG using resonant controllers in a rotor rotating reference frame

This paper proposes an adaptive rotor current controller for doubly-fed induction generator (DFIG), which consists of a proportional (P) controller and two harmonic resonant (R) controllers implemented in the rotor rotating reference frame. The two resonant controllers are tuned at slip frequencies ωslip+ and ωslip−, respectively. As a result, the positive-and negative-sequence components of the rotor current are fully regulated by the PR controller without involving the positive-and negative-sequence decomposition, which in effect improves the fault ride-through (FRT) capability of the DFIG-based wind power generation system during the period of large transient grid voltage unbalance. Correctness of the theoretical analysis and feasibility of the proposed unbalanced control scheme are validated by simulation on a 1.5-MW DFIG wind power generation system.

Estimation of the number of rotor slots and rotor speed in induction motors using current, flux or vibration signature analysis

Effective condition monitoring of induction motors requires knowledge of the number of rotor slots and the rotor speed. These were primarily obtained in the literature by multiple measurements and using design knowledge of the motor under test. Furthermore, the earlier studies have mainly concentrated on stator current analysis. This paper investigates the use of the stator current, axial flux and vibration signals in order to provide accurate rotor speed and rotor slot number estimation by utilising the eccentricity harmonics, slip frequency, rotor frequency and rotor slot passing frequency. The proposed methods are examined using an extensive series of measurements on a 2.2 kW squirrel-cage and a 5 kW wound-rotor induction motor over a wide range of loading conditions.

Frequency Domain Analysis of Beat-Less Control Method for Converter-Inverter Driving Systems Applied to AC Electric Cars

In inverter-converter driving systems for AC electric cars, the DC input voltage of an inverter contains a ripple component with a frequency that is twice as high as the line voltage frequency, because of a single-phase converter. The ripple component of the inverter input voltage causes pulsations on torques and currents of driving motors. To decrease the pulsations, a beat-less control method, which modifies a slip frequency depending on the ripple component, is applied to the inverter control. In the present paper, the beat-less control method was analyzed in the frequency domain. In the first step of the analysis, transfer functions, which revealed the relationship among the ripple component of the inverter input voltage, the slip frequency, the motor torque pulsation and the current pulsation, were derived with a synchronous rotating model of induction motors. An analysis model of the beat-less control method was then constructed using the transfer functions. The optimal setting of the control method was obtained according to the analysis model. The transfer functions and the analysis model were verified through simulations.

Indirect Field Orientation Control of Induction Machine With Detuning Effect

Induction motors (IM) arc characterized by complex, highly nonlinear time varying dynamics and inaccessibility of some states and outputs for measurements and hence may be considered as a challenging problem. Field orientation control (FOC ) methods of an induction machine achieve decoupled torque and flux dynamics leading to independent control of torque and flux as for separately excited DC motor, but there are sensitive to motor parameter variations. The present work select the indirect field orientation control (IFOC) as an effective method for eliminating the coupling effect. The results showed how well the drive performance has been improved by this control strategy. However, to what extent the control strategy can perform the decoupling relies on the accuracy of the slip frequency calculation. Unfortunately, the slip frequency depends on the rotor time constant that varies continuously according to the operational conditions and then the coupling effect may again arise. This paper investigates the improvement in the performance of the induction machine dynamics as the IFOC technique is utilized. Also, it investigates the degradation in dynamic performance when the rotor resistance is deviated from its nominal value.

Sensorless Induction Motor Drive Based on Flux Acceleration Torque Control

A novel structure for sensorless induction motor drive is proposed based on flux vector acceleration torque control. The proposed structure combines direct torque control with speed estimation based on slip frequency evaluation. A stable drive operation is enabled in a wide range of operating speeds, including at standstill

Sensorless vector controlled converter for variable speed wind generation system using an induction generator

AbstractThis paper proposed two types of speed sensorless converters that can control rotational speed and electric power. One is based on a slip frequency control system. The other is based on a vector control system. The rotational speed of the wind turbine is estimated with the phase voltage and phase current of the induction generator by the adaptive rotor flux observer. The estimated wind turbine rotational speed ωrest is used as the feedback of the speed control loop in the converter control system. Also, the estimated rotor flux ϕ2dest is used for the vector control. The simulation results confirm that both of them perform satisfactorily under the speed sensorless operation. The method based on the vector control system generates more electrical energy than does the method based on the slip frequency control system. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 62–75, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20323

Tectonic control on peritidal carbonate parasequence formation: an investigation using forward tectono‐stratigraphic modelling

AbstractStudies of Quaternary extensional faults indicate that they have instantaneous amounts of throw (0·4 to 4 m), average slip rates (0·05 to 2·8 m kyr−1) and frequency of recurrence (<40 000 years) accounting for the accommodation space required for the accumulation of peritidal carbonate parasequences (PCPs). Hangingwall sites and graben are characterized by fault down‐dropping together with regional subsidence, and footwall sites and horsts by fault‐related uplift alternating with periods of regional subsidence. The relative sea‐level curves generated by these processes operating in a maritime rift setting are used as inputs to a forward stratigraphic modelling program SedTec2000 to simulate how fault‐related changes in accommodation space can account for high‐frequency PCP formation. Each instantaneous fault slip generates a flooding surface or aggradation in hangingwall and graben settings. High‐frequency cycles in hangingwall sites are either symmetric (deepening then shallowing upward) or asymmetric (shallowing‐upward). The major factor controlling cycle types is the balance between rates of carbonate accumulation and generation of accomodation space. High‐frequency cycles in footwall sites and horsts comprise shallow subtidal facies, with no distinctive bathymetric trends, capped by erosional boundaries generated by footwall uplift. The modelled cycles are of the same thickness, with bathymetric trends and frequency to cycles commonly interpreted to be due to orbitally driven eustatic sea‐level changes or autocyclic processes. These numerical experiments demonstrate that high‐frequency PCPs can be generated by tectonic, fault‐related processes, a hypothesis that is frequently discounted.

Parameter determination of an induction machine for integrated starter alternator

This paper presents a study on parameter variations of an induction machine for integrated starter alternator (ISA) with respect to stator frequency, magnetisation and slip frequency. No-load and stand-still tests are conducted under variable-frequency and variable-voltage instead of conventional constant frequency tests, using a PWM inverter in order to obtain the variations of rotor resistance, rotor leakage inductance, magnetising inductance and core-loss. In addition to these tests, impressed stator voltage and impressed stator current tests are carried out. Theory, analysis and results of the above parameter determination methods are presented. The parameter variations obtained from the variable-frequency variable-voltage no-load and stand-still tests are compared with conventional tests parameters as well as the parameters obtained from impressed stator voltage and stator current tests. The parameter variations found in this study can be used to obtain a detailed model that predicts the behaviour of the induction machine over wide speed range and under dynamic loading conditions more precisely than the conventional constant parameter model.

Current Control of Induction Machines in the Field-Weakened Region

This paper presents a novel current regulation algorithm for induction machines that enables smooth operation and maximum torque-per-ampere capability over the entire field-weakened region. The algorithm enables robust current regulation with maximum torque capability despite significant variation in voltage source and machine parameters. The algorithm identifies when the current regulator begins to saturate and determines the optimum d-axis current command for the machine. The q-axis current command is determined as a function of the torque command and the d-axis current feedback. In the field-weakened region, the -axis current is monitored not to exceed the maximum -axis current. The maximum q-axis current is calculated based on the maximum slip frequency, which is a function of rotor frequency, q-axis current gesmaximum q-axis current (in motoring mode) indicates that the machine entered field-weakened region II, and the -axis current is limited to its maximum value. Experimental results from a machine prototype show that the algorithm provides good overall dynamic response and smooth transitions into the field-weakened region with maximum torque-per-ampere capability in all four quadrants of operation.