Dynamic End Effects Research Articles

Performance evaluation of a high flow rate annular linear induction pump using a simple equivalent circuit model taking into account dynamic end effects

ElectroMagnetic Induction Pumps are a relevant technical solution for the transportation of alkali metals in applications where safety and reliability are fundamental. Especially, Annular Linear Induction Pumps (ALIPs) are preferred when high flow rates are required. In the early stage design of an ALIP, simple analytical models are convenient to get an estimate of performances. Equivalent circuit models are often used to this purpose. Their accuracy has been found variable, depending on pumps configuration and operating conditions. To assess the relevance for high flow rate applications, circuit models are applied to the ALIP of PEMDyn facility, in CEA Cadarache research centre. The simplest equivalent circuit model for a LIM is tested. Then, a modification to account for dynamic end effects is added. Results are compared to experimental measurements. The correction for dynamic end effects allows a significant reduction of the relative error, especially for the range of highest flow rates.

Thrust Ripple Suppression Based on Negative Current Control for Short-Primary Low-Speed Large LIM Under Transient Operation

End effect of linear induction motor (LIM) leads to magnetic asymmetry and thrust ripple, which seriously restricts the performance and application of LIM. Existing methods for thrust ripple modeling and compensating have mostly focused on the steady state, which suffer from poor transient performance. Moreover, the influence of asymmetric currents on output thrust is not considered. In this paper, the thrust ripple characteristics and impact factors of a low-speed large LIM with negligible dynamic longitudinal end effect are analyzed in details, firstly. Then, a data-driven extracting and modeling method for transient thrust ripple is proposed. The non-stationary time-varying thrust ripple signal is extracted through wavelet decomposition and reconstruction, the polynomial parameters of thrust ripple model are trained off-line by particle swarm optimization algorithm. Finally, an improved suppressing scheme for transient thrust ripple is proposed, considering the decoupling and feedback control of positive and negative currents, based on the dynamic model of six-phase LIM. Full-scale experimental results have fully demonstrated the accuracy of proposed data-driven transient thrust ripple model is more than 90%. During the high-thrust operating stage, the axial vibration acceleration level of LIM within 100Hz is reduced by more than 12dB, with the adoption of improved control scheme.

A Thrust Ripple Suppression Method for Long-Primary Double-Sided Linear Induction Motors Based on Harmonic Current Injection

For the long-primary double-sided linear induction motor (LP-DSLIM) excited by the symmetrical current, there are double slip frequency ripple in the thrust due to the dynamic longitudinal end effect. The expression of thrust ripple fluctuation caused by the dynamic longitudinal end effect are deduced firstly. Secondly, the method of suppressing the injected harmonic current is adopted, the expression of each part of thrust after injection are deduced and its characteristics are analyzed, from which the feasibility of this method to reduce the thrust ripple is illustrated. Finally, finite element simulation and experiment results indicate that the thrust ripple is significantly reduced after the injection of the harmonic current.

Performance Analysis of Nested-loop Secondary Linear Doubly-fed Machine Considering End Effects

Nested-loop secondary linear doubly-fed machine (NLS-LDFM) is a novel linear machine evolved from rotary brushless doubly-fed induction machine, which has a good application prospect in linear metro. In order to analyze the performance of NLS-LDFM, the mechanism and action rules of end effects are investigated in this paper. Firstly, the mechanism of static and dynamic end effects is analyzed in aspect of direct coupling, winding asymmetry and transient secondary current. Furthermore, based on the winding theory for short primary linear machines, the machine parameters are established qualitatively considering pulsating magnetic field of NLS-LDFM. Finally, the NLS-LDFM performance analysis is supplemented by the finite element algorithm (FEA) simulation and experiments under different operating conditions.

Input–Output Feedback Linearization Control of a Linear Induction Motor Taking Into Consideration Its Dynamic End-Effects and Iron Losses

This article proposes a new input–output feedback linearization control (FLC) technique of linear induction motors (LIMs), taking into consideration both the dynamic end-effects and the iron losses. Starting from a previously conceived dynamic model, including the dynamic end-effects and the iron losses, all the theoretical framework of the FLC has been developed. The proposed FLC improves a previous version of FLC in accounting also the iron losses, which in LIMs with fixed-secondary sheet play a pivotal role more than in rotating induction motors (RIMs). The proposed FLC has been experimentally tested on a suitably developed test setup, and experimental comparisons between the proposed FLC, the classic field-oriented control and a previously developed FLC, not accounting for the iron losses, have been shown in variable flux working conditions.

Longitudinal Dynamic End Effect of Single-Sided Linear Induction Motor for Medium–Low Speed Maglev

Longitudinal Dynamic End Effect of Single-Sided Linear Induction Motor for Medium–Low Speed Maglev

A Modified Dynamic Model of Single-Sided Linear Induction Motors Considering Longitudinal and Transversal Effects

This paper proposes a modified dynamic equivalent circuit model for a linear induction motor considering both longitudinal end effect and transverse edge effect. The dynamic end effect (speed-dependent end effect) is based on conventional Duncan’s approach. The transverse edge effect is investigated by using three correction factors applied to the secondary resistance and magnetizing inductance. Moreover, the iron saturation effect, the skin effect, and the air-gap leakage effect are incorporated into the proposed model by using the field-analysis method. A new topology of the steady-state and space-vector model of linear induction, regarding all mentioned phenomena, is presented. The parameters of this model are calculated using both field analysis and the finite-element method. The steady-state performance of the model is first validated using the finite-element method. Additionally, the dynamic performance of the proposed model is studied. The results prove that the proposed equivalent circuit model can precisely predict the dynamic and steady-state performances of the linear induction.

Loss Minimization Control of Dual Three‐Phase Linear Induction Motor with System‐Level Loss Model

Traditional loss model of linear induction motors usually only considers iron loss and copper loss. However, the neglect of power electronic losses will reduce the accuracy of model calculations. Moreover, in multi‐phase motor drive systems, power electronics losses are relatively higher and cannot be omitted. Considering the above problems, loss models of six‐phase inverter under various PWM modulation methods were derived. And combined with an improved dynamic end effect loss model of dual three‐phase linear induction motor, a system‐level loss model is obtained. Furthermore, optimal excitation current can be calculated based on the model using Newton–Raphson method to minimize system loss. Simulation results showed that this strategy can always bring efficiency improvement under all working conditions, especially under certain light load working conditions (0.2 pu, 5 m/s), the loss reductions of both the inverter and the overall system can achieve by 50% approximately. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Dual layer barrier functions based adaptive higher order sliding mode control

AbstractThis article presents an adaptive discontinuous higher order sliding mode control (HOSMC) strategy for a disturbed chain of integrators of order n. This strategy employs a barrier function‐based dual layer adaptation and it ensures the convergence of the sliding variable and its (n − 1) first derivatives to zero without requiring any information on the bounds of the disturbances or their derivatives. It consists in applying a barrier function‐based adaptive super‐twisting methodology compensating Lipschitz disturbances with some error, and a growing gain‐based adaptive HOSMC which just needs to counteract this error. Real‐time simulation platform is used to test the efficacy of the proposed strategy to control a linear induction motor considering dynamic end effects.

Sliding Mode Observer for Speed Sensorless Linear Induction Motor Drives

In this paper, a sliding mode observer (SMO) for the speed-sensorless direct torque vector control of linear induction motor(LIM) is proposed, considering the influence of dynamic end effects. The proposed SMO estimate the motor speed, the rotor flux, the angular position of the rotor flux, and the speed dependent parameter w, only by using the measured stator voltages and stator currents. The nonlinear sliding mode technique guarantees very good performance for different situations of motor speed. The proposed SMO does not use complicated observer gains and robust to the parameter variation over the full-speed range. Moreover, the convergence of SMO is proven by using the Lyapunov theory. Furthermore, LIM Drive state observability is presented with detailed analysis. The performance of the proposed SMO is verified by hardware-in-the-loop test (HIL) system. Furthermore, a comparative study with and Luenberger observer(LO) and model reference adaptive system(MRAS) is presented.

Improved vector control strategy of linear induction motors for electromagnetic launch

Due to the change of parameters caused by the dynamic longitudinal end effect, the operation characteristics of linear induction motors (LIMs) applied in an electromagnetic launch field are different from that of ordinary LIM. Due to the continuous increase of the LIM port voltage under high acceleration, the phase voltage is close to the inverter output limit. The conventional indirect field-oriented control (IFOC) strategies of LIM based on the flux attenuation compensation or maximum thrust control cannot solve the problem well. Based on the LIM mathematical model, this study analyses the output thrust characteristics of the LIM and discusses different control methods. This study presents an improved vector control strategy. By dynamically adjusting the value of ‘ k ’ based on the moving speed of the LIM, the maximum thrust output is maintained at medium and low speeds, and the voltage rise of a motor port is restrained at high speed. The effectiveness of the proposed control method is verified by simulation and experiment. The method proposed in this study is helpful to broaden the application of the LIM in the higher speed field.

Effect of Winding Connections on Thrust and Current Asymmetry of Linear Induction Machines Considering End Effect

Linear induction motors (LIMs), applied in the field of electromagnetic emission, due to end effect, show the characteristics of thrust rapid decline, and current asymmetry increasing in the process of high-speed movement. This article studies the effect of stator winding connections on thrust and current asymmetry of six-phase shifted 30° LIM considering the static and the longitudinal end effect. The study compares three connections by finite-element analysis, namely, open-end, star, and triangular connections. The theory of symmetric component method is introduced to analyze the asymmetric characteristics caused by the end effect. The output thrust and current asymmetries of the motor under three connection modes are compared in detail. The simulation results show that there is no difference among the three connection modes when only considering static end effect, but once considering dynamic end effect, the output current symmetry of star connection is better than that of the open and triangular connection. Also, Adopting variable slip frequency control method can not only improve output thrust of motor, but also improve current symmetry, especially at high speed obviously, when compared with constant slip frequency control method. The research will be helpful to motor thrust optimization control and winding design in the future.

Control strategy for optimising the thrust of a high‐speed six‐phase linear induction motor

In this study, a short primary six-phase linear induction motor (LIM) operating in high-speed non-periodic transient conditions is used as an object of study. In consideration of the coupling terms related to the dynamic end effect, the motor model is simplified and the vector control equation is deduced. A vector control strategy for the real-time modification of slip-frequency and torque current is proposed for dynamic thrust compensation. On this basis, considering the problems of thrust decay caused by dynamic end effect and dc-link voltage drop, this study puts forward a field-weakening control method to keep thrust constant before its decrease in the field-weakening region. The method makes it possible for the LIM to overcome the thrust decay and the narrowing of voltage limits under the high-speed operating conditions. The simulation and experimental results show that the proposed control strategies are useful for optimising the thrust in the transient process thus to realise the high-speed operation of the motor.

Mathematical model and vector control of a six-phase linear induction motor with the dynamic end effect

This study investigates a short primary double-side six-phase linear induction motor (LIM) operating in non-periodic transient conditions. The main purpose is to solve the problems arising from the dynamic end effect. The equivalent circuit method is used for intensively studying the transient time-varying law of eddy current and excitation inductance, and the finite element method is adopted for verification. The calculation of eddy current loss leads to an expression of secondary equivalent resistance. Then, a mathematical model is established for the six-phase LIM involving the dynamic end effect. Furthermore, the matrix reconstruction method is adopted for the coupling of windings. Based on the time-varying characteristics of the model, an improved vector control method that can update the velocity-related correction coefficients through on-line calculation is proposed. During the transient process, the slip frequency and the torque current are modified in real-time to achieve the maximum output thrust of the motor. This approach can compensate for the thrust drop caused by the dynamic end effect, thereby improving the control precision. Simulations and experiments show that the related theory and the proposed control method are feasible and effective.

State-Space Vector Model of Linear Induction Motors Including End-Effects and Iron Losses—Part II: Model Identification and Results

This is the second part of an article, divided into two parts, dealing with the definition of a space-vector dynamic model of the linear induction motor (LIM) taking into consideration both the dynamic end-effects and the iron losses as well as the offline identification of its parameters. This second part is devoted to the description of an identification technique that has been suitably developed for the estimation of the electrical parameters of the LIM dynamic model accounting for both the dynamic end-effects and iron losses. Such an identification technique is strictly related to the state formulation of the proposed model and exploits genetic algorithms for minimizing a suitable cost function based on the processing of both the primary current and speed estimation errors. The proposed parameters’ estimation technique has been validated experimentally on a suitably developed test set-up. It has been further validated by a finite element analysis model of the LIM.

State Space-Vector Model of Linear Induction Motors Including End-Effects and Iron Losses Part I: Theoretical Analysis

This is the first part of the article, divided into two parts, dealing with the definition of a space-vector dynamic model of the linear induction motor (LIM) taking into consideration both the dynamic end-effects and the iron losses and its offline identification. This first part specifically treats the theoretical formulation of this model, which has been expressed in a state form, so to be, in perspective, suitably adopted for developing novel nonlinear control techniques, nonlinear observers as well as electrical losses minimization techniques. Besides the formulation of the dynamic model in space-vector state form, a steady-state analysis is proposed, highlighting the combined effects of the dynamic end-effects and the iron losses on the main electrical quantities of the LIM.

Accelerated Computation of Relative Permeability by Coupled Morphological and Direct Multiphase Flow Simulation

Computation of two-phase flow in porous media with low capillary numbers is challenging due to slow convergence and the presence of spurious currents at the phase interfaces that are greater than the viscous flow. The relative permeability of such systems is a critical parameter for upscaling flow properties but requires steady state flow configurations at low capillary numbers; a computationally slow problem to calculate. By using a morphologically coupled multiphase Lattice Boltzmann Method (LBM), it is observed that phase distributions converge an order of magnitude faster (1,000-50,000 timesteps) than flow fields (250,000-350,000 timesteps) during capillary dominated regimes. The proposed method couples a quasi-static, morphological method with direct LBM simulation that combines the efficiency of morphological calculations with the accuracy of direct simulation. The system fluid distribution is initialised morphologically instead of using simulated forced primary drainage to reduce dynamic simulation time and remove saturation end effects. The approach preconditions the simulation towards steady state conditions and the LBM routine relaxes the phase distributions until phases are stable. The steady state velocity fields are obtained by solving for flow in each stable connected phase distribution with a fast Semi Analytical Laplace solver to overcome spurious currents. A morphological Shell Aggregation method is then applied, condensing the displacing phase as a shell over pre-existing phase distributions and allowed to again reach phase equilibrium. Results obtained from the simulations are consistent with experimental relative permeability curves and phase morphology obtained from Gildehauser sandstone. This method allows rapid computation of phase distributions and relative permeability for capillary dominated flows. Shell Aggregation typically reaches steady state within 50,000-150,000 LBM timesteps opposed to 250,000-350,000 by spinodal decomposition for the tested 500 cubed Bentheimer sandstone and 150 cubed sand pack samples. Solving for flow in each connected phase body after Shell Aggregation LBM reaches steady state is furthermore shown to require down to 1,000-10,000 LBM timesteps at the expense of some interfacial physics.

Thrust Control of a Double-Sided Linear Induction Motor With Segmented Power Supply

Due to the dynamic longitudinal end effect, the motor flux is lagging and the thrust is fluctuated in a long-primary double-sided linear induction motor (DSLIM). In this paper, a thrust fluctuation reduction method is proposed for the DSLIM with segmented power supply. The mathematical model of the DSLIM module considering the dynamic longitudinal end effect is established first, and a new field orientation is presented by solving variation of the motor flux when the secondary enters or leaves a motor module. Then, the thrust expression is deduced based on the new field orientation, and a coefficient is proposed to present the thrust bias in a single module. The restraint of the thrust bias is implemented by increasing or changing the slip frequency according to the orientation in the movement. The proposed coefficient and the thrust control method are validated by simulation and experiment results.

Time-varying state observer based twisting control of linear induction motor considering dynamic end effects with unknown load torque

This paper presents a time-varying state observer based twisting control (TC) technique scheme for linear induction motor (LIM) considering dynamic end effects. With Ducan’s T-model, indirect field oriented control strategy is introduced and the state space equation of LIM is obtained in (d, q) rotary reference frame. On this basis, LIM’s model is extended to two subsystems: flux extended model and speed extended model. Twisting algorithm (TA) is applied into these two subsystems to achieve speed tracking and flux tracking with finite time convergence in the presence of disturbance and uncertainty. For the rotor flux estimation, a time-varying state observer is designed, and its stability and convergence have been proved with Lyapunov’s theory. Moreover, the value of estimated LIM speed derivative is obtained via second order sliding mode observer. Furthermore, a reduced order load torque observer is designed to estimate the external load torque. The feasibility and effectiveness of proposed method has been validated by Hardware-in-the-loop (HIL) test experiment.

Electrical Losses Minimization of Linear Induction Motors Considering the Dynamic End-Effects

This paper proposes an original electrical losses minimization technique (ELMT) suitably devised for field-oriented controlled linear induction motor (LIM) drives, taking into consideration the LIM's dynamic end-effects. The proposed technique improves the very few approaches in the scientific literature dealing with ELMTs applied to LIMs in the following aspects: 1) it accounts for the LIM dynamic end-effects not only considering the variation of the LIM parameters with speed but also including the braking force caused by the end-effects in the ELMT formulation; and 2) it considers the iron losses. The proposed approach has been tested in numerical simulation and validated experimentally on a suitably developed test setup. Results show that the application of the proposed ELMT permits a consistent losses reduction of about 22% even at low speed (0.75 m/s), as well as an increase in the overall drive efficiency ranging from 18%, at rated constant flux, up to 24% with the ELMT.