Electrical Engineering

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Shiv Nadar University

In this paper, design and implementation of an optimized controller for a single magnet-based electromagnetic levitation system (EMLS) where an electromagnet of 2.6-kg mass is levitated over a large gap under a fixed ferromagnetic guide-way has been discussed. EMLS is inherently unstable and strongly nonlinear in nature. A single position controller (lead type) along with an outer proportional-integral (PI) controller has been designed that will stabilize the EMLS represented mathematically by three different plants corresponding to three different operating points. An optimization technique utilizing the random search method with interval reduction, proposed by Luus and Jaakola, has been used for designing the controller. A "model matching control" design procedure has been utilized for the design of outer PI controller. The inner controller stabilizes the three unstable plants, whereas the outer PI control action is used to modify the three position outputs as per the desired model response. The combined control action provides good stability and satisfactory performance (like fast response, less overshoot, and zero steady-state error) for the different operating zones of EMLS. Stability has been confirmed by Kharitonov-Nyquist enclosure diagrams. The simulated controllers have been successfully implemented, thus validating the modeling and controller design procedure. © 2008 IEEE.

World University root node

(SoE) School of Engineering

IEEE Transactions on Control Systems Technology

Controller design for large-gap control of electromagnetically levitated system by using an optimization technique

This paper enhances the recently proposed twin SVM Jayadeva et al. [Jayadeva, Khemchandani, R., Chandra, S., 2007. Twin support vector machines for pattern classification. IEEE Trans. Pattern Anal. Machine Intell. 29 (5), 905-910] using smoothing techniques to smooth twin SVM for binary classification. We attempt to solve the primal quadratic programming problems of twin SVM by converting them into smooth unconstrained minimization problems. The smooth reformulations are solved using the well-known Newton-Armijo algorithm. The effectiveness of the enhanced method is demonstrated by experimental results on available benchmark datasets. © 2008 Elsevier B.V. All rights reserved.

Pattern Recognition Letters

Application of smoothing technique on twin support vector machines

This paper describes design and implementation of a control philosophy for simultaneous stabilization and performance improvement of an electromagnetic levitation system. An electromagnetic levitation system is an inherently unstable and strongly nonlinear system. To determine the overall closed loop stability for such a system, cascade lead-lag compensation has mostly been reported [1,2]. However, a single lead controller can not satisfy both stability and performance for such unstable systems [3]. Performance enhancement to satisfy the conflicting requirements of fast response with almost zero overshoot and zero steady state error has been successfully achieved by using a two loop controller configuration. The lead controller in the inner loop is designed to ensure stability while the outer loop PI controller is designed for performance enhancement. This approach decouples the twin requirements of stabilization (by the inner loop) and performance achievement (by the outer PI loop). The outermost PI controller has been designed using the 'Approximate Model Matching' technique [4]. The proposed control strategy has been implemented and the experimentation has been demonstrated successfully. Different experimental results have been included for verification.

Asian Journal of Control

Novel method of controller design for simultaneous stabilization and performance improvement of an electromagnetic levitation system

In this paper, we use the approach of adaptive critic design (ACD) for control, specifically, the action-dependent heuristic dynamic programming (ADHDP) method. A least squares support vector machine (SVM) regressor has been used for generating the control actions, while an SVM-based tree-type neural network (NN) is used as the critic. After a failure occurs, the critic and action are retrained in tandem using the failure data. Failure data is binary classification data, where the number of failure states are very few as compared to the number of no-failure states. The difficulty of conventional multilayer feedforward NNs in learning this type of classification data has been overcome by using the SVM-based tree-type NN, which due to its feature to add neurons to learn misclassified data, has the capability to learn any binary classification data without a priori choice of the number of neurons or the structure of the network. The capability of the trained controller to handle unforeseen situations is demonstrated. © 2007 IEEE.

IEEE Transactions on Neural Networks

SVM-based tree-type neural networks as a critic in adaptive critic designs for control

In this paper an overview of power amplifier for multi-magnet based DC electromagnetic levitation system has been presented. The general requirement of power amplifier for levitation system has been described. The proposed multi-magnet based single axis levitation scheme has been described in brief. Different possible switched mode power circuits for the multi-magnet based electromagnetic levitation system have been discussed and a comparative study has been made of the different topologies of power amplifiers based on their structure and practical results that derived from the proposed experimental set-up. In the actual work design, fabrication and testing of multimagnet based electromagnetic levitation scheme has been made as a complete project. But in this paper the emphasis is given on the power amplifier portion due to limitation of space. © 2007 IEEE.

Proceedings of the International Conference on Power Electronics and Drive Systems

A study of different possible switched modi chopper circuits for multi-magnet based DC electromagnetic levitation system

We present for the first time, analysis of irreversible snapback caused due to the regenerative n-p-n turn-on in a DENMOS through a critical understanding of 'thermal runaway' under ESD conditions. The estimated It2 value from transient simulations has been correlated with the quasi-steady TLP data. A new regenerative bipolar turn-on induced failure model has been proposed and corroborated with experimental observations and failure analysis. We have also investigated the current crowding mechanism to understand the improvement in It2 value under gate and substrate biasing. © 2007 IEEE.

Technical Digest - International Electron Devices Meeting, IEDM

A microscopic understanding of nanometer scale DENMOS failure mechanism under ESD conditions

Drain current model for undoped symmetric double-gate FETs using a velocity saturation model with exponent n= 2

IEICE transactions on electronics

Parasitic effects in multi-gate MOSFETs

A simple hardware realization of direct torque control (DTC) scheme for fast control of induction motor torque has been presented. The proposed hardware scheme mimics the conventional switching table based DTC scheme and does not require use of any online fast computing device like microprocessor, PC or DSP. The controller uses only commonly used discrete hardware components. The experimental results of the proposed hardware implementation have been presented and supported with simulation results. Another alternate hardware scheme without using the switching table has also been proposed and the experimental results of both the schemes have been compared and found to be in agreement with each other. © 2006 Elsevier B.V. All rights reserved.

Electric Power Systems Research

A simple hardware realization of switching table based direct torque control of induction motor

This paper describes the design and implementation of a single axis DC attraction type suspension system, where a platform (vehicle structure) of around 14 kg mass is made to remain suspended at the desired operating gap under a ferromagnetic guide-way. The prototype has four electromagnetic actuators of attraction type and four inductive gap sensors, all located at the corners of the platform. The four actuators are controlled independently through four identical controllers, and the stable levitation of the platform is achieved through the single input and single output (SISO) control of each air-gap. The emphasis of this work is on the design and development of the switched mode power amplifier cum controller unit for the four actuators. The proposed single switch-based power circuit simplifies the overall hardware, and it can be extended to any number of magnet-coils. A cascade lead compensation control scheme utilizing an inner current loop and outer position loop has been designed and implemented for the stabilization of such a highly unstable and strongly nonlinear system. The prototype has been successfully tested, and stable levitation was demonstrated with the desired operating gap. © 2007 ISA.