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Dive into the research topics where K.R. Rajagopal is active.

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Featured researches published by K.R. Rajagopal.


ieee international magnetics conference | 2005

Calculation of the flux-linkage characteristics of a switched reluctance motor by flux tube method

N.K. Sheth; K.R. Rajagopal

The torque developed by a switched reluctance motor (SRM) is dependent on the change of flux-linkage and rotor position. The flux-linkage is a function of both the excitation and the rotor position. Due to the nonlinear nature of this motor, estimation of the flux-linkage characteristics is cumbersome. In this paper, a simple analytical method to estimate the flux-linkage characteristics of SRM is presented. Here, equations for the calculation of inductance and the flux-linkage for three identified regions based on the rotor position; a) fully unaligned to starting of pole overlap, b) starting of pole overlap to full pole overlap, and c) full pole overlap to fully aligned conditions, are derived in terms of motor dimensions, the magnetic properties of the materials used, and the stator excitation. The validation of the results obtained from this new analytical method is carried out using the finite element analysis of the motors.


IEEE Transactions on Magnetics | 2004

Torque profiles of a switched reluctance motor having special pole face shapes and asymmetric stator poles

N.K. Sheth; K.R. Rajagopal

In this paper, the results of a finite-element (FE) analysis carried out on an 8/6 switched reluctance motor (SRM) having special pole face shapes, such as: 1) noncircular stator pole face with varying airgap under a pole; 2) flat topped rotor pole faces; and 3) noncircular airgap caused by elevated rotor poles, are presented. Apart from this, the case of an asymmetrical centering of a stator pole is also analyzed. The analysis has revealed that the motor with noncircular stator pole face gives higher average torque. Thus, for motors intended for operation in one direction only, such noncircular airgap is preferred. In case of flat topped rotor poles, the average torque reduces drastically. The rotor poles projected slightly outward on one side with corresponding decrease in pole heights in the stator pole will create airgap with varying mean diameters under a pole pair. This configuration of the motor poles results in more average torque with high torque ripple. The case of the motor with one of the stator pole shifted by an angle from the center keeping the stator bore diameter constant is also analyzed. It is observed that the average as well as the maximum torque produced by the motor decreases with the increase in shift in either direction.


IEEE Transactions on Magnetics | 2003

Design of a compact hysteresis motor used in a gyroscope

K.R. Rajagopal

This paper presents the computer-aided design and test results of a compact three-phase hysteresis synchronous motor used as the drive motor of a gyroscope. Hysteresis motor is the best choice for this application because of its compactness and reliability. Also, it has a self-starting capability and it does not require any position sensor and commutation circuits. The design of a three-phase 32-V 400-Hz 6000-r/min hysteresis motor in full is presented. A computer program in MATLAB is created for the design and analysis of the hysteresis motor and used extensively in this work. The test results of the developed motor are fairly matching with the computed values. Results of a detailed study conducted to identify the harmonic torque components reveal that the net torque available with a six-pulse inverter supply is only 92.89% of that with a sinusoidal supply.


ieee international magnetics conference | 2006

Performance Prediction of Multi-Phase Doubly Salient Permanent Magnet Motor having Non-Uniform Air-gap

A.R.C.S. Babu; K.R. Rajagopal; P.R. Upadhyay

This paper presents the effect of the non-uniform air-gap on the various characteristics of a 6/4 doubly salient permanent magnet motor (DSPM). Three important cases among the air-gap non-uniformities namely: (i) relative eccentricity between stator and rotor axes; and (ii) concentricity error on one-half and both halves of the rotor (elliptical rotor) have been analyzed for a 6/4-DSPM using the 2D finite element (FE) method.


IEEE Transactions on Magnetics | 2003

Optimal tooth-geometry for specific performance requirements of a hybrid stepper motor

K.R. Rajagopal; Bhim Singh; B.P. Singh

In this paper, a detailed account of the results of 2-D and 3-D Finite Element (FE) analyses, conducted with different tooth-width/tooth-pitch ratios (t//spl lambda/) and also with various tooth/slot shapes such as rectangular, trapezoidal, triangular and circular, is presented.


IEEE Transactions on Magnetics | 2004

Design of a compact winding for an axial-flux permanent-magnet brushless DC motor used in an electric two-wheeler

P. R. Upadhyay; K.R. Rajagopal; B.P. Singh

This paper describes the design of a compact winding for an axial-flux permanent-magnet brushless dc motor used in an electric two-wheeler. Once the motor design is carried out using the conventional method and the dimensions of the motor, magnet, etc. are determined, the electric loading and the magnetomotive force (MMF) required to obtain the peak torque can be calculated. From the knowledge of the MMF requirement, a compact and efficient winding configuration has been achieved using a parametric study. The factors considered for the winding design are: 1) operating voltage; 2) number of poles; 3) cross-sectional area available for the winding; 4) conductor size; 5) number of parallel paths; 6) length of mean turn; 7) and the peak torque for a given value of AT/pole/phase. The motor voltage is decided based on the speed of the motor and aspects of the battery and the controller. The selected winding configuration for an 80-Nm peak torque, 48-V, three-phase motor is having 48 coils with each coil of 18 turns made out of 15 standard wire gauge copper wire. The resistance per phase is calculated as 0.0203 /spl Omega/.


ieee international magnetics conference | 2005

A novel integral-force technique for the analysis of an axial-field permanent magnet brushless DC motor using FE method

Paras R. Upadhyay; K.R. Rajagopal

In this paper, a novel integral-force technique to calculate the developed torque of an axial-field permanent-magnet brushless dc (PM BLDC) motor using minimum requirement of two-dimensional (2-D) finite-element (FE) analyses is presented. Using this method, the designer can find out the actual performance of the axial-field PM BLDC motor using 2-D FE analysis rather than a three-dimensional (3-D) FE analysis. The design data of a 70 W, three-phase, 24 V, 6 pole, 350 rpm axial-field PM BLDC motor designed using a developed computer-aided design program have been used to work on the developed torque using the proposed new method as well as using 3-D FE analysis. The peak torque calculated in 3-D FE analysis is 2.2608 Nm as against the 2.2705 Nm obtained from the integral-force technique.


IEEE Transactions on Magnetics | 2001

Novel methods of temperature compensation for permanent magnet sensors and actuators

K.R. Rajagopal; Bhim Singh; B. P. Singh; N. Vedachalam

In this paper, the adverse effects of variation in operating temperature on the performance of PM sensors and actuators used in aerospace and military applications, and methods to provide inherent temperature compensation by design, are presented. Unlike the conventional shunt compensation, the proposed method uses the direct leakage path between two neighboring permanent magnets. This novel method arrived at after conducting finite element (FE) analysis, is capable of giving complete temperature compensation over the entire operating temperature range. In a gyroscope designed and developed under this scheme, the temperature sensitivity of the torquer scale factor of the gyroscope in an operating temperature range of -60 to +80/spl deg/C is measured to be less than -10 ppm//spl deg/C against the normal value of -450 ppm//spl deg/C, observed in a gyroscope having no inherent temperature compensation.


ieee international magnetics conference | 2002

Computer aided design of an axial-field PM brushless DC motor for an electric vehicle

P.R. Upadyay; K.R. Rajagopal; B.P. Singh

Summary form only given. This paper presents the computer-aided design and analysis of a pancake-type three-phase axial-field permanent magnet brushless DC motor meant for the direct drive of an electric two-wheeler. The motor is accommodated inside the rim of the wheel. On comparison of various kinds of permanent magnet motors, it is found that the axial-flux type having sandwiched coil configuration with two-airgaps is the best choice, the advantages being the lack of any axial or thrust load on the bearings, better cooling, better winding utilization, low inductance, reduced torque ripple and acoustic noise, and negligible effect of demagnetization of the permanent magnets. Effects of all machine parameters on the performance of the motor have been studied in detail and the results of this parametric study are provided. Results of the 2-D and 3-D FE analyses conducted on this motor to arrive at the most economical and viable design are also given. The effect of armature reaction is studied in detail using the FE model and the variation in performance is accurately predicted. The entire design procedure is explained in detail with the help of a flow chart. All the steps involved in the design of the motor such as selection of configuration, design of magnetic circuit, selection of materials, calculation of machine parameters and calculation of performance are discussed. Fabrication aspects of the motor components and tuning required for the design for easy fabrication are also discussed.


ieee international magnetics conference | 2006

Involvement of Armature Reaction Property in the Computer Aided Design of Radial-Flux Permanent Magnet Brushless DC Motor

P. R. Upadhyay; K.R. Rajagopal

The effect of armature reaction on the performance of a 70 W, 24 volt, 6-pole, 350-rpm surface mounted radial-flux permanent magnet brushless dc (PM BLDC) motor is presented. The two distinct effects viz. demagnetizing and cross magnetizing effects of the armature reaction on the performance of radial-flux PM BLDC motor are discussed.

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B. P. Singh

Indian Institute of Technology Delhi

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Bhim Singh

Indian Institute of Technology Delhi

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