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In this article, it is shown that in a linear induction machine (LIM), the force ripple that arises due to the magnetic asymmetry does not depend on whether the LIM is being fed from a voltage source or a current source. When the LIM is fed from a three-phase balanced voltage source, the primary voltage is balanced but the LIM draws an unbalanced current from the supply. When the LIM is fed from a three-phase balanced current source, the primary current is balanced but an unbalanced voltage appears across the LIM terminals. In both these cases, the unbalance creates a ripple in the propulsive force of the LIM. This force ripple increases with the increase in the speed of the LIM. This article shows that at any given speed, the percentage of the ripple component in the propulsive force remains constant irrespective of all operating conditions. The variation of the force ripple with the speed can be represented by a curve, which is unique for one LIM. This curve neither depends on the value of the primary voltage or primary current, nor does it depend on the nature of the energy source from which the LIM is being supplied. The force ripple arises from the flux distortion due to end effects and can, therefore, be instrumental in estimating the amount of end effects existing in an LIM. [ABSTRACT FROM AUTHOR]

This paper proposes a simplified analytical averaged model of a thyristorized commutatorless series motor. The motor operation is generally complicated due to the complexities present in the three-phase synchronous machine used and the nonlinearities introduced by the switching operation of the power electronic converter that is feeding the electrical machine. The simple analytical model is formulated in light of a conventional dc series motor and is found to be approaching the simplicity of a conventional dc series motor both in dynamic condition and steady state. The developed simplified model is found to yield results closely tallying with those obtained from a ‘detailed numerical model’ developed earlier, which is totally numerical in nature. The results are also validated experimentally on a small laboratory-built prototype. The developed model lays the foundation of controlling the motor for different industrial loading applications. One such application, viz., constant torque loading, is considered to show that the control strategy adopted on the basis of the discussed model works satisfactorily to develop a constant torque according to a given torque reference irrespective of load disturbances. [ABSTRACT FROM AUTHOR]

Assesses the steady-state model of a silicon-controlled-rectifier based load-commuted commutatorless series motor. Influence of harmonics in the production of steady torque; Computation of the harmonic torque; Component of the armature current and level field current.