AC voltage controllers are used as induction motor starters in fan or pump drives and the crane hoist drives. This paper presents a method of identifying the end of soft start of an ac voltage-controller-fed induction motor (IM) drive based on the voltage across the nonconducting thyristor through a dynamic simulation of the whole drive system. A two point current minimization technique is adopted to operate the drive system at the required optimal voltage under all operating conditions. This minimizes the motor losses. Graphic modeling of the whole drive system is done in a modular format using Design Star and dynamic simulation is done using SABER. The dynamic simulation results of the whole drive system are supported with experimental data.

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The Boundary Value Approach is used to obtain the steadystate analysis and digital simulation of voltage-controlled a.c. motor drives such as a capacitor-run single-phase induction motor with a pair of thyristors in the main winding and a 3-phase wyeconnected induction motor with a pair of thyristors in each phase.The steady-state solution is obtained without changing the elements and the rank of the matrix differential equation defining the motor for all modes of operation. In addition no iteration is required to get the steady-state initial vectors. Computed results include the predicted stator currents, voltages and the developed electro-magnetic torque and there is good qualitative and quantitative agreement with the earlier published results. NOMENCLATURE List of Symbols ids' i qs i dr, i qr irs' i y s' N a , N m

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