This paper proposes a new modulation scheme providing unbalanced output terminal voltages of a standard threeleg voltage source inverter (VSI) for unsymmetrical type two-phase induction motors. This strategy allows a control method of the output voltages with typically constant V/Hz for a main winding and with voltage boost to compensate magnitude of current for an auxiliary winding. Harmonic voltage characteristics and the motor performance are investigated under a wide range of operating conditions. Practical verification is presented to confirm correctness and capabilities of the proposed technique. All results are compared to those of a conventional two-leg half bridge topology. The results show that the simulation results well agree with the experimental ones, and also the proposed scheme is superior to the conventional drive. Keywords: unsymmetrical two phase induction motor, harmonic voltages, unbalanced output terminal voltage, pwm voltage source inverter List of SymbolŝV D = main winding voltagê V Q = auxiliary winding voltagê I m = main winding current I a = auxiliary winding current E f m = forward induced voltage of main windinĝ E f a = forward induced voltage of auxiliary windinĝ E bm = backward induced voltage of main windinĝ E ba = backward induced voltage of auxiliary winding a = turns ratio of auxiliary to main windings s = slip ω s = synchronous angular frequency (rad/sec) φ = phase angle between the main and the auxiliary winding currents T e = average electromagnetic torque T pulse = amplitude of pulsating torque R 1m , X 1m = main winding resistance and leakage reactance R 1a , X 1a = auxiliary winding resistance and leakage reactance X m = main winding magnetizing reactance R 2 , X 2 = rotor resistance and leakage reactance referred to main winding R 2 a 2 ,

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-This paper presents a simplified modulation strategy for the three-leg VSI fed twowinding induction motor. The strategy provides independent unbalanced voltage control for the main and auxiliary windings. This make the motor can be reversed rotation through the range of motor speed operation without limitation of voltage boost of the auxiliary winding. To study the advantages of the proposed drive, the experimental results such as voltage stresses, hysteresis band of the currents in locus, and also acoustic noise levels of the three-leg VSI are compared with those of the conventional two-leg topology. The results obviously show that the proposed technique achieves superior performance compared with the traditional scheme in case of dramatic increase of DC bus utilization, effective reduction of harmonic voltages content, and also significant enhancement of motor efficiency.

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