A scheme for sensorless flux estimation for the induction motor drives is presented in this paper, where the flux information is derived from the current ripple. The scheme measures the stator current phasor deviation to determine the back emf vector position during the zero vectors of the inverter. The position of the rotor flux is detected indirectly by computing the position of the motor back emf, which is orthogonal to the rotor flux position. The space vector PWM generates a current ripple pattern in the machine current, which depends upon the ripple voltage and equivalent stator leakage inductance. For high speed operation when the time duration for the zero vector switching states are small, an indirect method for estimation of flux position is proposed, where the effect of active voltage vectors on the stator ripple current is eliminated by creating a virtual short circuit at the motor terminals. This is achieved by linear transformation of the fundamental components of two immediate current space phasor deviations within a switching period. The whole scheme is implemented in a space phasor based PWM drive with constant inverter switching frequency. The position of the back emf is estimated for both high speed and low speed by implementing the proposed method in a TMS320LF2407 DSP based board.
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