Microprocessor based feedback control using reactive power measurement for squirrel cage induction motor drives

A scheme to control the air gap flux of a three-phase squirrel-cage induction motor operating with a PWM inverter for variable-speed operation is presented. The scheme is based on the measurement of the fundamental component of motor terminal voltage, current, and the phase angle between them, and calculation of the motor reactive power using a microprocessor. The measured total reactive power fed to the induction motor, the motor leakage, and magnetizing inductances are used to calculate the motor magnetizing current by the processor. The calculated magnetizing current is used to regulate the air gap flux at the desired level in a variable-frequency induction motor drive.<>