Comparative study of total harmonic distortion on the current waveform by PWM fed and Vector controlled Induction motor drives

Adjustable speed drive is becoming a significant load component for power distribution. It involves the use of Induction motors comprising of Wound rotor type & squirrel cage. This paper involves analysis, control and modeling of induction motors and also investigates its effects on Total current harmonic distortion on an adjustable speed by the use of PWM generator and Vector control method. By using Park´s transformation, we can convert three phase system to two phase and then convert it to stationery two axes system (d, q) By varying two vectors of flux and torque, (one on quadrature and other on direct axis) we can control the rotor current and therefore, speed and THD for current and voltage can be calculated. Harmonics are lesser in amplitude and more in frequency as compared to the fundamental. Vector control and direct torque control are employed extensively in variable-speed ac drive systems, particularly for induction machine drives. In order to generate PWM signals, an error value is calculated by comparing the current reference and actual current, and it is used as an input for hysteresis control. The voltage vector is obtained, and the motor is driven by using the inverter to follow current reference values.