Scaler and vectorel speed control of induction motor

Induction motors (IM) are commonly used in current industry because of the fact that their considerable superiorities such as low-cost, need for less-maintenance, long life and high efficiency in comparison with other electricity motors. The best known speed control method of the IM is scalar control method (SCM) due to its simple and easy-to-implement structure. This method is also called as v/f control. SCM is only based on keeping the ratio between the voltage and frequency applied to IM constant and thus the magnetic field in air gap constant.In addition to this, another speed control method, which is also briefly known as vector control, is the field oriented speed control (FOC). However FOC is more complicated than SCM, it has higher performance in general. For this reason, it is widely preferred in the IM drive applications such as position control and etc. requiring high performance.In this study, the mathematical modeling of a three-phase induction motor driven by indirect rotor field oriented speed control (IRFOC) method and SCM is carried out and the results of comparative performance analysis on the basis of simulations is presented. In the drive system, the three-phase currents feeding IM and the rotor speed are supposed to be measurable and available for feedback. A proportional-integral (PI) controller is used as speed controller and the voltages applied to IM have been acquired by a three phase two level voltage source inverter. The control of inverter has been performed through applying hysteresis band pulse width modulation (HBPWM) method to the three phase currents feeding IM. Taking all the dynamics of IM and inverter into consideration yields that the simulation studies are high compatible with the real world and thereby the validity of the results increases.Time varying different operating points are obtained through step reference speed input and variable load torque. As a result of the performance analysis for these operating points, it is clearly concluded that IRFOC is more robust to the variable load torque and the torque produced by IM is smoother with this method.