The speed control of induction motor with modified V/f

When induction motor is controlled with constant V/f, there is still problematic at low frequency range.

When the speed of IM is controlled with constant V/f, there is still problematic at low frequency range. Therefore, it is necessary to further modification to operated the induction motor in that region. In this control algorithm, two sinusoidal reference waves which are phase-shifted 90 degree is produced from the relationship of angle "thida" and modulation index. Using Clark transformation, three sinusoidal reference waves which are phase-shifted 120 degree is obtained. By comparing the available reference waves with carrier wave ( sawtooth wave, ) using switching frequency 4Hz, the gate signals can be obtained to switch the inverter.