8 (f). Circuit diagram of V/f control of VSI fed Induction Motor drive.
gate signals to the IGBTs T1-T6 from SPWM generator. The
gate signals for T1, T4 are generated by comparing the
high frequency (fcar) triangular carrier signal vcar with
sine control signal vc_R of frequency fo. Similarly, the
gate signals for T3, T6 and T5, T2 are
generated by comparing the same vcar with sine control signals vc_Y
and vc_B of frequency fo. The peak magnitude
of control sine signal controls the modulation index ma which in
turn controls the rms output voltage. The output frequency is controlled by
setting control signals frequency (fo).
the waveforms of PWM pulses and across each element of the power circuit with three-phase
output rotor speed, rms voltage, rms currents and their instantaneous waveforms
are to be observed for different values of reference speed (Nr*).
reference speed the reference frequency (f*) and
reference voltage (V*) commands are calculated such that V/f ratio
maintained to be constant. The same can be repeated also for
different values of load torque.