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8 : V/F Control Of VSI Fed Three-Phase Induction Motor

1.      What will be the change in torque speed characteristics of the induction motor if there is change in V/f ratio?

2.      Can higher starting torque be obtained at very low frequencies? Comment on the basis of the observations.

3.      Is the speed regulation (variation of speed from no-load to full-load) the same at different frequencies?

4.      What are the advantages and disadvantages of this method of speed control?

5.      How are the equivalent circuit parameters affected by frequency?

6.      What is the effect of variation of frequency on maximum torque, starting torque, slip at maximum torque, if V/f is kept constant?

7.      At constant V/f, is the developed power at all frequency same at rated input current?

8.      What do you expect, will happen to the characteristics of the induction machine, if v/f ratio is held constant during generator mode of operation?

9.      Is the flux really held constant by keeping v/f constant? If not, how do you ensure that flux will be held constant?

10.  How do you achieve operation above base speed?

11.  What is the major difference in performance of the induction machine fed by a sinusoidal voltage and PWM voltage?


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