
7
INVERTER-FED INDUCTION MOTOR
DRIVES
INTRODUCTION
We saw in the previous chapter that the induction motor can
only run efficiently at low slips, i.e. close to the synchronous
speed of the rotating field. The best method of speed control
must therefore provide for continuous smooth variation of
the synchronous speed, which in turn calls for variation of
the supply frequency. This is achieved using an inverter (as
discussed in Chapter 2) to supply the motor. A complete
speed control scheme which includes tacho (speed) feedback
is shown in block diagram form in Figure 7.1.
Figure 7.1 General arrangement of inverter-fed variable-frequency
induction ...