0195136047.pdf

16.1 POWER SEMICONDUCTOR-CONTROLLED DRIVES 773

T=

3

ωS











Vrated^2 (R′ 2 /aS)

(

R 1

a

+

R′ 2

aS

) 2

+(Xl 1 +X′l 2 )^2











,a< 1

Here,

ωS=

120 × 60

6

×

2 π

60

= 40 π= 125 .66 rad/s

Vrated=

440

√

3

=254 V

S=

30

1200

= 0. 025

Witha=1,

Trated=

3

125. 66











2542 ( 0. 1 / 0. 025 )

(

0. 2 +

0. 1

0. 025

) 2

+( 0. 75 + 0. 7 )^2











= 312 .11 N·m

At half the rated torque,

0. 5 × 312. 11 =

3

125. 66











2542 ( 0. 1 /aS)

(

0. 2

a

+

0. 1

aS

) 2

+ 1. 452











or

(

0. 2

a

+

0. 1

aS

) 2

+ 2. 1 =

0. 987

aS

Also,

S=

aωS−ωm

aωS

or a=

ωm

( 1 −S)ωS

=

59. 7

( 1 −S) 125. 66

=

0. 457

1 −S

(Note:ωm= 570 × 2 π/ 60 = 59 .7 rad/s.)

Based on the last two equations, we can solve foraandSusing an iterative procedure,

a= 0. 4864 ; S= 0. 0235

Therefore, frequency=0.4864× 60 =29.2 Hz.

The inverter can also be operated as a pulse-width modulated (PWM) inverter. Figure 16.1.20
shows the schemes when the supply is dc and when it is ac.

SLIP-POWERCONTROLLEDWOUND-ROTORINDUCTION-MOTORDRIVES

Slip poweris that portion of the air-gap power that is not converted into mechanical power. The
methods involving rotor-resistance control and voltage injection into the rotor circuit belong to this