0195136047.pdf

16.1 POWER SEMICONDUCTOR-CONTROLLED DRIVES 765

Km=

E

ωm

=

202. 66

188. 57

= 1. 075

For continuous conduction, Equation (16.1.38) holds:

2 Vm

π

cosα=IaRa+Kmωm=IaRa+E

At rated torque,

Ia= 11 .56 A

Back emf at 1200 r/min=E 1 =

1200

1800

× 202. 66 = 135. 11

Substituting these values, one gets

2 × 325. 27

π

cosα= 11. 56 × 1. 5 + 135. 11 = 152. 45

or

cosα=

152. 45 ×π

2 × 325. 27

= 0. 7365 ,orα= 42 .6°

(b) At−1800 r/min,

E=− 202 .66 V

So it follows that

2 × 325. 27

π

cosα= 11. 56 × 1. 5 − 202. 66 =− 185. 32

or

cosα=−

185. 32 ×π

2 × 325. 27

=− 0. 8953 ,orα= 153 .5°

(c) From part (a),Km= 1 .075. Corresponding to a speed of 500 r/min,

ωm=

500 × 2 π

60

= 52 .38 rad/s

From Equation (16.1.29), we have

52. 38 =

2 × 325. 27

π× 1. 075

cos 60°−

1. 5

1. 0752

Ta,orTa= 33 .82 N·m

(d) From part (a),Km= 1 .075. From Equation (16.1.39), we obtain

480 × 2 π

60

=

2 π× 325. 27

π× 1. 075

cosα−

1. 5

1. 0752

× 35

or,

cosα= 0. 497 or α= 60 .2°

The most widely used dc drive is the three-phase, fully controlled, six-pulse, bridge-rectifier-
fed, separately excited dc motor drive shown in Figure 16.1.14. With a phase difference of