UNIT-I Control of DC motors by Single phase Converters
OBJECTIVE QUESTIONS
1. The internal impedance of an ac source supplying a converter is largely ______in nature.
2. Due to the presence of source ______commutation in a converter is not ______.
3. The period over which the commutation process continues is called the ______period.
4. Length of the overlap period depends on the valve of the source inductance and load ______.
5. In a single phase converter ______thyristors conduct during the overlap period.
6. In a three phase converter ______thryistors conduct during the overlap period provided the overlap angle is less than ______degrees.
7. The average output voltage of a ac-dc converter ______as a result of commutation overlap.
8. In the dc equivalent circuit of a converter the input ac source inductor appears as a loss less resistance called the ______resistance.
9. Commutation overlap decreases the ______angle of a converter and may cause commutation failure during ______mode of operation.
10. Commutation overlap introduces ______in the supply voltage waveform.
11. In a half controlled converter two ______of a fully controlled converter are replaced by two ______.
12. Depending on the positions of the ______the half controlled converter can have ______different circuit topologies.
13. The input/output waveforms of the two different circuit topologies of a half controlled converter are ______while the device ratings are ______.
14. A half controlled converter has better output voltage ______compared to a fully controlled converter.
15. A half controlled converter has improved input ______compared to a fully controlled converter.
16. At the boundary between continuous and discontinuous conduction the value of the output current at ωt = α is ______.
17. The output voltage and current waveform of a single phase fully controlled and half controlled converter will be same provided the extinction angle β is less than ______.
18. For the same value of the firing angle the average output voltage of a single phase half controlled converter is ______in the discontinuous conduction mode compared to the continuous conduction mode.
19. Single phase half controlled converters are most suitable for loads requiring ______voltage and current.
20. The output voltage form factor of a single phase full wave rectifier is ______.
21. The output voltage of a single phase full wave rectifier supplying an inductive load is ______of the load parameters.
22. The peak to peak output voltage ripple of a single phase split supply full wave rectifier supplying a capacitive load is ______compared to an equivalent half wave rectifier.
ANSWER:
(1) inductive; (2) inductance, instantaneous; (3) overlap; (4) current ; (5) four;
(6) three, sixty; (7) decreases; (8) commutation; (9) inverter, (10) notches.
(11) thyristors, diodes; (12) diodes, two; (13) same, different; (14) form factor;
(15) power factor.(16) zero; (17) π; (18i) higher; (19) unidirectional. (20) π22 ;
(21) Independent (22) smaller.
1) The three phase fully controlled bridge converter is obtained by replacing six ______of an uncontrolled converter by six ______.
2) The pulse number of a three phase fully controlled bridge converter is ______.
3) In a three phase fully controlled converter each device conducts for an interval of ______degrees.
4) In a three phase fully controlled converter operating in continuous conduction there are ______different conduction modes.
5) The output voltage of a three phase fully controlled converter operating in the continuous conduction mode consists of segments of the input ac ______voltage.
6) The peak voltage appearing across any device of a three phase fully controlled converter is equal to the ______input ac ______voltage.
7) The input ac current of a three phase fully controlled converter has a ______step waveform.
8) The input ac current of a three phase fully controlled converter contains only ______harmonics but no ______harmonic.
9) A three phase fully controlled converter can also operate in the ______mode.
10) Discontinuous conduction in a three phase fully controlled converter is ______.
11) Higher pulse number converters can be realized by ______and ______connection of six pulse converters.
12) Constituent six pulse converters of a 12 pulse converter have ______firing angles.
13) The input supply voltages to the converters of a 12 pulse converter have ______magnitudes and are phase shifted from one another by ______degrees.
14) The input supply to a 12 pulse converter can be obtained through a ______connected transformer.
15) Dual converters are used for supplying ______quadrant dc motor drives.
16) In a dual converter if one converter is fired at an angle ‘α’ the other has to be fired at ______.
17) In ______current dual converter only one converter conducts at any time.
18) In a circulating current type dual converter an ______is used between the converters to limit the circulating current.
19) To obtain a linear control relation between the control voltage and the output dc voltage of a converter ______control logic is used.
20) In a three phase fully controlled converter the carrier waves for firing pulse generation are obtained using three ______connected single phase transformers.
ANSWERS:
(1) diodes, thyristors; (2) six; (3i) 120; (4) six; (5) line; (6) peak, line; (7) six;
(8) odd, tripler; (9) inverting; (10) rare. (11) Series, parallel; (12) same, (13) equal, 30,
(14) star – star – delta; (15) four; (16) π - α, (17) non-circulating ; (18) inductor,
(19) inverse-cosine; (20) delta-zigzag.
UNIT-II Four Quadrant operation of DC Drives
1. The dual converter used for the speed control of dc motor, will have two bridges theare.
(a) two rectifiers (b) two inverters[]
(c) one rectifiers and ane inverter(d) none
2. For dc motors a dual converter is used to obtain []
(a) reversible speed control(b) regenerative braking
(c)plugging(d) all of the abov
3. Four quadrant operation can be obtained in the[]
(a) HCR(b) FCR(c) dual converter
4.A four quadrant operation requires []
(a) two full converters in seriesb) two full converters connected in back to back
(c) two full converters in parallel(d) two semiconverters are connected back to back.
5. in dual converter, converter 1 and 2 works as under[]
(a) both as rectifiers (b) both as inverters(c) 1 as rectifier and 1 as inverter
6. In a circulating current type dual converter ,the nature of the voltage across reactor is[]
a. alternatingb. pulsatingc. directd. triangular
7. Two full converters connected back to back the same dc load is called a []
a. chopperb. inverterc. rectifierd. dual converter
ANSWERS:
1-c.2-d,3-c,4-b,5-c,6-a,7-d