Experiment II

6/18 PULSE AC TO DC CONVERTER

Group III

1. Adlan Bagus Pradana

2. SVSS Chandrasekhar

DEPARTMENT OF ELECTRICAL ENGINEERING

M. Tech Power Electronics, Electrical Machines & Drives (PEEMD)

EEP842 POWER ELECTRONICS LABORATORY - 1.5 Credits

6/18 PULSE AC TO DC CONVERTER

EXPERIMENT NO. 2

I. Motivation:

DC supply is gaining very much importance than AC in recent years with the improvement in

electronic equipment. But rectification circuits introduce more harmonics into the AC system. Hence

the quality of the supply reduces. So rectifier should be designed such that the quality of AC supply

should be maintained. As per the IEEE standards current THD should be less than 5%. To attain this

there are two ways. One is to design filters to reduce harmonics and other to go for multilevel or

multipulse converters. This experiment introduces some of the multipulse AC to DC converters. With

the input three phase supply the output pulses can be multiple of six. In this experiment 6 and 18

converter performance are observed. A different autotransformer is used to obtain 3-phase outputs

with 20 degrees for 18 pulse configuration.

II. Objective:

1. Study characteristics of a 6-pulse, and 18-pulse uncontrolled three-phase bridge rectifiers with

filtered output.

(a) Record the AC supply voltage and current waveform, harmonic spectrum, THD, crest factor, rms

value, distortion factor, displacement factor and power factor, output DC voltage average value,

peak-peak ripple and ripple factor in 6-pulse and 18-pulse uncontrolled rectifiers with (i) resistive

load (ii) dc series inductor filter, (iii) dc shunt capacitor filter, and (iv) dc series inductor and shunt

capacitor (LC) filter at two loads.

(b) Simulate in MATLAB with SPS toolbox, the AC supply voltage and current waveform, Harmonic

spectrum, THD, crest factor, rms value, distortion factor, displacement factor and power factor,

output DC voltage average value, peak-peak ripple and ripple factor in 6-pulse and 18-pulse

uncontrolled rectifiers with (i) resistive load (ii) dc series inductor filter, (iii) dc shunt capacitor filter,

and (iv) dc series inductor and shunt capacitor (LC) filter at two loads using same parameters as in

part 1(a).

With this transformer arrangement the dc link voltage obtained is slightly higher than that of a 6-

pulse diode bridge rectifier output voltage, due to 18-pulse rectification. To make the proposed ac-

dc converter suitable for retrofit applications, the transformer design is modified to make the dc link

voltage same as that of 6-pulse diode bridge rectifier.

Fig.5 shows the schematic diagram of an 18-pulse ac-dc converter suitable for retrofit applications. It

also shows the winding connection diagram for achieving different voltage ratios from the

autotransformer by simply varying the tapping positions on the windings. This ensures that both the

output voltages are still having the required phase shift of ±200 (for achieving the eighteen-pulse

operation).

III. Theory:

To achieve the 6-pulse rectifier operation, the following connections are been done, To achieve the

18-pulse rectifier operation, the following conditions have to be satisfied:

a) Three sets of balanced 3-phase line voltages are to be produced, which are either 200 or 400 out

of phase with respect to each other. Here, ± 200 phase shift is used to reduce the size of magnetics.

b) The magnitude of these line voltages should be equal to each other to result in symmetrical pulses

and reduced ripple in output dc voltage. Fig.1 (a) shows the winding connection diagram of the

proposed autotransformer for achieving an 18-pulse rectification and Fig.1 (b) represents the

relationship among various phase voltages. From the supply voltages, two sets of 3-phase voltages

(phase shifted through +200 and -200) are produced. The number of turns required for +200 and -

200 phase shift are calculated as follows. Consider phase ‘a’ voltages as shown in Fig. 1a:

Figure 1 (a)

Figure 1(c) shows the 18 pulse configuration for AC to DC converter with differential transformer

configuration. The interface transformer connections at the output of the bridges avoid the

circulating currents to flow between the bridges and give 18 pulse output. The simulink diagram of

the interface transformer is shown at right side. The operation is as follows. When a circulating

current tries to flow from bridge1 to bridge-2 then EMF’s will induce in the windings such that it

opposes current flow through them. Thus circulating current can be made zero and the current from

the bridges flows out to load.

Figure 1 (b)

IV. Pre-experimental questions:

1. What is the advantage of configuration used in this experiment?

2. What is the phase shift required at the output for 18 pulse output?

3. What is meant by pulse multiplication and how it can be obtained?

V. Equipment and components:

1. 18 pulse AC-DC converter setup.

2. DC and AC voltmeters.

3. DC and AC ammeters.

4. 3-phase auto transformer.

5. Power analyzer.

6. Multimeter.

18-PULSE CONFIGURATION

Figure 1 (c)

VI. Procedure:

18-pulse converter:

1. Connect the circuit diagram as per the circuit diagram.

2. Apply the three phase input voltage.

3. Vary the load and obtain the input voltage, input current, pf, DPF, DF, THD, and ripple factor at

two different loads.

VII. Experiment Observations:

A. Tabulation Table

No Vi Ii CF-V CF-I THD-I DPF Vo Vo (p-p) Filter Pulse1 51.8 1.128 1.4 1.7 28.9 1 69.3 3.6 No filter 62 52.1 3.279 1.4 1.3 28.4 1 67.5 3.6 No filter 6

3 50 1.089 1.4 1.7 28.9 1 66 3.3 L filter 64 49.6 3.117 1.4 1.3 28.4 1 65.05 3.1 L filter 65 50.28 2.02 4.3 1.4 87.5 0.89 68.92 0.09 C filter 66 50 4.78 3.2 1.4 79.2 0.94 67.56 0.37 C filter 67 50.89 1.247 2.2 1.4 60.4 0.96 67.46 0.21 L-C filter 68 50.52 3.205 1.6 1.4 36.7 0.99 66.53 0.2 L-C filter 69 50.45 3.398 1.4 1.4 6.9 0.98 100.2 1.6 No filter 18

10 51.35 8.04 1.4 1.4 7.3 0.99 100.6 1.8 No filter 1811 50.81 1.249 1.4 1.4 7.6 1 96.4 1.7 L filter 1812 48.9 2.672 1.3 1.4 6.5 1 92.4 1.3 L filter 1813 50.17 1.603 1.4 1.7 22.7 0.98 96.9 0.3 C filter 1814 48.7 2.887 1.4 1.8 16 0.98 92.8 0.4 C filter 1815 49.99 3 1.4 1.4 8.1 1 94.2 0 L-C filter 1816 98.8 3.324 1.4 1.4 8.3 1 193 0 L-C filter 18

B. Graph

1. 6 Pulse, No Filter

No Remark Graph

1 V & I

2 Power

3 THD-I

4 Vo (p-p)

2. 6 Pulse, L Filter

No Remark Graph

1 V & I

2 Power

3 THD-I

4 Vo (p-p)

3. 6 Pulse, C Filter

No Remark Graph

1 V & I

2 Power

3 THD-I

4 Vo (p-p)

4. 6 Pulse, L-C Filter

No Remark Graph

1 V & I

2 Power

3 THD-I

4 Vo (p-p)

5. 12 Pulse, No Filter

No Remark Graph

1 V & I

2 Power

3 THD-I

4 Vo (p-p)

6. 12 Pulse, L Filter

No Remark Graph

1 V & I

2 Power

3 THD-I

4 Vo (p-p)

7. 12 Pulse, C Filter

No Remark Graph

1 V & I

2 Power

3 THD-I

4 Vo (p-p)

8. 12 Pulse, L-C Filter

No Remark Graph

1 V & I

2 Power

3 THD-I

4 Vo (p-p)

C. Result

Input Current THD

0

20

40

60

80

100

1 2

Load

% T

HD

6P-No filter"

6P-L Filter

6P-C Filter

6P-LC Filter

12P-No Filter

12P-L Filter

12P-C Filter

12P-LC Filter

Output Voltage Peak-Peak

00.5

11.5

22.5

33.5

4

1 2

Load

V p

-p

6P-No filter"

6P-L Filter

6P-C Filter

6P-LC Filter

12P-No Filter

12P-L Filter

12P-C Filter

12P-LC Filter

D. Conclusion

From experiment we can conclude as follow :

1. Current input THD and output voltage peak to peak are relatively independent from load change

2. Effect of pulse increasing from 6 to 18 pulse is decreasing input current THD and output voltage

peak to peak (ripple)

VIII. Simulation Observation

Continuous

powergui

V4

v+-

V3

V2

66.57

V1

Vabc

I abcA

B

C

a

b

c

V-I

v+-

V

A

B

C

Three-Phase Source

0.6614

0.7177THD1

signal THD

THD

RMS

RMS1

RMS

RMS

PQ1

V

I

PQ

PQ

Load

L

I3

27.22

I2

0.02263

I1

i+ -

I

C

A

B

C

+

-

Bridge

6-Pulse Model

Continuous

powergui

V4

v +-

V3

V2

64.94

V1

Vabc

I abcA

B

C

a

b

c

V-I

v+-

V

A+

B+

C+

A-

B-

C-

a3

b3

c3

Transformer2

A+

B+

C+

A-

B-

C-

a3

b3

c3

Transformer1

A+

B+

C+

A-

B-

C-

a3

b3

c3

Transformer

A

B

C

Three-Phase Source

0.04264

0.05529THD1

signal THD

THD

RMS

RMS1

RMS

RMS

PQ1

V

I

PQ

PQ

Load

L

I3

28.75

I2

0.05478

I1

i+ -

I

A

B

C

N

GroundingTransformer 1

A

B

C

N

GroundingTransformer

C

A

B

C

+

-

Bridge2

A

B

C

+

-

Bridge1

A

B

C

+

-

Bridge

18-Pulse Model

A. Tabulation Table

No Vi Ii THD-I Vo Vo (p-p) Filter Pulse1 49.1 0.2849 25.55% 69.44 10 No filter 62 46.31 0.4292 23.74% 65.5 12 No filter 63 49.08 0.2847 25.49% 69.39 12 L filter 64 46.31 0.4284 23.71% 65.39 15 L filter 65 50.35 0.2987 25.74% 71.2 12 C filter 66 45.51 0.4406 24.15% 64.37 12 C filter 67 50.25 0.2985 25.73% 71.08 10 L-C filter 68 45.51 0.4394 24.22% 64.22 13 L-C filter 69 49.16 0.2582 4.035% 62.36 1.5 No filter 1810 48.95 0.3919 1.305% 61.91 0.8 No filter 1811 49.16 0.2582 3.766% 62.32 1.5 L filter 1812 48.95 0.3919 1.415% 61.9 0.8 L filter 1813 49.14 0.258 3.729% 62.31 1 C filter 1814 48.94 0.3924 1.282% 61.89 0.7 C filter 1815 49.27 0.2592 4.028% 62.54 2 L-C filter 1816 48.93 0.3924 1.251% 61.88 0.8 L-C filter 18

B. Graph

1. 6-Pulse, No Filter

No Remar

k

1 Vin

2 I

3 Vout

2. 6-Pulse, L Filter

No Remar

k

1 Vin

2 I

3 Vout

3. 6-Pulse, C Filter

No Remar

k

1 Vin

2 I

3 Vout

4. 6-Pulse, L-C Filter

No Remar

k

1 Vin

2 I

3 Vout

5. 6-Pulse, No Filter

No Remar

k

1 Vin

2 I

3 Vout

6. 12-Pulse, L Filter

No Remar

k

1 Vin

2 I

3 Vout

7. 12-Pulse, C Filter

No Remar

k

1 Vin

2 I

3 Vout

8. 12-Pulse, L-C Filter

No Remar

k

1 Vin

2 I

3 Vout

C. Result

Input Current THD

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

1 2

Load

% T

HD

6P-No filter"

6P-L Filter

6P-C Filter

6P-LC Filter

12P-No Filter

12P-L Filter

12P-C Filter

12P-LC Filter

Output Voltage Peak to Peak

02468

10121416

1 2

Load

Vp

p

6P-No filter"

6P-L Filter

6P-C Filter

6P-LC Filter

12P-No Filter

12P-L Filter

12P-C Filter

12P-LC Filter

D. Conclusion

From experiment we can conclude as follow :

1. Current input THD and output voltage peak to peak are relatively independent from load change

2. Effect of pulse increasing from 6 to 18 pulse is decreasing input current THD and output voltage

peak to peak (ripple)

3. Filter usage is not quite effective for decreasing input current THD

4. Decreasing of output voltage peak to peak by usage of filter is more effective for 6 pulse

converter, but not so effective for 18 pulse converter

IX. Precautions:

1. Connections must be tight.

2. Capacitor must be discharged before disconnecting and conducting another experiment.

X. REFERENCES:

1. Bhim Singh, G.Bhuvaneswari and Vipin garg, “A Novel Polygon Based 18-Pulse AC– DC Converter

for Vector Controlled Induction Motor Drives.”, IEEE transactions on power electronics, vol-22, No-2,

pg-488-496 March-2007.

XI. INFERENCE:

From both of experiment and simulation we can conclude as follow :

1. Current input THD and output voltage peak to peak are relatively independent from load change

2. Effect of pulse increasing from 6 to 18 pulse is decreasing input current THD and output voltage

peak to peak (ripple)

3. Decreasing of input current THD and decreasing of voltage peak to peak by increasing pulse is

clearer in simulation than inexperiment. It is caused by factor below :

a. Experiment carefullness

b. Measurement equipment carefullness

c. Experiment apparatus