The document discusses converter configurations and analyzes a 12 pulse converter. It begins by explaining pulse number and valve/switch types in converters. It then discusses how converter configuration is selected based on pulse number to maximize valve and transformer utilization. It provides equations for peak inverse voltage, utilization factor, and transformer rating calculations. Finally, it analyzes a 12 pulse converter, explaining how two transformers connected in star-star and star-delta configurations produce 12 pulses of output with each pulse having a 30 degree duration.

1. Choice of converterconfiguration
content
 Converter configuration
 Analysis of 12 Pulse converter
Prepared By
Mr.K.Jawahar, M.E.,
Assistant Professor
Department of EEE
Choice of converter configuration
Kongunadunadu College of Engineering and Technology Department of EEE

2. Choice of converter configuration
1. Pulse number
• The number of pulsations ( cycle of ripple ) per cycle of
alternating voltage.
• The conversion from AC to DC involves switching sequentially
different sinusoidal voltages on to the DC circuit.
• The output voltage of the converter consists of a DC component
and a ripple whose frequency is determined by the pulse
number.
hdc= np
hac= np ± 1
Choice of converter configuration
Kongunadunadu College of Engineering and Technology Department of EEE

3. 2. Valve and switches
• It can be treated as switch which can be turned on at any
instant, provided the voltage across it is positive.
• A diode is an uncontrolled switch which will turn on immediately
after the voltage becomes positive where as thyristors switching
can be delayed by an angle.
• the opening of the switch (both for diode and thyristor) occurs at
the current zero.
Choice of converter configuration
Kongunadunadu College of Engineering and Technology Department of EEE

4. 3. Converter configuration
• The configuration for given pulse number is selected in such a
way that both the valve and transformer utilization are maximized.
• converter configuration can be defined as basic commutation
group and the number of groups connected in series and
parallel.
Kongunadunadu College of Engineering and Technology Department of EEE
Choice of converter configuration

5. 4. Valve rating
• The valve rating is specified in terms of PIV. The ratio of PIV to
the average dc voltages is an index of the valve utilization.
𝑣 𝑑𝑜 = 𝑆
𝑞
2𝜋 −𝜋
𝑞
𝜋
𝑞
𝐸 𝑚 𝑐𝑜𝑠𝜔𝑡 𝑑𝜔𝑡
• −𝜋
𝑞
𝜋
𝑞
𝐸 𝑚 𝑐𝑜𝑠𝜔𝑡 𝑑𝜔𝑡 =2 0
𝜋
𝑞
𝐸 𝑚 𝑐𝑜𝑠𝜔𝑡 𝑑𝜔𝑡 𝑝𝑟𝑖𝑜𝑟𝑖𝑡𝑦 𝑖𝑠 𝑒𝑣𝑒𝑛
𝑣 𝑑𝑜 = 2𝑆
𝑞
2𝜋 0
𝜋
𝑞
𝐸 𝑚 𝑐𝑜𝑠𝜔𝑡 𝑑𝜔𝑡
= 2𝑆
𝑞𝐸 𝑚
2𝜋
sin 𝜔𝑡 0
𝜋
𝑞
= 𝑆
𝑞𝐸 𝑚
𝜋
𝑠𝑖𝑛 𝜋
𝑞 − 0
= 𝑆
𝑞𝐸 𝑚
𝜋
𝑠𝑖𝑛 𝜋
𝑞Kongunadunadu College of Engineering and Technology Department of EEE
Choice of converter configuration

6. 5. Peak inverse voltage
• If q is even, 𝑃𝐼𝑉 = 2𝐸 𝑚
• If q is odd, 𝑃𝐼𝑉 = 2𝐸 𝑚 𝑐𝑜𝑠
𝜋
2𝑞
6. Utilization factor
The ratio of PIV to the average DC voltage is known as utilization
factor.
For q is even
𝑃𝐼𝑉
𝑉 𝑑𝑜
=
2𝐸 𝑚
𝐸 𝑚
𝑆𝑞
𝜋
𝑠𝑖𝑛
𝜋
𝑞
𝑃𝐼𝑉
𝑉𝑑𝑜
=
2𝜋
𝑆𝑞𝑠𝑖𝑛
𝜋
𝑞
𝑓𝑜𝑟 𝑞 𝑖𝑠 𝑜𝑑𝑑
𝑃𝐼𝑉
𝑉𝑑𝑜
=
𝜋
𝑆𝑞𝑠𝑖𝑛(
𝜋
2𝑞
)
Kongunadunadu College of Engineering and Technology Department of EEE
Choice of converter configuration

7. S.No. q r S PIV/Vdo
1 2 1 3 1.047
2 2 3 1 3.142
3 3 1 2 1.047
4 3 2 1 2.094
5 6 1 1 2.094
Kongunadunadu College of Engineering and Technology Department of EEE
Choice of converter configuration

8. 7. Transformer rating
The current rating of a valve is given by
𝐼𝑣 =
𝐼 𝑑
𝑟 𝑞
𝑆𝑡𝑣 = 𝑃
𝐸 𝑚
2
𝐼𝑣
𝑆𝑡𝑣 = 𝑃
𝑉𝑑𝑜 𝜋
2𝑆𝑞𝑠𝑖𝑛
𝜋
𝑞
∗
𝐼 𝑑
𝑟 𝑞
P =6, S=2, q=3, r=1 to find transformer utilization factor
𝑆𝑡𝑣
𝑉𝑑𝑜 𝐼 𝑑
=
𝑃𝜋
2𝑆𝑞𝑠𝑖𝑛
𝜋
𝑞
𝑟 𝑞
𝑆𝑡𝑣
𝑉𝑑𝑜 𝐼 𝑑
=
6𝜋
2 ∗ 2 ∗ 3 ∗ 𝑠𝑖𝑛
𝜋
3
∗ 1 ∗ 3
Kongunadunadu College of Engineering and Technology Department of EEE
Choice of converter configuration

9. =
6𝜋
2 ∗ 6 ∗ 1 ∗ 3 ∗ sin
𝜋
3
=
𝜋
2.449 ∗ 0.866
𝑆𝑡𝑣
𝑉𝑑𝑜 𝐼 𝑑
= 1.480
Choice of converter configuration

10. Analysis of a 12 pulse converters
• Two transformers with primary windings connected in star and
connected to the common supply voltage.
• The current supplied by the supply are sum of the currents
flowing in the two primary.
• Let the phase voltages of the 12 pulse converter are star
connected of the transformer phase voltage as,
Kongunadunadu College of Engineering and Technology Department of EEE
Analysis of 12 pulse converters

11. Kongunadunadu College of Engineering and Technology Department of EEE
Analysis of 12 pulse converters

12. In delta connected transformer whose ratio is 1: 3 where line voltage
is equal to phase voltage.
Kongunadunadu College of Engineering and Technology Department of EEE
Analysis of 12 pulse converters

13. • Comparing the above equations we note that the voltages applied
to the bridges has difference of 30 degree to the voltage applied to
bridge 1.
• Thus the valve 3 is second bridge will be fired 30 degree after the
valve 3 in bridge 1 is fired.
• Thus 12 pulse converter has 12 pulse of output with each duration
of 30 degree. Then the transformers are connected on star-star and
star-delta in bridge 1, bridge 2 respectively, to obtain the output of
12 intervals
Kongunadunadu College of Engineering and Technology Department of EEE
Analysis of 12 pulse converters

14. Kongunadunadu College of Engineering and Technology Department of EEE
Analysis of 12 pulse converters

15. Reference:
• Padiyar, K. R., “HVDC power transmission system”, New Age
International (P) Ltd., New Delhi, Second Edition, 2010.
Analysis of 12 pulse converters
Kongunadunadu College of Engineering and Technology Department of EEE