The document presents a detailed analysis of High Voltage Direct Current (HVDC) systems, highlighting their cost efficiency and advantages over AC systems, such as requiring fewer cables and using adaptable pole designs. It explains the operational characteristics of converters which can function as rectifiers or inverters, focusing on key parameters like firing angles and voltage control. Additionally, it discusses the implications of various operational modes and adjustments to voltage for power flow management in HVDC systems.

1. Presented by: Aazim Rasool
1134200011
Presented to: Dr. Chongru Liu
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North China Electric Power University,
Beijing , China

2. AC
DC
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3. 
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4. Cost of HVDC is less
One cable required instead of three
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5. Same poles can be use. Moreover, slim and smart
poles are used for DC transmission
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6. AC Transmission Line Corridor
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7. DC Transmission Line Corridor
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8. DC Transmission Line Corridor
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9.  DC transmission system
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10.  In 6-phase;each transistor
operate for 120o .
Eac -- T1&T2
Ebc -- T3&T2 Ebc -- T3&T4 Eba - T5&T4
Eca - T5&T6 Ecb - T1&T6
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11.  Graph representation of operation.
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12.  Figure representing, when firing
delay angle ‘α’ changes
 To make eac(α=0) ; switch ON
transistors 1 & 2
 at ‘-60o ‘
 for ‘60o ‘.
 To make eac(α≠0) ; switch ON
transistors 1 & 2
 at ‘-60o + α’
 For ‘60o + α‘.
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13. 
V 1 V 3 V 5
V 2V 6V 4
Phase A
Ud
Phase B
Phase C
Id
Power FlowAC System DC System
V 1 V 3 V 5
V 2V 6V 4
Phase A
Ud
Phase B
Phase C
Id
AC System DC SystemPower Flow
30 60 90 120 150 180
0
+Ud
-Ud
160
5
Rectifier
Operation
Inverter
Operation
a
Rectifier Operation Inverter Operation
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14. 30 60 90 120 150 180
0
a
+Ud
-Ud
160
Limita Inv
5
Limita Rect.
Rectifier
Operation
Inverter
Operation
tw
o
60=a
Ud
o
30=ao
0=a
o
90=a o
120=a o
150=a
-Ud
tw
Ud
Ud
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15.  Direct current from the rectifier to the inverter
 Power at the rectifier terminal
 Power at the inverter terminal
cilcr
doidor
d
RRR
VV
I


=
a coscos
ddrdr IVP =
2
dLdrddidi IRPIVP ==
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16. α:
 Ignition delay angle for rectifier
 α min = 5 o (Required to charge thyristor)
 α op. = 15-20 o (Room for VR )
 α ≤ 900
γ:
 Extinction advance angle
 γmin = 15o (50Hz)/ 18o (60Hz) – avoid comm. failure
** 1800 ≥ α ≥ 900 (For inverter mode)
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17. * µ= overlap angle
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18. B
A
2
C
1
a
u u
Vd
u
3
a a
α= firing Angle
μ= Commutation
Interval
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19.  Internal voltages, Vdorcosa and Vdoicos are used to control
the voltages at any point on the line and the current flow
(power)
 This can be accomplished by:
 Controlling firing angles of the rectifier and inverter (for fast action)
 Changing taps on the transformers on the AC side (slow response)
 Power reversal is obtained by reversal of polarity of direct
voltages at both ends
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20. Ideal Characteristic:
 Under normal Condition;
 Rectifier maintains CC (Constant Current)- α
 Inverter maintains CEA (Constant Extinction Angle) γ min
dciLdoid IRRVV )(cos = 
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21. Actual Characteristic
Abnormal Condition
FA represents min. ignition angle (CIA mode)
AB represents Constant Current (CC mode)
Rectifier
*CIA shows maximum
rectifier voltage
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22. Actual Characteristic
Abnormal Condition
GD represents min. extinction angle (CEA mode)
GH represents Constant Current (CC mode)
Inverter
*CEA shows maximum
inverter voltage
Operating Point
Operating Point
at abnormal
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23.  Each converter can work as a rectifier as well as
inverter.
 O.P 1
 C1=rectifier(CC)
 C2=inverter(CEA)
 O.P 2
 C2=rectifier(CC)
 C1=inverter(CEA)
Operating Point 2
Operating Point 1
Current is same
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24. Decrease voltage at station B or increase voltage at station A. power flows from A B Normal
direction
Decrease voltage at station B or increase voltage at station A. power flows from A B Normal
direction
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26. Power reversal is obtained by reversal of polarity of direct voltages at both ends.
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27. CONSTANT VOLTAGE MODE CONSTANT B MODE
 V-I characteristic is flat
 Higher value of γ
 Back-up type
 γ is comparatively less
γ is set at higher; maintain low constant voltage
γ is se at medium; make greater voltage then CVM
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28.  Small change in AC-Voltage cause large change in
DC-Current.
 There is a Mode Ambiguity.
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29.  Fig a, represents constant β mode.
 Fig b , represents constant Voltage mode.
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30.  Voltage-Dependent Current-Order Limit.
 Under low voltage(drop >30%);current also decreases to
low level
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31. Graph shows the function of VDCOL in control graph
of rectifier and inverter characteristic
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32.  “Power system stability and control”, parabha
qundar
 Course Lectures “HVDC” , A.M Gole.
 “Presentation of HVDC Transmission”,Zunaib Ali
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