1. HVDC and its System Benefits
IEEE PES General Meeting July 2014
(PSACE) Economic Systems
Panel Session : “System Economic/Technical Benefits of Unconventional Transmission Provision: Transmission Switching, Embedded HVDC, and Others”
HVDC and its System Benefits
Neil Kirby – Alstom Grid
Gaylord National Resort & Convention Center
National Harbor, MD

2. Agenda
HVDC Technology
HVDC Functions
Embedded Applications of HVDC

3. HVDC Technology

4. HVDC Technology Classic Line-Commutated Converters Based on Thyristors
Need AC System Voltage present to operate
Very limited control of Reactive Power
Require AC filters to reduce generated harmonics
Very high power capability
1100 kV
11000 MW
Links in operation
Approx 130 by end of 2015

5. HVDC Technology Voltage Source Converters
Based on Transistors or similar
Create their own AC Voltage from DC source
Dynamic, Independent and Simultaneous control of MW and Mvars
Limited harmonics
Limited, increasing capacity
+/-320kV (cable limit)
1100MW
Links in operation
Approx 30 by end of 2015

6. VSC vs. LCC HVDC Line-Commutated Converter (LCC) HVDC
Voltage-Sourced Converter (VSC) HVDC
VDC_A
VDC_B
IDC
Power flow A → B
Power flow B → A
VDC_A
VDC_B
IDC
Power flow A → B
Power flow B → A
VDC_A
VDC_B
VDC_A
VDC_B
IDC
With LCC multi-terminal difficult for the network operator as a change in power direction at one terminal necessitates DC voltage reversal, hence, a Global network impact
With VSC current direction changes not DC voltage therefore only a Local change

7. HVDC Functions

8. “Traditional” Applications
Asynchronous interconnections, Bulk power transfer, Water crossings, etc
Control Modes
Power, Frequency, Swing Damping, AC Voltage, Reactive Power
Both VSC and LCC are capable

9. Stability Improvement
Steady-State vs. Dynamic
Dynamic Voltage/Reactive Power Control
Power Stability in Parallel AC lines
Angular Stability
Oscillatory Stability
HVDC Can Reduce Stability Margins
Allows use of Line Rating up to Thermal Capacity

10. DC Link Control Power Control Constant Real Power
VSC can also control Mvar at each terminal
Dynamic Linear AC Voltage Control
STATCOM Functionality
Even if DC power transfer is zero
LCC can only control MW
Coarse Control of Mvar through Filter Switching
Here, a power level is ordered. Current order = (power demand/voltage order)
Mvar MW
Mvar

11. DC Link Control Frequency Control Constant Frequency VSC and LCC
VSC can also control Mvar and AC voltage at each terminal
Here, a power level is ordered. Current order = (power demand/voltage order)
Mvar MW
Mvar

12. DC Link Control Power Modulation Control Preset response
Control system adjusts power to offset phase error P
time
Mvar MW
Power Oscillation Damping controls oscillations in an adjacent line,
Following a disturbance. The principle is to add an antiphase amount of
DC power, so as to damp the AC power oscillations.
Multimodal tuning methods are used from Transient Stability analysis.
Mvar

13. DC Link Control Power Modulation Control Preset response
Control system adjusts power to offset phase error P
time
Mvar MW
Mvar

14. DC Link Control Power Modulation Control Preset response
Control system adjusts power to offset phase error P
time
Mvar MW
Phase error is a good measurement of power swing and is used to produce
An antiphase signal to damp out the oscillation
Mvar

15. DC Link Control Power Runback / PDO
Preset response from Transient Stability Analysis
Control system adjusts power flow to defined value P
time
Mvar MW
Power is reduced from rectifier side to promote stability, in the same
manner as as reduction of load to alleviate the effects of PV instability
Mvar

16. DC Link Control Power Runback / PDO
Preset response from Transient Stability Analysis
Control system adjusts power flow to defined value P
time
Mvar MW
Power is reduced from rectifier side to promote stability, in the same
manner as as reduction of load to alleviate the effects of PV instability
Mvar

17. DC Link Control Reactive Power Control
VSC Offers Linear Reactive Power Control, independent of Real Power MW MW MW
Power is reduced from rectifier side to promote stability, in the same
manner as as reduction of load to alleviate the effects of PV instability
Mvar
Mvar

18. DC Link Control AC Voltage Control
VSC Offers Linear Reactive Power Control, independent of Real Power MW MW MW
Power is reduced from rectifier side to promote stability, in the same
manner as as reduction of load to alleviate the effects of PV instability kV kV

19. Embedded Applications of HVDC

20. Nelson River, Canada
Hydro electric power transmitted over 900km of OHL supplying half of Manitoba load
4000MW, ±500kV
Double Bipole with series bridges
BP1 originally commissioned with mercury arc
BP2 added in two stages 1978 & 1985 (by German HVDC Group)
BBC (now ABB)
AEG (now Alstom)
Siemens
BP1 re-valved with thyristors & uprated in 1993
BP3 coming soon
First HVDC link with:
AC system damping
4 - terminal operation
Hudson Bay
Lake Winnipeg
Limestone 1330 MW
Longspruce 980 MW
SASKATCHEWAN
Nelson River
MANITOBA
ONTARIO
Kettle 1272 MW
Winnipeg

21. Nelson River HVDC Effect of Damping Controls
Damping OFF Hz 64 62 60 58 10 20 30
0.2
0.1
-0.1
-0.2
t (sec) 10 20 30
Damping ON Hz 64 62 60 58
t (sec)
0.2
0.1
-0.1
-0.2
Kettle Generator Speed
Manitoba Equivalent Machine Frequency

22. Pacific Intertie / Intermountain
Intermountain Power Project (IPP)
Path 27 (Delta, UT – Adelanto, CA)
Pacific DC Intertie (PDCI)
Path 65 (Celilo, OR – Sylmar, CA)
2 Embedded HVDC
Pacific DC Intertie
3100 MW / 500 kV
Intermountain Power Project
2400 MW / 500 kV
Both run parallel with many AC lines
Swing Damping

23. Alberta, Canada Under Construction 2 Embedded HVDC Improve Power Flows
EATL
1000 MW /500 kV
WATL
Improve Power Flows
N-S
S-N
Under Construction
West Alberta Tie Line
(WATL)
East Alberta Tie Line
(EATL)

24. New Embedded HVDC In Europe
France-Spain
2 x 1000 MW U/G Cable
Improve power flows across border
Germany
Multiple Parallel N-S HVDC Corridors
Closing down Nuclear in South
Adding new Offshore Wind In North

25. New Embedded HVDC In Europe
Sweden
2 x 720 MW Cable / Line
Improve N-S Power Flows
Reduce Energy Price Differential
Phase 1
Phase 2

26. HVDC Cost Benefit Analysis
55 k$/MVAr
$/MVAr/h
$/MVAr/h + 6 $/MVAr/h
1.2 k$ per year and MW capacity
Ref: Cigre Publication : Report 492 – Table 4.11 (….. EUR to USD converted at 1.347)

27. Overlay grid - Supergrid
Renewables unevenly distributed
Wind in NW Europe
Solar in N Africa and S Europe
Hydro can be used for storage
HVDC bringing efficiency and stability
Efficiency over long distances
Oscillation damping
“Firewalls” to blackout
Right of way complicated
Cable underground/water vs. overhead lines
3000km
So back to the concept of the Supergrid.
In terms of offshore wind power and Mediterranean/north african solar power, HVDC connections will allow the connection of these renewable sources to be shared across country and continental boundaries.
This meshed DC and AC grid with multi-terminal interconnections known as a Supergrid is already underway in many areas of the world, notably Europe, India, Brazil, China and the Middle East.
Future is multi-terminal meshed DC and AC Grid

28. Supergrid / DC Grid
“DC Grids” – Multiple converters connecting AC power networks to a DC power network
DC circuit breaker, to interrupt DC fault current in 2 ms
DC – DC voltage converter, equivalent to an AC transformer
Fault protection system, detect and discriminate faulted sections
Control system, dispatch of power from multiple terminals
Existing AC grid
DC Grid

29. References & Further Reading
Cigre Report 492
“Voltage Source Converter (VSC) HVDC for Power Transmission – Economic Aspects and Comparison with other AC and DC Technologies”
European Supergrid Program – “Friends of the Supergrid”
“High Voltage Direct Current Transmission”
by J. Arrillaga, Publisher IET (UK) Power & Energy Series. ISBN