1. Devices used for Grid scale AC-DC and DC-AC power conversion
Charlie Hendrickson
EE 4611
4/19/17

2. Overview Where these devices would be used
Why High Voltage Direct Current (HVDC) transmission
Thyristors
Current Source Converters (CSC)
Insulated Gate Bipolar Transistors (IGBT)
Voltage Source Converters (VSC)
Summary
References
5 Key points

3. Where would these devices be used
HVDC transmission
Large amounts of energy over long distances
Lot of the optimal locations for renewables are long distances from load
Renewable energy
Solar Photo Voltaic – produces DC
Wind and Hydro variable output AC/DC – by inserting DC link able to sync with 60 Hz Grid

4. Why HVDC?
DC is more efficient than AC for transmitting large amounts of power over long distances
3,500 MW transmission line, 600 mi. long
Losses on AC line ~ 15%
Losses on DC line ~ 4.54%
Only 2 conductors vs. 9 (3 per phase)
Smaller towers require less right of way
Break even distances
600 km (373 mi.) for above ground lines
50 km (31 mi.) for submarine lines
Allows two unsynchronized AC grids to be connected

5. Thyristor “controlled diode”
Made up by four alternating P and N layers
Like a Diode a Thyristor only conducts current in one direction
The thyristor is turned on by a current signal on the gate
The thyristor continues to conduct as long as the voltage across the device is forward biased

6. Thyristor cont. 𝑃= 𝛼 𝜋 𝑆𝑖𝑛 𝜃 𝑑𝜃
The work horse of High Voltage Direct Current (HVDC) conversion on both rectification and Inversion side
Allows for easy control of power flow on DC transmission lines
𝑃= 𝛼 𝜋 𝑆𝑖𝑛 𝜃 𝑑𝜃

7. 5 kV ETT (Electronically Triggered Thyristor) 3.77 kA
151 mm in diameter
~ 6 inches
~ 6 lbs
~ $ 900
LTT (Light Triggered Thyristor)

8. Current Source Converter (CSC)
Used in HVDC from 1970’s – Present day
Replace the diodes in a bridge rectifier with thyristors
The thyristors are controlled by the AC line voltages
In order to transmit, need existing AC on both ends of line

9. Thyristor Valves Module Cooling Isolation
Contains 6-10 high power thyristors,
High power thyristors
1-10 kV
1-5 kA
Cooling
Constant circulation of deionized water
Isolation
Thyristors operating a high potential relative to ground the gate signal needs to be isolated

10. Thyristor Valves cont. Tray Valve Example 4 Modules connected
10-12 Trays connected in series
Example
We have a module with 6, 5 kV – 4 kA thyristors connected in series (30 kV – 4 kA)
Tray has 4 modules 2 in series with 2 in parallel (60 kV – 8 kA)
Valve has 10 trays ( 600 kV – 8 kA, 240 thyristors -> 4800 MW)

11. Insulated Gate Bipolar Transistor (IGBT)
Combination of N-channel MOSFET and PNP Transistor
MOSFET provides insulated gate and fast switching speeds
Up to 30 kHz
BJT provides the Voltage and Current capabilities

12. IGBT cont. IGBT Module Rated current of 1200 A
Maximum Voltage of 3.3 kV

13. Gate Turn Off Thyristor (GTO)
Fully controllable thyristor
Turn on is caused by positive current flow on gate
Turn on is not as reliable
Turn off is accomplished by a negative voltage applied between gate and cathode
Maximum switching frequency of 1 kHz

14. Voltage Source Converter (VSC)
Used in HVDC from 1997 – Present day
Voltage levels are slightly lower with VSC than CSC
Use IGBT’s or GTO’s in place of Thyristors
Self commutating
No need for existing AC on receiving end of line
Makes DC transmission utilizable for black start procedures

15. IGBT Valve Same principle as the thyristor valve
Several hundred IGBTs connected in series
Cooled by deionized water
Gate also needs to be isolated for same reason of being at high potential relative to ground

16. Summary
Thyristor is the work horse of grid scale AC-DC power conversion
Used in Current Source Converters
Insulated Gate Bipolar Transistors
Used for Voltage Source Converters
VSC allows DC to work without existing AC on receiving end
DC transmission allows two unsynchronized AC systems to be connected

17. References
Web:
engineers-sixteenth-edition/ch15lev1sec06
breakthrough/
Text
Mohan, N. (2007). First Course on Power Electronics. Minneapolis, MN: MNPERE
Neamen, D.A. (2012). Semiconductor Physics and Devices 4th ed. New York, NY: McGraw-Hill

18. Five Key Points
Thyristor can only be turned on, needs zero crossing of conducting current in order to be turned off
Thyristor allows control of power flow with firing angle alpha
IGBT combines MOSFET’s switching speed with BJT’s power capabilities
HVDC allows more efficient transmission of Large power over Long distances
VSC allows DC to be implemented into black start procedures