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

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

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

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 http://www.electricaleasy.com/2016/02/hvdc-vs-hvac.html

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 http://www.daenotes.com/electronics/industrial-electronics/thyristor-working-construction-operation-types

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 http://www.circuitstoday.com/scr-control-circuits 𝑃= 𝛼 𝜋 𝑆𝑖𝑛 𝜃 𝑑𝜃

5 kV ETT (Electronically Triggered Thyristor) 3.77 kA 151 mm in diameter ~ 6 inches ~ 6 lbs ~ $ 900 http://theelectrostore.com/DCR1675SZ50500806-Dynex-New.html LTT (Light Triggered Thyristor) www.sailing-tech.com/product/en/Fast-Switching-Thyristor.html

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 https://upload.wikimedia.org/wikipedia/commons/d/dd/6_pulse_bridge_with_inductance.png

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 http://www.industrial-electronics.com/elec_pwr_3e_22.html

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) http://www.industrial-electronics.com/elec_pwr_3e_22.html

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 http://www.electronics-tutorials.ws/power/insulated-gate-bipolar-transistor.html

IGBT cont. IGBT Module Rated current of 1200 A Maximum Voltage of 3.3 kV https://en.wikipedia.org/wiki/Insulated-gate_bipolar_transistor

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 https://en.wikipedia.org/wiki/Gate_turn-off_thyristor

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 https://en.wikipedia.org/wiki/HVDC_converter#/media/File:2_level_converter.png

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 http://www.industrial-electronics.com/elec_pwr_3e_22.html

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

References Web: https://www.accessengineeringlibrary.com/browse/standard-handbook-for-electrical- engineers-sixteenth-edition/ch15lev1sec06 http://www.electricaleasy.com/2016/02/hvdc-vs-hvac.html http://electrical-engineering-portal.com/advantages-of-hvdc-over-hvac-transmission http://www.electronics-tutorials.ws/power/insulated-gate-bipolar-transistor.html http://www.industrial-electronics.com/elec_pwr_3e_22.html http://news.nationalgeographic.com/news/energy/2012/12/121206-high-voltage-dc- breakthrough/ https://www.youtube.com/watch?v=J1qOv4w_FTs&feature=youtu.be https://en.wikipedia.org/wiki/HVDC_converter https://en.wikipedia.org/wiki/Thyristor#HVDC_electricity_transmission 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

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