Introduction to HVDC Transmission. High Voltage Direct Current (HVDC) Transmission

Transcription

1 Lecture 29 Introduction to HVDC Transmission Series Compensation 1 Fall 2003 High Voltage Direct Current (HVDC) Transmission Update to Edison s Vision AC Power Generation at Relatively Lower Voltage» Step Voltage Up to High Levels Convert From AC to DC and Back» DC Voltages Pole to Ground up to 800 kv» Currents up to about 3000A Most Systems Presently Point to Point Evolving Multiterminal Grids HVDC Transmission 2Spring

2 A Little History First Static Var Compensator (Germany, late 1930 s)» saturated reactors in combination with capacitors» Continued into the 1960 s (Dr. Erich Friedlander) First HVDC project: Berlin-Charlottenburg 1942 Moscow 1951 Gotland 1954 (first successful operating project) Pacific HVDC Intertie 1970 (one of last Mercury Arc Valve) Thyristor Controlled Reactors (TCR), GE, 1970 HVDC projects move to Thyrsistors in early 1970 s HVDC Transmission 3 Berlin Mercury Arc Valves 1942 HVDC Transmission 4 2

3 Gotland Mercury Arc Valve HVDC Transmission 5 LCC versus VSC HVDC The majority use line commutated converter (LCC) VSCs are have advantages in several applications» Independent control of real and reactive power injection» Provide dynamic voltage support to the ac system» Less harmonic filters requirement» Easier for multiterminal HVDC Also disadvantages» Losses» Lower Vdc and MW ratings (so far)» DC faults HVDC Transmission 3

4 HVDC Power Transmission No distance limitation for stability No distance limit for underground/sea cables Controlled power flow High power transfer, fewer lines,» Narrower ROW» Lower losses Potentially a firewall against cascading outages HVDC 7 Transmission Basic Concepts with HVDC Overhead Lines» Bulk Power Transfer Over Long Distances» Possibly Connecting Asynchronous Systems Underwater or Underground Cables» Distance Limits Underwater Cables» Longer Distances Where Overhead Lines Infeasible Back-to-back interconnections» Asynchronous systems same or different frequency HVDC Transmission 8Spring

5 Fast Control Available Control Power Flow on DC Link (point to point)» Control DC Voltage» Control DC Current Damp AC Power Systems Oscillations VSC HVDC Converters Can Directly Control AC Side Voltage or Reactive Power LCC HVDC converters can to an extent HVDC Transmission 9 LCC HVDC Transmission Common Applications Long-distance, bulk-power transmission Sea and land cable transmission Asynchronous interconnections Power flow control Congestion relief Ratings Power range up to 4000 MW at ± 500 kv Power range up to 4800 MW at ± 600 kv Voltage range increasing to ± 800 kv with Power range up to 6400 MW HVDC Transmission 10 5

6 Generator Outlet Transmission More power on fewer lines Improved stability Lower installed cost Reduced losses Double circuit (bipolar line) Reduced ROW One line vs. two HVDC Transmission 11 Interconnections Firm capacity Bypass congestion Avoid loop flow No limit due to parallel paths Interconnect diverse regions HVDC Transmission 12 6

7 Comparison of Transmission to Rail Transport of Coal 3000 MW power plant Coal haul distance 900 miles Fuel sub-bituminous coal 8500 BTU/lb Plant heat rate 8500 BTU/kWh, 85% load factor 3 unit trains per day (100, 100 ton cars/train) Annual hauling cost $560 M at $50 per ton $186 per kw-yr $25 per MWh 20 million gallons of diesel fuel per 500 net ton miles per gallon Subject to escalation, congestion Cannot deliver energy from renewable resources HVDC Transmission 13 HVDC Operating Configurations and Modes HVDC Transmission 14 7

8 Asynchronous Interconnections Economic Firm transactions Shared reserves Increase diversity Economy energy trade Asynchonous borders HVDC in North America Reliability Emergency power support Mutual assistance Isolate disturbances Fire-wall against cascading outages Reserve sharing HVDC Transmission 15 The HVDC Classic (LCC) Converter Station Converter station Transmission line or cable Converter Smoothing reactor AC bus DC filter Shunt capacitors or other reactive equipment AC filters Telecommunication ~~ Control system HVDC Transmission 16 8

9 The HVDC Classic Converter Station HVDC-CSC Converter Transformers DC Filters AC AC Filters DC Outdoor Indoor Thyristor Valves HVDC Transmission 17 The CCC* Converter Station *Capacitively-commutated converter station Transmission Line, Cable or Back-Back Converter Smoothing reactor AC bus Weaker Systems Back-to-Back MW Contune AC filters Commutation capacitors DC filter Telecommunication ~~ Control system HVDC Transmission 18 9

10 Modular Back-toBack CCC Asynchronous Tie HVDC Transmission 19 VSC HVDC Station Converter station Voltage Source(d) Converter - VSC Strong or Weak Systems Dynamic Voltage Control Underground Transmission Up to ±150kV, 550MW Up to ±300kV, 1100MW AC bus Phase Reactor Transmission Cable Dry DC Capacitor AC filters DC Capacitor Control system IGBT Valves HVDC Transmission 10

11 Topology Options Simplest three-phase VSC topology to build Consist of six IGBTs with six antiparallel diodes. Produce two voltage levels Use PWM switching technique to control dc voltage and ac phase voltage. Two-Level, Six-Pulse Bridge VSC HVDC Transmission Multilevel Converters Additional lgbts/diodes Plus clamp diodes Produce three voltage levels (or more) Use PWM switching technique Less harmonics amplitudes More efficient than a Two- Level Bridge VSC Less device stress More complex and expensive than a Two-Level Bridge VSC Three-Level, Neutral Point Clamped VSC HVDC Transmission 11

12 Modular Multilevel Converter Preferred VSC topology in new orders Consist of 100s of single phase VSC modules in series that switch in and out to control voltage magnitude and phase Half-Bridge Sub-Module Two Sub-Modules MMC HVDC Transmission What is LCC HVDC? Line commutated converter Bridge connected converter» Originally mercury arc valves, later thyristors» Inductive filter on dc side current stiff Reverse direction of power flow by reversing voltage polarity ur us ut IR IS IT pulse bridge Id Ud HVDC Transmission 12

13 HVDC Classic Control Id IR IS IT u ur us ut IR IS IT Ud HVDC Transmission 25 13