with Fault Blocking Capability for OHL Applications

Transcription

1 VSC HVDC Converter Design with Fault Blocking Capability for OHL Applications N M MacLeod, C D Barker, R S Whitehouse, W Liang GRID

2 LCC vs VSC Comparison LCC HVDC Good overload capability Requires strong AC systems, SCR > 3 No black start capability Generates harmonic distortion, AC & DC harmonic filters required Weak reactive power control Large site area, dominated by harmonic filters Mature technology VSC HVDC Weak overload capability Operates into weak AC systems, SCR not critical Black start capability No harmonic generation, hence no filters required Good reactive power control Compact site area, 50 60% of LCC site area Emerging technology, MMC version

3 LCC vs VSC Comparison LCC HVDC Needs converter transformers,, built by specialist facilities Significant system interaction studies required Significant ifi application engineering i required Low station losses, 0.75% Lowest cost High power capability, up to 7200MW at ±800kV High reliability VSC HVDC Uses conventional transformers, built by any facility Minimal system interaction studies required Reduced d application engineering i required Higher station losses, 1.1% Higher cost by 10 15% Limited power capability, up to 1000MW at ±320kV Lower reliability, due to high power electronic component count

4 LCC vs VSC Comparison LCC HVDC Power is reversed by changing g polarity of the converters Requires use of MI cables Multi-terminal schemes are difficult to engineer DC grids are not considered possible Able to suppress DC side fault currents VSC HVDC Power is reversed by changing g direction of current flow Ideal for use with XLPE cables Multi-terminal schemes are easier to engineer DC grids become possible using stations from multiple vendors Not able to suppress DC side fault currents

5 VSC-HVDC 2 Level Converter Series-Connected IGBTs V V Conceptually simple circuit Requires Pulse Width Modulation (PWM) control -V -V -V High switching losses Harmonic filters are required to create an adequate waveform ½U dc U -½U dc

6 VSC Single Phase, 2-level Alternating Voltage Output Steady DC Voltage Input VSC Neutral

7 VSC-HVDC Modular Multi-level Converter Multi-level circuit V V Low switching losses Easily scaleable to high voltages Virtually no harmonics generated -V = chain link module -V More complex control algorithms ½U dc U -½U dc

8 VSC Multi-Level Converter Output Voltage Steady DC Voltage Input Multi-level VSC

9 Modular Multi-level Converter : Half-bridge (HB) T1 Module Output voltage T2 U V V -V -V Lowest component count Only one possibility of output voltage polarity

10 Modular Multi-level Converter : Half-bridge (HB) T1 Module Output voltage T2 U V V -V -V No capability of suppressing DC-side faults AC circuit breakers must be tripped

11 Modular Multi-level Converter : Full-bridge (FB) Module Output voltage U V V -V -V Same circuit as ALSTOM STATCOM chain circuit Output t DC voltage can be either polarity

12 DC fault current suppression Full-bridge (FB) Va Vb Vc Can suppress DC side faults No need to trip AC side circuit breakers

13 Half-bridge/Full-bridge IGBT mounting Half-bridge requires a protective thyristor Full bridge IGBTs

14 Assembled sub-module (HB or FB)

15 VSC Valve Hall

16 FB Converter Issues/Solutions Issues Higher station losses than FB topology % Higher capital cost due to additional IGBT devices Protective thyristor is not required Solutions Hybrid topology using FB and series connected IGBTs Lower semi-conductor losses Lower component costs

17 Series Hybrid Circuit Full chain links Series IGBT valve

18 Series Hybrid Circuit Integrated chain link Series Switch

19 Conclusions VSC HVDC provides additional functionality to operators compared with LCC technology To date most VSC schemes have been cable systems so the need to ride through DC faults is not a key issue Current generation of VSC converters can not suppress DC side faults The Full Bridge topology can suppress DC fault currents thus avoiding the need to trip AC circuit breakers, but with higher loss/cost Second generation VSC converters using hybrid topologies can overcome these limitations

20