Enrique Acha & Luis M Castro

Transcription

1 1 La Cátedra Endesa de la Universidad de Sevilla 21 de febrero de 2017 Aula 216 Escuela Técnica Superior de Ingeniería Universidad de Sevilla, Sevilla, España Enrique Acha & Luis M Castro

2 Content The early HVDC Links The advent of the new technology Modern HVDC systems Power converters modelling for network-wide studies Future applications

3 The Early HVDC Links

4 The Early HVDC Links A classical monopolar HVDC link comprises the rectifier and inverter stations L DC R DC L DC T r T 1 T 3 T 5 T 1 T 3 T 5 T i F F T 4 T 6 T 2 T 4 T 6 T 2 C F F C The operation of a six-pulse converter station produces the so-called characteristic harmonics: 5 th, 7 th, 11 th, 13 th, 17 th, 19 th, 23 th, 25 th on the AC currents The DC voltage modulation is achieved at the expense of consuming reactive power at both converter stations

5 Voltage and Current Waveforms in HVDC Transmission The DC voltages are non-flat even if the DC currents were to be a constant DC line, which are not Likewise, the AC currents are non-sinusoidal even if the AC voltages are sinusoidal, due to the process of rectification/inversion AC and DC voltages DC and AC currents J. Arrillaga HVDC Transmission, IEE monograph

6 HVDC Power Flows X c,r R r I DC R DC P i R i X c,i V f k V o,r V DC,r V DC,i V o,i V f m Assuming perfect filtering, the steady-state relationships between the variables is given by the following basic equations: V V R I DC, r DC, i DC DC 0 3 2, cos 3 VDC r TrVk X c, ridc 3 2, cos 3 VDC i TV i m X c, iidc P V I DC, r DC, r DC P V I DC, i DC, i DC P P R I 2 DC, r DC, i DC DC

7 Classical HVDC Transmission Schemes I DC P DC =V DC I DC P DC =-V DC I DC AC 1 AC 2 AC 1 + or - V DC AC 2 50 Hz 60 Hz Monopolar, (zero distance) back-to-back Monopolar, point-to-point + or - V DC AC 1 AC 2 - or + V DC For all its worth, classical HVDC has limited flexibility due to the inherent limitations of the thyristor valves Bipolar, multi-terminal, radial (SACOI scheme) Bipolar, point-to-point + or - V DC AC 1 AC 2 AC 3 - or + V DC Converter 1 Converter 2 Converter 3

8 The Advent of the New Technology: semiconductor valves and Converters

9 Anode (A) Diode Cathode (K) Semiconductor Valves Anode (A) Gate (G) Cathode (K) Thyristor Anode (A) Gate (G) Cathode (K) Gate Turn-Off (GTO) Thyristor Gate (G) Collector (C) Emitter (E) Insulated-Gate Bipolar Transistor (IGBT) Metal-Oxide Field Effect Transistor (MOSFET) MH Rashid

10 1. IGBT and PWM Technology Six-Pulse Bridge L s Six-Pulse Bridge C1 C3 + C5 T A+ T B+ T C+ C + V a V b V c V ca V ab V bc Phase control (PLO) C4 C6 C2 - Graetz bridge V a V b V c V ca V ab V bc PWM T A- D A+ D B+ D A- T B- D B- T C- D C+ D C- o C Two-level converter V DC - In practical power systems the switching frequency lies between 1 and 2 khz AC and DC voltages PWM control signals AC output voltages

11 Power Converters with IGBTs and PWM Control Three-phase The harmonic content of the output voltage waveform of the three-phase inverter made up of three half-bridges, is shown in the figures below, in normalized form k odd l is even f 1 with fh km l f 0m 1 k even l is odd a Notice that, V 3 m V mV LL,1 a DC a DC and for this particular case, VLL, p.u.

12 Three-Phase Multi-Level Inverter Each module switches once per cycle of the fundamental, at different times to form a step up waveform PU PU PU PU PU PU PU PU PU V A PU V B V DC V C PU PU PU PU PU PU PU PU PU Practically any number of Power Units can be added in series to achieve a rather sinusoidal waveform and output voltage

13 Flexible AC Transmission Systems and HVDC V k bus k bus m V m + V DC - I v m a E v bus k V k I vr E + vr V DC - V vr Shunt Series I ci m a,vr vr m a,cr V cr cr Unified control system E ci UPFC with IGBTs STATCOM (VSC and transformer) bus k E vr + V DC V k I vr m ar - m ai E vi I vi bus m V m V vr vr V vi vi Back-to-back VSC-HVDC link with IGBTs

14 VSC-HVDC Transmission Systems I DC I DC R DC AC 1 AC 2 AC 1 AC 2 Back-to-back HVDC link using IGBT valves, 350 MW and operating at ±150 kv R DC Point-to-point bipolar HVDC link using IGBT valves, 1400 MW operating at ±525 kv (NORDLINK) I DC AC 1 AC 2 VSC 1 VSC 3 Radial DC Grid AC 3 VSC 2

15 Multi-Terminal VSC-HVDC Systems AC 1 VSC 1 AC 3 AC 2 VSC 2 VSC 3 Common DC bus AC 1 VSC 1 AC 3 VSC 3 VSC 2 AC 2 Meshed DC Grid

16 Multi-Terminal VSC-HVDC System AC 2 AC 1 DS 1 DS 2 DS 3 DC ring AC 3

17 Multi-Terminal VSC-HVDC System AC 2 AC 1 DC DC DS 2 DS 3 DC ring DS 1 DC DC DC DC AC 3

18 Other DC Systems

19 Other DC Systems I dc PM Synchronous Generator D a+ D b+ D c+ a b D a- D b- D c- c Diode bridge rectifier + V dc - C C S a+ S b+ S c+ S a- a S b- b S c- Voltage Sourced Inverter c I a I b Z Z Z Load I c GB Doubly-fed Induction Generator UPFC + Series converter a b c V dc - a b c Shunt converter

20 Other DC Systems I dc + E B - R B + V B - Battery pack I B C 2 S D L C 1 Boost/buck converter + V dc - C C S a+ S a- VSI a S b+ S b- b S c+ S c- c I a I b Z Load Z Z I c I dc I d I p nr s + + I nv D nr P V d o - - PV panels I o L I L + V L - C S Boost converter + V dc - C C S a+ S a- a VSI S b+ S b- b S c+ S c- c I a I b Z Load Z Z I c

21 Power Converter Modelling for Network-wide Applications

22 Voltage Source Converter (VSC) Model + E DC C DC V 1 + I 0 0 1: ma V 0 I 2 I 2 I 2 V1 I 1 jx 1 R 1 V vr I vr - E DC - C DC G 0 jb eq m a V 0 I 2 VALVE SET Re( V 1 I * 1 ) 3 V m Vˆ 2 2 LL,1 a AN,1 V k m e E j 1 1 a DC V 0 G I 2 V 1 ( I * 1 I * ' 1 ) V 2 nom I 2 0 G act sw I 2 1 I * 1 jb eq V 2 1 I vr Y 1 k1ma cos jsin Y 1V vr 2 2 I 0 0 k1ma cos jsin Y 1 Gsw k1 ma ( Y 1 j Beq ) V0

23 Voltage Source Converter (VSC) Model S vr V vr 0 I vr S 0 E I 0 DC 0 ( evr j fvr ) 0 ( G1 j B1 ) klma cos jsin ( G1 j B1 ) ( evr j fvr ) E DC klma cos jsin ( G1 j B1 ) Gsw kl ma ( G1 j( B1 Beq )) EDC 2 2 PvR G1 ( evr fvr ) klmaedc evr G1 cos B1 sin fvr G1 sin B1 cos 2 2 QvR B1 ( evr fvr ) klmaedc evr G1 sin B1 cos fvr G1 cos B1 sin sw l a DC l a DC vr cos sin vr sin cos l a eq DC l a DC vr sin cos vr cos sin P G k m G E k m E e G B f G B Q0 k m B1 B E k m E e G1 B1 f G1 B1 E. Acha and B. Kazemtabrizi (2013), A New STATCOM Model for Power Flows Using the Newton- Raphson Method, IEEE Trans. on Power Systems, vol. 28, no. 3, pp

24 VSC Model with DC Cable Extension V 0I 1: km 1 a I 2 V1 I 1 jx 1 R 1 V vi I vi + I 2 I 2 V 0R G DC V 0I + E DC - V vi E DC - C DC G sw jb eq (b) m a (a) I 0R V 0R G DC V 0I I 0I (c)

25 Point-to-Point VSC-HVDC Model The nodal admittance matrix of the combined inverter VSC-cable system is: I G G 0 E 0R DC DC DCR 2 2 I 0I GDC GDC k1mai ( Y 1I j BeqI ) GswI k1mai I Y 1I EDCI I vi 0 k1mai I Y 1I Y 1I V vi where the nodal admittance of the cable is: I0R GDC GDC EDCR I G G E 0I DC DC DCI Adding the nodal admittance matrix of the rectifier VSC to the nodal expression of the VSC-cable system: I vr Y 1R k1mar R Y 1R 0 0 V vr 2 2 I0R k1marr Y 1R k1mar ( Y 1R j BeqR ) GswR GDC GDC 0 EDCR 2 2 I 0I 0 GDC GDC k1mai ( Y 1I j BeqI ) GswI k1mai I Y 1I E DCI I vi 0 0 k1m 1I 1I V vi ai I Y Y E. Acha, B. Kazemtabrizi and L.M. Castro (2013), A New VSC-HVDC Model for Power Flows Using the Newton-Raphson Method, IEEE Trans. on Power Systems, vol. 28, no. 3, pp

26 Three-Terminal VSC-HVDC System MG 1 G DC1 VSC 1 G DC2 MG 2 G DC3 VSC 2 MG 3 DC Grid VSC 3 I i1 Y t1 T1 Y t V i1 2 I v1 T1 Y t1 T1 Y t1 Y v1, v1 Y v1, V v1 I 01 0 Y v1,011 Y 01, GDC1 GDC GDC1 0 0 G E DC 2 DC,1 I i Y t2 T2 Y t V i2 2 I v T2 Y t 2 T2 Y t 2 Y v2, v2 Y v2, V v2 I Y v2,02 2 Y , GDC1 0 0 GDC1 GDC3 0 0 G DC3 EDC,2 I i Y t3 T3 Y t V i I 2 v T 3 3 3, 3 3,03 3Y t T3 Y t Y v v Y v V v3 3 I Y v3,03 3 Y03, GDC GDC3 0 0 GDC 2 G DC3 E DC,3

27 Multi-Terminal VSC-HVDC Steady-state frame-of-reference FVSC,R1 JRR ΔΦVSC,R1 JRDC F VSC,Rn 0 JRR n 0 0 ΔΦVSC,R n FVSC,I JII 1 0 ΔΦVSC,I 1 J IDC FVSC, m JI Im ΔΦVSC, Im FDC JDCR JDCI J DC ΔEDC ( r) ( r) FAC ( r) ΨAC FVSC,R ΦVSC,R J AC/DC FVSC,I ΦVSC,I FDC EDC F Ψ ( r) ( r) AC/DC AC/DC E. Acha and L.M. Castro (2016), A Generalized Frame of Reference for the Incorporation of multiterminal VSC-HVDC Systems in Power Flow Solutions, Electric Power Systems Research, vol. 136,, pp

28 Multi-Terminal VSC-HVDC Model DS 1 PEV charging station DS 2 VSC 1 P ba b P bc VSC 2 P ab P cb v1 a DC ring c v2 P af P cd v6 Micro-grid 2 P fa e VSC 5 v5 P fe P ef e P ed P de d VSC 3 P dc DFIG-based wind farm VSC LTC tap P loss (MW) Micro-grid 1 v4 VSC Convergence: ε= 10-6 takes 5 iterations and ε= takes 6 iterations Network V (p.u.) θ (deg) P inj (MW) Q inj (MVAr) DS DS MG MG WF E. Acha, T. Rubbrecht and L.M. Castro (2016), Power Flow Solutions of AC/DC Micro/Grid Structures, Power Systems Computation Conference DOI: /PSCC

29 VSC type E DC φ LTC tap m (p.u.) a (deg) P loss (MW) VSC Slack VSC Psch VSC Pass VSC Pass VSC Pass Convergence: ε= 10-6 takes 5 iterations and ε= takes 6 iterations DC cables P DC (MW) P loss send-rec rec-send (kw) a b b c c d d e e f f a

30 Multi-Terminal VSC-HVDC Dynamic frame-of-reference t+t ( rt, ) AC/DC ( rt, ) ( rt, ) ΔP ΔQ J AC J AC,SG J AC,VSC F FACTS Fω F δ JSG,AC JSG 0 Fdq F VSC,R F VSC,I JVSC,AC 0 J VSC FDC F J ( rt, ) AC/DC Δθ ΔV ΔX Δω Δδ ΔE Φ Φ E Ψ ' dq VSC,R VSC,I DC ( rt, ) AC/DC ( rt, ) L.M. Castro and E. Acha (2016), A Unified Modeling Approach of Multi-Terminal VSC-HVDC Links for Dynamic Simulations of Large-Scale Power Systems, IEEE Trans. on Power Systems, vol. PP, Issue 99, pp (DOI: /TPWRS )

31 Multi-Terminal VSC-HVDC Dynamic frame-of-reference 2000 MVA 230 kv, 50 Hz Source impedance V k OLTC 200 MVA 230:100 kv V vr Phase reactor AC filter 40 MVAr Rectifier L dc C dc R dc L dc C dc DC link Inverter Phase reactor AC filter 40 MVAr V vi OLTC 200 MVA 100:230 kv V m Source impedance 2000 MVA 230 kv, 50 Hz

32 e.g. 15 kv PMU Off-shore wind farm e.g km e.g. 400 kv dead load CSP plant CSP plant Multiterminal CSC-HVDC Link STATCOM PMU e.g. 132 kv SVC Mainland e.g. 100 km Multi-terminal VSC-HVDC grid Island PMU e.g. 400 km e.g. 60 km TCSC Off-shore wind farm

33

34 Future Applications

35 AGC Wind Farm Support O f f s h o r e Wind farm contributing to AGC support Manned Control Center Communication channels W i n d f a r m s deloaded generators Wind farm not contributing to AGC support Multi-terminal HVDC link On-shore AC network L.M. Castro and E. Acha (2016), Contribution of VSC-HVDCconnected Wind Farms to the Automatic Generation Control of Power Systems, IEEE Trans. on Power Systems, under review.

36 Multi-PV Infeed Systems Common DC bus Collector VSC AC Load

37 Conventional AC distribution system DC distribution system with DER DC

38 Conclusions The advent of new power semiconductor valves and PWM control have added unparalleled control flexibility to HVDC transmission The long-established concept of feasibility of an HVDC link, based on the notion of an extra-long distance transmission scheme may no longer apply The existence of truly multi-terminal HVDC systems, has become a technical reality, whether on-shore or off-shore The supply of oil platforms and resort islands with no generation, and the tapping of off-shore wind power is also possible DC rings may provide an effective solution for dealing with the very real issue of rising short-circuit levels in large center areas DC distribution is an area of active research by the Finnish distribution industry