The rapid evolution of voltage Source Converters as applied to High Voltage DC power transmission Carl Barker

Transcription

1 The rapid evolution of voltage Source Converters as applied to High Voltage DC power transmission Carl Barker Chief Engineer HVDC Applications Tuesday 30 June 2015

2 HVDC Today Finding an increasing market demand Firewall Protects one AC system from the other Controllable Lower transmission cost Lower transmission losses Installed DC Power (GW) Presentation title - 06/07/2015 P 2

3 Basic HVDC Transmission Sending End Transformer Rectifier DC link R T Inverter Receiving End V1 V2 Idc I ac I dc I ac t t t Idc V1 V R T 2 Presentation title - 06/07/2015 P 3

4 HVDC Today Point-to-Point Links are dominant Brazil Gulf States Rio Madeira Bipole MW 2375 km Transmission GCCIA 1800 MW 50 Hz / 60 Hz Back-to-Back Presentation title - 06/07/2015 P 4

5 Why the predominance of Line Commutated Converter HVDC? Presentation title - 06/07/2015 P 5

6 LCC not VSC L d i A L S ~ A C 6 2 V d V d i B L S ~ B i C L S E 1 ~ C A I d In thyristor based converters the topology that provides economic AC-DC-AC conversion also suffers the risk of Commutation Failures B Presentation title - 06/07/2015 P 6

7 LCC not VSC Valve Current Maximum Stress Time ( elec) Typical Rating (125mm, 8.5kV thyristor) ~35kA peak Valve Voltage Typical Conduction angle = 330 Breaker opens here Typical Conditions at first positive peak of recovery voltage: Junction Temperature V ~ 5kV peak T j ~ 140 C Presentation title - 06/07/2015 P 7

8 LCC not VSC Voltage Withstand Normal Operation Commutation Failure Thyristor Capability Junction Temperature Presentation title - 06/07/2015 P 8

9 LCC not VSC L d I fault I fault C d i A i B i C L S L S L S E 1 A ~ B ~ C ~ i A i B i C L S L S L S E 1 A ~ B ~ C ~ I d Voltage source conversion not ideal considering thyristor technology I d Current source conversion universally adopted for HVDC transmission Presentation title - 06/07/2015 P 9

10 Evolution of HVDC Transmission Voltage 1200kV 1000kV Multiple 12-pulse bridges per pole Single 12-pulse bridge per pole First 1100kV project planned in kV 600kV Cahora -Bassa 533kV Itaipu 600kV Xiangshaba-Shanghai; Yunnan-Guangdong Ningdong-Shandong Rio-Madeira 400kV 200kV 500kV becomes de facto standard for single 12-pulse bridge per pole Presentation title - 06/07/2015 P 10

11 Early HVDC Transmission Mercury Arc Valves Italy-Sardinia HVDC MW, 200 kv Presentation title - 06/07/2015 P 11

12 Thyristor Development Series. H100 H200 H300 H400 Oil-insulated, oil-cooled. 4kV, 37mm thyristors, 3 in parallel. Air-insulated, air-cooled. 4.0kV 56mm thyristors, 2 in parallel. Air-insulated, water-cooled. 5.2kV, 100mm thyristors. Air-insulated, water-cooled. 8.5kV or 7.2kV 100mm, 125mm or 150mm thyristors Air-insulated, water-cooled. 8.5kV or 7.2kV 100mm, 125mm or 150mm thyristors. ~ 1970 ~ 1980 ~ 1988 ~ 2004 Presentation title - 06/07/2015 P 12 ~ 2015

13 HVDC Today Two product types in todays market Presentation title - 06/07/2015 P 13

14 Early VSC for HVDC Transmission Presentation title - 06/07/2015 P 14

15 VSC for HVDC Five-Level Floating Capacitor Converter Presentation title - 06/07/2015 P 15

16 Early VSC and its development 2 level converter (SPWM) Up to 60 MW ( ) 1st generation 3 level converter (3PWM and SPWM) 260 MW to 350 MW ( ) 2nd generation 2 level converter (OPMW) 350 MW and above (2004.) 3rd generation All IGBT valves Presentation title - 06/07/2015 P 16

17 SPWM, 3PWM and OPWM what s it mean? Basic Structure of VSC Pulse Width Modulation (PWM): ±Udc Uout Uac Uout Uac t Presentation title - 06/07/2015 P 17

18 Early VSC Stations Noting that: ±Udc Uout v= L d dt i Uac It can readily be seen that the inter-turn voltage stress on the phase reactor will be very high. This has necessitated the need for a special reactor design with a high-degree of shielding/inter-winding insulation. Presentation title - 06/07/2015 P 18

19 Early attempts at multi-level converters Presentation title - 06/07/2015 P 19

20 Early attempts at multi-level convertion Five-Level Floating Capacitor Converter V dc V dc 2 V dc 2 V dc V dc3 V dc2 V dc1 eout V dc Note: For the output voltage waveform shown: Vdc1=Vdc/2, Vdc2=Vdc, Vdc3=3Vdc/2 V dc Presentation title - 06/07/2015 P 20 e e e out out out e out V dc V V dc dc V V dc dc V V dc dc V 3 Vdc / 2 3 Vdc2 Vdc / 2 2 Vdc1 Vdc / 2 dc 1 Vdc / 2

21 The development of power rated semiconductors with turn-off capability Presentation title - 06/07/2015 P 21

22 The History of MMC Neptune's Staircase Two-Level The Anderton Boat Lift Built by Emmerson Murgatroy & Co. Ltd in 1875 to lift boats 50 feet from the River weaver to the Trent & Mersey Canal Presentation title - 06/07/2015 P 22 Built by Thomas Telford in 1822 to lift boats 64 feet between two levels of the Caledonian Canal.

23 Early MMC Converters Presentation title - 06/07/2015 P 23

24 Early MMC Converters Presentation title - 06/07/2015 P 24

25 What is a Modular Multi-Level Converter? Volts Volts Time Presentation title - 06/07/2015 P 25

26 STATCOM Principles A Chain with three Links V V V 3V 2V Output Voltage V 0 -V -2V -3V T Presentation title - 06/07/2015 P 26

27 Power system applications of multi-level converters The first practical device for power applications with turn-off capability was the: Gate Turn Off (GTO) Thyristors Presentation title - 06/07/2015 P 27

28 Power system applications of multi-level converters STATCOM TCR - TSC SVC V S V S X L ~ 0.2pu X L =1.0pu X c =1.0pu V S STATCOM TSC TCR T Presentation title - 06/07/2015 P pu I Leading 1.0pu I Lagging

29 One STATCOM Link Auxiliary Inverter GTO Gate Drive Units Overvoltage limiting dump capacitors GTO Anti-parallel Diode di/dt reactor T6732 Presentation title - 06/07/2015 P 29

30 Today s Modular Multi-Level Converter Presentation title - 06/07/2015 P 30

31 AC current path in a VSC converter + ve DC 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) Viewed from the AC side the + and DC busbars are star points for two parallel 3-phase circuits - ve DC Presentation title - 06/07/2015 P 31

32 AC and DC current paths in a VSC converter I DC 1 / 3 I DC 1 / 3 I DC 1 / 3 I DC 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) Presentation title - 06/07/2015 P 32 I DC

33 The MMC for HVDC Transmission Applications Presentation title - 06/07/2015 P 33

34 Modular Multi-level Converter Half Bridge T1 + T2 C Vm Vcapacitor T1 + Vm T2 C T1 + T2 conducting T1 conducting C T2 = Sub-Module Presentation title - 06/07/2015 P 34

35 Comparison of IGBT Technologies IGBT Module The device operation was proposed in the late 60 s but further work in the 70 s led to the first commercial product in Further developments led to an improved device (avoiding DC lock-up) in 1984 with a voltage rating of 1200V Advantage Available from many suppliers Many sizes and ratings available Relatively low cost Presentation title - 06/07/2015 P 35 Disadvantage Open-circuit failure mode Maximum rating available: 4.95MW (3.3kV, 1500A) Poor transient current rating of diode

36 The need for fast controls Five-Level Floating Capacitor Converter In todays high voltage multi-level converters we are effectively controlling many controllers in parallel, both their interactions with the AC and DC system and with each other. It s a bit like flying in formation! Presentation title - 06/07/2015 P 36

37 The need for better communications Fibre Optics Applications Sensors Early fibre was used in bundles for illumination and image transfer (cool-light, endoscopes, image-intensifiers). Fibre communication has been the major application for many years. Data rates and distances have increased following huge advances in the technology. But fibre sensors are set to dominate in the future. Communications Illumination and image transfer Presentation title - 06/07/2015 P 37

38 Fibres for data communication Step index fibre: Light is guided by total internal reflection. Different rays travel at different angles arrive different times. Suits low data rates and short distance with LED sources. Graded index fibre: Higher angle rays travel faster to arrive together. Higher data rates and longer distance, works with LED sources. Single mode fibre. Single wave front is guided by the core, not contained by it. Ideally matched to Surface Mount laser sources for long haul and high data rates. Presentation title - 06/07/2015 P 38

39 The first multi-level converter for HVDC transmission Five-Level Floating Capacitor Converter Presentation title - 06/07/2015 P 39

40 VSC Generation 1: Modular Multi-Level Converter (MMC) V Presentation title - 06/07/2015 P 40

41 The ALSTOM Modular Multi-Level Converter IGBT (x2) Capacitor +ve Test Connection Main Terminal 1 Capacitor Capacitor -ve Main Terminal Half Bridge Power Module Circuit HALF-BRIDGE POWER MODULE Bleed Resistor (x2) By-pass Switch Presentation title - 06/07/2015 P 41 Thyristor and Clamp Capacitor +ve Laminated Bus-Bar

42 VSC: Sweden - South West Phase 1 Power: 2 x 720MW monopole scheme Voltage DC: +/-300kVdc Voltage AC: 420kVac Client: Svenska Kraftnät Technology: VSC Distance Point to Point: 200km Ground Cable Phase 1: South West Link -4 x VSC Converter Stations -2 x 720MW links, +/- 300kV DC, OHL & Cables (by others) 3m Award in December 2011 to Alstom Grid Presentation title - 06/07/2015 P 42

43 Voltage (pu) Modelling and Testing Modular Multi-Level Converter operation has many discrete steps Development of a Modular Multi- Level Electro-Magnetic Transient Model of the Alstom Grid VSC (MaxSine), C D Barker, N M Kirby, W Liang, R S Whitehouse, Dr A Gole, U Gnanarathna, CIGRE Canada 2011, Halifax, Paper But then how do we test the controllers? -1 Electrical Degrees ( ) Presentation title - 06/07/2015 P 43

44 New testing Requirements Presentation title - 06/07/2015 P 44

45 Progress of HVDC VSC schemes Presentation title - 06/07/2015 P 45

46 Where are we going? Presentation title - 06/07/2015 P 46

47 Modular Multi-level Converter Half Bridge - DC Fault DC Pole to Pole Fault:- T1 + T2 Diode Conducts Fault current uncontrolled Fault current can only be stopped by a) AC breaker b) DC breaker C T2 Presentation title - 06/07/2015 P 47

48 LCC HVDC Recovery from a line-to-ground fault Overhead Transmission Line Fault Fault recovery Time Fault Reignition Recovery to 0.8pu Voltage Fault Clearing Time Fault recovery to pre-fault DC voltage Failed recovery to pre-fault voltage followed by recovery to 0.8pu DC voltage Presentation title - 06/07/2015 P 48

49 Modular Multi-level Converter Full Bridge T1 T2 + C T3 T4 Vm T1 + T3 OR T2 + T4 conducting +Vc T1 + T3 T1 + T3 T2 C T4 T2 C T4 -Vc Vm T1 + T3 T1 + T4 conducting C T2 + T3 conducting T2 T4 Presentation title - 06/07/2015 P 49

50 Modular Multi-level Converter T1 T2 + C Presentation title - 06/07/2015 P 50

51 HVDC: The Alternate Arm Converter Full-Bridge Series Valve Presentation title - 06/07/2015 P 51

52 We don t just have to use sinewaves! AC System VSC 3 rd harmonic voltages balance across delta windings. Hence, no voltage differential so no 3 rd harmonic current flow. Presentation title - 06/07/2015 P 52

53 We don t just have to use sinewaves! Valve voltage Line-to-line voltage Presentation title - 06/07/2015 P 53

54 Series Bridge Converter Half-Bridge Full-Bridge Series Valve Red, H-Bridge converts 80% of power Switching losses are minimised by, Yellow, half-bridge chainlinks providing zero voltage softswitching 6 th harmonic voltage cleaned by a few full-bridge, blue, chainlinks on H-bridge output Low footprint (over HB-MMC) as only one HB Chainlink valve across the DC rail Cost savings over HB-MMC Presentation title - 06/07/2015 P 54

55 Controlled Transition Bridge Half-Bridge Full-Bridge Series Valve Parallel converter style approach Allows switching losses to be managed by Chainlinks Reduces filtering requirements over LCC Maintains high current capability Chainlink capacitor small Complex control requirements Presentation title - 06/07/2015 P 55

56