CREATING NEW POSSIBILITIES Future DC Grid & Technology Dr. Junzheng Cao, Smart Grid Research Institute, SGCC October 2014
Table of Contents 1 Challenges 2 Chinese HVDC schemes & plan 3 Europe HVDC schemes & plan 4 America HVDC schemes & plan 5 Key HVDC technology 1
1. Sustained Demand for Energy Demand for Energy will increase by 44% from 2013 to 2040. By 2040, China will be the world's largest energy consumer, projected to consume more than twice as much energy as the United States. 2
2. CO 2 Emission Control Gigatonnes of CO 2 15 12 9 6 Rest of non-oecd China Rest of OECD United States 2009 Copenhagen Accord CO 2 emission reduction targets United States European Union 3 0 1990 2000 2010 2020 2030 CO 2 emission is growing faster than energy demand. By 2020, China s per GDP CO 2 emission to be 40%-45% less than in 2005 Japan Australia China India 3
3. Increased Use of Renewables Europe s total generation capacity by 2012 (*10 4 kw) 天然气 21213 26% 煤炭 23105 28% 非化石能源 37587 46% 光伏,2574 3% 其他,1305 2% 风能,8428 10% 水电,12542 15% 核能,12738 16% Europe s newly installed generation capacity in 2012 (*10 4 kw) 天然气 2828 51% 煤炭 406 7% 非化石能源 2304 43% 核能, 15 0.7% 光伏, 1241 22% 风能, 930 17% 其他, 95, 2% 水电, 23, 1% Photovoltaic and wind powers account for 22% and 17% of Europe s newly installed generation capacity in 2012. Hydropower and wind power respectively represent 18% and 15% of China s newly installed generation capacity in 2012. China s total generation capacity by 2012 (*10 4 kw) 火电 70663, 74% 非化石能源 25599 27% 光伏,70 0.1% 风能,3107 3.2% 水电,21340 22.2% 核能,1082 1.1% China s newly installed generation capacity in 2012 (*10 4 kw) 火电 5872 64% 非化石能源 3274 37% 光伏,40 1% 风能,1399 15% 水电,1661 18% 核能,174 2% 4
4. Demand for Efficient Energy Conv. 2/3 of the total power is lost due to lowefficiency energy conversions. Scotland s power system, (x1 billion kwh) Distribution losses are as high as 6%-15%. 5
Table of Contents 1 Challenges 2 China HVDC schemes & plan 3 Europe HVDC schemes & plan 4 America HVDC schemes & plan 5 Key HVDC technology 6
China Energy and Grid Development Plan Source: China Energy and Grid Development Plan, by Jianhua Bai 7
China s Supergrid Development Plan SGCC plans to construct 28 HVDC projects from 2010 to 2020, including 15 UHVDC schemes by 2015 (6 constructed by 2014). Total investment up to 250 billion CNY. 8
China West DC Grid Proposal DC transmission grid could be developed for the sending network in China west: To strength power transmission capability; To connect renewable energy; To minimize transmission corridor; To supply power to less populated areas. Source: Construction proposal for future electricity network in China west, by Xiaoxin Zhou 9
China s VSC-HVDC Project Project Shanghai- Nanhui Rated capacity DC voltage Commission time 18MW ±30kV 2011.7 Nanao 35MW ±160kV 2013.12 Zhoushan 1000MW ±200kV 2014.12 Xiamen 1000MW ±320kV 2015.12 10
Table of Contents 1 Challenges 2 China HVDC schemes & plan 3 Europe HVDC schemes & plan 4 America HVDC schemes & plan 5 Key HVDC technology 11
Europe s Supergrid Proposed in 2008 To promote the exploitation of renewable energy To facilitate power trade between countries To achieve 20/20/20 goal Connection of wind power in the North Sea and the Baltic Sea CO 2 emission down by 20% Power efficiency increased by 20% 20 20 20 Renewable energy accounts for 20% of total power consumption Connection of abundant solar energy in the Mediterranean 12
UK Offshore Wind Project Plan Region Rated capacity Scottish England Wales 11,410MW 30,940MW 6,199MW Total 29 offshore wind projects planned by UK for period to 2025. Total capacity up to 48,549MW. 13
Norway UK Connection HVDC Grid First stage Point-to-point transmission, multi-terminal enabled Second stage Multi-terminal formed with partially application of disconnectors Third stage Connection of multi-terminals of same voltage levels using DC Breakers Fourth stage DC Grid formed by connecting different multi-terminals using DC breakers and DC/DC-converters 14
German Offshore Wind Farm Project Plan Germany plans to construct 15 Offshore wind schemes in the next ten year or so. Total capacity up to 17,909MW. Project status Project in operation Project under construction Project for tender Project quantity Total capacity 3 568MW 8 12,107MW 5 10,800MW 15
German National Grid Expansion Plan Optimization of existing routes: 4,400km AC circuit enhancements on existing routes: 1,300km Construction of new AC circuits in existing routes: 2,800km Construction of new DC circuits in existing routes: 300km Grid expansion in new routes: 3,800km New AC route construction: 1,700km New DC corridor construction: 4 corridors for 10GW and 2,100km 16
Table of Contents 1 Challenges 2 China HVDC schemes & plan 3 Europe HVDC schemes & plan 4 America HVDC schemes & plan 5 Key HVDC technology 17
USA Grid Plan Low reliability, Aged technology, Low renewable power usage Existing grid issues Plan Invest up to $120 billion in HVDC by 2020 Renewable energy up by 80% by 2035 Goal Washington Oregon California Canada British Columbia Nevada Idaho Utah Arizona Montana Wyoming Colorado New Mexico North Dakota South Dakota Nebraska Kansas Minnesota Missouri Virginia Canada Québec North Tennessee Carolina Oklahoma Arkansas South Carolina Mississippi Georgia Louisiana Alabama Texas Maine Wisconsin New York Michigan Iowa Pennsylvania Massach Ohio usetts Illinois Indiana Delaware Florida USA Renewable Energy Planning Atlantic wind connection(awc) 18
USA Grid Plan Project Power (MW) Voltage (kv) Distance (km) TransWest Express 3000 600 1167 Chinook and Zephyr Lines 3000 500 1610 Overland Transmission Project 2000-3000 Plains & Eastern Clean Line transmission project 3500 Centennial West Clean Line 3500 1450 GBX 3500 600 Rock Island Clean Line 3500 805 Atlantic Wind Connection 7000 320 483 Champlain Hudson Power Express 1000 320 536 Northeast Energy Link (NEL) 1100 354 Green Line (ME MA) 800 West Coast Cable 1600 900 Juan de Fuca 550 (CNC) 500 1610 Northern Pass 1200 USA plan to construct 6 HVDC schemes in the west and 9 in the middle-east regions by 2035, total power capacity up to 35GW. 19
Table of Contents 1 Challenges 2 China HVDC schemes & plan 3 Europe HVDC schemes & plan 4 America HVDC schemes & plan 5 Key HVDC technology 20
DC Grid Key Technology Control technology Control strategy for coordinated operations of DC grid and AC grid Coordinated flow control and voltage control in a DC Grid with increased DC nodes and less inertia (DC Grid contains fewer inertial elements, and therefore calls for a faster responded control system) Pm AC Turbine Generator Te P 1 P 2 Pe DC + U DC Tm - U dc Pm>Pe, system frequency rises; Pm<Pe, system frequency drops. U dc U dc U dc P1>P2, DC voltage rises; P1<P2, DC voltage drops. U dc U dc 逆变 整流 I dc I min 0 I max 逆变 U dcmax U ref U dcmin 整流 I dc I min 0 I ref I max 逆变 I ref Voltage margin control U dcmax U ref 整流 U dcmin I dc I min 0 I max 逆变 整流 U ref1 I I min 0 I dc ref I max 逆变 U ref2 整流 I I min I dc ref 0 I max 逆变 Voltage drop control Uref3 整流 I I min I dc ref 0 I max 21
DC Grid Key Technology Protection technology Protection action AC t<5ms DC Terminal 1 DC Terminal 2 AC DC Grid fault features high di/dt, high current amplitude, requiring rapid protection (ms~μs). DC Grid protection deployment depends on gird scale, converter topology and circuit breaker configuration, and can be implemented in a diverse manner. AC DC Terminal 4 DC Terminal 3 AC Converter station 1 DC Busbar 1 DC circuit DC busbar 2 breaker AC Selective protection Converter station 2 AC Converter station n AC DC cable 1 DC cable 2 DC cable n DC system fault current The small cable impedance can cause big measurement errors, thus excluding the traditional distance protection. 22
DC Grid Key Technology Wide area measurement and fault detection Wide area measurement methods are required for DC grid equipment, like converters, DC circuit breakers, etc. Fast C&P actions for future DC grids require improved fault detection technologies. GPS 23
DC Grid Key Technology DC Grid Standardization Standardizations of DC grid power, voltage, short circuit capacity, power control, communications, corridors, etc. Standardizations of key equipment such as interruption time and current for DC circuit breakers, ratios for DC/DC converter, and configurations for converter valves, etc. AC AC AC DC AC 500kV, 220kV, 110kV ±800kV, ±660kV ±600kV, ±320kV ±200kV, ±125kV AC 24
DC Grid Key Technology UHVDC LCC converter Particular useful for long distance HVDC transmission; Converter valve with voltage up to 1100kV and current up to 6250A available; ±800kV UHVDC schemes already in operations in China and India; The first Brazil ±800kV project awarded to SGCC, China in 2014; World s first ±1100kV UHVDC scheme planned by SGCC, China for 2015. 25
DC Grid Key Technology Novel voltage-sourced converter topology Available technologies include: half-bridge and full-bridge MMC, Cascade MMC, PWM; Solution providers include: ABB, Siemens, Alstom and ; Maximum rating: 500kV/2000MW. 相单元 MMC 阀 + SM1 SM1 SM1 T1 iq1 SM2 SM2 SM2 uq1 C0 T2 SMn SMn SMn L L L Ud T 1 T 3 L L L T 2 C 0 T 4 SM1 SM2 SM1 SM2 iq2 SM1 SM2 uq2 SMn SMn SMn Modular multi-level converter 26
Comparison between LCC & VSC Device: Half-controlled thyristor Control of active power only Large compensators and filters are requirement Inter-station communications required Power reversal requires change of DC polarity High demands for DC cables Suitable for bulk power transmission over long distance or undersea, asynchronous interconnection of AC grids. Device: Fully-controlled IGBT Control of both active and reactive power No need for large filters and compensators No need for station communication Power reversal doesn t involve change of DC polarity Less demands for DC cables Suitable for large-scale intermittent power source integration, island in-feed, city in-feed, multi-terminal systems and DC grids. 27
DC Grid Key Technology DC Breaker Interruption of none zero-crossing DC current; Absorption of MJ levels of discharge energy from DC grids; Prevention of fault spreading; Reclosing capability. s IGBT1 IGBT2 s IGBT1 ZnO IGBT2 ZnO C ZnO L Rated voltage Rate current Max. interrupting current Interrupting time ABB 320kV 2.6kA 16kA 2ms ALSTOM 200kV 1.5kA 7.5kA <1.6ms 200kV 1.2kA 10kA 3-5ms 28
DC Grid Key Technology DC/DC Transformer Flexible transform ratio; Applicable for different DC voltage levels; Compatible with different converter technologies; Bi-directional power flow; Low losses, low cost, compact size; High fault current withstand capability. Highfrequency transformer Based on high-frequency transformer No large power DC/DC converter commercially available yet. Present work mainly focuses on topology, simulation, and prototype development. Two DC/DC prototypes were developed by ABB using thyristor and IGBT technologies, maximum ratings being 4/80kV-5MW and 2/40kV-3MW. C-PER s 3MW, 10kV/20kV DC/DC converter to be delivered in 2015. 29
DC Grid Key Technology High-voltage DC cable technology The highest voltage rating commercially applied is ±320kV; Cable prototype of 525kV/2000A rating available in 2014; In the next 10 years, DC cable ratings are expected to reach up to 750kV/3000MW; The emerging DC Grid market keeps driving the development of DC cable technology. Oil-filled cable MI cable XLPE cable 30
DC Grid Key Technology Issues related to offshore wind farm development Platform corrosion and installation Cooling of power equipment using sea water Lifetime impact due to salt, wind, waves and seabed movement Structure capability to survive a hurricanes. 31
Conclusion & Prospects UHVDC will remain an effective means for long distance bulk power transfer. However, for regional renewable energy integrations, VSC- HVDC may serve as a necessary supplement. The next decade will see a speedy construction of China s Supergrid. A Strong-AC & Strong-DC interconnections will become China s basic electricity network structure. With the technical improvement of turn-off devices and DC cables, VSC- HVDC will play a leading role in near future. VSC-HVDC with more than 500kV DC voltage could be expected shortly. 32
Deliver Green Power Shape Future Grid Thank you very much for your attention. Email: caojunzheng@sgri.sgcc.com.cn