MICROGRIDS Large Scale Integration of Micro-Generation to Low Voltage Grids Nikos Hatziargyriou, nh@power.ece.ntua.gr National Technical University of Athens Interconnection of small, modular generation to low voltage distribution systems can form a new type of power system, the MicroGrid. MicroGrids can be operated connected to the main power network or islanded, similar to power systems of physical islands, in a controlled, coordinated way. What are MICROGRIDS?
Technical, economic and environmental benefits Energy efficiency Minimisation of the overall energy consumption Improved environmental impact Improvement of energy system reliability and resilience Network benefits Cost efficient electricity infrastructure replacement strategies Cost benefit assessment Technical Challenges for Microgrids Relatively large imbalances between load and generation to be managed (significant load participation required, need for new technologies, review of the boundaries of microgrids) Specific network characteristics (strong interaction between active and reactive power, control and market implications) Small size (challenging management) Use of different generation technologies (prime movers) Presence of power electronic interfaces Protection and Safety
Market and Regulatory Challenges Coordinated but decentralised energy trading and management Market mechanisms to ensure efficient, fair and secure supply and demand balancing Development of open and closed loop price-based energy and ancillary services arrangements for congestion management Secure and open access to the network and efficient allocation of network costs Alternative ownership structures, energy service providers New roles and responsibilities of supply company, distribution company, and consumer/customer MICROGRIDS Project Large Scale Integration of Micro-Generation to Low Voltage Grids Contract : ENK5-CT-2002-00610 GREAT BRITAIN UMIST URENCO PORTUGAL EDP INESC SPAIN LABEIN 14 PARTNERS, 7 COUNTRIES UMIST URENCO ARMINES EDF ISET SMA GREECE GERMANOS ICCS/NTUA PPC /NAMD&RESD GERMANY SMA ISET NETHERLANDS EMforce USA EPRI INESC EDP LABEIN CENERG ICCS / NTUA GERMANOS PPC/NAMD&RESD FRANCE EDF Ecole des Mines de Paris/ARMINES CENERG EPRI http://microgrids.power.ece.ntua.gr
The Microgrids Project R&D Objectives: Contribute to increase the share of renewables and to reduce GHG emissions; Study the operation of Microgrids in normal and islanding conditions; Optimize the operation of local generation sources; Develop and demonstrate control strategies to ensure efficient, reliable and economic operation; Simulate and demonstrate a Microgrid in lab conditions; Define protection and grounding schemes; Define communication infrastructure and protocols; Identify legal, administrative and regulatory barriers and propose measures to eliminate them; Microgrids Highlights Islanding and interconnected operation philosophy Control philosophies (hierarchical vs. distributed) Energy management within and outside of the distributed power system Device and interface response and intelligence requirements Steady State and Dynamic Analysis Black Start capabilities Economics of Operation Permissible expenditure and quantification of reliability benefits
Microgrids Hierarchical Control Microgrid Central Controller (MGCC) promotes technical and economical operation, provides set points to LC and MC; Interface with loads and micro sources and DMS; MC and LC Controllers: interfaces to control interruptible loads and micro sources (active and reactive generation PV Flywheel levels). MC AC DC AC LC DC MC LC MC AC DC LC Storage DMS MV LV MGCC MC CHP MC AC DC Fuel Cell MC AC DC LC Micro Turbine Interconnected vs. Islanded Operation Normal Interconnected Mode : Connection with the main MV grid; Supply, at least partially, the loads or injecting in the MV grid; MGCC: Interfaces with MC, LC and DMS; Perform studies (forecasting, economic scheduling, DSM functions, ); - Island Mode : In case of failure of the MV grid; MGCC: Changes the output control of generators from a dispatch power mode to a frequency mode; Primary control MC and LC; Improved Eventually, triggers a black start function. reliability and resilience
Parallel operation of inverters Inverters are controlled by droops (MC): f u f 0 u 0 f -1% u -4% -1 0 1 Frequency droop P P N -1 0 1 Q Q N Voltage droop Approach: Set-values for droops of the MC are calculated (by enhanced SunnyIsland API) of set-values for P and Q provided by the MGCC. This way convenient EMS is enabled but in case of islanded operation primary control is still operable. Indirect operation of droops in case of resitive coupling (LV-case) - Applied droop concept is based on inductive coupled voltage sources. - In a LV-grid components are coupled resistive, thus voltage determines the active power distribution - There are two effects of droops - direct (inductive coupling) - indirect (resistive coupling) f f 0 f +1% u u 0 u +4% - The indirect effect requires droops, which have the same sign for the frequency as well as the voltage droop and therefore the stable operation point is in phase. 0-1 0 1Q -1 1P PN QN
Electronic switch: possible faults 400 420 440 460 480 500 520 540 560 580 600 300 v MicroGrid [v] 0-300 I MicroGrid [A] 100 80 60 40 20 0-20 -40-60 -80-100 1000 800 600 400 200 grid connected island I Grid [A] 0-200 -400-600 -800-1000 400 420 440 460 480 500 520 540 560 580 600 time [ms] LV network with multiple feeders 20 kv Off-load TC 19-21 kv in 5 steps 0.4 kv 3+N 20/0.4 kv, 50 Hz, 400 kva 3 Ω u k 4%, r k 1%, Dyn11 Single residencial consumer 3Φ, I s 40 A S max 15 kva S 0 5.7 kva Residential load 3x250 A 3+N Overhead line 4x120 mm 2 Al XLPE twisted cable Pole-to-pole distance 35 m Twisted Cable 3x70mm2 Al XLPE + 54.6mm 2 AAAC Possible neutral bridge to adjacent LV network 2 Ω 3x160 A Underground line 3x150 mm 2 Al + 3x160 A 50 mm 2 Cu XLPE cable 4x35 mm2 Al 3+N conductors 3Φ, I s 40 A S max 20 kva S 0 11 kva 1Φ, I s 40 A 4x1Φ, I s 40 A 200 m Phase: a Phase: abcc S max 8 kva S max 25 kva S 0 4.4 kva S 0 13.8 kva Overhead line 4x50,35,16 mm 2 Al conductors Pole-to-pole distance 30 m 3+N 3Φ, I s 63 A S max 30 kva S 0 16.5 kva 4x16 mm2 Al conductors 4x50 mm2 Al conductors Group of 4 residences 4 x 3Φ, I s 40 A S max 55 kva S 0 25 kva Appartment building 1 x 3Φ, I s 40 A 6 x 1Φ, I s 40 A S First max 47 kva S 0 25 International kva Conference on Integration of RES and DER, Brussels, 1-3 December 2004 Appartment building 5 x 3Φ, I s 40 A 8 x 1Φ, I s 40 A S max 72 kva S 0 57 kva Single residencial consumer 3Φ, I s 40 A S max 15 kva S 0 5.7 kva Industrial load 50 Ω Workshop 3Φ, I s 160 A S max 70 kva S 0 70 kva Commercial load 4x1Φ, I s 40 A Phase: abbc S max 25 kva S 0 13.8 kva 2x1Φ, I s 40 A Phase: ab S max 16 kva S 0 8.8 kva 3x1Φ, I s 40 A Phase: abc S max 20 kva S 0 11 kva 1Φ, I s 40 A Phase: c S max 8 kva S 0 4.4 kva 4x35 mm2 Al conductors
20 kv Off-load TC 19-21 kv in 5 steps 0.4 kv 3+N 20/0.4 kv, 50 Hz, 400 kva u k 4%, r k 1%, Dyn11 3 Ω Study Case LV Feeder with DG sources Flywheel storage Rating to be determined Single residencial consumer 3Φ, I s 40 A S max 15 kva S 0 5.7 kva 10 Ω 3+N+PE First International Conference on Integration of RES and 30 Ω DER, Brussels, 1-3 December 2004 3+N+PE 3+N+PE Group of 4 residences 4 x 3Φ, I s 40 A S max 50 kva S 0 23 kva 3+N+PE Wind Turbine 3Φ, 15 kw Photovoltaics 1Φ, 4x2.5 kw Appartment building 3+N+PE 1 x 3Φ, I s 40 A 6 x 1Φ, I s 40 A S max 47 kva S 0 25 kva 1+N+PE Fuel Cell 3Φ, 30 kw Circuit Breaker Possible sectionalizing CB Circuit Breaker instead of fuses 10 Ω 30 Ω 4x6 mm 2 Cu 20 m 4x16 mm 2 Cu 30 m 4x25 mm 2 Cu 20 m 4x16 mm 2 Cu 30 m 3+N Overhead line 4x120 mm 2 Al XLPE twisted cable Pole-to-pole distance 35 m 3x70mm2 Al XLPE + 54.6mm 2 AAAC Twisted Cable 4x6 mm 2 Cu 20 m Possible neutral bridge to adjacent LV network 30 m Appartment building 2 Ω Other lines 3x50 mm 2 Al +35mm 2 Cu XLPE 5 x 3Φ, I s 40 A 8 x 1Φ, I s 40 A S max 72 kva S 0 57 kva Single residencial 3+N+PE consumer 3Φ, I s 40 A S max 15 kva S 0 5.7 kva Microturbine 3Φ, 30 kw Photovoltaics 1Φ, 3 kw Main Characteristics of Simulation Tool to deal with LV Phasor approach for network and sources to increase simulation efficiency. Natural phase quantities (a-b-c). Lines with any X/R ratio can be handled. Radial and non-radial network topologies. Allbasic neutral earthing schemes represented (TN, TT, IT). Unbalanced conditions (network, sources, loads) modelled and simulated.
Study Case E Two battery invs + two PVs + one WT - Isolation + wind fluctuations P inverter A,B Frequency Q inverter A,B Study Case E Two battery invs + two PVs + one WT - Isolation + wind fluctuations V per phase - Node C P,Q of PV inverter D P,Q per phase Node E
Sequence of Actions During Microgrids Black-start Local black-start of the microgrid after a general system blackout Disconnect all loads and create small islands inside the microgrid Start energizing the LV cables and the distribution transformer (at what moment?) Synchronize the other microsources with the LV network Verification of the synchronization conditions Connect controllable loads taking into account the available storage capability Connect non-controllable generators (PV, WTs) Connect as much load as possible taking into account local production capability Synchronize with MV grid Blackstart: Building LV Network Frequency and active power in each VSI Own loads connection Microturbine synchronization Load connection
Economic Operation Policy 1-1 Microgrid serving its own needs MGCC tries to minimise the energy cost for the Microgrid knowing : Prices of the open market for Active and Reactive power Forecasted demand and renewable power production Bids of the Microgrid producers. Technical constraints Policy 2 Economic Operation Policy 2-Buying Buying and selling via an Aggregator The MGCC tries to maximise the value of the micro-sources based on : The market prices for buying and selling energy to the grid (Same prices for end-users of the Microgrid) Demand and renewable production forecasting Bids of micro-sources The technical constraints for the interconnection line and the micro-sources
Study Case of Microgrid Operation All three feeders taken into account Typical demand pattern and actual renewable power production time-series Amsterdam Power Exchange Prices. Bids from micro sources reflecting their production and installation cost Installation cost for RES Wind 2500 Euro/kW Depreciation time 10 years PV 7000 Euro/kW Depreciation time 20 years Highlight: MGCC Simulation Tool
Residential Feeder with DGs Policy1 Cost Reduction : 12.29 % Policy 2 Cost reduction : 18.66% Greater cost reduction when selling to the Grid kw 90 80 70 60 50 40 30 20 10 0-10 -20-30 Load & Power exchange with the grid (res idential feeder) 1 2 3 4 5 6 7 8 9 101112131415161718192021222324 Hour Power exchanged with the grid Load Pattern Steady state security increases cost by 27% and 29% respectively. Environmental Benefits Average values for emissions of the main grid Data about emissions of the micro-sources sources. 27% reduction in CO 2 emissions due to policy1 Maximum reduction in CO 2 emissions 548kgr/day- 22.11% higher cost
MICROGRIDS Highlight 3: Reliability Assessment of LV Network System Maximum Load Demand: 188 kw Capacity of System Infeed: 210 kw (100%) Installed Capacity of Wind Generation: 15 kw Installed Capacity of PVs: 4*2,5+1*3 13 kw Installed Capacity of Fuel Cells: 30 kw Installed Capacity of Microturbines: 30 kw Reliability Assessment FLOL (ev/yr) LOLE (hrs/yr) LOEE (kwh/yr) Infeed Capacity 100% (no microsources) 2,130 23,93 2279,03 Infeed Capacity 80% (no microsources) 58,14 124,91 3101,52 Infeed Capacity 80% (with Wind + PV) 14,02 41,67 2039,41 Infeed Capacity 80% (all microsources) 2,28 15,70 716,36
Highlight - Permissible expenditure to enable islanding Customer Sector: Residential Commercial Annual benefit 1.4 /kw pk 15 /kw pk Net present value 15 /kw pk 160 /kw pk Peak demand 2 kw 1000 kw Perm. expenditure 30 160,000 MicroGrid (2,000kW) 30,000 320,000 Implementation of the flywheel energy storage system by UM Flywheel Inverter interface
ISET scaled micro grids Schematic of DeMoTec Laboratory installation at NTUA 600 500 P load 400 P (W) 300 200 100 0-100 P bat P pv P grid 50.15-200 0 100 200 300 400 500 Time (s ) 230 50.1 228 U mg f (Hz ) 50.05 50 f grid f mg U (V) 226 224 U grid 49.95 222 49.9 0 100 200 300 400 500 220 0 100 200 300 400 500 Time (s ) First International Conference Time (s ) on Integration of RES and DER, Brussels, 1-3 December 2004
The Kythnos Microgrid Pilot plant on Kythnos (before June 2003) PV-Generator PV-Generator AC-Grid: 3 400 V Battery PV Diesel Battery PV MORE PV-Generator PV-Mode AC Grid: 3 400 V Supply of 11 buildings (EC projects MORE and PV-Mode)
The Kythnos Microgrid The Kythnos Microgrid
The Kythnos Microgrid The Kythnos Microgrid
The Kythnos Microgrid The Kythnos Microgrid
Conclusions Further Work Microgrids: A new paradigm for future power systems We have shown distinct advantages regarding efficiency, reliability, network support, environment, economics Further needs Field trials to test control strategies on actual Μicrogrids Need for quantification of Microgrids effects on Power sysetm operation and planning Need for cooperation and learning from alternative, complementary approaches, under development in US, Canada and Japan http://microgrids.power.ece.ntua.gr