SEVILLA, APRIL 2010 Campus da FEUP Rua Dr. Roberto Frias, 378 4200-465 Porto Portugal T +351 222 094 000 F +351 222 094 050 cmoreira@inescporto.pt www.inescporto.pt Microgeneration and Microgrids (modeling, islanding operation, black start, multi-microgrids) J. Peças Lopes Power Systems Unit 2010
MicroGrid: A Flexible Cell of the Electric Power System MG Hierarchical Control: PV MC MGCC, LC, MC Communication infrastructure MC LC Microturbine LC Wind Gen MC LC LC MGCC MC Storage Device LC MC Fuel Cell 2010 2
The MicroGrid Concept A Low Voltage distribution system with small modular generation units providing power and heat to local loads A local communication infrastructure A hierarchical management and control system MV MGCC LV MC AC DC PV DC AC MC Storage MC LC LC MC MC LC MC LC MC AC DC Microturbine AC DC DC AC Wind Generator Fuel Cell PV Operation Modes: Interconnected Mode Emergency Mode AC DC LC Microturbine 2010 3
Microgeneration technologies: Micro-wind turbines 2010 4
Microgeneration technologies: Micro-wind turbines 2010 5
Micro-wind turbines Vertical axis micro-wind turbines 2010 6
Microgeneration - Solar Photovoltaic (PV) I 1/R opt I SC I max M N A P 1/R O V max S V OC V 2010 7
Microgeneration technologies: BIPV Other solutions: surfaces coating (Glasses, Roofs, etc.) with thin films. 2010 8
Microgeneration - Microturbines Microturbine of 80 kw In general the microturbine is connected to the grid through an electronic converter. 1,5 khz to 4kHz (single shaft) 2010 9
Micro CHP (Stirling engines) Packaged as a domestic boiler for mass market 2010 10
Fuel-Cells Different Types (PEM, SOFC, Alkaline, PAC ) 2010 11
Energy storage - flywheels Key element for the operation of a microgrid 2010 12
MicroGrids Modes of Operation MicroGrids can operate: Normal Interconnected Mode : Connection with the main MV grid; Supply, at least partially, the loads or injecting in the MV grid; Emergency Mode : In case of failure of the MV grid; Possible operation in an isolated mode as in physical islands: Moving to island mode; Load following; In this case, the MGCC: Requires dynamic behavior analysis Changes the output control of generators from a dispatch power mode to a frequency mode; Primary control MC and LC; Secondary control MGCC; Eventually, triggers a black start function. 2010 13
Emergency operation requires specific studies Development of models for microgenerators: Inverters Microturbines (single shaft and split-shaft); Fuel cells (SOFC); PV arrays; Wind generators; Flywheels; Frequency and voltage controls. Controllable loads Identification of possible control strategies (load shedding included) 2010 14
DevelopmentofModelsofMicrosources(MT) Turbine modeling w r D tur P in LV gate V max 1 1? Ts 1 1 1? Ts 2 + - P m V min + KT + + - 1 1? Ts 3 L max 2010 15
DevelopmentofModelsofMicrosources(FC-SOFC) Nerst equation plus the Ohm law r 2 2 V N E r I fc 12 RT ph p O 0 0 ln 2 F p HO 2 r fc P ref + - P dem in V fc Limit U max 2K r in I fc in q H 2 1 T s 1 e r I fc Electrical response of the FC in q H 2 U min 2K r 2K r Kr r + - r I fc 2K r U opt 1 T s 1 f in q H 2 1 r H _ O in q O 2 1 K H2 H2 1 s 1 K 1 HO 2 HO 2 s - + 1 K O2 O2 1 s Dynamic response of the flow ph 2 p H 2 O p O2 N R T 2 F E 0 0 ln p H p p 1 2 2 O 2 H 2 O + - r V fc r I fc X P e Chemical response of the fuel processor FP Q e 2010 16
Inverter control types PQ inverter control: the inverter is used to supply a given active and reactive power set-point. DC Microsource V dc AC u=u grid +k(i ref -i) i ref Set Point u, i i act i react Current controlled voltage source V dc ref - PI x x i act i react Voltage Source Inverter control logic: the inverter is controlled to feed the load with pre-defined values for voltage and frequency. Depending on the load, the Voltage Source Inverter (VSI) real and reactive power output. P Q Decoupling P vs f droop Q vs V droop References U 2010 17
Frequency and voltage control When in islanding mode, micro generators participate in voltage and frequency regulation using the proportional concept of frequency and voltage droops. f u f 0 u 0 f -1% u -4% -1 0 1 frequency droop P P N -1 0 1 Q voltage droop Q N 2010 18
MicroGrid Islanded Operation The MicroGrid can operate autonomously in case of Failure in the upstream MV grid forced islanding Maintenance actions intentional islanding In this case the MGCC: Performs frequency and voltage control in close coordination with the local controllers in order to not jeopardize power quality Triggers a black start function for service restoration at the low voltage level if the MicroGrid was unable to successfully move to islanded operation and if the main power system is not promptly restored after failure removal MicroGrid flexibility will contribute to the improvement of the energy system reliability and quality of service 2010 19
Islanding operation modes Single Master Operation: A VSI or a synchronous machine directly connected to the grid (with a diesel engine as the prime mover, for example) can be used as voltage reference when the main power supply is lost; all the other inverters can then be operated in PQ mode; Multi Master Operation: More than one inverter is operated as a VSI, corresponding to a scenario with dispersed storage devices; other PQ inverters may also coexist. V DC VSI Control DC AC VSI Droop Settings Electrical Network MGCC V, I V, I PQ Control AC Loads P&Q Settings DC Q Set Point V DC Controller P Primer Mover V DC VSI Control DC AC VSI Droop Settings Electrical Network MGCC V, I V, I V, I PQ Control AC DC Loads VSI Control AC DC P&Q Settings Q Set Point V DC V DC Controller P Primer Mover Controller P Primer Mover 2010 20
Proving the Technical Feasibility of the MicroGrid Concept Microgrid Islanded Operation Development of control strategies Dynamic behavior in the moments subsequent to MicroGrid islanding Seamless transition to islanding operation MicroGrid Black Start Identification of rules and conditions for service restoration at the LV level after a general blackout Evaluation of fast transients associated with the initial stages of the restoration procedure Synchronization with the main power system Development of simulation tools Assessment of system performance in laboratorial tests 2010 Microgeneration: Changing the Paradigm of the Electric Power System 21
LV Test System 2010 22
Test System in the MATLAB/Simulink Simulation Platform SSMT VSI + STORAGE WIND GENERATOR SOFC PV LOAD 2010 23
Test System in the MATLAB/Simulink Simulation Platform Grid Side Converter Frequency Control Microturbine 2010 24
Test System in the MATLAB/Simulink Simulation Platform Grid Side Converter SSMT Mechanical Part Machine Side Converter Frequency control Microturbine PMSG 2010 25
Results from Simulations MG Frequency and VSI Active Power 50.2 50 Frequency (Hz) 49.8 49.6 49.4 49.2 0 50 100 150 200 250 50 VSI Active Power (kw) 40 30 20 10 0-10 -20 0 50 100 150 200 250 Time (s) 2010 26
Results from Simulations Controllable Microsources Active Power 30 25 20 Active Power (kw) 15 10 SSMT1 & SSMT2 5 SSMT3 SOFC 0 0 50 100 150 200 250 Time (s) 2010 27
Improving MicroGrid Robustness Regarding Islanding When the MicroGrid is disconnected from the upstream MV network, several key issues must be considered in order to guarantee system survival in the moments subsequent to islanding: Is the energy available in storage devices enough for a seamless transaction to islanded operation? How much load must be shed? How much dump loads must be connected? How much power reduction should be performed in the islanded MG? On-line evaluation of system robustness and fast determination of remedial actions 2010 28
Evaluating MicroGrid Security in case of Islanding Preventive Control Strategy Load Shedding: 5 4 Energy Injected by the FESS (MJ) 3 2 1 0 E max -1 40 60 80 100 120 140 160 MicroGrid Total Load (kw) 2010 29
Using MicroGrids for Service Restoration DG maturation can offer ancillary services, such as the provision of Black Start in low voltage grids Black-Start is a sequence of events controlled by a set of rules A set of rules and conditions are identified in advance and embedded in a MGCC software module These rules and conditions define a sequence of control actions to be carried out during the restoration stages The electrical problems to be dealt with include: Building LV network Connecting microsources Connecting controllable loads Controlling frequency and voltage Synchronization with the MV network (when available) 2010 30
MicroGrid Black Start Fault in the upstream MV network followed by unsuccessful MG islanding PV Microturbine MV LV Wind Gen Storage Device Fuel Cell 2010 31
MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell 2010 32
MicroGrid Black Start PV Microturbine MV LV Wind Gen Storage Device Fuel Cell 2010 33
MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell 2010 34
MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell 2010 35
MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell 2010 36
MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell 2010 37
MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell 2010 38
MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell 2010 39
MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell 2010 40
Results from Simulations Initial BS Stages SSMT1 MG main storage MG main storage SSMT1 2010 41
Results from Simulations Long Term Dynamics An Overview of the Service Restoration Procedure Frequency (Hz) Active Power (kw) Active Power (kw) 50.4 50.2 50 49.8 49.6 90 100 110 120 130 140 150 160 170 180 190 200 210 220 40 20 0 MG main storage -20 90 100 110 120 130 140 150 160 170 180 190 200 210 220 SSMT 1 60 SSMT 2 SSMT 3 40 20 0 load connection WG connection PVs connection Motor load start up 90 100 110 120 130 140 150 160 170 180 190 200 210 220 Time (s) 2010 42
Laboratorial Tests: INESC Porto, University of Kassel and ISET - Institut für Solare Energieversorgungstechnik 2010 43
Pre-islanding Scenario http://www.iset.uni-kassel.de/abt/fb-a/publication/2006/2006_napa_strauss.pdf 2010 44
Micro-Grid Islanding http://www.iset.uni-kassel.de/abt/fb-a/publication/2006/2006_napa_strauss.pdf 2010 45
Frequency Control After Islanding http://www.iset.uni-kassel.de/abt/fb-a/publication/2006/2006_napa_strauss.pdf 2010 46
Load Disconnection and Frequency Control http://www.iset.uni-kassel.de/abt/fb-a/publication/2006/2006_napa_strauss.pdf 2010 47
Evolution of the MicroGrid Concept Microgrids Diesel HV Network DFIM Fuel Cell VSI Capacitor Bank DFIM Microturbine Storage (VSI) Sheddable Loads MicroGrid PV Large VSI LargeDFIM Hydro CHP MicroGrid Small Diesel Sheddable Loads CHP Hydro MicroGrid 2010 48
Evolution of the MicroGrid Concept New concept Multi-Microgrids 250 kva 400 kva 400 kva 250 kva 160 kva 160 kva 160 kva 250 kva 160 kva G Requires a higher level structure, at the MV level, consisting of LV Microgrids and DG units connected on several adjacent MV feeders Microgrids, DG units and MV loads under DSM control can be considered as active cells, for the purpose of control and management An effective management of such a system requires the development of a hierarchical control architecture, where intermediate control will be exercised by a Central Autonomous Management Controller (CAMC) to be installed at a HV/MV substation 2010 49
New Control Architectures (Distribution Grid) DMS Distribution Management System CAMC Central Autonomous Management Controller MGCC MicroGrid Central Controller RTU Remote Terminal Unit MV LV PV DC AC MC LC Flywheel MC AC DC LC MC LC AC DC DMS MGCC MC AC DC MC MC LC CHP AC DC Fuel Cell Micro-Turbine 2010 50
SmartMetering infrastructure - the platform for developing Grids ICTs 2010 51
Conclusions The feasibility of the MicroGrid concept was proved: Flexibility to operate autonomously under emergency conditions Demonstration by laboratorial tests Using Low Voltage MicroGrids for service restoration The MicroGrid is a very flexible cell of the Electric Power System and can contribute to enhance the quality of service by reducing the number and duration of interruptions. Smartmetering can be used to foster and support the development of microgrids and Smartgrids 2010 52