SEVILLA, APRIL Microgeneration and Microgrids (modeling, islanding operation, black start, multi-microgrids) J. Peças Lopes Power Systems Unit

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1 SEVILLA, APRIL 2010 Campus da FEUP Rua Dr. Roberto Frias, Porto Portugal T F cmoreira@inescporto.pt Microgeneration and Microgrids (modeling, islanding operation, black start, multi-microgrids) J. Peças Lopes Power Systems Unit 2010

2 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

3 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

4 Microgeneration technologies: Micro-wind turbines

5 Microgeneration technologies: Micro-wind turbines

6 Micro-wind turbines Vertical axis micro-wind turbines

7 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

8 Microgeneration technologies: BIPV Other solutions: surfaces coating (Glasses, Roofs, etc.) with thin films

9 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)

10 Micro CHP (Stirling engines) Packaged as a domestic boiler for mass market

11 Fuel-Cells Different Types (PEM, SOFC, Alkaline, PAC )

12 Energy storage - flywheels Key element for the operation of a microgrid

13 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

14 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)

15 DevelopmentofModelsofMicrosources(MT) Turbine modeling w r D tur P in LV gate V max 1 1? Ts 1 1 1? Ts P m V min + KT ? Ts 3 L max

16 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 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 O 2 H 2 O + - r V fc r I fc X P e Chemical response of the fuel processor FP Q e

17 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

18 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% frequency droop P P N Q voltage droop Q N

19 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

20 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

21 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

22 LV Test System

23 Test System in the MATLAB/Simulink Simulation Platform SSMT VSI + STORAGE WIND GENERATOR SOFC PV LOAD

24 Test System in the MATLAB/Simulink Simulation Platform Grid Side Converter Frequency Control Microturbine

25 Test System in the MATLAB/Simulink Simulation Platform Grid Side Converter SSMT Mechanical Part Machine Side Converter Frequency control Microturbine PMSG

26 Results from Simulations MG Frequency and VSI Active Power Frequency (Hz) VSI Active Power (kw) Time (s)

27 Results from Simulations Controllable Microsources Active Power Active Power (kw) SSMT1 & SSMT2 5 SSMT3 SOFC Time (s)

28 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

29 Evaluating MicroGrid Security in case of Islanding Preventive Control Strategy Load Shedding: 5 4 Energy Injected by the FESS (MJ) E max MicroGrid Total Load (kw)

30 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)

31 MicroGrid Black Start Fault in the upstream MV network followed by unsuccessful MG islanding PV Microturbine MV LV Wind Gen Storage Device Fuel Cell

32 MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell

33 MicroGrid Black Start PV Microturbine MV LV Wind Gen Storage Device Fuel Cell

34 MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell

35 MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell

36 MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell

37 MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell

38 MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell

39 MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell

40 MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell

41 Results from Simulations Initial BS Stages SSMT1 MG main storage MG main storage SSMT

42 Results from Simulations Long Term Dynamics An Overview of the Service Restoration Procedure Frequency (Hz) Active Power (kw) Active Power (kw) MG main storage SSMT 1 60 SSMT 2 SSMT load connection WG connection PVs connection Motor load start up Time (s)

43 Laboratorial Tests: INESC Porto, University of Kassel and ISET - Institut für Solare Energieversorgungstechnik

44 Pre-islanding Scenario

45 Micro-Grid Islanding

46 Frequency Control After Islanding

47 Load Disconnection and Frequency Control

48 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

49 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

50 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

51 SmartMetering infrastructure - the platform for developing Grids ICTs

52 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