SEVILLA, APRIL 2010 Microgeneration and Microgrids (modeling, islanding operation, black start, multi-microgrids) Campus da FEUP Rua Dr. Roberto Frias, 378 4200 - 465 Porto Portugal T +351 222 094 000 F +351 222 094 050 J. Peças Lopes [email protected] www.inescporto.pt Power Systems Unit © 2010 MicroGrid: A Flexible Cell of the Electric Power System MG Hierarchical Control: PV MC • MGCC, LC, MC LC • Communication MC infrastructure Microturbine LC Wind Gen MC LC LC MC MC Storage MGCC Device LC 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 PV Microturbine MC AC DC DC AC LC PV MC MC DC LV Operation Modes: LC AC LC MV • Interconnected Mode MC Wind Generator • Emergency Mode LC Fuel Cell MC AC MC AC Storage MGCC DC DC MC 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) 1/Ropt I MN ISC A Imax P 1/R S O Vmax VOC 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; Requires dynamic behavior analysis • In this case, the MGCC: – 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 Dtur wr Vmax - Pin LV 1 1 + Pm gate 1 ? Ts1 1 ? Ts2 Vmin + - 1 KT 1 ? Ts3 ++ Lmax © 2010 15 DevelopmentofModelsofMicrosources(FC-SOFC) • Nerst equation plus the Ohm law RT pp 12 VNErr ln HO22 rI fcfc002Fp HO2 U max qin 2K H2 Pref r Electrical response of the FC + - in r I I P fc 1 fc dem Limit 1Tse in Vfc U 2Kr Kr r qin min H2 2Kr - + qin qin - H2 O2 r 2Kr 1 1 + I fc Uopt 1Ts r f H _O Dynamic response 1 K 1 K 1 K H2 HO2 O2 1 s 1 s HO2 1O s H2 2 of the flow p p p H2 H2O O2 - V r RT pp 12 + fc NE ln HO22 002 Fp HO2 Pe r I fc X Qe Chemical response of the fuel processor FP © 2010 16 Inverter control types • PQ inverter control: – the inverter is used to supply a given active and reactive power set-point. DC Microsource Vdc AC u, i u=ugrid +k(iref -i) Current controlled voltage source Set Point i act iref i react i x react Vdc ref - i act PI x • Voltage Source Inverter control logic: the inverter is controlled to “feed” the P load with pre-defined values for voltage P vs f droop U and frequency. Depending on the load, Decoupling References Q the Voltage Source Inverter (VSI) real and Q vs V droop reactive power output. © 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 u0 f -1% u -4% -1 0 1 P -1 0 1 Q frequency droop PN 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. Droop Settings P&Q Settings Droop Settings P&Q Settings MGCC MGCC Q Set Point VSI V, I V, I PQ Control Control Controller VSI V, I PQ Q Set Point V, I VDC P Control Control Controller DC AC Electrical Primer VDC VDC P AC Network DC Mover AC VSI DC Primer Loads VDC Electrical AC DC Mover Network VSI VSI Control Controller Loads V, I VDC P AC Primer DC 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 Microturbine Frequency Control © 2010 24 Test System in the MATLAB/Simulink Simulation Platform SSMT Mechanical Part Grid Side Converter Machine Side Converter Microturbine PMSG Frequency control © 2010 25 Results from Simulations • MG Frequency and VSI Active Power 50.2 50 49.8 49.6 Frequency (Hz) 49.4 49.2 0 50 100 150 200 250 50 40 30 20 10 0 VSI Active Power (kW) -10 -20 0 50 100 150 200 250 Time (s) © 2010 26 Results from Simulations • Controllable Microsources Active Power 30 25 20 15 Active Power (kW) 10 SSMT1 & SSMT2 SSMT3 5 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 3 2 Emax 1 Energy Injected byEnergy FESS the Injected (MJ) 0 -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 PV network followed by unsuccessful MG islanding Microturbine LV Wind Gen MV Storage Device Fuel Cell © 2010 31 MicroGrid Black Start PV Microturbine Wind Gen Storage Device Fuel Cell © 2010 32 MicroGrid Black Start PV Microturbine LV Wind Gen MV 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