Modeling, Islanding Operation, Black Start, Multi-Microgrids) Campus Da FEUP Rua Dr

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

MG Hierarchical Control: PV MC • MGCC, LC, MC LC • Communication MC infrastructure Microturbine LC Wind Gen MC LC

MC MC Storage MGCC Device LC

Fuel Cell

•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

• Vertical axis micro-wind turbines

1/Ropt I

MN ISC A Imax

1/R

Other solutions: surfaces coating (Glasses, Roofs, etc.) with thin films.

• Microturbine of 80 kW In general the microturbine is connected to the grid through an electronic converter.

1,5 kHz to 4kHz (single shaft)

• Packaged as a domestic boiler for mass market

• Different Types (PEM, SOFC, Alkaline, PAC…)

• Key element for the operation of a microgrid

• 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.

• 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)

• Turbine modeling

Dtur wr

Vmax - Pin LV 1 1 + Pm gate  1 ? Ts1 1 ? Ts2

Vmin

+ - 1  KT  1 ? Ts3 ++

Lmax

• Nerst equation plus the Ohm law RT pp 12 VNErr ln HO22  rI fcfc002Fp HO2

U max qin 2K H2 Pref r Electrical response of the FC + -  in r  I I P fc 1 fc dem Limit 1Tse  in Vfc 

U 2Kr Kr r qin min H2 2Kr - + 

qin qin - H2 O2 r 2Kr 1 1 + I fc  Uopt 1Ts r f H _O Dynamic response 1 K 1 K 1 K H2 HO2 O2 1 s 1 s HO2 1O 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

– 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.

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 P -1 0 1 Q frequency droop P N voltage droop Q N

• 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

• 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

• 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

SSMT

VSI + STORAGE

WIND GENERATOR

SOFC PV

LOAD

Grid Side Converter

Microturbine Frequency Control

SSMT Mechanical Part Grid Side Converter Machine Side Converter

Microturbine PMSG Frequency control

• MG Frequency and VSI Active Power

50.2

49.8

49.6 Frequency (Hz) 49.4

49.2 0 50 100 150 200 250

VSI Active Power (kW) -10

-20 0 50 100 150 200 250 Time (s)

• Controllable Microsources Active Power

Active Power (kW) 10

SSMT1 & SSMT2 SSMT3 5 SOFC

0 0 50 100 150 200 250 Time (s)

• 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

• Preventive Control Strategy – Load Shedding:

2 Emax

1 Energy Injected byEnergy FESS the Injected (MJ) 0

-1 40 60 80 100 120 140 160 MicroGrid Total Load (kW)

• 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)

Fault in the upstream MV PV network followed by unsuccessful MG islanding Microturbine

LV Wind Gen MV

Storage Device Fuel Cell

Microturbine

Wind Gen

Storage Device Fuel Cell

Microturbine

LV Wind Gen MV

Storage Device Fuel Cell

Microturbine

Wind Gen

Storage Device Fuel Cell

Microturbine

Wind Gen

Storage Device Fuel Cell

Microturbine

Wind Gen

Storage Device Fuel Cell

Microturbine

Wind Gen

Storage Device Fuel Cell

Microturbine

Wind Gen

Storage Device Fuel Cell

Microturbine

Wind Gen

Storage Device Fuel Cell

Microturbine

Wind Gen

Storage Device Fuel Cell

SSMT1

MG main storage

SSMT1

• An Overview of the Service Restoration Procedure

50.4

50.2 load connection

49.8 WG connection PVs connection Frequency (Hz) 49.6 90 100 110 120 130 140 150 160 170 180 190 200 210 220 40 Motor load start up 20

Active Power (kW) 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

Active Power (kw) 90 100 110 120 130 140 150 160 170 180 190 200 210 220 Time (s)

•Microgrids Diesel HV Network

–DFIM Capacitor VSI Bank DFIM – Fuel Cell – Microturbine Sheddable –Storage Loads (VSI) MicroGrid –PV • Large VSI •LargeDFIM •Hydro

•CHP MicroGrid MicroGrid • Small Diesel CHP Hydro • Sheddable Loads

• New concept  Multi-Microgrids 250 kVA 250 400 kVA 400 400 kVA 250 kVA 250 160 kVA 160 160 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

DMS – Distribution Management System CAMC – Central Autonomous Management Controller MGCC – MicroGrid Central Controller RTU – Remote Terminal Unit

PV Flywheel MC AC DC DC AC LC MC MC AC MV LV LC DC LC MC CHP

DMS MGCC Fuel Cell MC AC DC MC AC DC LC

Micro-Turbine

••

ICTs

• 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