Download Using Low Voltage MicroGrids in Emergency Conditions

September 10th, 2009
Campus da FEUP
Rua Dr. Roberto Frias, 378
4200 - 465 Porto
Portugal
Decentralised Energy Systems
in Developing Countries
T +351 222 094 000
F +351 222 094 050
[email protected]
J. A. Peças Lopes
© 2009
Electrical Systems in Developing Countries
• Small isolated electrical grids fed by small power stations
frequently with small Diesel units are frequent.
– These grids correspond often to a small geographical area
where a population nucleus is located.
– Large distances among the load centres makes unfeasible
the development of interconnected electrical grids.
– Reliability is week and electricity is present only a few hours
per day.
A change is required to improve quality of life
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Selecting Renewable Generation Technologies
• The selection of the renewable energy technologies to be used
for generating electricity in remote areas can be made using
GIS:
– Availability of the resources
– Costs of installation
– Costs of transportation
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Developing Countries: New paradigms are under development
Breaking the Rules
Yesterday
Central power station
Tomorrow: distributed/ on-site
generation with fully integrated
network management
Photovoltaics
power plant
Tra n s m is s io n Ne tw o rk
Storage
Storage
Flow
Control
Storage
Storage
House
Dis trib u tio n Ne tw o rk
Local CHP plant
Power
quality
device
Wind
power
plant
Factory
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Power
quality
device
House with domestic CHP
Commercial
building
4
Developing Countries: New paradigms are under development
• The change of paradigm that DG introduced started at HV and MV level
DG units have been operated
without any control, injecting
active and reactive power in the
grid.
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DG Technologies
• Distributed Generation (DG) has attained a considerable
penetration level in HV and MV networks, involving different
types of sources and conversion technologies;
– The most relevant ones are:
• Mini-hydro using synchronous or asynchronous generators;
• Cogeneration using mainly synchronous units;
• Biomass generation units with synchronous generators;
• Wind generation, using conventional asynchronous or DFIM units and
synchronous machines with electronic converters.
– Usually these generation devices do not participate in
voltage control and frequency regulation
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DG Technologies
• Microgeneration directly connected to the LV network is
becoming a reality:
– Next 10 years:
• The change that occurred in MV networks will also happen in LV
networks:
– Connection of small modular generation sources;
– Typically in the range from 5 to 100 kW;
– Fuel cells, renewable generation (wind turbines and PV systems),
micro turbines (natural gas or bio fuels), micro-CHP;
• LV networks are also becoming active;
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MicroGrid: A Flexible Cell of the Electric Power System
MG Hierarchical Control:
•
MGCC, LC, MC
•
Communication
infrastructure
PV
MC
LC
MC
Microturbine
LV
LC
MV
Wind Gen
LC
MC
LC
MC
MGCC
Storage
Device
MC
LC
Fuel Cell
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Microgeneration technologies: Micro-wind turbines
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Microgeneration - Solar Photovoltaic (PV)
1/Ropt
I
M
ISC
N
A
Imax
P
1/R
O
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Vmax
S
VOC
V
10
Energy storage – flywheels or batteries
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Dynamic Modelling of Components – Inverters
• Inverter Control Modes
– PQ control
• Designed for grid-connected operation
• The inverter is controlled to meet an active and reactive power set-point
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Dynamic Modelling of Components – Inverters
• Inverter Control Modes
– Voltage Source Inverter Control - VSI
• Designed for standalone operation (however, in some cases, grid-connected
operation is also possible)
• The inverter “feeds” the load with pre-defined values for voltage and
frequency
w  w0  k P  P
V  V0  kQ  Q
w01  wgrid  k P  P1
V01  Vgrid  kQ  Q1
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MicroGrid Operation and Control
• Control Modes for MG Islanded Operation
– Energy storage is required to balance local load and generation in
the moments subsequent to transients (disconnection of the MV
network or load following during islanding operation) aiming
voltage and frequency control.
– Combining Inverter Control Modes, two control strategies are
possible:
• Single Master Operation
• Multi Master Operation
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MicroGrid Operation and Control
• Storage device’s active power output is proportional to the MG
frequency deviation (droop control)
DP
DPmax
Correct permanent
frequency
deviations during
islanding operation
Dfmin
Dfmax
Df=f0-f
DPmin
f ref = 50 Hz
S
PI
MC
Microsource
f MG
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MicroGrids Dynamic Simulation – Test System
20 kV
0.4 kV
MG Main
Storage
30 kW SSMT
Group of 4
Residences
10 kW PV
Appartment
building
2x30 kW SSMT
Industrial
Load
15 kW wind
generator
Appartment
building
30 kW SOFC
10 kW PV
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Results from Simulations
• MG Frequency and VSI Active Power
50.2
Load shedding
Frequency (Hz)
50
49.8
49.6
Load reconnection
49.4
49.2
0
50
100
50
100
150
200
250
150
200
250
VSI Active Power (kW)
50
40
30
20
10
0
-10
-20
0
Time (s)
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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 MGCC software
– These rules and conditions define a sequence of control actions
to be carried out during the restoration stages
Increased reliability
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Growing the system
With microgrids and DG
• Increase reliability to end user consumers  increase
consumption levels (lighting, refrigerators, TV set, …)
• Interconnect nearby systems and define common operating
strategies that improve economics and global reliability
• Introduce more renewable power sources
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Integrating Wind Power and other intermittent power sources
• A reliable integration of intermittent power sources in na
islanded system requires:
– Advanced management and control systems to minimize
operation costs and assure security of operation;
– Exploitation of storage facilities, involving specific
management and control strategies.
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Conclusions
• Extend and adapt the concepts of distributed generation
and microgeneration pursued lately in developed countries
to the existing reality of developing countries
• Increase renewable power sources presence
– Reliability improvements;
– Reduce economic costs
– Increases quality of life and economic development in local
populations
– Avoids CO2 emissions
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