Title: CIRED
1Controllability of DG helps managing
Distribution Grids
- J. A. Peças Lopes
- (jpl_at_fe.up.pt)
2Exploiting DG to improve system operation
- DG has been considered as non controllable and
non dispatchable, since all the energy production
has priority to be absorbed by the network - The increase in DG foreseen for the next years
will require a different approach regarding the
way how DG units will be operated - Concepts of controllability should be developed
and exploited - Participation in reactive power control
- Interruptability
- Delivery of ancillary services (primary and
secondary reserves, according to the conversion
technology and primary energy sources) - Participation in system restoration strategies
- Development of concepts related with control of
clusters of DG and virtual power stations
3Main characteristics of DG units and
controlability concepts
- Three main types of energy conversion systems can
be found among DG units - Conventional synchronous machines (cogeneration,
CHP, mini-hydro) - Asynchronous generators (wind power, mini-hydro)
- AC/DC/AC electronic conversion systems used
together with synchronous or induction machines
(micro-turbines, fuel cells, wind generators). - Classification (according to primary energy
source and conversion system used) - Non- controllable (Ex Wind park with
asynchronous stall generators) - Partially controllable (Ex Wind park with
synchronous variable speed gen. and AC/DC/AC
converters) - Controllable (Ex Mini-hydro or Cogeneration
plant with synchronous units).
4DG units used to optimise the distribution system
operation
- DG can be used to optimise the operation strategy
of distribution networks. - The Problem can be formulated an optimisation
problem - Min (active power losses)
- Subj. to
- Vmax lt Vi lt Vmin
- Sij max lt Sij
- Qgmaxilt Qgi lt Qgmini taking into
account the type of generator - Qimpor max lt Qimpor
- Transformer tap limits are kept
- Control variables Qg, capacitor banks and
transformer taps - The need to use a motor of optimisation
- (Evolutionary Particle Swarm Optimisation
EPSO)
5Some results of the participation of DG in
Voltage VAR control
- Test System 60 kV distribution network with a
large penetration of DG (mini-hydro and wind
generation).
Activate control on reactive power generated in
the DG Units.
6Some results of the participation of DG in
Voltage VAR control
- Changes in active Losses
- Peak load scenario
- A clear reduction on actives losses was obtained
7Some results of the participation of DG in
Voltage VAR control
- Results concerning voltage in network busses
8Dynamic Impacts
- Dynamic behaviour impacts need to be addressed
using adequate DG modelling and DG equivalent
representation - Considering disturbances resulting from DG
operation - Considering disturbances in distribution
networks - Considering disturbances in the transmission
system
9Dynamic behavior analysis
- Scenario Week peak with maximum dispersed
generation - Disturbance Outage of Power Plant H 7,346MVA,
production of 6,692j3,03 MVA, injection of
2,678j1,081 MVA (tg j 0,404) - Voltage profile
- 60kV bus at the substation
10Dynamic behavior analysis
15 kV bus of the feeder where the power plant was
connected
15 kV bus of the feeder where the power plant was
not connected
11Dynamic behavior analysis (Impact in the other
generators)
12Relay coordination
- Under voltage relay coordination is needed
- Energy conversion systems need to able to
withstand low voltages during short-circuits
up-stream.
Frequency changes
Changes in contractual inter-area power flows
13Impacts on Operation
- Load flows become bi-directional
- Voltage profiles have different patterns
- Losses change as a function of the production and
load levels - Congestion in system branches is a function of
the production and load levels - Short-circuit levels increase
- Power quality may be affected
- Voltage transients will appear as a result of
connection disconnection of generators - Risk of islanding operation
- Reliability may be reduced
- System dynamic behavior may be largely affected
-
- Protections coordination is needed
14Conclusions
- The future
- DG units should be more actively used to help in
the management of the distribution grid - New DMS tools need to be developed
- Topology processor with capabilities of
identification of energised areas - Voltage and reactive power control
- Load and current forecasting
- Load flow including new generator models and load
allocation algorithms to allow load flow to run - Optimum network reconfiguration
- State estimation (considering that some DG units
will not be monitored and new pseudo-measures
need to be defined) - Cluster control strategies should be implemented,
involving the development of local dispatch
centres - Development of DMS training simulators for
distribution grids with large amounts of DG
(steady state and dynamic behaviour).