Page 5 - Risorse_Energetiche_Favignana_2005

Proposal APERTURES. PART B Priority6.1.3.1.1.2 - FP6-2005-TREN-4 p 5 of 49
For the local optmisation the reduction of the losses of the local demand is carried out (e.g. by maximising the
efficiency of electrical drive loads) together with the optimal exploitation of local RES (e.g by employing one wind
turbine at maximum efficiency rather than several at reduced efficiency, or by incorporating matched local energy
storage).
For the global optimisation, the load power flows are to be managed suitably in order to have optimal power
dispatch. The realization of this 2 level optimisation can be accomplished by the interface of power
converters. There does however remain a considerable amount of research to be done to determine:
1. The best power electronic topologies and control methods for RES interfaces
2. The best power electronic topology and control methods to interface a microgrid to the transmission system
3. The design rules required to determine the best ratio of PV/Wind/fossil energy sources within a particular
local energy community, for instance based on cost, maintenance, environmental impact, payback period.
4. The amount and type of local energy storage required to match generation capability to load cycles.
Indeed, energy storage itself is of significant importance as the traditional technologies – batteries, pumped
hydrostorage, flywheels – are now being challenged by newer technologies such as hydrogen (eg fuel cells),
supercapacitors & new battery technologies. The dynamic response of the energy recovery from each of these
storage devices in the presence of supply dips and load surges are of paramount importance when investigating the
best strategy for overall power flow matching within a microgrid. The control and management of small RES-
dominated networks is emerging as a strategically important area of research to underpin the design of future power
transmission systems. However the reduction of energy waste in electrical loads is also of paramount importance
and should also be encouraged. Electrical loads with minimal losses and maximum efficiency are as important as
the reduction of fossil fuel usage.

In addition to the increase in RES and enhancement of efficiency in some types of load, there has also been a more
predominant reduction in power quality due to, for example harmonic problems resulting from the increased use of
non-linear loads, especially power electronic systems. Load current harmonics now cause considerable supply
voltage distortion, increasing losses and reducing equipment reliability. Significant international research has
resulted in equipment and control techniques for harmonic compensation. These include semiconductor solutions
such as Flexible AC Transmission Systems (FACTS), Unified Power Controllers (UPCs) and Active Power Filters
(APFs).

However, reliability and control stability are still an issue, especially under conditions where the there are
significant renewable energy sources embedded into the system, and where there can be a large variation in the
impedance of the power supply.

A matter of equal importance when considering DG (Distributed Generation) is the behaviour in the presence of
faults. Current regulations enforce DG to trip when faults are detected. This however may compound problems
when the grid has significant DG, resulting in a cascade of shutdown and a blackout. It would be better for the DG
controller to distinguish between a fault remote from its site and one close to it. The DG should be able to ride
through remote faults, maintaining supply to the local (possibly islanded) network. Intelligent power
electronic RES will facilitate this kind of behaviour.

The incorporation of RES and energy storage systems onto microgrids or standard grid systems demands the use of
power electronic interfaces and intelligent controllers. The interfaces must be able to adapt to present network
conditions to optimise the energy flow within the network and best utilise the energy available. This intelligent
control demands a knowledge of the network state – loads, transmission impedance, faults – to determine the
optimum operating conditions for the interface connected and avoid instability. The use of on-line impedance
estimation can provide this information. However it can also enhance the interface behaviour to provide facilities
for local harmonic control and power quality improvement, and also to provide more accurate discrimination
between local and remote faults. This latter capability may encourage islanded operation such that part of a power
network or microgrid may continue to operate in the presence of a fault.

The development of intelligent, (autonomous) interfaces to interact with the main supply grid is essential to
the future uptake of RES. This project proposes the design of tools, techniques and equipment which will
contribute to this development, and will demonstrate their effectiveness by deploying them on a small
microgrid.