What is it about?
In order to ensure long-term stable operation under various load conditions, any microgrid must
have a control system with different time frame adjustments. Typically, three time frame
adjustments are used:
Starting from an initial stabilized steady state,
any fault occurring in the system must not cause transitory decrease of the frequency
in such manner to exceed the
activation threshold of automatic load-shedding control equipment.
The primary adjustment is distributed implemented.
Secondary adjustment: For sources which are
in operation, the control algorithm varies the produced active powers.
The purpose of secondary adjustment consists of maintaining the desired value of frequency
and the power balance in order to ensure the primary adjustment reserve.
This adjustment can also be used to synchronize the microgrid with the
main system facilitating the transition from stand-alone to grid-connected mode.
The secondary adjustment is centralised implemented, at the entire microgrid level.
Tertiary adjustment: Consists of starting or stopping
some sources, varying the active powers produced by sources which are in operation and
varying the active power consumed of loads.
The tertiary adjustment is also centralised implemented.
There is an obvious distinction between primary and secondary adjustment.
On the other hand, there is not a unique distinction between secondary and tertiary adjustment and
the secondary adjustment can be considered as a mixture between the secondary and the
tertiary. In this case, the secondary and the tertiary are merged in a single one adjustment strategy.
The secondary adjustment, or secondary mixed with the tertiary, operates on a slower time frame and
must be linked with an energy management system which is responsible for each decision in the microgrid.
The problem of energy management in microgrids consists of finding the optimal or near optimal
unit commitment and dispatch of the available sources and energy storage systems so that certain
selected criteria are achieved.
How it works?
The algorithm is based on several innovative remarks and ideas which make it unique, fast and effective:
For more, please read the main ideas on
this "Advanced Engineering Forum" journal article.
The Bellman's principle of optimality
is not satisfied for energy management problem because of the energy storage devices
Focused on the principle: avoid wastage of the existing renewable potential at each time interval
Introducing the concept of "Pivot Source"