Information Technology Reference
In-Depth Information
Fig. 1.
Structure of a CHP. Straight lines: electrical power fluxes, dotted lines: thermal
power fluxes.
In each time interval (
i
), thermal and electrical power of a CHP are linked by a
linear relation
P
t
(
i
)=
k
t
P
e
(
i
)
(1)
The energy management problem of the CHP system regards the definition
of the best arrangement of production levels of the power unit to minimize the
management costs and fulfilling all loads requirements. The problem is defined
over a scheduling period (e.g. one day, one week etc.) where loads, costs, fares
etc. can change. The scheduling period is subdivided in
N
intervals
time intervals
of length
Δt
. During each interval all CHP characteristics and load data are
assumed to be constant.
Besides plant data, some operational constraints have to be imposed on the
power source like:
-
Minimum On Time
(MOT): minimum time interval during which CHP must
be on when it is switched on;
-
Minimum Shut-down time
(MST): minimum time interval which CHP must
be off since it was turned off;
-
Maximum ramp rate
: maximum power rate of the source
The unit production costs of the node, expressed in
A
C
/
kWh, are:
-
c
e
: cost coecient of electric energy produced by the CHP;
-
c
t
: cost coecient of thermal energy produced by the boiler;
-
c
p
(
i
),
c
s
(
i
): prices of purchased and sold energy at
i
-th time interval.
By using the previous definitions it is possible to write a global cost function (in
A
C) over the scheduling period
N
intervals
f
CHP
=
[
c
e
P
e
(
i
)+
c
p
(
i
)
P
p
(
i
)
−
c
s
(
i
)
P
s
(
i
)+
c
t
B
t
(
i
)]
Δt
(2)
i
=1
