Page 147 - Decision Making Applications in Modern Power Systems
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112 Decision Making Applications in Modern Power Systems
i NL1 i NL2
i DGs Z L1 Z Lg
Z i1
i Grid
L f 1 L f 2 L f n Load 1 Load 2
i DG 1
i DG 2 i DG n
R f 1 R f 2 R f n
NLL 1 NLL n
1 ∂ n ∂ V PCC i PCC
S3 1 S4 1 S3 2 S4 2 S3 n S4 n
i DG1 I nll-local 1 I nll-local n
i DG2 λ 1
MOMPC P and Q
S 1 1 S2 1 S 2 1 S2 2 S n 1 S2 n λ n calculation
V DC 1 V DC 2 V DC n Low bandwidth
i DGn
i fund
i h
DG 1 Z e1 DG 2 Z e2 DG n Z en communication
Switching signals Main controller
FIGURE 4.11 A prototype smart grid with computational intelligence and communication
links.
where f 1 ½k 1 1, f 2 ½k 1 1; ... and f n ½k 1 1 are related to different control
objectives that should be minimized in the cost function in accordance with
their weighting values ðλ 1 ; λ 2 ; ...; and λ n Þ in the cost function. It should
be mentioned that the application of mentioned weighting factors will define
the priority of each control objective. MOMPC could be applied to several
MFDGs that operate in parallel; this is the main advantage of the MOMPC
to handle several objectives at a time for several converters. These objectives
could be reference tracking, fundamental and harmonic power sharing, power
management, output current THD minimization, switching frequency control,
etc. Since the idea behind MOMPC is to fulfill multiple objectives in an
acceptable way and not having the best performance over an objective and
affecting the other objectives in an inverse way, to fulfill the control objec-
tives in an acceptable way, a decision-making should be done over defining
weighting factors. This decision-making could be based on heuristic methods
or learning, which is dependent on system smartness. An example of
MOMPC could be applied to the microgrid shown in Fig. 4.11; the control
objectives would be tracking the defined current reference to compensate the
nonlinear load harmonics, fundamental and harmonic power sharing, and
switching frequency control.
The multiobjective cost function for this purpose will include three con-
trol terms: the first term for reference current tracking, the second one for
fundamental and harmonic power sharing, and the third term will control the
switching frequency. The cost function will be as follows:
g½K 1 1 5 λ 1 3 I DG1 1 I DG2 2 I ref 1 λ 2 3 @ 1 I DG1 2 I ref
ð4:10Þ
1 λ 3 3 f sw ðS sw ðkÞ; S sw ðk 1 1ÞÞ
where λ 1 , λ 2 , and λ 3 are the weighting factors defining the priority of each
control objective. And @ 1 is the power-sharing factor that in this case defines
the power-sharing ratio between first and second MFDG and is defined as
