Page 240 - Decision Making Applications in Modern Power Systems

Effects of electrical infrastructures in grid with high penetration Chapter | 8 205

These limits can either be related to equipment and infrastructures techni-
cal limits as conductors, transformers, etc., Eqs. (8.2) and (8.3), or operative
limits as undervoltage or system stability, (8.4) and (8.5).
Once determined the maximum loadability, the maximum storage capac-
ity of each node can be determined by Eq. (8.6). The actual usable amount
of the storage capacity after considering technical and operative limits is
described in Eq. (8.7), while the total available storage capacity of the net-
work is obtained by Eq. (8.8). This process must be repeated for each inte-
gration interval, since variations in demand and charging of EVs and storage
elements can lead to different network storage capacities.

n ðÞ 5 β nðÞ 2 p demand nðÞ ð8:6Þ
p available Node n
P available ; if
8
< Node P available , P max
technical
Node
P storable 5 ð8:7Þ
P max ; if
: P available $ P max
technical Node technical
N
X
5 p storable nðÞ ð8:8Þ
p storable Network
n51
With this knowledge, it is possible to efficiently coordinate the operation
of renewables with flexible loads determining the amount of surplus genera-
tion possible to be stored without compromising the network operating con-
ditions. It is worth mentioning that agreements between EV owners,
charging stations, and utilities must be performed to flexibilize these units
operation either as flexible load or resources. The use of EVs will depend on
owners’ acceptance to provide some energy to the grid in return of economic
compensation; otherwise, they will remain as typical loads connected to the
grid. Several devices focused on enabling these features and depicting the
necessary infrastructure are in development [28,29].

8.3 Flexible resources applied to distribution network
assistance
The flexible operation capacity of EVs and storage units enable their use for
management actions as load shaving and reduction of transmission conges-
tion. These actions can significantly increase the grid service capacity and
defer investments in new generating units and/or transmission infrastructures.
In this sense, during peak load, these flexible units are triggered into genera-
tor mode, assisting the grid with the energy stored during the moments of a
surplus generation, which provides additional benefits as losses reduction
once the current flow is no longer concentrated from the main grid to the dis-
tribution system branches.
The impact of this strategy will depend on how close to the operational
limit are the transmission lines and which is the percent capacity of