Page 185 - From Smart Grid to Internet of Energy

160 From smart grid to internet of energy

through 75 kW resistive and inductive load. The fifth, seventh, ninth and eleventh
harmonics,whicharesupposedasthemostimportantharmonicorders,areobserved
lower than1% for thiscase. The third analysisshowsthat the THD of line currents is
calculated as 2.37% as can be seen from Fig. 4.16C when the MLI is loaded with
13 kW resistive and inductive load.
Acquired performance analysis results for the observed loads are illustrated
in Figs. 4.17 and 4.18, respectively. Each load plant comprises a BPSK modem
that is able to quantize applied power consumption rate to its input, and mod-
ulates this data to convey over transmission lines. The first axis of Figs. 4.17 and
4.18 shows the measured power consumptions of loads while the second axis
depicts modulating data that are obtained by attenuating the measured power
data at a rate of 1:1000. The first plant is modulated via a carrier signal with
8 kHz frequency while the second is modulated via a carrier signal with
6 kHz frequency. The filtering analyses are conducted for both different filter
order and cut-off frequency values where 400 Hz with second order, 200 Hz
with second order and 50 Hz with fourth order cases are taken into account
as can be seen from the results.
When the presented analysis results are considered, it is evident that the
designed remote monitoring system for solar microgrids can be exploited for
observing the RESs located in different places in an efficient way. Moreover,
it is important to note that this monitoring system eliminates installation costs,
due to using power lines as a communication medium, when compared to other
monitoring systems based on SCADA, wireless communications or in any
Ethernet-based systems. Besides, this system can be simply upgraded for
increased number of the load plants.
The second case study focuses on a multi-channel PLC infrastructure that is
particularly modeled for monitoring a hybrid RESs constituted with solar and
wind sources. The wind turbine structure of the modeled system is based on a
permanent magnet synchronous generator (PMSG). Six-pulse uncontrolled rec-
tifier and DC-DC buck converter are used to connect wind energy conversion
system (WECS) to the DC bus. The solar plant of the designed test bed is created
with eight PV panels that are similar panels explained in the first case study. The
employed buck converter in the design is managed with P&O MPPT algorithm
while the inverter part of the design is modeled with SPWM method. The
designed system aims to carry several measurement data obtained from the
hybrid RESs. The voltage, current and power rates of each energy plant are sep-
arately measured and are conveyed to monitoring center thanks to the designed
PLC modems that are based on QPSK mapping scheme. A modulated signal
that is composed of six-channel measurement data is conveyed over transmis-
sion lines to the energy monitoring center. Transmission line length is adjusted
as 25 km with realistic parameters given in Table 4.9. The schematic diagram of
the modeled hybrid RES system is shown in Fig. 4.19. This system is modeled
with a DC coupled configuration where several RESs may be connected to a DC
bus over DC-DC converters or AC-DC rectifiers.