Page 62 - Hybrid-Renewable Energy Systems in Microgrids

46 Hybrid-Renewable Energy Systems in Microgrids

power and then it feeds to the AC main grid which depends on the weather condition.
P b a t > 0 The converter of the battery controls the charging (P bat 〈0) and discharging (P bat 〉0) of
Pbat<0
the battery bank.
The power flow of the hybrid energy sources are balanced condition when it is
depends on the PV power output, AC and DC loads, grid demand, state of charge
PPV+Pbat=PDCload+PACload+Pgrid (SoC) of battery are provide normal reference values in the controllers. The power
management equations are based on both the grid connected and islanded mode of
operation as given below.

load
load
P PV + P bat = P DC + P AC + P grid (3.1)
load
load
PPV+Pbat=PDCload+PACload P Pv + P bat = P DC + P AC (3.2)
PPV where, P —PV array output power
PV
Pbat P —Converter power flows in the battery
bat
Pgrid P —Power flows between main grid and microgrid
grid
Power equations can be obtained by the various constraints such as energy con-
servation law and microgrid operation, which has been explained in Eq. (3.3). In the
below equation, the losses of the power grid can be neglected.

t
t
t
Pload(t)=PPG(t)+PESS(t)+P P load t () = P () + P () + P () (3.3)
ESS
PG
grid
grid(t)
t
t
P'(t)=Pload(t)−PPG(t)−PESS(t) P ' load t () = P load t () − P () − P () (3.4)
PG
ESS
Eq (3.4) can be considered as a three modes of operation that is charging mode,
t
PESS(t)<0 discharging mode, and synthetic load. When ESS is in charging mode, P () < 0; the
ESS
t
t
t
t
P
)=
Pgrid(t)>0,Pg PESS(t)>0t) discharging mode P () > 0 and the P () > 0, P () = P ' load t () requires load from
i
r
(
d
'(
ESS
grid
grid
the grid, then the microgrid supplies power to the load.
t
t
t
Pout(t)=PPG(t)+PESS(t)−Pload(t) P () = P () + P () − P load t () (3.5)
ESS
PG
out
t
t
Pgrid(t)=Pout(t) In Eq (3.5) when P () < 0 and P grid t() = P (), this condition represents the
Pgrid(t)<0
out
grid
t
Pout(t) microgrid supports the power to the large grid. Here, P () represents the microgrid
out
output power. The solar PV array is maintained at maximum output power and the
inverter control, which ensures that the maximum power at the PCC is in the equal
range by the utility grid.
5 Characteristics and modeling of renewable
energy sources
5.1 Solar PV
Mathematical modeling of PV array has given by the several studies. The characteristic
of PV array mainly depends on the irradiation and temperature; thus the temperature