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356 CHAPTER 11 Energy Management for PV Installations

Therefore, the load power is given as:

(11.10)
P load ¼ðK 2 þ K 1 Þ$P pv þðK 3 þ K 1 Þ$P batt
3.1.1.2 Second Structure of PMC
In this structure, four switches (K 1 ,K 2 ,K 3 , and K 4 ) have been used. The fourth
switch is used to store the power excess, if there is, in a derivate load or an auxiliary
source (Fig. 11.5).
The available power DP(Eq. (11.1)) has to be determinate. According to its
mathematical value, it is noticed in three cases. If DP > 0, the load will be supplied
by PV panels while the batteries are charging and if there will be an excess of power,
it will be dissipated through a dump load, hence, the need of adding the fourth switch
K 4 (Fig. 11.5). In the second case, where DP < 0, the load is supplied only by bat-
teries until their discharging, and in the last case, where DP ¼ 0, the load will be sup-
plied only by PV panels (Table 11.5).
The EM strategy of PV/battery system based on four switches can be represented
in the following flowchart (Fig. 11.6). Depending on the different tests on DP, P pv ,
P load , and SOC, the system operates in one of the different modes.
Mode 1: In this mode, the photovoltaic power (P pv > P load ) is quite sufficient to
supply the load and charge batteries.
Mode 2: The power supplied by PV panels is insufficient (0 < P pv < P load ); in
this case, the power of batteries is added to satisfy the power load demand. It is
the compensation mode.
Mode 3: This mode is operating when no energy provides from the PV generator
(P pv ¼ 0), so the batteries alone supply the load.

R aux

K 4
P pv
K 2

K 1 K 3
SOC

FIGURE 11.5
Power management based on four switches (PV/battery system).