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2. PV System Under Nonshading Conditions 133

NB NM NS ZE PS PM PB
Error, E
MFs

NB NM NS ZE PS PM PB
Change of
Error,
MFs

NB NM NS ZE PS PM PB
Change in
Duty Ratio
MFs

FIGURE 4.15
A fuzzy system with 1 inputs, 1 output, and 7 MFs each.

membership function is sometimes made less symmetric to give more importance to
specific fuzzy levels, or it can be symmetric as shown in reference [40]. The inputs to
an MPPT FLC are usually an error E and DE. Once E and DE calculated and con-
verted to the linguistic variables based on membership functions shown in Fig. 4.15,
the FLC output, which is typically a change in duty ratio, DD of the power converter,
can be looked up in a rule base Table 4.2. FLC membership functions for both inputs
and output variables can be used as a triangle-shaped function, which is the easiest
way to be implemented on the hardware digital control system. The linguistic

Table 4.2 Rules for an FLC System With Two Inputs and One Output With
Seven-Membership Functions in PV Applications

E DE
NB NM NS ZE PS PM PB
NB NB NB NB NB NM NS ZE
NM NB NB NB NM NS ZE PS
NS NB NB NM NS ZE PS PM
ZE NB NM NS ZE PS PM PB
PS NM NS ZE PS PM PB PB
PM NS ZE PS PM PB PB PB
PB ZE PS PM PB PB PB PB