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120 CHAPTER 4 Performance of MPPT Techniques of Photovoltaic Systems

Start

Sense V, I

( )
(
–
Ii () Ii – 1) Ii
е = +
Vi () –Vi 1) Vi ( )
( –
No Yes
e>0
=0
D(i)=D(i-1)-k*e D(i)=D(i-1) D(i)=D(i-1)+k*e

return
FIGURE 4.4
State-flow chart of Incremental Conductance MPPT technique.

1.6 PARASITIC CAPACITANCE ALGORITHM
The parasitic capacitance algorithm [35] is similar to IncCond technique except that
the effect of the solar cells’ parasitic junction capacitance, which models charge
storage in the pen junctions of the solar cells, is included.

1.7 RIPPLE CORRELATION CONTROL
Ripple Correlation Control (RCC) [36] uses ripple in PV voltage and current to
perform MPPT. RCC correlates the time derivative of the time-varying PVarray po-
wer with the time derivative of the time-varying PVarray current or voltage to drive
the power gradient to zero, thus reaching the MPP. Simple and inexpensive analog
circuits can be used to implement RCC. An example is given in Midya et al. [37].
Experiments were performed to show that RCC accurately and quickly tracks the
MPP, even under varying irradiance levels. The time taken to converge to the
MPP is limited by the switching frequency of the power converter and the gain of
the RCC circuit. Another advantage of RCC is that it does not require any prior in-
formation about the PV array characteristics, making its adaptation to different PV
systems straightforward.