In order to compare the efficiency of a DPP-based system
with microinverters or dc optimizers, we consider a system with
ten PV modules (i.e., 30 PV submodules) as an example. The
irradiances on the PV submodules are set randomly by drawing
from a Gaussian distribution with a standard deviation equal to
10%of the mean; the resulting maximum power of each PV
submodule is displayed in Fig. 2 using striped red bars. The
differential power, i.e., the power difference between the maximum power of each PV module and the power common to all
PV modules, is also shown in Fig. 2 using dotted blue bars. In
a dc optimizer-based system, the dc optimizers have to process
the full power of all PV submodules (represented by the striped
red bars), which adds up to 2218W. In a DPP-based system,
each DPP only needs to process the differential power (represented by the dotted blue bars), which only adds up to242.5W.
Both the dc optimizer-based system and the DPP-based system
then use a string-level inverter to convert dc string voltage into
ac voltage. In a microinverter system, the PV module voltage is
directly converted to ac, but the efficiency of a microinverter is
typically lower and its per-watt cost is typically higher than that
of a string-level inverter or a central inverter. Table I summarizes
the power losses of these three different solutions for the irradiance condition in this example. DC optimizers are assumed to
have an average efficiency of96%, while that of DPP converters is assumed to be92%since they often operate in light-load
conditions. For both the dc optimizer- and DPP-based system,