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44 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
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PV converters is mandatory for safety and reliability of the panels [11]. Moreover, reliability is of
much importance in the power electronics–based PV systems, as also shown in Figure 3.2. This is
motivated by extending the total energy production (service time), thereby further reducing the cost
of energy [7, 34–36]. Finally, because of exposure or a smaller housing chamber, the PV converter
system (power electronics system) must be more temperature insensitive (i.e., with temperature
management), which will also be beneficial for the reliability performance. As has been illustrated
in Figure 3.2, improving the monitoring, forecasting, and communication technologies will also be
crucial to implementing future grid-friendly PV systems into a mixed power grid.

3.3 POWER CONVERTER TECHNOLOGY FOR
SINGLE-PHASE PV SYSTEMS
According to the state-of-the-art technologies, there are mainly five configuration concepts
[2, 9, 37, 38] to organize and transfer the PV power to the grid as is shown in Figure 3.3. Each
grid-connected concept consists of a series of paralleled PV panels or strings, and they are con-
figured by a couple of power electronics converters (DC–DC converters and DC–AC inverters) in
accordance with the output voltage of the PV panels as well as the power rating.
A central inverter is normally used in a three-phase grid-connected PV plant with the power
greater than tens of kWp, as it is shown in Figure 3.4. This technology can achieve a relatively
high efficiency with a lower cost, but it requires high-voltage DC cables [9]. Besides, due to its low
immunity to hot spots and partial shading on the panels, the power mismatch issue is significant in
this concept (i.e., low PV utilization). In contrast, the MPPT control is achieved separately in each
string of the string/multistring PV inverters, leading to a better total energy yield. However, there are
still mismatches in the PV panels of each string, and the multistring technology requires more power
electronics converters, resulting in further investments. Considering the issues mentioned earlier, the
module converters (DC-module converters and/or AC-module inverters) are developed, there being
a flexible solution for the PV systems of low power ratings and also for module-level monitoring and
diagnostics. This module-integrated concept can minimize the effects of partial shadowing, module
mismatch, and different module orientations, etc., since the module converter acts on a single PV
panel with an individual MPPT control. However, a low overall efficiency is the main disadvantage
in this concept due to the low power.
As it can be seen in Figure 3.3, the module concept, string inverter, and multistring inverters are
the most common solutions used in single-phase PV applications, where the galvanic isolation for
safety is an important issue of concern. Traditionally, an isolation transformer can be adopted either
at the grid side with low frequencies or as a high-frequency transformer in such PV converters as
it is shown in Figure 3.5a and b. Both grid-connected PV technologies are available on the market
with an overall efficiency of 93%–95% [26], mainly contributed to by the bulky transformers. In
order to increase the overall efficiency, a large number of transformerless PV converters have been
developed [9, 11, 26], which are selectively reviewed as follows.

3.3.1 Transformerless AC-Module Inverters
(Module-Integrated PV Converters)

In the last years, much more effort has been devoted to reduce the number of power conversion
stages in order to increase the overall efficiency, as well as to increase the power density of the
single-stage AC-module PV inverters. By doing so, the reliability and thereby the cost may be
reduced. Figure 3.6 shows a general block diagram of a single-stage grid-connected AC-module
PV topology, where all the desired functionalities, as shown in Figure 3.2, have to be performed. It
should be noted that the power decoupling in such single-stage topology is achieved by means of a
DC-link capacitor, C , in parallel with the PV module [9, 11].
DC