10-07-2012, 02:55 PM
A Single-Stage Grid Connected Inverter Topology for Solar PV Systems With Maximum Power Point Tracking
ASingle-StageGridConnectedInverter.pdf (Size: 1.65 MB / Downloads: 107)
INTRODUCTION
HIGH initial investment and limited life span of a photovoltaic
(PV) array makes it necessary for the user to extract
maximum power from the PV system. The nonlinear i–v
characteristics of the PV array [1] and the rotation and revolution
of the earth around the sun, further necessitate the application
of maximum power point tracking (MPPT) [2] to the
system. In this context, grid connected PV systems have become
very popular because they do not need battery back-ups to ensure
MPPT. Stand alone systems can also achieve MPPT, but
they would need suitable battery back-ups for this purpose.
SURVEY OF SINGLE-STAGE TOPOLOGIES SUITABLE FOR GRID CONNECTED PV SYSTEMS
Caceres and Barbi [20] have proposed an elegant single-stage
boost cum inverter topology [Fig. 3(a)] having two boost converters
operating in a complementary manner. Though, not
specifically intended for PV applications, this circuit is a good
candidate for a single-stage, compact grid connected PV application.
However, the topology suffers from the following
drawbacks. All the devices are simultaneously hard switched at
high frequency, rendering the system prone to EMI problems
and causing more switching losses.
PROPOSED TOPOLOGY
The proposed topology consists of two dc-to-dc, buck-boost
converters connected as shown in Fig. 2. Each of these converters
operates in DCM for one half cycle of the fundamental
grid voltage. The resulting circuit acts as a current source inverter
which feeds sinusoidal current into a low value capacitor
across the grid. DCM operation helps in feeding sinusoidal current
with near unity power factor (UPF) into the grid because
the energy can be drawn in the form of “energy packets,” whose
magnitudes vary in a sinusoidal manner.
MAXIMUM POWER POINT TRACKING
“Hill climbing” or the “perturb and observe method” [1] has
been used to track the maximum power point (MPP) of the PV
source. This algorithm has been appropriately implemented in
conjunction with the grid connected dc/ac configuration proposed
in the paper.
Sine-triangle comparison technique is used to ensure that
near-sinusoidal currents are fed into the grid. As inverter is
feeding sinusoidal power into the grid, the second harmonic
power is reflected on the PV source side.