ABSTRACT:
Transformerless
grid-connected inverters have been extensively popular in renewable
energy-based applications owing to some interesting features like higher
efficiency, reasonable cost and acceptable power density. The major concern of
such converters is the leakage current problem and also the step-down feature
of the output voltage which causes a costly operation for a single stage energy
conversion system. A new five-level transformerless inverter topology is
presented in this study, which is able to boost the value of the input voltage
and can remove the leakage current problem through a common-grounded
architecture. Here, providing the five-level of the output voltage with only
six power switches is facilitated through the series-parallel switching of a
switched-capacitor module. Regarding this switching conversion, the self-
voltage balancing of the integrated capacitors over a full cycle of the grid’s
frequency can be acquired. Additionally, to inject a tightly controlled current
to the local grid, a peak current controller-based technique is employed, which
can regulate both the active and reactive power support modes. Theoretical
analyses besides some experimental results are also given to corroborate the
correct performance of the proposed topology.
KEYWORDS:
1. Transformerless inverter
2. Common ground type
3. Switched Capacitor module and Grid
connected applications
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. The overall block diagram of the controlled system.
Fig.
2. (a) Inverter’s output voltage (200 V/div) and the injected grid’s current (4
A/div) (b) Inverter’s output voltage (200V/div) and the local’s grid voltage
(200V/div) (c) Injected grid’s current (4A/div) and local grid’s voltage (100
V/div) (d) the voltage across (200V/div) and the voltage across (100V/div). 2 C
1 C
Fig.
3.(a) The leading injected grid’s current (4 A/div) with the grid’s voltage
(100 V/div) (b) The lagging injected grid current (4 A/div) with the grid’s
voltage (100 V/div) (c) The grid’s voltage (blue trace) (200 V/div) and the
injected grid current (green trace) (4 A/div) under the step-change of the PF
from unity to a non-unity one.
Fig.
4. The measured current waveform through 1 C and 2 C (4 A/div).
Fig.
5. The measured PIV of power switches; (100 V/div) and (200 V/div). 1 2 / SS4 5
6 / / S S S
Fig.
6. The current stress waveforms of (a) (5 A/div) and (5 A/div), (b) (5 A/div),
and (2 A/div) (c) (2 A/div) and (5 A/div). 1 S 2 S 3 S 6 S 4 S 5 S
Fig.
7. Dynamic performance of the proposed system under a voltage sag in the local
grid’s voltage (a) The injected current (blue trace) (4 A/div) and the local
grid’s voltage (red trace) (200 V/div) (b) The injected current (4 A/div) and
the voltage across C1 (100 V/div) (c) The injected current (4 A/div) and
the voltage across C2 (200 V/div).
CONCLUSION:
A new five-level SC-based
transformerless grid-connected inverter has been presented in this study. The
proposed topology is able to remove the leakage current concern with a common-grounded
architecture. Also, with the reasonable number of active and passive involved
elements, it offers a two times voltage boosting feature that makes it suitable
for PV string applications. A PCC-based strategy has also been employed in
following to regulate the value of the injected current. Details of such a
controlled system besides some analysis as for the conduction losses, the
design guidelines and voltage/current stresses of the switches were also given
to further explore the performance of the proposed topology. Finally, a
comprehensive comparative study alongside the experimental results of a 590 W
built prototype have been presented to confirm the superiority and accurate
operation of the proposed system.
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