This document describes a proposed transformer-less inverter topology for grid-tied photovoltaic systems. The existing dual-parallel buck converter topology has issues where the grid can short circuit if there is no dead time between switches. The proposed topology addresses this by using six MOSFET switches and six diodes in a configuration that allows reactive power injection while overcoming reliability issues. It has advantages like utilizing only MOSFET switches, low leakage current, and not requiring PWM dead times. The proposed single-phase inverter is intended for grid-tied PV applications.

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Efficient Single Phase Transformer less
Inverter for Grid-Tied PVG System with
Reactive Power Control
Introduction:
In general, PV power generation system includes solar arrays and
power conversion unit. In most countries and areas, a line-frequency
transformer or a high-frequency transformer has been utilized in the
grid-tied PV system to create a galvanic isolation between the PV
module and the grid. However, the use of line-frequency or high-
frequency transformer makes the entire system bulky, costly, and less
efficient. In contrast, transformer less PV inverter system has been
drawing more attention for its low cost, high efficiency, small size and
light weight. The exclusion of transformer, and hence its isolation
capability, has to be considered carefully due to the issues raised from
no galvanic isolation between the PV module and the grid. In this case,
because of the parasitic capacitance between the PV module and the
ground, the fluctuating CM voltage that depends on the topology
structure and switching scheme can cause of a capacitive leakage
current. The existence of leakage current increases grid current
harmonics and system losses, deteriorates the electromagnetic
compatibility and, more significantly, lead to a safety threat.
Existing system:
Dual-parallel- buck converter, consists of four Cool MOS switches
and four SiC diodes. The main drawback of this topology is that the grid
will be short circuit if no dead time is present between the switches S3
and S4, through which the grid is directly connected. The main

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Copyright © 2016LeMenizInfotech. All rights reserved
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Pondicherry-605 005.
Call: 0413-4205444, +91 9566355386, 99625 88976.
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advantage of these two topologies is that when a phase difference will be
occurred between the output voltage and current, the diodes D1 & D2 or
D3 & D4 will be activated depending on the positive or negative half
cycle. As a result, these topologies may be implemented with MOSFET
switches even when inject reactive power.
Drawbacks:
 The grid will be short circuit if no dead time is present between the
switches S3 and S4, through which the grid is directly connected.
Proposed system:
The proposed transformer less inverter topology consists of six
MOSFET switches (S1-S6) and six diodes (D1-D6). L1A, L1B, L2A,
L2B, L1g, L2g and Co make up the LCL type filter connected to the
grid. VPV and Cdc represent the input dc voltage and dc link capacitor.
The proposed topology is derived overcome the low reverse-recovery
issues of MOSFETs body-diode when injects reactive power into the
utility grid. Therefore, the proposed topology can be implemented with
MOSFET switches without reliability and efficiency penalty. The

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Copyright © 2016LeMenizInfotech. All rights reserved
LeMenizInfotech
36, 100 Feet Road, Natesan Nagar, Near Indira Gandhi Statue,
Pondicherry-605 005.
Call: 0413-4205444, +91 9566355386, 99625 88976.
Web :www.lemenizinfotech.com/ www.ieeemaster.com
Mail : projects@lemenizinfotech.com
proposed topology can also employ unipolar-SPWM with three-level
output voltage.
Advantages:
 Utilizing MOSFET switches even though when inject reactive
power into the utility grid.
 Low leakage current flows through the system
 PWM dead time is not required for the proposed topology that
reduces the THD at the output.
Applications:
 Grid-tied PV system.

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Copyright © 2016LeMenizInfotech. All rights reserved
LeMenizInfotech
36, 100 Feet Road, Natesan Nagar, Near Indira Gandhi Statue,
Pondicherry-605 005.
Call: 0413-4205444, +91 9566355386, 99625 88976.
Web :www.lemenizinfotech.com/ www.ieeemaster.com
Mail : projects@lemenizinfotech.com
Block diagram:
Solar supply Transformer less
inverter
LoadCoupled inductor
Micro-controller circuit
Buffer circuit
Driver circuit
5V DC
Supply
12V
DC