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Note that
switches Q10 and Q11 are activated to
produce the voltage levels of -2Vdc,
-Vdc, Vdc and 2Vdc for the line-to-line
voltage waveforms of the three phases. They are truly shared among the three
phases. The switch-sharing capability presented by this inverter promote reduces
the number of switches, thus it greatly eases the circuit complexity. Table 3.1 presents the comparison of the component count and
its expected level of impact on volume, control complexity and cost between the
proposed inverter and the three-level and four-level diode-clamped inverters. It
can be observed that the inverter offers the lowest number of power switches
used, namely 11 in contrast to 12 and 18 employed in the three-level and
four-level diode-clamped inverters, respectively. In terms of the total
component count, the inverter proceedings 40, which is higher by 25% when
compared with the three level diode-clamped inverter, but is lower by 21.6%
when referring to the four-level diode-clamped inverter as the standard.

The circuit is
shaped from the combination of the conventional three-phase full-bridge configuration
with five bidirectional switching devices arranged in the manner shown in the
figure. To generate the four voltage levels at a low switching frequency, the
inverter has to activate in accordance with the operational modes.

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A.
Proposed System            

In this proposed system, the fuzzy logic controller has been proposed.
Because it has some advantages over than the PI controller. i.e., the fuzzy
logic controller has small starting overshoot and less settling time and this
fuzzy logic controller provides sudden response to the system. The Circuit
configuration of an optimized multilevel inverter with bi-directional switches
is as shown in Fig 3.3. This paper
presents a new three-phase multilevel inverter topology based on the modified
full-bridge configuration with bidirectional-switch-sharing capability. The
next section provides the details of the proposed topology.

II             SYSTEM DESCRIPTION

 In general, the commercial three-phase
inverters for PV systems recognize the conventional two-level full-bridge topology.
With the purpose of form a transformer less configuration for connection to the
grid, some modifications are made to the topology, which result in the split
DC-link concept and the four-leg arrangement. To conquer the problems of the
two-level inverters in maximizing the power extracted, minimizing the
electromagnetic interference level, dropping the switching loss, lowering the
harmonic distortions and decreasing the filter size, multilevel inverters have
been introduced. There are various configurations to understand the three-phase
multilevel circuits with the following three are the most common ones: Diode
clamped /Neutral clamped Multilevel Inverter, Flying capacitors /Capacitor
clamped Multilevel Inverter, Cascaded H-bridge Multilevel Inverter.

                In
low-power PV applications, single-phase inverters are normally used. However,
when the PV system is connected to the grid through single-phase inverters, a
concern arises due to the fact that a certain phase may have more such
connections as compared with other phases in the three-phase network. Coupled
with uneven distribution of single-phase loads among the three phase power
systems, voltage unbalance is typically observed as the result. This observable
fact is undesirable as it causes unsteadiness to the power systems. Therefore,
this leads to further losses and heating effects, concentrated efficiency and
decreased life of motors, unnecessary current in one or two phases that can
trip overload protection circuits, large voltage ripple in DC link and high
reactive power for pulse-width-modulated rectifiers used in variable speed
drives. Besides, another inadequacy is that single-phase inverters are not able
to transmit as much power as the three-phase inverters. Quite the opposite, the
three-phase counterparts can produce a continuous power when operated at unity
power factor.  Consequently, the DC-link
voltage ripple is small sufficient that smaller DC-link capacitors can be used.
This contributes to a reduction in cost, enhanced reliability and higher
lifetime for the PV systems.

Every day, the
sun radiates an enormous amount of energy called solar energy. It radiates more energy in one day than the world
uses in one year. This energy comes from within the sun itself. The
photovoltaic cells are used to generate electric energy from light energy. The
output of PV cell is in DC form. So an inverter is used to convert this DC
output into AC. In renewable energy generation systems such as photovoltaic
(PV) systems, the inverter has become the most important component as it converts
the DC power from the PV modules into AC power to be fed to the grid. The
inverter also plays a noteworthy role in electric motor drive systems especially
in adjustable speed drives where a substantial level of energy saving can be expert.

I              INTRODUCTION

Key
words: Bi-directional switches, Multilevel inverter, Fuzzy logic controller.

Abstract: In renewable energy generation systems such as
photovoltaic (PV) systems, the inverter has become the most important component
as it converts the DC power from the PV modules into AC power to be fed to the
grid. Despite the advantages offered by multilevel
inverters, one of the main drawbacks is their circuit complexity as the number
of power switches employed is usually high. This report presents a multilevel
inverter topology with a considerable reduction in the number of power switches
used through the switch-sharing approach based on Fuzzy logic controller. The
fact that the inverter applies two bidirectional power switches for giving out
among the three phases does not prevent it from producing four levels in the
line-to-line output voltage waveforms. Shared power
switches based multilevel inverter can be constructive to convert DC-AC for
low-power photovoltaic applications. Nevertheless this multilevel inverter has
to control to get preferred output. Hence, this study presents an active
control strategy based on Fuzzy logic controller. The performance of the
proposed inverter with fuzzy logic controller is analyzed through
MATLAB/SIMULINK simulations. By using fuzzy logic controller the total harmonic
distortion is concentrated for four level output voltage.

AN
OPTIMISED INVERTER WITH SHARED POWER SWITCHES BASED ON FUZZY LOGIC CONTROLLER

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