A Bridged New Five-Level Inverter for DC–AC Conversion With Reduced Harmonics M.KARTHIK (10F41D4307) Under the esteemed guidance of Dr.Venugopal.N.,HOD EEE Department Kuppam Enigeering College KES nagar, Kuppam, AP. 517425

ABSTRACT Multilevel converters offer high power capability, Associated with lower output harmonics and lower commutation losses. The new topology produces a significant reduction in the number of power devices and capacitors required to implement a multilevel output. The new topology is used in the design of a five-level inverter. The new topology achieves a 37.5% reduction in the number of main power switches required. Additionally, the dedicated modulator circuit required for multilevel inverter operation is implemented using a FPGA circuit, reducing overall system cost and complexity.

INTRODUCTION The different topologies presented in the literature as multilevel converters it reduce the commutation frequency applied to the power components, reduction in the voltages applied to the main power switches, enabling operation at higher load voltages and transient voltages automatically limited. The main disadvantage associated with the multilevel configurations is their circuit complexity, requiring a high number of power switches and they also require a great number of auxiliary dc levels. As a contribution to solve these twin problems, this work proposes a new converter topology, presented as a block diagram in Fig. 1.

BLOCK DIAGRAM Gate driver circuit FPGA Output Aux Switch H-Bridge AC to DC conversion Filter AC Supply Fig.1. This topology includes an H-bridge stage with an auxiliary bidirectional switch, drastically reducing the power circuit complexity. And a modulator and firing control circuit developed using a field programmable gate array (FPGA) programmable circuit, to simplify the modulator circuit design and implementation.

PROPOSED INVERTER CIRCUIT Single-phase five level H-bridge is formed by the four main power devices, Disp1 to Disp4. A capacitor voltage divider, formed by C1 and C2 provides a half supply voltage point, node An The auxiliary switch, formed by the controlled switch Disp5 and the four diodes, D5 to D8, connects The center point of the left hand half-bridge to node A. The new topology achieves a 37.5% reduction in the number of main power switches required. The auxiliary switch voltage and current ratings are lower than the ones required by the main controlled switches. The new configuration reduces the number of diodes by 60% and the number of capacitors by 50% when compared with the diode clamped configuration. Fig.3.Single-phase five level inverter

CONFIGURATION AND OPERATIONAL PRINCIPLE OF PROPOSED INVERTER: Fig. 4. Switching combination required to generate output voltage level Vs/2. Fig. 3 Switching combination required to generate output voltage level Vs . Fig.5. Switching combination required to generate output voltage level zero. Fig.6. Switching combination required to generate output voltage level -V /2. Fig.7. Switching combination required to generate output voltage level -Vs.

Table.I.Five level Output stages SWITCHING COMBINATIONS REQUIRED TO GENERATE THE FIVE-LEVEL OUTPUT VOLTAGE WAVEFORM : Table.I.Five level Output stages

Harmonics Harmonics are voltages / currents having frequencies that are integer multiples of fundamental supply frequency. Harmonics are generated on source and load side. Harmonics due to load: Nonlinear operation of switching devices Including power converters Arc-furnaces Gas discharge lighting devices Over heating of magnetic core of transformer and motor. Harmonics due to source: Source harmonic are mainly due to power supply with non-sinusoidal voltage waveform.

Total Harmonic Distortion (THD) Calculation

ANALYSIS OF TOTAL HARMONIC DISTORTION: Fig 11 Total harmonic distortion according to the variation of modulation index. The graph gives the variation of Modulation index, Ma with Amplitude of total Harmonic Distortion. From the graph it is clear that the THD of the proposed inverter has lower values than those of conventional inverter. With the growth of modulation index Ma≤1.0 in the linear region, THD of the proposed inverter will slightly increase. This is because that the larger the value of Ma being increased, the smaller the regions of half level of dc bus voltage are reduced.

Comparison between Four Different Five-Level Inverters Topologies

ADVANTAGES OF MULTILEVEL INVERTER The voltage capacity of the existing devices can be increased many times without the complications of static and dynamic voltage sharing that occur in series-connected devices. Spectral performance of multilevel waveforms is superior to that of their two- level counterparts. Multilevel waveforms naturally limit the problems of large voltage transients that occur due to the reflections on cables, which can damage the motor windings and cause other problems.

SIMULATION OF THE AUXILIARY H-BRIDGE INVERTER AND ITS RESULTS

Simulink Model of Conventional Inverter

Simulink model of H- Bridge inverter using simple pulse generator

output voltage and current waveforms for R=50ohms

CONCLUSION Multilevel inverters have become an effective and practical solution for increasing power and reducing harmonics of ac waveforms. Its operated at very high modulation frequencies, producing a very clean output. This configuration reduced circuit complexity will be adequate for low-medium power applications. The modulator circuit implemented using a FGPA IC is able to generate all the control signals required to operate the five-level converter, controlling both the commutation sequences and the output amplitude by pulse width modulation. The combined use of these two technologies may lead to the design of multilevel converters at a cost competitive with that of standard two-level converters.

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