Parallel Operated Inverters As A Multilevel Case

Presentation by,T.Anandkumar.ME (PED) – I Year

• Introduction• Multilevel Inverters• Multipulse transformer• Diode-Clamped Inverter• Flying-Capacitor Inverter• Parallel Inverters• Filtered Output Voltage Waveforms• Conclusions• References

Contents

Introduction

• It consider the classification of parallel operation of voltage source inverters in the context of multilevel inverter systems

• It proposed that one may use multilevel inverters as a backdrop in which to discuss the parallel operation of voltage source inverters.

Multilevel Inverters

• Power inverter is an electrical power device which is used to convert direct current (DC) into alternating current (AC)

• Each cell contains one H-bridge and the output voltage generated by this multilevel inverter

• The sum of all the voltages generated by each cell Is equal to the Output Voltage.

• Multilevel inverter uses several H-bridge inverters connected in series to provide a sinusoidal output voltage.

• There are several topologies of multilevel inverters available

i).Cascaded H-bridge multilevel inverters

ii).Diode Clamped multilevel inverters

iii).Flying Capacitor multilevel inverters.• Capacitors, Batteries and renewable energy

voltage sources can be used as the multiple dc voltage sources.

Multilevel Inverters Structure

Single phase structure of a Multilevel Inverter

Multipulse Transformer

• In a 12-pulse converter system a 3-phase auto transformer with 4 windings per phase is used to power two 6-pulse converter bridges connected in parallel with a large dc filter capacitor

• The voltage ratio is typically 1:1 so that the average dc output of a multi-pulse converter is generally the same as that of a conventional 3-phase bridge rectifier without transformer

• Instead of using Batteries, Multipulse transformer will reduce the ac input harmonic currents greatly.

Structure of a Multipulse Transformer

Diode Clamped Multilevel Inverters

• The diode-clamped multilevel inverter employs clamping diodes and stacked dc capacitors in the input side to produce an ac voltage with multiple levels.

• A four level single phase diode clamped inverter `

Diode Clamped Multilevel Inverters Structure

Simulated waveforms of the four level diode clamped

Flying-Capacitor Inverter

• A typical circuit topology of a four-level flying capacitor inverter.

• Each inverter leg contains three complementary paris of semi-conductor switches pairs.

Flying-Capacitor InverterStructure

Simulated waveforms of the three level Multistage

Parallel Inverters Operation

Harmonic current ITHD

Filtered Output Waveforms

Conclusion

• Comparing the output waveform of the inverters we can see an apparent similarity between the output of the parallel scheme is presented

• A major contribution of this presentation is to attempt to unify the areas of research for parallel operated and multi level inverters, and it is hoped, by doing so, to stimulate more research interest in parallel inverter operation in practical situations.