Solar Power Convertion Using Multilevel Inverter

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Solar Photovoltaic Power Conversion Using Modular Multilevel Converter Rajasekar S., Student Member IEEE and Rajesh Gupta, Senior Member IEEE conventional two-level and multilevel inverter has been reported in the literature [2]. In case of two-level inverter, it inject maximum PV power into the grid with a unity power factor, however the system fails to be free from higher order harmonics, high voltage stress across the semiconductor power switch and high power losses due to high switching frequency [6]. In order to overcome the above mentioned problems, multilevel inverter came into picture and attracted more attention because of their significant properties. They offer lower total harmonic distortion (THD), low dv/dt device switch voltage stress, lowering the switch voltage and power rating etc. The multilevel inverter is well suited for high power medium voltage applications and in particular dominated by cascaded multilevel inverter and neutral point clamped multilevel inverter. In these medium voltage applications cascaded multilevel inverter and neutral point clamped multilevel inverter requires transformer to obtain electrical isolation between active DC sources of the H-bridge or NPC converter cells. This condition introduces losses, increases converter footprint, making converter costly, bulky and complex. The main drawback of the cascaded multilevel converter coupled with the transformer makes circulation current between phase during unbalanced network conditions and it may cause asymmetrical phase voltages. The modular multilevel inverter has strong potential to replace cascaded multilevel converter in medium voltage applications [10]. This paper, presents the design of a solar photovoltaic power conversion system with single stage modular multilevel converter. Currently intensive research is going on in MMC and it has high potential for medium power applications. Modular multilevel converters have several advantages over conventional multilevel topologies. Those significant are as follows. • Generate low harmonic output voltage, this eliminates filtering requirements. • For medium voltage application, it allows to avoid interfacing transformer. • Modular structure allows to extend higher number of levels easily. • Capacitor voltage balancing is attainable independent of the load. Although MMC are investigated with many applications, but it has not been reported in the literature with single stage solar PV power conversion system. This paper demonstrates the effective implementation of the photovoltaic supported MMC for grid interface which satisfy all the control objectives like maximum power transferring under varying environmental conditions, synchronizing grid utility voltage with output current for unity power factor operation and low total harmonic distortion. Ssection II gives introduction about

Abstract— This paper makes an attempt to develop grid connected solar photovoltaic array power conversion using modular multilevel converter. The proposed system makes use of single stage power conversion with maximum power point tracking and modular multilevel converter (MMC) as interfacing unit into the grid. Here perturb & observe method of maximum power point algorithm is used to regulate the DC link voltage of the MMC and to synchronize the grid utility voltage with the current for attaining near unity power factor operation under varying environmental conditions. The simulation results presented in this paper verifies the operation of proposed MMC topology such that the AC output is free from the higher order harmonics and grid voltage and current are in phase. The simulation studies are carried out under power system computer aided design PSCAD/EMTDC 4.2 environment. Index Terms— Grid, modular multilevel converter (MMC), photovoltaic (PV) array, total harmonic distortion (THD).

I. INTRODUCTION

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renewable energy power supplied into the utility grid has been paid much attention due to increase in...
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