Performance Evaluation of Different Modulation Strategies Applied to Modular Cascaded Multilevel Inverter based Shunt Hybrid Active Power Filter

摘要

In recent years, high power equipment has been employed in industrial applications due to the megawatt power level for many medium voltage applications. Due to this condition, multilevel power converters are to be used as an alternative solution in medium and high voltage applications. Multilevel converters have the ability to increase the output voltage without raising the voltage rating of switching components. Thus, they are preferred to connect to medium voltage grids without using transformers. Among the various multilevel converters topologies, cascaded inverters consist of several converters connected in series. Thus, the high power and/or high voltage from the combination of the multiple modules would favor this topology in medium and high voltage applications. The modular multilevel inverter has been used as an alternative choice to conventional multilevel inverters. It has been designed to mitigate the drawbacks of conventional multilevel inverters such as the difficulty of balancing the capacitor voltage on higher order levels, the need for an output filter and interfacing transformer. Also conventional multilevel inverters are not capable of fault management and fault ride through. The modular cascaded H-bridge multilevel inverter is one of the cascaded inverter topologies. The output multilevel voltage waveforms enable the reduction of harmonics in the synthesized current, reducing the size of the needed output filters. The cascaded multilevel inverter also has other advantages such as reduced voltage stresses on the semiconductor switches, as well as having higher efficiency when compared to other converter topologies. Using identical power cells leads to a modular structure, which is an effective means for cost reduction. The increase of nonlinear loads causes several power quality problems in power systems. The grid voltage and currents become non sinusoidal due to these types of loads. The traditional yet ineffective solution to reduce current harmonic distortion is passive filters. Active power filters have become a new research emphasis on power electronics technology as a new and improved solution to the problem. Hybrid active power filters effectively smooth the problems of passive filters and an active power filter solution may ensure a cost effective harmonic compensation. The aforementioned reasons caused to compose the modular cascaded multilevel inverter based SHAPF investigated in this paper. On account of the limitations between existing literatures, the purpose of this paper is to investigate the performance of the modular cascaded multilevel inverter based shunt hybrid active power filter for reactive power compensation and harmonics elimination with applying different modulation strategies.