Unequal DC Sources Research Articles

A Grid Connected Hybrid Asymmetrical Nine level Inverter Topology Using Boost Converter

This paper presents the distributed energy re-source (DER)-based single-phase inverter is usually adopted. In order to reduce conversion losses, the key is to save costs and size by removing any kind of transformer as well as reducing the power devices. This paper deals nine-level multi-string inverter topology for DERs-based dc/ac conversion system. Multilevel inverter (MLI) is a new breed of power converter that is suited for higher power applications. The various topologies of MLI are diode-clamped, capacitor clamped and cascaded H-bridge. This paper focuses on cascaded MLI using two unequal dc sources in order to produce nine-level output. In this study, a high step-up converter is introduced as a front-end stage to improve the conversion efficiency of conventional boost converters and to stabilize the output dc voltage of various DERs such as photovoltaic and fuel cell modules for use with the simplified MLI. The simplified MLI requires only eight active switches instead of the sixteen required in the conventional cascaded H-bridge MLI. This MLI offers strong advantages such as improved output waveforms, smaller filter size, and lower electromagnetic interference and total harmonics distortion. Simulation results show the effectiveness of the proposed solution.

Harmonics Elimination in a Multilevel Inverter with Unequal DC Sources Using a Genetic Algorithm

In this paper, an optimal solution to the harmonic reduction problem in a cascaded multilevel inverter with non-equal DC sources using a genetic algorithm (GA) is presented. Switching angles are generated for different values of modulation index by the proposed algorithm, considering minimum voltage total harmonic distortion (THD) whereas selected harmonics are controlled within the allowable limits at all desired modulation indices including the point of discontinuity. Results are stored as a look-up table to be used to control the inverter for a certain operating point. The computed angles are used in a simulated circuit in Matlab\Simulink to validate the results.

Calculating the Formula of Line-Voltage THD in Multilevel Inverter With Unequal DC Sources

Multilevel inverters introduce harmonics to the network besides their remarkable advantages. Total harmonic distortion (THD) is one of the most important indexes to evaluate the harmonic contents of waveforms. The conventional method of line-voltage THD calculation gives approximate answers, because high-order harmonics are ignored. In this paper, an analytical algebraic method based on formulating the line-voltage THD of multilevel inverters with unequal dc sources is presented. This method, which is general and applicable to each number of switching angles, is implemented to a five-level inverter with staircase waveform as a case study. The implementing process of this method can be easily repeated for each number of levels. The accuracy of the proposed method is illustrated in comparison with the approximate method. Some advantages of the extracted formulas of line-voltage THD are simplicity and rapidity in calculations, considering all harmonics and the possibility of finding optimal switching angles analytically. Experimental results are presented to validate the theory.