A Novel Modulation Scheme to Improve the Injected Power Quality for Modular Multilevel Medium Voltage Grid-Tied Power Converters

Abstract

Advancement in solid-state semiconductor technologies has led to the medium-voltage power converters, by obviating the need of step-up transformers in renewable power generation systems. To improve the injected power quality of medium-voltage grid-tied power converters i.e., the harmonic components (e.g. total harmonic distortions) of the output current is minimized by various types of pulse width modulation (PWM) switching schemes. In this paper, a composite harmonic injected pulse width modulation (CHIPWM) switching scheme is proposed based on the modular multilevel cascaded (MMC) converter. The main feature of this modulation scheme is that it can improve the frequency spectra while reducing the switching power losses. In order to validate the performance of the proposed switching scheme, a 55-level, 3-phase MMC inverter is made in the MATLAB/Simulink environment for an 11kV renewable energy based power system. The performance of the proposed switching scheme is compared with different existing switching schemes in terms of THDs and switching power loss. From the simulation and numerical results, it is obvious that the 55-level MMC inverter with the proposed modulation scheme improves the injected power quality and reduces the inverter power losses as compared to the existing modulation schemes, which are very essential for the integration of renewable energy sources (RESs) to the existing utility grid.