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JPE, Vol. 19, No. 4, July 2019
Optimal Selection of Arm Inductance and Switching Modulation for Three-Phase Modular Multilevel Converters in Terms of DC Voltage Utilization, Harmonics and Efficiency
Ali Osman Arslan, Mehmet Kurtoglu, Fatih Eroglu, and Ahmet Mete Vural
Area High Power Converters
Abstract The arm inductance (AI) of a modular multilevel converter (MMC) affects both the fault and circulating current magnitudes. In addition, it has an impact on the inverter efficiency and harmonic content. In this study, the AI of a three-phase MMC is optimized in a novel way in terms of DC voltage utilization, harmonics and efficiency. This MMC has 10 submodules (SM) per arm and the power circuit topology of the SM is a half-bridge. The optimum AI is adopted and verified in an MMC that has 100 SMs per arm. Then the phase shift (PS) and phase disposition (PD) pulse width modulation (PWM) methods are investigated for better DC voltage utilization, efficiency and harmonics. It is found that similar performances are obtained for both modulation techniques in terms of DC voltage utilization. However, the total harmonic distortion (THD) of the PS-PWM is found to be 0.02%, which is slightly lower than the THD of the PD-PWM at 0.16%. In efficiency calculations, the switching and conduction losses for all of the semiconductor are considered separately and the minimum efficiency of the 100-SM based MMC is found to be 99.62% for the PS-PWM and 99.64% for the PD-PWM with the optimal value of the AI. Simulation results are verified with an experimental prototype of a 6-SM based MMC.
Keyword Modular multilevel converter,Modulation techniques,Multi-level power converter,Optimal arm inductance selection
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