Abstract
This paper outlined the basic concepts of two selected types of hybrid multi-level inverters that were capacitor voltage-source dependent. A natural capacitor voltage balancing involving hysteresis with redundant switching states was analyzed in this paper. Simulations using MATLAB 7.14 were carried out for an unbalanced and a well-balanced capacitor voltage supply under 0V, 100V and 200V pre-charged capacitor voltage conditions. A comparative analysis of the two types of hybrid multi-level inverters (Type A and Type B) with pertinent to %THD values of [35.77% and 23.79%] for Type A and [92.10% and 84.94%] for type B during fault occurrence were evaluated in this work. These harmonic values can lead to thermal run away and total malfunction of the semi-conductor switches. An experimental vali-dation of Type A hybrid multi-level inverter with a three level flying capacitor input stage and H-bridge output stage using a three phase RL-Load of 15Ω and 45mH was accomplished in the laboratory with results compared with the simulations for experimental verification. Â
Highlights
Capacitor voltage balancing is one of the major challenges for modular multilevel converters (MMC’s)
A model predictive control strategy was presented in [2] to carry out the capacitor voltage balancing of the modular multilevel converters with reduced switching frequency
The waveforms obtained showed that a close similarity exists between the simulation results and the laboratory results as indicated in Figures 14, 15 and 34, 35
Summary
Capacitor voltage balancing is one of the major challenges for modular multilevel converters (MMC’s). Reference [3] introduced a voltage balancing control for modular multilevel converters at fundamental switching frequency where the pulse-widths were the same but the phase angles were different in each fundamental frequency period. In this reference, voltage balancing was realized by shifting the pulses in sequence in each fundamental frequency period. In [8], a capacitor voltage balancing method for the modular multilevel converter with the switching frequency as grid frequency was proposed In this reference, the low switching frequency can effectively reduce excess switching loss though the drive pulses have different pulse-widths but the same phase angle in each switching period.
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