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Cascaded H-bridge multilevel power electronic converters generally require several dc sources. An alternative option is to replace all the separate dc sources feeding the H-bridge cells with capacitors, leaving only one H-bridge cell with a real dc voltage source. This will yield a cost-effective converter. However, the required capacitor voltage balancing is challenging. In this paper, using the phase-shift modulation approach, a new control method for cascaded H-bridge multilevel converters fed with only one independent dc source is presented. The proposed method has a wide voltage regulation range for the replacement capacitors in the H-bridge cells. Experimental and simulation results support the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper describes a research conducted on a single-phase flying capacitor active rectifier. An online process that reduces the total number of switching events, which leads to a reduction of switching losses in the converter, is introduced. This method is based on redundant state selection, which is used to regulate the voltage of flying capacitors. The proposed approach is general and can be applied to flying capacitor converters with any number of levels. Furthermore, in order to control the inrush current at the start of operation and avoid extra voltage and current stress for active switches and capacitors, a start-up procedure that precharges the flying capacitors is proposed. With this precharge procedure, no additional hardware is needed. Simulation and laboratory results demonstrate these new concepts. [ABSTRACT FROM PUBLISHER]

Two active capacitor voltage balancing schemes are proposed for single-phase (H-bridge) flying-capacitor multilevel converters. They are based on the circuit equations of flying-capacitor converters. Consequently, they can be implemented using straightforward control rules. In particular, the first technique is based on an algorithm which follows the standard multilevel modulation. Then, it utilizes a redundant state selection table for capacitor voltage balancing. In the second method, multiple duty cycles are defined and modulated in direct response to the capacitor voltages. The most important advantage of these two proposed methods is that they can be utilized to converters with any desired number of levels in their output voltage. Moreover, the analysis and implementation of both methods are straightforward. Through simulation and experimental implementation, these methods are shown to be effective on capacitor voltage regulation in flying-capacitor multilevel converters. [ABSTRACT FROM PUBLISHER]

Multilevel power electronic converters have gained popularity in high-power applications due to their lower switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters which generally require several separate dc voltage sources. By utilizing the redundant switching states, it is possible to replace the separate dc voltage sources with capacitors and keep only the one with the highest voltage level. Redundancy in the charge and discharge modes of the capacitors is assumed to be adequate for their voltage regulation. However, the effects of the output current of the converter as well as the time duration of the redundant switching states have been neglected. In this paper, the impacts of the connected load to the cascaded H-bridge converter as well as the switching angles on the voltage regulation of the capacitors are studied. This paper proves that voltage regulation is only attainable in a much limited operating conditions that it was originally reported. In addition, based on the analysis of the converter, a simplified formula is found which can be used to find those modulation indices that regulate the voltage of the capacitor. This formula can be used in harmonic minimization problems while capacitor voltage regulation is ensured. Simulation and laboratory results are provided to confirm the analysis. [ABSTRACT FROM PUBLISHER]