Multilevel cascaded H-Bridge converters (CHB) have been presented as a good solution for high power applications. In this way, several control and modulation techniques have been proposed for this power converter topology. In this paper the steady state power balance in the cells of the single phase two cell CHB is studied. The capability to be supplied with active power from the grid or to deliver active power to the grid in each cell is analyzed according to the dc-link voltages and the desired ac output voltage value. Limits of the maximum and minimum input active power for stable operation of the CHB are addressed. Simulation results are shown to validate the presented analysis.

Space-vector modulation (SVM) is a well-suited technique to be applied to multilevel converters and is an important research focus in the last 25 years. Recently, a single-phase multilevel modulator has been introduced, showing its conceptual simplicity and its very low computational cost. In this paper, some of the most conventional multilevel SVM techniques have been chosen to compare their results with those obtained with single-phase multilevel modulators. The obtained results demonstrate that the single-phase multilevel modulators applied to each phase are equivalent with the chosen well-known multilevel SVM techniques. In this way, single-phase multilevel modulators can be applied to a converter with any number of levels and phases, avoiding the use of conceptually and mathematically complex SVM strategies. Analytical calculations and experimental results are shown, validating the proposed concepts.

-In this paper, a Direct Power Control (DPC) using Output Regulation Subspaces (ORS) for a three-phase two-level converter is presented. An optimal controller design and the use of optimized modulation techniques permit to improve the system performance minimizing the necessary grid-connection inductance. ORS plus proportional controllers are proposed for the generation of the reference vector to decrease active and reactive power errors and to achieve unity power factor. The generation of the reference vector is carried out thanks to simple Pulse Width Modulation techniques. The computational cost of the proposed control is really low and all the calculations can be done online allowing its implementation in low cost microprocessors. Simulation and experimental results are shown in order to illustrate the good performance of the proposed control strategy.

Abstract-Single-Phase multilevel converters are suitable for medium power applications as photovoltaic systems and switched reluctance machines. An overview of possible modulation methods including carrier-based Pulse Width Modulation and Space Vector Modulation techniques for multilevel single-phase converters is presented. A new space vector modulation for this type of converters is proposed. This space vector modulation method is very simple presenting low computational cost. Different solutions for the space vector modulation are presented achieving similar output results but imposing restrictions on the power converter topology. Optimization algorithms balancing the DC-Link voltage or minimizing the commutation losses are presented. Experimental results using a 150 kVA five-level diodeclamped converter are shown to validate the proposed modulation and optimization methods.

No abstract