Asymmetrical Cascaded-Bridge Converter With Equal Modules and Sensorless Voltage Balancing for High-Quality Output

The cascading of power modules can generate multilevel voltage output to enhance power transmission capacity and quality. However, conventional cascaded converters require an excessively large number of modules for high quality and precision due to the only linear increase of the voltage levels with the number of modules. Modules whose voltages follow a decreasing sequence, e.g., a binary geometric progression (1, ½, ¼,…) imitate analog-to-digital conversion and generate very fine output shapes through a linear combination of modules with finer and finer steps. However, the use of modules with decreasing voltages rapidly reduces the energy content per module and typically requires dedicated module designs for each module voltage level. This article proposes a novel asymmetric converter design with a very different sequence of module voltages, an optimal low-cost control scheme, and accurate sensorless module-voltage regulation. The circuit does not operate any module below half of the highest-voltage module. Compared to previously suggested asymmetric cascaded circuits, modules will have significantly closer voltages. The proposed tighter rated voltage range allows for a uniform module design with fully interchangeable modules. Moreover, we introduce a pseudo-parallel mode for efficient module-to-module energy exchange. The reduced voltage difference between neighboring modules exponentially reduces the total size and dimensions of the inductors required to limit the balancing current. Simulations in MATLAB/Simulink and a hardware prototype confirm the effectiveness of this approach.