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Hybrid multilevel converters are contemplated in an attempt to optimize the performance of voltage source converters in terms of magnitude of semiconductor losses and converter footprint, and to achieve additional features such as dc short circuit proof, which is essential for a high integrity multiterminal HVDC grid. Therefore, this paper considers an emerging hybrid cascaded converter that offers the dc side short circuit proof feature at reduced loss and footprint compared to the existing multilevel and other hybrid converters. Its operating principle, modulation, and capacitor voltage balancing strategies are described in detail. Furthermore, hybrid converter scalability to high voltage applications is investigated. The validity of the modulation and capacitor voltage strategy presented are confirmed using simulation and experimentation. The hybrid cascaded converter is extendable to a large number of cells, making it applicable to high voltage applications, and operation is independent of modulation index and power factor. On these ground, the converter is expected to be applicable for both real and reactive power applications. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive and generalized analysis of the bidirectional dual active bridge (DAB) dc–dc converter using triple phase shift (TPS) control to enable closed-loop power regulation while minimizing current stress. The key new achievements are a generic analysis in terms of possible conversion ratios/converter voltage gains (i.e., Buck/Boost/Unity), per unit based equations regardless of DAB ratings, and a new simple closed-loop controller implementable in real time to meet desired power transfer regulation at minimum current stress. Per unit based analytical expressions are derived for converter ac rms current as well as power transferred. An offline particle swarm optimization (PSO) method is used to obtain an extensive set of TPS ratios for minimizing the rms current in the entire bidirectional power range of –1 to 1 per unit. The extensive set of results achieved from PSO presents a generic data pool, which is carefully analyzed to derive simple useful relations. Such relations enable a generic closed-loop controller design that can be implemented in real time avoiding the extensive computational capacity that iterative optimization techniques require. A detailed Simulink DAB switching model is used to validate the precision of the proposed closed-loop controller under various operating conditions. An experimental prototype also substantiates the results achieved. [ABSTRACT FROM AUTHOR]