Cascaded Multi-Level Based 6kV MVDS without Input and Output Transformers and its Control

Compared with the traditional MVDs, including two-level, three-level, hybrid and cascaded multi-level (CML) with poly-phase multi-winding transformer structure, new cascaded multi-level based 6 kV MVDs without input and output transformers is developed. Then, its corresponding multi-input and multi-output nonlinear mathematic model is built in this paper with the phase-shifted carrier pulse modulation (PSCPWM) applied. For the MVDs wider working range, input-state linearization is used to transform the proposed nonlinear model to be linear one. Consequently, the DC capacitor voltage is selected to be the feedback to achieve well voltage sharing among the series connected power units. For the purpose of modular and redundant design, decentralized coordinated control strategy is studied, which lead no message exchange among series connected power units. Furthermore, the active and inactive decouple control is realized in the rectifier of the MVDs. Mathematic simulations show the efficiency of the proposed control scheme