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The current-source modular multilevel converter (CSMMC) is a good alternative for high-power applications with medium-voltage and high-current requirements. In such applications, to obtain the multilevel current output and for current scaling, a large number of submodules are required in CSMMC. The detailed representation of such systems in electromagnetic transient-type simulation programs brings computational complexity with a large computing burden. This paper presents a computationally efficient equivalent model of CSMMC based on the Norton equivalents. Each arm of the converter is represented by a two-node Norton equivalent in this model, which eliminates the internal intermediate nodes and, hence, significantly reduces computing time. The proposed model is implemented in PSCAD/EMTDC by using the module component coded in FOR-TRAN and results are validated with the full-size traditional model in PSCAD/EMTDC. Moreover, hybrid models are presented and validated for the submodule level studies such as fail-safe functionality with redundant submodules. This paper also focuses on the control method and dynamic studies of the CSMMC-based back-to-back system. The results of these studies are compared with the proposed equivalent model, and accurate matching of the results confirms the usefulness of the proposed model in such studies.

For the safe operation of transformerless grid connected photovoltaic (PV) inverters, the issue of common mode (CM) leakage current needs to be addressed carefully. In this paper, a novel multilevel transformerless inverter topology is proposed, which completely eliminates CM leakage current by connecting grid neutral point directly to the PV negative terminal, thereby bypassing the PV stray capacitance. It provides a low-cost solution consisting of only four power switches, two capacitors, and a single filter inductor. As compared to half-bridge topologies, with this inverter a minimum of 27% and maximum of 100% more output voltage is obtained for the same dc-link voltage. The proposed inverter is analyzed in detail and its switching pattern to generate multilevel output while maintaining the capacitor voltage is discussed. Simulations and experiments results confirm the feasibility and good performance of the proposed inverter.

In this paper, a dual-transformer-based asymmetrical triple-port active bridge converter (DT-ATAB) is proposed to interface two different dc-sources and a load. DT-ATAB consists of three active power electronic converters and two high-frequency transformers. All switches of these converters can be turned on with zero-voltage switching to reduce the switching losses. The bidirectional power flow operation is possible between the ports. The DT-ATAB also reduces the circulating powers between the ports for well-matched transformer turns ratios as compared to those in the other existing triple-port active bridge converters (TAB). Furthermore, the magnetic short-circuit conditions arising in the three-winding transformer of the TAB are mitigated in DT-ATAB. The principle of operation, steady-state analysis, various modes of operation (three-port and two-port modes), and a closed loop controller of DT-ATAB are presented. The theoretical analysis of this paper is verified using both simulation and experimental studies. The illustrated results show that DT-ATAB can be used as a promising multiport converter to interface the multiple sources and load to achieve wide-ranging outputs with the minimal losses.