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In this paper, a dc–ac buck converter is proposed as a grid-side converter in high voltage dc (HVdc) transmission systems for high-power renewable energy source grid integration. The proposed architecture consists of multimodules of half-bridge voltage source converters (HB-VSCs). The dc terminals of the HB-VSCs are connected in series across the entire dc link (i.e., capacitor tapped), whereas their ac outputs are connected to multiwinding transformers to provide the three-phase terminals for ac grid integration. The proposed grid-connected capacitor-tapped multimodule converter (CT-MC) architecture, inspired from the HVdc shunt tap proposed by ABB, provides a dc–ac conversion with a relatively moderate voltage rating of semiconductor devices. It also provides operation with a lower number of semiconductor devices, gate driver circuits, voltage sensors, and lower total MVA rating of semiconductor devices (67%) compared with the conventional three-phase HB modular multilevel converter, which positively affects the system cost and reduces the computational burden of the employed controller. In this paper, the operational concept and control of the CT-MC are presented along with a capacitor voltage balancing approach. Simulation results are presented during normal and abnormal conditions to show the viability of the proposed architecture. Finally, a scaled down prototype for the CT-MC is employed to validate the converter operation. [ABSTRACT FROM AUTHOR]

Pulsed electric field is a commonly used and effective disinfection method in drinking water treatment applications. In this paper, a transformerless unipolar/bipolar high-voltage pulse generator is presented with well-regulated pulsed output voltage for drinking water treatment via underwater pulsed corona discharge. The proposed high-voltage pulse generator is fed from a relatively low-voltage dc supply. Then, capacitor–diode voltage multiplier centrally fed from a dc–dc boost converter is used to elevate the input voltage to a proper high-voltage level. Finally, a modular multilevel converter is employed to chop the elevated voltage into unipolar or bipolar pulsed output voltage (based on the user selection). The suggested arrangement provides a high-voltage gain with relatively low-voltage components, i.e., neither high-voltage nor series-connected components are needed in the proposed approach. A comparison between the proposed approach and the other Marx-Based pulse generators has been held to show the merits of the proposed approach. A detailed design of the generator passive components and semiconductor devices has been presented. Simulation and experimental results are presented for the unipolar as well as the bipolar pulsed output to validate the proposed concept. [ABSTRACT FROM AUTHOR]