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This article presents two single-phase to single-phase three-wire converters based on two-level and three-level neutral-point-clamped legs. The converters present a shared-leg between the grid and load. A space-vector pulsewidth modulation technique considering the harmonic distortion and the semiconductor losses is presented, besides the dc-link voltage-balance technique to balance the neutral-point voltage. The converters can supply the loads with constant amplitude and frequency under grid voltage disturbances. These characteristics make the proposed converters suitable for applications as uninterrupted power supply. The proposed converters are compared to a conventional two-level converter from simulated results for evaluating the semiconductor losses and harmonic distortion. The experimental results are provided to illustrate and validate the operation of the proposed systems. [ABSTRACT FROM AUTHOR]

This paper proposes two hybrid topologies based on a single ac–ac modular multilevel cascade cascade converter (MMCC) with double-star chopper cells (DSCC), in each of which a voltage reference technique (VRT) is associated for generating the output modulating references. In doing so, either the grid-connected leg or the shared leg can be switched at the line frequency, thus reducing the switching losses. For proper operation of the VRTs in real-time, the input and output converter voltages must be in sync, hence a synchronization technique is proposed. Furthermore, when no dc-link capacitor is used in a DSCC converter, the dc-link is subjected to voltage ripples derived from the pulsewidth modulation (PWM) technique. In that case, high-frequency PWM techniques can produce high-frequency components across the arm inductors, which are reflected in the dc-link. Therefore, this paper focuses on the operability of the hybrid modular multilevel DSCC converters, but also on the investigation of the proposed VRTs in reducing the dc-link voltage ripple on the conventional DSCC converter using PWM with phase-shifted carriers (PSCs). Simulated and experimental results are presented to validate the proposed techniques and converters. [ABSTRACT FROM AUTHOR]