Abstract
This paper presents a nine-leg (9L) multilevel inverter to drive a six-phase induction machine in an open-end winding (OEW) configuration. The system is based on three conventional two-level three-phase voltage source inverters (VSIs) and three, two, or one isolated dc links. A machine with two sets of 30 degrees shifted three-phase stator windings is considered. The inverter operating principles are discussed and a simple space-vector pulse-width modulation (SV-PWM) is proposed. The 9L-OEW system is compared with two conventional drives: the six-leg two-level (6L), and the 12-leg OEW (12L-OEW) systems. The number of components, the required dc-link voltage, voltage and current harmonic distortions, torque ripple, and semiconductor losses are considered as figures of merit. Simulations and experiments were also performed, showing steady-state results for a 1 HP machine operating at constant torque.

Abstract

Abstract
This article proposes a series compensator with unbalanced voltage sag ride-through capability applied to grid-connected induction motors. A conventional three-phase voltage source inverter (VSI) is intended to regulate the motor voltages. The VSI is connected in series with the grid and a three-phase machine with open-ended windings. The proposed system is suitable for applications in which no frequency variation is required, like large pumps or fans. The VSI dc-link voltage operates as a floating capacitor through the energy minimized compensation (EMC) technique, in which there is no dc source or injection transformer. The motor load condition determines the minimum grid voltage positive component (sag severity) to keep EMC operation. Meanwhile, a voltage unbalance may increase the dc-link voltage requirements. A 1.5-hp four-pole induction motor has been used to verify the ride-through capability of the proposed compensator under grid voltage disturbances. A total harmonic distortion (THD) analysis of grid currents demonstrates that the proposed system provides low THD even if no passive filter is used. The operating principle, converter output voltage analysis, pulsewidth modulation technique, control strategy, and components ratings are discussed as well. Simulation and experimental results are presented to demonstrate the feasibility of the system.

Abstract
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
This article proposes four converters for interfacing a single dc power source and loads of a single-phase three-wire system. The topologies of the proposed converters are based on two-level (2L) and three-level neutral point clamped (NPC) legs. For regulating the dc-link capacitors of the NPC-based converters, a dc-link voltage-balancing technique is proposed to balance the neutral-point voltage using the space-vector pulsewidth modulation, considering the harmonic distortion of the output voltages and the semiconductor losses from an algorithm that defines the vector sequences to be applied. These characteristics make the proposed converters suitable for applications in microgrid employing dc distributed energy resources or ac power supply by adding ac-dc stage. The proposed converters are compared to a conventional 2 L converter from simulated results for evaluating the semiconductor losses in balanced and unbalanced load scenarios. Experimental results are presented to verify the effectiveness of the proposed voltage-balancing technique and to validate the converters.

Abstract