Abstract
This paper proposes and investigates a multilevel ac six-phase motor drive. The system is composed of five isolated three-leg voltage source inverters feeding the open-end windings of an asymmetrical six-phase induction motor (SPIM), which is adequate to generate multilevel voltages for high-power systems with voltage rating restrictions. A simple space vector pulse-width modulation (PWM) based on three similar individual planes and its implementation by means of equivalent level-shifted PWM are presented. A space vector pattern with a high number of voltage vectors redundancies is obtained. These redundancies and the application sequence of the voltage vectors are selected to minimize the amount of changes in the switching states and to decrease the harmonic distortion of the generated voltages. The vector pattern of this optimal modulation is obtained by analyzing only one plane and applied in the same way to the three planes as if they were independent. The developed PWM techniques have low computational complexity and are suitable for low-cost hardware implementations. Simulation results are used to compare the proposed topology with a conventional configuration in terms of harmonic distortion and semiconductor losses. Experimental results demonstrate the feasibility of the proposed drive system.

Abstract
An unidirectional single-phase three-wire rectifier is proposed in this paper. Such topology is composed of a noncontrolled leg, two controlled legs, and a capacitor bank. A suitable model, pulse-width modulation, and control strategies of the system are proposed as well. The control strategy includes the synchronization method, in which it imposes the grid currents with the same phase angle of the voltages generated by the rectifier. This method ensures sinusoidal grid currents and mitigates the zero-crossover distortions normally caused by the use of diodes. A comprehensive comparison with two conventional configurations is also presented in this paper. Simulation and experimental results are also presented for validation purposes.

Abstract
This paper investigates the utilization of two different six-leg configurations of single-phase to three-phase converters. One of the topologies is transformerless and the other is transformer based. The studied converters allow feeding the load voltage with sinusoidal voltages with constant amplitude and frequency, and to operate with sinusoidal grid current with high power factor. The system model and pulse-width modulation techniques for one of the topologies are given. Control strategies for both topologies are provided. The studied topologies are compared with the conventional in terms of dc-link specification, voltages harmonic distortions, semiconductor losses, and other characteristics. Simulation and experimental results are provided to illustrate the operation of the systems.

Abstract
This paper proposes two unidirectional single-phase ac-dc-ac converters with a reduced number of controlled switches composed of two three-leg converters connected in series. The proposed converters allow us to feed the load voltage with sinusoidal voltages with constant amplitude and frequency and to operate with sinusoidal grid current with a high power factor. The converters can then be used as uninterruptible power supplies and unified power quality conditioners for nonregenerative applications. The system model, space-vector pulse width modulation technique, and a complete control system are given. A method to regulate the dc-link voltages using the voltage vector redundancies is presented. The proposed topologies are compared with the conventional one in terms of operation range, capability to operate with a unity grid power factor, voltage harmonic distortions, semiconductor losses, and others characteristics. Simulation and experimental results in many operating conditions are provided to validate the feasibility of the system.

Abstract
This paper investigates an ac-dc-ac multilevel power converter. The studied configuration is composed of two single-phase ac-dc-ac three-leg modules and series-connected H-bridges in the shared part of system. Because the proposed converter has shared legs between the input and output, it is employed in applications with same input and output frequency. Uninterrupted power supply and unified power quality conditioner are application examples for this converter. Such multilevel topology has lower dc-link voltage rating, which, consequently, presents low switch blocking voltages when compared to conventional topologies. System model, a space-vector pulsewidth modulation (PWM) strategy to symmetrical and asymmetrical dc-link voltages, and an overall control strategy to adjust the system variables are presented. A power flux analysis shows the operation zone in which the individual dc-link voltage balancing is possible. PWM and control strategies are developed to reduce the semiconductor total losses, harmonic distortion, and switching stress. Two ac-dc-ac multilevel conventional structures are used for comparison. Simulation and experimental results demonstrate the feasibility of the studied converter.

Abstract
This study presents an ac-dc-ac converter with eight controlled switches. The proposed topology is applied as a universal active power filter, compensating for disturbances in the grid voltage, voltage sags/swells, and harmonics generated by non-linear loads. The difference between the proposed and conventional solution is the addition of an uncontrolled leg (composed only of diodes) to increase the number of voltage levels, reducing harmonics and the average switching frequency. For performance comparisons, current total harmonic distortion (THD), voltage weighted THD, switching and conduction losses of the semiconductors, and average switching frequency were used as parameters. Control and pulse-width modulation techniques based on space vector approaches were developed to eliminate zero-crossing distortions caused by the use of the uncontrolled leg. Simulation and experimental results were presented for validation of the mathematical model.