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Common-mode voltages appear in pulse-width modulated current-source inverters (PWM-CSIs) drives due to the operating principles of the input rectifier and the output inverter. This paper presents the modeling and analysis of a medium voltage current-source inverter drive, using the Matlab software. Simulated results of the model are in close agreement with experimental waveforms obtained from an industrial ac drive, which shows overvoltages of up to 100%, generating important insulation stresses at the motor stator terminals. Index Terms-Common-mode voltages, medium voltage ac drives, PWM-CSI. NOMENCLATURE Three phase source terminals. Motor terminals. Ground of the three-phase source. Neutral point of the motor. Rectifier output terminals. Inverter input terminals. Voltage of phase of the source with respect to the ground. Voltage of phase of the motor with respect to neutral. I. INTRODUCTION I N THE last decade, an important development in medium voltage drives has been observed [1]-[3]. A very important aspect in the use of these converters is the voltage stress presented at the motor terminals, especially in retrofit applications. Usually, the isolation of the stator windings in medium voltage motors is not so oversized as in low voltage machines. An important source of overvoltages, are the common-mode voltages generated by rectifiers and inverters when they change their topology, due to the commutation of the power semiconductors. This aspect is especially important in pulse-width modulated current-source inverter (PWM-CSI) drives and has received increasing attention lately [4]-[6]. In addition, PWM converter-fed drives have been found to be a very important

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The increasing use of photovoltaic systems entails the use of new technologies to improve the efficiency and power quality of the grid. System performance is constantly increasing, but its reliability decreases due to factors such as the uncontrolled operation, the quality of the design and quantity of components, and the use of nonlinear loads that may lead to distortion in the signal, which directly affects the life of the system globally. This article presents an analysis of the reliability of a single-phase full-bridge inverter for active power injection into the grid, which considers the inverter stage with its coupling stage. A comparison between an L filter and an LCL filter, which comprise the coupling stage, is made. Reliability prediction is based on metrics, failure rate, mean time between failures, and total harmonic distortion. The analysis and numerical simulation are performed. Finally, filter considerations are suggested to extend the reliability of the inverter in a photovoltaic system.

Nowadays, the microprocessors family normally require for the input source not only low voltage but also high current. There exists an increasing necessity for developing new applied techniques on topologies and control strategies, which may be able to fulfil such requirements. Although a considerable amount of applications use the conventional buck converter for step-down for DC/DC conversion, when a high step-down conversion is required is a much better choice to implement the quadratic buck converter (QBC); however, the problem for obtaining a high step-down conversion at wide duty ratio still remains. This document proposes the delayed quadratic buck converter, which offers a very high-step-down dc-dc conversion with a wide duty cycle. The QBC is modified in its topology by adding an inductor, which allows us to obtain for the duty cycle a higher increment than this normally obtained by a quadratic one. Converter behaviour and analysis are illustrated. Experimental results are also shown for a conversion from 36 to 1.5 V and an output power of 20 W.