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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