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This paper describes the application of a single-stage unity-power-factor buck-type pulsewidth modulation (PWM) rectifier to medium- and high-power variable-speed dc motor drives. The advantages of the developed system are low harmonic distortion in AC supply currents (complying with IEEE Std. 519 and IEC 555), nearly unity power factor over a wide operating shaft speed range, and nearly level armature current and voltage waveforms. These properties of output voltage and current quantities of the converter eliminate entirely any failure risk in current commutation even for oldest motor designs, and further motor problems such as accelerated aging in motor insulation, and mechanical failure due to circulating bearing currents. The design criteria and operating features and characteristics of the buck-type PWM rectifier employed in a unity-power-factor DC motor drive are discussed in the paper. The performance of the resulting system has been tested on 25-65-kW 100-150-A 10-20-kHz DC motor drives, used in various processes of an iron and steel plant.