PERFORMANCE INVESTIGATION OF HIGH POWER FACTOR BIDIRECTIONAL CONVERTER FED DC DRIVE

Abstract

Smooth and precise speed control over a wide range with reliabity and good transient response is the main requirement of almost all the drives. DC drives have been preferred from the very beginning due to the fulfillment of above -requirements. Nowadays for speed control WARD-LEONARD static control method is generally used and DC motors are powered by power-converters. The main problems with the conventional converters are the poor input power factor and a large harmonic content in the AC supply current, ".... thus, resulting in the polluted power supplies which have a.very bad effect over, the health of the power systems. Many harmonic standards_ have already been published to check the harmonic content and to ensure the unity power-factor. A lot of researches have been devoted towards the development of power filters. While some research work has been done on the passive filters, active filters have also been a subject of research. Hybrid filters have also been developed. The power filters are costlier and bulky which led -to the development of high power-factor converter. This dissertation work deals with the application . of a single-stage unity-power-factor buck-type pulse width modulation (PWM) bi-directional rectifier to medium- and high-power 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 wavd'orms. These _ properties of output voltage and current quantities of the converter eliminate entirely any failure risk in current commutation even for oldest motor designs. The design criteria and operating features and characteristics of the buck-type PWM bi-directional rectifier employed in a unity-power-factor dc motor drive are discussed in the report