DC-DC converter current source fed naturally commutated brushless DC motor drive

Abstract

The aim of this work is to reduce the cost and size of a brushless dc motor (BLDC) drive as well as increase the reliability and ruggedness of that drive. Traditional BLDC drives use Voltage Source Inverters (VSI) that utilize hard switching, thereby generating switching losses and entail the use of large heatsinks. VSI needs a huge dc link capacitor that is inherently unreliable and is one of the most expensive components of a drive. Hence, a Current Source Inverter (CSI) is used to replace the hard switchings by natural turn-off, thereby eliminating the heatsinks as well as the large dc link capacitor. A controlled rectifier together with a large inductor act as the current source. The only disadvantage is the large value of the dc link inductor and the huge number of turns needed to achieve these values of the inductances lead to huge resistive losses. Therefore, it is shown that it is possible to replace the controlled rectifier and the large inductor with a suitable dc-dc converter based current source switching at high frequencies and a much smaller value of the dc link inductor. Switching at high frequencies makes it possible to reduce the value of the dc link inductor without increasing the current ripple. Hence, it is possible to have the advantages of using a CSI as well as reduce the value of the dc link inductor without a corresponding increase in the heat sink and snubber requirements.