Brushless dc motor still suffers from commutation torque ripple, which primarily depends on transient line current in the commutation interval. In order to control the incoming and outgoing phase currents to change at the same rate during commutation, this paper presents a novel high boost ratio DC-DC circuit topology in the front end of the inverter. With a suitable closed loop control scheme, the proposed high boost ratio DC-DC converter is operated with two different duty ratios one during commutation period and the other during non commutation period. The cause of commutation ripple is analyzed, and the way to adjust the duty ratio for obtaining the desired dc link voltage is introduced in detail. Finally, simulation and experimental results show that, compared with the existing dc-dc converter topologies, the proposed method can obtain the desired voltage much faster and minimize commutation torque ripple more efficiently.
Keyword:Brushless
INTRODUCTIONBrushless dc motors (BLDCM) possessing simple structure, high power density, high torque/current ratio, robustness, and better dynamics have been widely used in all kinds of areas, such as electric vehicles, robotics, small actuators, industry and automotive electronics [1]- [3]. The performance of such motors has been significantly improved due to the great development of power converters, magnetic performance of magnets, and motion control technology in recent years [4]- [6]. However, commutation torque ripple has always been one major factor in preventing BLDCM from achieving high performance. The causes for torque ripple in BLDCM are the imperfection of motor design and manufacture, non-ideal EMF and unequal current sharing between the phases during commutation [7] and [8]. Since torque smoothness is an essential requirement for such high-performance applications, a wide variety of techniques have been proposed by many researchers during the past two decades to minimise the torque ripple [9]-[14].In recent years, multilevel inverters have gained much attention in the application areas of BLDC motor drives [21]. The problem of imperfection in the motor design is overcome in [13] [3], the inverter is operated in 120 mode for lower speed range of the machine and in 180 mode for higher speed range thereby optimizing the commutation