The disadvantages of the Brushless DC Motor over the AC motors are:
higher maintenance (due to brushes)
more expensive
In addition to the above the Brushless DC Motors have the same advantages over AC motors but they also have more advantages over Brushed DC Motors
lower maintenance (no brushes)
even higher starting torque ( Due to rare earth magnets)
even higher efficiency (over 90%) on sub fractional motors
even more compact design
better heat dissipation
lower noise
This paper presents a novel application of the Variable Structure System Control (VSS) for on-line tracking of dc motors. By the proposed technique, the rotor position, speed and current can follow preselected tracks (a track is a time history selected in advance). The theory of the VSS is modified to include the tracking option for the general case of multi-input/multi-output system. The robustness of the proposed tracking controller is ensured at all time. By selecting the tracks as proposed in this paper, the electrical and mechanical stresses on the motor are substantially reduced, and the "soft starting" of the motor is achieved. The entire drive system is built and tested in the laboratory by using off-the-shelf components and software. The test results show the effectiveness of the proposed tracking controller in the high performance drive applications such as robotic, manipulation and actuation.
