Comparison of true running at different concepts of controlling brushless DC-motors

A comparison of true running between servo motor drives has been performed until now only by examination of the torque ripple. As the torque ripple can only be minimized-several possibilities are shown briefly in the presented paper-the influence of the current control method and of the speed controlling concept cannot be neglected because of the controller´s capabilities to reduce the always existing torque ripple of a brushless dc motor. In order to investigate these capabilities a new method of measurement and suitable criteria are to be introduced. The measurement system presented in this paper allows one to examine the variation of speed and acceleration very precisely after an off-line evaluation of the measurement dataset, whereas the presented criteria are used for the real comparison of the servo motor drives concerning their true running. The control concepts compared in this paper are: PI speed controller combined with rectangular and sinusoidal current waveforms; current waveforms with additional harmonics in order to compensate known (i.e. measured) torque ripple, and a state controller with a load torque observer