A Microprocessor-Based Current Controller with an Internal Current-Rate Loop for Motor Drives

A new current-control method that is suitable for microprocessor-based speed regulation of motor drives is described. The method achieves fast-response and high-accuracy performance by using a major current loop and an internal current rate loop. The former loop is used to control precisely the mean value of the motor current by employing a current feedback signal obtained from a smoothing filter of the rippled current. The latter loop is used to stabilize the major loop with a high gain and to limit the variation rate of the motor current by employing the current feedback signal obtained from the instantaneous current without time delay. A current controller using a microprocessor was trail-manufactured and tested with a thyristor-converter-driven dc motor. It was found that fast-controlled current response can be obtained, even with a relatively long sampling period.