DC Motor Precise Speed Control System by Applying PLL-IC

In recent years, Phase-locked-loop electric circuits manufactured by integrated circuits techniques have promoted development of the precise motor speed control. The most popular example nowadays used is the speed control of Direct Drive Motor in a Stereo-turntable. The authors aim to apply the PLL motor speed control to industrial motor drive. In this paper, we regarded this system as a Sampled-data feedback control system and analyzed its stability by using a Z-transform method. By experiment, the following results were confirmed. 1) When the sampling frequency becomes low, the stability limit gain is decreased. 2) At the low sampling frequency, the stability limit gain is inversely propotional as the mechanical time constant and damping factor over 0.5 is necessary. 3) The steady state error of motor speed is zero. 4) Speed change under driving is very difficult.