Automatic Mode Switching of P/PI Speed Control for Industry Servo Drives Using Online Spectrum Analysis of Torque Command

Conventional proportional/proportional-integral (P/PI) speed controller for today's servo drives has to be manually tuned at the controller switching set point by trial and error, which may translate into drive system downtime and a subsequent loss of productivity. The adjustable drive performance is heavily dependent on the quality of expert knowledge. The performance becomes inadequate in applications where the operating conditions change in a wide range, i.e., tracking command, acceleration/deceleration time, and load disturbances. In this paper, we discuss the demands on simple controls/setups for industry servo drives. Analyzing the frequency content of the motor torque command, P/PI speed control mode switching is automatically performed with only a prior knowledge of the mechanical time constant. The dynamic performance of the proposed scheme assures a desired tracking response curve with minimal oscillation and settling time over the entire set of operating conditions. For a comprehensive comparison of conventional P/PI control scheme, we carried out extensive tests on an actual servo system.