Design of Large Telescope Elevation Axis-dual Motor Synchronous Drive Control System

Abstract

Aiming at the characteristics of large elevation axis span, large moment of inertia and low resonance frequency of large ground-based telescope, a dual motor synchronous drive control system is designed. The control system uses two identical permanent magnet synchronous motors to drive the elevation axis synchronously. The two motors are controlled by two independent drivers, and the electrical angle offset is calibrated independently to ensure the driving consistency. The controller transmits electric angle offset and torque reference through EtherCAT bus. The control algorithm consists of two current loops and one speed loop, both of which are PI controllers. The current loop is the first-order control system and the speed loop is the optimal 2-order control system of ideal closed-loop. In order to further improve the control bandwidth of the speed loop, a structural filter is added to suppress the mechanical resonance peak. Experimental results show that the first order anti resonance frequency of the servo system is increased from 14 Hz to 20.4 Hz. After adding the structure filter, the -3dB bandwidth of the speed closed-loop can reach 6.4HZ. Through the step response test and low-speed tracking test, the system has good dynamic response process and low-speed stability, which can meet the high-precision control requirements of ground-based large aperture telescope.