Performance analysis of a high-bandwidth torque disturbance compensator

Recent availability of encoder with millions of counts per revolution makes it possible to enlarge the bandwidth of the torque disturbance observer (TDO) equipping a servo drive. As a consequence, the TDO dynamics are no more decoupled from those of current and the behavior of the torque disturbance compensator (TDC) is influenced by the current dynamics as well as by the discrete-time implementation of TDO. The purpose of this paper is to analyze the TDC performance under the above-mentioned circumstances. The main outcome is the underdamped or even unstable behavior of TDC. Another outcome is the limited range of values allowable for the parameter mismatch to preserve stability. The conditions on the TDO bandwidth and the parameter mismatch for TDC to be stable and to be damped are provided. Experimental tests are given, which substantiate the theoretical findings.