Speed Sensorless Commissioning of Resonating Mechanical System in Electric Drives

Artificial excitation signal based commissioning routines has been widely applied for the identification of the resonating mechanical system in electric drives. The commissioning tests encountered in the industry are mostly related to the detection of the first resonating mode, to be more specific, to the estimation of the two-mass-system model approximation needed for the velocity PI controller tuning. A standard identification procedure uses the torque reference as an input signal and the output is the measured velocity signal obtained from the encoder. However, most of the industrial drives are based on sensorless operation, thus there is no possibility to measure the velocity, but some information from the mechanical system is needed for the control design. This paper addresses to the issues related to the speed sensorless identification under closed loop control. A closed loop identification routine where a pseudo random binary sequence (PRBS) is superposed to the velocity control output is studied experimentally by considering a standard commercial frequency converter in sensorless mode driving an induction machine that is connected to resonating mechanical system.