Method for extracting motor impedance characteristics online

Abstract

Due to increases in switching frequency, the electromagnetic interference of motor drive systems has been receiving more attention. In a motor drive system, the devices in the inverter produce serious electromagnetic interference during high-frequency switching. It is necessary to model the motor drive system to predict the electromagnetic interference level. Extraction of the motor impedance characteristic is necessary for the modeling of a motor drive system. At present, most research only studies the measurement method of a motor in the static state. However, motor impedance characteristics in the static state cannot represent motor impedance characteristics in operation. In this paper, an online measurement method of motor impedance characteristics is proposed. For the three-phase asymmetric circuit caused by modulation, the motor impedance characteristics in operation are calculated by establishing Kirchhoff voltage equations. A precision power scope PX8000 is used to measure the harmonic components of single-phase voltage, single-phase current, and common-mode current. The time-delay difference of the precision power scope PX8000 between different probes is also considered. Experiments prove that the time-delay difference does not affect the measurement results. Through comparing the motor impedance characteristics measured by different filters, the method of extracting the motor impedance characteristics online is validated. Finally, the motor impedance characteristics in the static state and the motor impedance characteristics of online extraction are experimentally compared. The motor impedance characteristics of the online extraction method proposed in this paper have more advantages than traditional methods.