An instrument for measurement of induction motor drives based on phasor and modelling techniques

This paper describes a practical instrument for realtime visualization of t he necessary quantities for analysis, diagnosis and investigations of AC ma chine drives on an oscillographic display. The instrument needs no shaft po sition or speed sensor, it uses exclusively the acquired stator currents an d voltages and provides information, in electrical and visual form, of: sta rer and rotor flux, torque, reactive power, torque current, flux current, t orque angle and slip frequency. In the present version, the instrument circ uitry is based on analogue signal processing techniques. The theoretical ba sis is a continuous-time machine model defined by a pair of simultaneous co mplex-coefficient differential equations. A formalization of the various ca lculation methods for the signal estimation is presented as well as one int erpretative computer simulation for the stator current pattern. Practical r esults obtained with the device when applied to test and measure a real mot or drive are presented and some conclusions are drawn. Main fields of appli cation of the calculator include: monitoring systems, control units, resear ch tools for induction motor drives, and test shops.