Analysis of the naturally commutated, convertor-fed induction motor drive system using a flux vector method

The paper presents a prediction method for the naturally commutated induction machine drive. Analytical models of the major components of the drive scheme suitable for time-stepping simulation are developed. The adoption of a reference frame for the motor that rotates with the net flux vector enables a full account to be made for the magnetic nonlinearity in the motor´s main flux path. Field-oriented d,q (FODQ) equivalent circuits for the induction machine are deduced. Both the capacitor bank and inverter models are expressed in this FODQ frame to produce compatible two-axis equivalent circuits, switching functions being evolved to represent the inverter tristate switch variables. Models for the DC link inductor and the rectifier, the latter also using switching function concepts, complete the drive system model. The system model is validated through comparison between calculated and test results obtained from an experimental rig