New method for rotor time constant tuning in indirect field oriented control

The purpose of this paper is to investigate and implement a new adaptive controller for correction of the rotor time constant used in the calculation of the slip frequency in Indirect Field Oriented Control (IFOC) of induction machines. The implementation of the controller is based on the machine air gap flux which is measured by detecting the third harmonic component of the stator phase voltages. The proposed adaptive controller depends only on a single, easily measurable machine parameter estimate, namely the magnetizing inductance. Moreover, a correction strategy to compensate for changes of the magnetizing inductance when changes in the air gap flux level occur is also proposed in this paper. Such strategy is based on a function that relates the value of this inductance to the amplitude of the third harmonic stator voltage component. This new controller does not require any sensors in the air gap of the machine nor does it require complex computations. Only access to the stator neutral connection is necessary to measure the air gap flux. Verification of the validity and feasibility of the technique is obtained from simulation and experimental results.