The development and testing of a double-loop resolution-level controller for a 3ϕ WM inverter-fed induction motor

This paper presents the development and the performance testing of a double-loop resolution-level controller (RLC) for adjusting outputs of the new wavelet modulated (WM) inverters when supplying three-phase (3phi) squirrel-cage induction motors. The basis of the proposed controller lies in the fact that adjusting the scale j of the successive dilated and translated version of the scale-based linearly-combined synthesis scaling function phitilde_j(t) can change the magnitude as well as the frequency of the WM outputs. The change in the scale j alone, which is achieved by single-loop RLC, can provide a limited range of magnitude variations while maintaining the output quality. This limited range is due to the fact that changing j creates a translation that is inherent in phitilde_j(t). To increase the range of varying the outputs of WM inverters, a double-loop RLC can be utilized such that one loop is responsible for correcting the translation as the scale j is changed. The double-loop RLC based WM inverter is realized for both MATLAB/SIMULINK simulation as well as experimental performance testing when incorporated in a 3phi capacitor-run induction motor drive. Simulation and experimental test results show effective responses to different changes in operating conditions of the tested drive. Also, some performance comparisons are conducted with the single-loop RLC as well as the conventional PI-based PWM inverter-fed 3phi drive to demonstrate the advantages of the proposed drive.