Study of main flux saturation effects in field-oriented induction motor drives

Effects caused by the variable degree of main flux saturation in induction machines with field-oriented control are considered. An indirect vector controller with a fixed value of magnetizing inductance is assumed, and the influence of variable saturation in steady-state and during transients is investigated. It is shown that the saturation effect is likely to be pronounced during operation in the field-weakening region, while its influence is small in the constant flux region if the value of magnetizing inductance in the controller is correctly set. Experimental identification of the rotor time constant in the field-weakening region is performed, and the results are presented. A modified flux calculator is derived, which can provide satisfactory operation in the field-weakening region. Its structure involves the magnetizing curve of the machine. The proposed flux calculator is verified by digital simulation.