Dynamics of Field-Oriented Control with Maximum Torque per Ampere of an Induction Motor

Abstract

The energy efficiency of electric drives in machines operated at low loads for a long time is improved by decreasing the rotor flux level. One of the most popular techniques used for this purpose is that of maximum torque per ampere (MTPA). The dynamics of this system will depend on the rotor magnetization speed, which, in turn, depends on the rotor time constant, which can be fairly high. The suggested technique of improving the dynamics of the induction motor with field-oriented control relies on using the maximum available inverter current, taking into account the restrictions of this current to induce engine rotor magnetization. It is proposed to replace steplike torque command with a profiled command shaped as a sloping straight line, which allows achieving an acceptable response speed of the drive and, at the same time, reduce the load on the mechanical part of the drive. Analytical and numerical techniques are used to determine the path that corresponds to the maximum torque dynamics, taking into account the accepted restrictions. It is shown that the suggested technique can help to achieve a dynamics of energy efficient control better than its traditional counterparts.