Tuning rules for the PI gains of field-oriented controllers of induction motors

In a recent contribution, the authors have shown that field-oriented controllers for induction motors preserve stability under a wide range of variations of the motor and controller parameters. However, as is well known, the transient performance critically depends on the tuning of the gains of the proportional-integral (PI) velocity loop, a task which is rendered difficult because of the high uncertainty on the rotor resistance. The problem me address in this paper is how to develop an offline procedure to choose these gains. The main contribution of our work is a very simple frequency-domain test that, for each setting of the PI gains, evaluates the maximum range of the relative rotor resistance estimate for which global stability is guaranteed. In this may, we provide a quantitative estimate of the performance of the PI controller. The stability result may also be used in a dual manner, fixing now the range of the rotor resistance, and estimating an admissible interval for the PI gains that preserves global stability. Instrumental for our study is the exploitation of an energy dissipation (strict passivity) property of the system.