Representation and compensation of iron loss in rotor flux oriented induction machines

Representation of stator iron loss in d-q axis models of induction machines may be done in a number of different, but always approximate ways. On the other hand, vector control principles are derived under the assumption that iron loss may be neglected. Studies of detuning caused by iron loss in indirect schemes of vector control indicate that the impact of iron loss on accuracy of field orientation is not always negligible. This paper concentrates on a direct rotor flux oriented control scheme with rotor flux estimation on the basis of measured stator currents and rotor speed (i-ω estimator) and examines at first detuning during dynamic operation caused by iron loss. An induction machine with included iron loss is represented for simulation purposes with a number of different models and the impact of induction machine model on simulated behaviour of the drive is assessed. The rotor flux estimator used in this part of the study is the standard i-ω, scheme with neglected iron loss. The second part of the paper presents a modified i-ω estimator that provides compensation for iron loss. It is shown that satisfactory compensation is achievable with an estimator that is insignificantly more complex than the standard one with neglected iron loss