Optimizing of the Efficiency by the Control of Inverter-Fed Induction Machines Especially Regarding Saturation and Heat Effects 1

Abstract The operation of inverter-fed induction motors at optimal efficiency and low current consumption demands an adaption of the magnetic flux to the several loads. The flux-torque characteristic suited for this purpose cannot generally be predicted for any machine, its derivation rather demands a detailed knowledge of the saturation and the additional losses. The paper presents an improved equivalent circuit taking these effects into account and derives for a given test machine a control characteristic producing the desired performance. If any method of indirect flux control is applied, the load dependant rotor temperature appears as considerable disturbance variable. An observer is presented which estimates the temperature without additional sensors using measured terminal voltage and current.