Method for deciding stator magnetic flux of asynchronous apparatus

PURPOSE: To provide a low-cost and reliable method by measuring only the voltage and the current of a stator of an asynchronous apparatus, and controlling it so that it may have desired torque property with a low frequency. CONSTITUTION: This method decides a stator magnetic flux of an asynchronous apparatus when a short circuit inductance σLs of an apparatus, the inductance Ls of a stator, and a time constant τr of a rotor are known, measuring a stator current is and a stator voltage Us of an asynchronous apparatus 40, and the estimate Ψse of the magnetic flux of the first stator is obtained by deciding the product of the current is of the stator and the estimate R of the stator resistance, and subtracting this product from the voltage Us of the stator, and integrating this voltage difference with time. Furthermore, an estimate Ψse.id of the magnetic flux of a second stator is decided, based on the stator voltage Us , a stator current is , a short circuit inductance σLs , the stator inductance Ls , the rotor time constant τr , and a stator resistance estimate Rse , and with this as the difference from the estimate Ψse of the magnetic flux of the first stator, a correction term ▵Ψse of the stator magnetic flux is decided, and this is multiplied by the weight of a fixed coefficient w and is added to the voltage difference.