apparatus is disclosed wherein parameter values for the stator resistance , the main inductance and the stray inductance of an asynchronous machine is detected without using information about the rotor position . thereby the apparatus consists of an emf - forming circuit , an arithmetic control circuit , an arithmetic model circuit , and a control circuit . all circuits are coupled to form an overall model circuit designed according to a closed loop circuit to simulate the operational conditions of an asynchronous machine . in a balanced position of the control circuit the output signals of the control circuit represent the actual parameter values to be determined .