A method of correcting the stator flux estimate midpoint in alternating-current systems, the method comprising the step of determining a stator flux estimate (&PSgr;s, est?). The method is characterized in steps of forming the sum of the squares of the rectangular components (&PSgr;sx, est?, &PSgr;sy, est?) of the stator flux estimate to obtain a reference variable (k), low-pass filtering the reference variable (k) in order to obtain a low-frequency component (kfilt) of reference variable, subtracting the low-frequency component (kfilt) from the reference variable (k) in order to obtain a difference variable (e), determining rectangular correction term components (&PSgr;sx, corr?, &PSgr;sy, corr?) of the stator flux estimate (&PSgr;s, est?) by multiplying the difference variable (e) by the rectangular components (&PSgr;sx, est?, &PSgr;sy, est?) of the stator flux and a correction coefficient (K&PSgr;corr), and forming a midpoint-corrected stator flux estimate (&PSgr;s, fin?) by adding the correction term components to the components of the stator flux estimate.