The optimum-seeking (in the sense of maximisation of torque) field weakening control scheme proposed by Kim and Sul (see IEEE Trans. Ind. Electron., vol. 44, no.4, p.512-18, 1997) is developed further. The performance under imperfect field orientation conditions is investigated, and it is shown that an overestimated-rather than an under-estimated-model leakage inductance should be used. A slightly modified algorithm, which offers better robustness and reduced computational complexity, is presented. The importance, for good performance, of combining the scheme with a current controller featuring anti-windup and improved disturbance rejection is emphasized. The dynamics of the resulting closed-loop system are analysed. Thus obtained are rules for selection of all controller parameters, allowing for straightforward implementation and commissioning. Good performance of the resulting system is verified experimentally.