VARIABLE-FREQUENCY SYNCHRONOUS MOTOR-DRIVES FOR ELECTRIC VEHICLES

The performance capability envelope of a variable-frequency, permanent -magnet synchronous motor drive with field weakening is dependent upon the product of maximum current and direct-axis inductance, To obtain a performance characteristic suitable for a typical electric vehicle d rive, in which short-term increase of current is applied, it is necess ary to design an optimum value of direct-axis inductance. The paper pr esents an analysis of a hybrid motor design which uses a two-part roto r construction comprising a surface-magnet part and an axially laminat ed reluctance part. This arrangement combines the properties of all ot her types of synchronous motor and offers a greater choice of design v ariables, It is shown that the desired form of performance may be achi eved when the high-inductance axis of the reluctance part is arranged to lead the magnet axis by 90 degrees (elec.).