Excitation control of DTC controlled salient pole synchronous motor in field weakening range

Synchronous motor drives are well suited for rolling mill applications, where good performance is required both at zero and high speed in field weakening. Direct torque control (DTC) sets high dynamic requirement for the excitation control too. DTC controls only the stator flux linkage and stator current is determined according stator flux linkage. The stator current and drive stability can be, however, controlled by the excitation current. For that reason, excitation current control has an important role in DTC controlled synchronous motor drives, especially at high speeds and high loads, when the drive is working near its stability and current limits