Wide-Speed Direct Torque and Flux Control for Interior PM Synchronous Motors Operating at Voltage and Current Limits

This paper proposes a wide-speed direct torque and flux control method associated with the inverter voltage and current constraints of interior permanent-magnet synchronous motors. The proposed approach has potential advantages controlling torque and flux linkage at the voltage and current limits, since no integrators are employed for torque control or flux weakening. The transition between the non-limited operation and maximum voltage modulation can be achieved automatically without modifying the control law. To confirm this, we provide a graphical and analytical analysis that naturally leads to a unique stator voltage vector selection on the hexagon. The proposed controller can maximize the available inverter voltage and generate a higher output torque than conventional current vector controllers at high speeds. The method developed in this paper also retains the beneficial features of classical direct torque control, such as its fast dynamics and direct manipulation of the stator flux linkage for flux weakening.