Direct torque control of PM synchronous motor drives

This chapter describes the direct torque control (DTC) technique for permanent magnet synchronous motors/machines (PMSMs). The DTC technique has evolved much since mid-1980s when a less complex, cheaper and potentially faster method of torque and flux control than the pre-existing rotor flux-oriented vector control (RFOCNC) for induction machines first emerged. The DTC technique is based on closed-loop regulation of torque and stator flux linkage obtained from estimators using voltage vectors and currents in the stator reference frame and the machine model. Drive dynamics under DTC control is as fast and can be faster than that under RFOCNC in which rotor position sensing is used for exercising control in the rotor reference frame. This chapter starts with a brief review of the context of these developments, including the underlying theory (which had existed prior) and methods that have been used to apply DTC to PMSMs. Some comparative evaluations are included that may help researchers and engineers to further develop the method and apply it to high-performance PMSM drives in various applications.