I. Introduction
Direct torque control (DTC) is first proposed for induction motor drives by Depenbrock [1] and Takahashi [2] in the middle of 1980s. The basic idea of DTC is to control the flux linkage and torque by selecting the voltage space vectors properly. Compared with Field Oriented Control (FOC), DTC does not require any current regulator, coordinate transformation and PWM signal generator. And the DTC has the advantages of simplicity, faster dynamic torque response, and less machine parameter dependence. In the late 1990s, DTC techniques began to apply in the permanent magnet synchronous machine (PMSM) machine drives [3]–[4].