Limitation of the load angle for direct torque control of PMSM

In direct torque controlled system, the load angle isn't the directly controlled variable, but it is an important one. If it isn't limited and exceed a certain range, it will influence the stability of the control system. In this paper, the problems of existing methods for the limitation of the load angle in direct torque controlled Permanent Magnet Synchronous Motor(PMSM) system are analyzed. By utilizing a classic PI regulator and the limitation of current, an improved comprehensive method combining the concepts of indirect and direct load angle limitation method is put forward. This method is proved to be validated by simulation and experiment in the end of the paper, and the results show good performance in steady and dynamic state.