The conventional direct torque control (DTC) features control structure simplicity, fast dynamic response, and parameter robustness. Nevertheless, it suffers from the problems of variable switching frequency and large torque ripples. This paper presents a modified DTC algorithm for interior permanent magnet synchronous motor drives with fast torque dynamics and constant switching frequency. The aforementioned problems are alleviated by adding a PI torque regulator to autonomously alter the effective duty cycle of the applied voltage vector. As a result, a constant switching frequency and also reduced torque ripples are obtained while retaining the benefits of the classical DTC. In addition, the torque dynamic response is further improved by introducing a modified switching table during transient conditions. By incorporating the modified switching table, the torque dynamic response is superior to that of the classical DTC. Simulation and experiment results included confirm the effectiveness of the proposed method.