Abstract: A mathematics model of speed observer of direct torque control (DTC) system is derived, and a DSP-based speed-sensorless DTC system is designed and tested. It exhibits extremely fast torque response, which is 0.86ms for a nominal torque step. The accuracy of shaft speed estimate is very good, which reaches 0.5% above 100r/min. This system is used extensively in aircraft due to its excellent performance and reliability.

Key words: direct to rque cont ro l, speed2senso rless, AC speed modulat ion, induct ion mo to r