High speed vector control without encoder for a high speed spindle motor

A 40000 RPM vector-controlled induction motor drive is introduced. In a previous paper by T. Kume et al. (see Proc. IPEC 1990 conf., Tokyo, p.1132-1136, 1990), conventional vector control with a shaft encoder was employed in a low-speed range, while constant V/f (volt-per-hertz) PWM control was employed in a high-speed range. The two control modes were switched at approximately 20000 RPM. By employing phase compensation and instantaneous current limit, the dead-time between two modes was minimized. This technique is further improved by the authors. The constant V/f PWM control in the high-speed range is replaced by vector control without an encoder. The current control loop is not interrupted for mode changing, and thus continuous operation over the entire range is established.<>