High bandwidth sensorless algorithm for AC machines based on square-wave type voltage injection

This paper describes a new control algorithm which can enhance the dynamics of a sensorless control system and gives a precise sensorless control performance. When high frequency injection methods with conventional manners (sinusoidal voltage injection) are used, Low pass filters (LPFs) should be used to get an error signal. However, these LPFs degrade sensorless control performances due to the time delay of LPFs themselves. To avoid this effect, the proposed method uses square wave type voltage injection instead of the sinusoidal type voltage injection. As the result, the error signal can be calculated without any delay, and the position estimation performance can be enhanced. This paper contains the voltage injection method and corresponding signal processing method. Using the proposed method, the performance of sensorless control can be enhanced remarkably. The bandwidth of current controller was enhanced up to 250 Hz and that of speed controller was up to 50 Hz.