Low speed performance improvement in sensorless drive using measured stator voltages of PWM voltage source inverter

Besides the quality of used parameters also the applied voltage is an important issue in the speed sensorless induction motor control. Information contained in the value of measured rotor speed has to be obtained from other available signals, especially the stator input voltages. However, the actual output voltage of the voltage source inverter differs from the reference value. This influence is especially important in low speed region where the error in calculated flux values might cause not only reduced pull-out torque and additional losses of the machine but also the unstability of the drive system. While one would like to avoid measurement of actual stator voltages because of its complexity and higher cost of the system, additional performance improvement in very low speed region can only be achieved with exact knowledge of voltage. But this can only be obtained by using measurements. The main goal of this paper is to present advantages of stator voltage measurements in low speed region of speed sensorless drives over cost effective solutions using dead time compensated inverter.