Steady state analysis of speed sensorless control of induction machines

This paper presents an advantageous way for calculating the speed of an inverter-fed induction machine if only the DC link voltage and the motor currents are measured. Using a complete machine model, the difference between estimated and measured currents is employed to calculate rotor speed and machine parameters like stator or rotor resistance. The paper treats the theoretical background of speed estimation at steady state especially at very low stator frequencies. The occurring instabilities in a small operating area around stator frequency zero can be overcome by processing the stator current difference in a suitable way. The deduction of the speed estimation scheme uses space vector theory. Its validity is shown with practical results