Abstract: Higher requirements for the stability of turbomachinery rotors are put forward due to large-scale industrial production，and demands for stability evaluation and modification method becomes extremely urgent as well. The sine-swept vibration excitation experiment with electromagnetic actuator is conducted, and the least square method is used to estimate the frequency response function (FRF) to improve the data accuracy in frequency domain. Additionally, mean filter is used to restrain the high-frequency noise to make the frequency response characteristic clearer. The traditional multiple input multiple output frequency response function (MIMO FRF) is transformed into direct frequency response function (dFRF) from real number field to complex field with a transformation matrix, eliminating the influence of forward and backward modal superposition. The modal parameters are abtained for stability estimation by using the rational polynomial method to fit and identify the traditional MIMO FRF and dFRF on complex field. Get through theory calculation and experimental verification, the results show that this method has enough accuracy.The method can provide both theory basis and technology foundation for improving the rotor stability of the centrifugal compressor.

Key words: centrifugal compressor;rotor stability;least square method;FRF;rational polynomial method