模態參數識別的過程中，模態干涉常會造成可識別性的問題，影響系統識別的精度。產生模態干涉的主要原因通常有相近頻率、高阻尼比及阻尼非比例性過大等等;此外在識別時產生虛假模態，影響判斷結構模態的正確性。本文主要在探討頻率域模態參數識別，針對前人所提出的有理正交多項式法以及最小二乘複頻域法進行深入研究。
根據結構動力學的理論，頻響函數可表示成有理分式的型式，因此可藉由曲線嵌合的方式得到有理分式的系數進而求得模態參數，虛假模態是在曲線嵌合過程中經由誤差所產生的模態，因此在不同的階數其參數並不穩定，結構模態的模態參數則較為穩定，可藉由此特性得到系統的真實模態資訊，在未提高階數的情況下，吾人提出利用系統特徵值的成對特性以及殘值數值的大小加以區別。吾人將非比例阻尼系統的頻響函數以各模態的疊加並以模態參數表示後認為非比例阻尼並不會造成識別上的問題。另外吾人比較最小二乘複頻域法以及有理正交多項式法，發現前者實模態模態參數較後者為穩定，因此在判別虛假模態的效果會比後者好。

Under the process of modal parameter identification, modal interferences often cause problem on identifiability and affect the accuracy of system identification. Major causes of modal interferences are closer frequency, high damping ratio, non-proportional damping too high…etc. In additions, the fictitious mode during identification will affect correct determinacy of structural modal. This article will investigate modal parameter identification in frequency domain and work on rational orthogonal polynomial method and least squares complex frequency domain method, which have been proposed by others earlier.
According to structural dynamics theory, the frequency response function could be expressed as a rational fraction formula. Therefore, via the curve fitting process method we can obtain the coefficients of the rational fraction and then get the modal parameter. The error from curve fitting process method will cause a fictious mode. The parameter is unstable in different order number. On the contrary, the modal parameter of structural model is much stable and the system’s true modal information could be obtained. While not increasing order number, we propose a method to distinguish based on the paired feature of system characteristic values and the values of residue. Based on modal superposition and modal parameter expression of the frequency response function of non-proportional damping system, we think there will no problem on identification for non-proportional damping system. Furthermore, comparing least squares complex frequency domain method with rational orthogonal polynomial method, the structural modal parameter of the former is much more stable than that of the latter; therefore the former is better in distinguishing the fictious modes.

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