The concept of parameter observability is given

which indicates that if the power spectrum of input excitation can cover the oscillation frequency of the system

then the frequency can be observed via the output. So the corresponding modality and parameters can be identified. The power spectral sensitivity based on parameters is proposed to quantitatively analyze the parameter observability. Parameters are identified by minimizing the sum of square error between the measured and the calculated values of power spectrum. By taking a second-order system as an example

the factors of parameter observability are analyzed upon input excitation

the amplitude-frequency characteristic of system

especially the system damping. Finally

the frequency-domain characteristics of the power load model are studied

and the correctness of the concept proposed is verified by parameter identification using two different kinds of excitation signals. This work is supported by National Natural Science Foundation of China (No. 51137002

No. 51190102

No. 51377046).