It is found that the system is subjected to the low-frequency excitation and occurs random vibration in the non-linear complex-mode form.

揭示了系统所受的是低频激励，以非线性复模态的形式作随机振动。

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This paper analyzed the effects of several excitation controllers, and found that the unsuitable controller can cause a low frequency oscillation on power system.

本文经理论分析提出“系统中产生负阻尼的原因是不适当的励磁控制方式”的结论。

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The data of polar motion, rotation of the earth and atmospheric excitation function are analysed by the Auto-Regression power spectrum method, and their spectra at low frequency band are obtained.

本文用自回归功率谱方法分析了极移、地球自转和大气激发函数的资料，得到了它们的低频谱。

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