正规形法揭示了电力系统中动态模式之间的非线性相互作用,可用于分析因模式间非线性相互作用而产生的复杂动态现象和动态行为.分析表明,动态模式间相互作用所产生的组合模式使得振荡频率减小或增大,可能导致超低频振荡或倍频振荡现象,而且其明显程度取决于系统的非线性作用程度.正规形变换系数和正规形变量初值乘积可反映超低频振荡模式或倍频振荡模式在状态量响应中的作用程度,其值大,则组合模式作用模值大:组合模式的实部绝对值可反映组合模式持续时间的长短,其值小,则组合模式作用时间长.该分析揭示了电力系统产生超低频振荡和倍频振荡的可能性和条件.对一2区域4机系统进行仿真,应用所提方法分析出了该系统在重载运行条件下出现的超低频振荡现象.%Normal form method reveals the nonlinear interactions among dynamic modes in electric power systems,which can be applied to analyze complicated dynamic phenomena and dynamic behavior of nonlinear interactions among dynamic modes. Study shows that the combined mode produced by the interactions among dynamic modes causes the decrease or increase of oscillation frequencies and may produce extra-low or double frequency oscillation phenomena,which depends on the degree of nonlinear interaction. The product of normal form transform coefficient and normal form variable initial value may reflect the active degree of extra-low or double frequency oscillation modes in state variable response:the bigger its absolute value is,the greater the modulus of combined mode will be. The real part of combined mode shows its effective time:the smaller its absolute value is,the longer the effective time will be. It reveals the probability and conditions of extra-low frequency oscillation and double frequency oscillation in power systems. The presented method is applied to the simulation of a two-area four-generator power system,showing that the extra-low frequency oscillation occurs under the operation condition of heavy load.
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