Using the matrix theory, we derived the modal matrices of some parameter matrices in transformation, and discussed the transformation with principle of power invariance also.

用矩阵理论求出几种形式的参数矩阵变换时的模态矩阵，并讨论了功率不变原则下的变换。

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Basing on the signal space model, the harmonics in power system was detected by combining the subspace rotational invariance and least squares method.

该方法以信号空间模型为基础，结合子空间旋转不变性和最小二乘法实现了电力系统的谐波检测。

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