This paper introduces an inter-harmonics detection device based on DSP. The major characteristic of the device is that it can detect the inter-harmonics based on the generalized dk-qk rotational coordinate transform theory. To increase the distinguish ability between two close frequencies, this paper introduces a flex time coordinate method, which decreases the spectral leakage greatly. The sampling data disparity problem is solved by using the external phase-locked loop, which overcomes the poor detecting accuracy of the former harmonics detection. Meanwhile, in order to meet the power system safety requirements, this paper develops a device protection module for the periphery power network data acquisition circuit. The practical application demonstrates that the detection device can detect both integral harmonics and inter-harmonics and operate well in the substation.
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