An innovative calibration scheme for interharmonic analyzers in power systems under asynchronous sampling

Power-quality analyzers are commonly used in power systems to estimate waveform distortion, including the parameters of harmonics/interharmonics. In our study, a calibration scheme was developed and verified. This scheme is capable of calibrating the interharmonics specification of power-quality analyzers under asynchronous sampling. In our scheme, the hardware structure is composed of an interharmonic signal source, a wide-frequency resistive voltage divider, a broadband current shunt, and a data acquisition system. A new algorithm, based on discrete Fourier transform and interpolation, is presented. The procedure is implemented by LabVIEW software to process the sampling data and obtain the final interharmonic parameters. The test results of the amplitudes of the interharmonic current and voltage indicate that the calibration accuracy is 3.0%(16 Hz-6 kHz) and 6.8%(6 kHz-9 kHz) for the voltage signal, and 3.5%(16 Hz-6 kHz) and 6.5%(6 kHz-9 kHz) for the current signal. This index is higher than that acquired by the recommended methods in the International Electrotechnical Commission (IEC) standard.