Abstract
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.
Highlights
The International Electrotechnical Commission (IEC)-61000-2-1 standard firstly defined the term “interharmonic”, and it was renewed with the subsequent IEC-61000-2-2 standard [1,2]
When the wide-frequency resistive voltage divider is replaced by a broadband current shunt, it can be used to calibrate the interharmonic current
We introduced and investigated an interharmonic calibration scheme for power-quality analyzers in power systems
Summary
The International Electrotechnical Commission (IEC)-61000-2-1 standard firstly defined the term “interharmonic”, and it was renewed with the subsequent IEC-61000-2-2 standard [1,2]. Interharmonic frequency refers to any frequency which is not a multiple of the fundamental frequency of a power supply or a frequency converter. Electrical engineers who study current and voltage waveform distortion in power systems are interested in interharmonics [5,6]. With nonlinear loads used increasingly in power systems, problems with interharmonics become more severe [7]. The amplitude of the interharmonic and its ratio to the amplitude of the fundamental component are important parameters for evaluating the power-quality [8]. Power-quality analyzers are commonly equipped in the power system to monitor its operation, including frequency deviation, voltage fluctuation and flicker, three-phase unbalance, and waveform distortion [9]. In terms of waveform distortion, measuring the amplitude of harmonics/interharmonics of the waveform is a significant issue [10]
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