Abstract
International Electrotechnical Committee Standard, IEC Std. 61000-4-15, gives functional and design specifications for a flickermeter which is the simulation process based on the response of human’s visual perception to the fluctuation of light. The simulation process, which includes square multiplier, band-pass filter, weighting filter, first-order sliding mean filter and statistic calculation of instantaneous flicker level curve (IFL), can effectively estimates value to assess the severity of voltage flicker. Interharmonics are spectra components whose frequencies are not integral number of the system fundamental frequency. When a voltage waveform contains interharmonics, the RMS value and the magnitude of the waveform will fluctuate. This fluctuating magnitude is essentially a form of voltage flicker. If the magnitude is sufficiently large and the fluctuation frequency is in a range perceptible by human eyes, a light flicker will occur. The IEC flicker meter has been widely applied to processing the waveform to measure the severity of flicker. However, the meter has a major deficiency: it is unable to measure flickers caused by interharmonics whose frequencies are higher than 102Hz. This thesis proposes an envelope detection method which is based on the Hilbert transform and the spectrum processing to detect the envelope system voltage flicker which contains the flicker caused by interharmonics. The proposed method can effectively replace of the envelope extraction function (which encompasses squaring demodulator and the band-pass filter) of IEC flickermeter and make it possible to assess the voltage flicker caused by interharmonics. The performance of the IEC metering procedure and the proposed method are compared. The comparison shows that the proposed method can work well with the system voltage containing the interharmonics whose frequencies are larger than 102Hz. The test also investigates the deficiency of proposed method and suggests future modification on the pre-processor of voltage to enhance the noise immunity and measuring stability of proposed method.