An Investigation On The Modeling And Characteristics And Flicker Effect Of Interharmonics

Interharmonics injected into power system are increasing due to high rapid development of power electronic technology, especially variable frequency drivers (VFD) in power system. Interharmonics will cause voltage fluctuation and flicker that is a power quality problem, and further cause light flicker on lamp that will impact on people's vision and work efficiency. Recent years, this problem attracted attentions of researchers and got many achievements, A lot more work is still needed. Nowadays, interharmonic problem is becoming a focus in power quality field of electrical engineering gradually.On the basis of investigation on relative literatures of interharmonics, for the purposes of understanding rules of interharmonics produced by interharmonic sources, relationship between parameters of interharmonics and voltage flicker and light flicker, criterion of deciding interharmonic limit values and evaluation method, this thesis puts emphases on studying interharmonic model of current source based VFD, characteristics of voltage fluctuation and light fluctuation of incandescent lamp caused by interharmonics. The main works and conclusions are as follows:Inductive motor was assumed as short circuit impedance of the motor and a voltage source that is provided with operating voltage and frequency of the motor, in series. According to the assumption and modulation theory, interharmonic model of current source based VFD was developed. This model shows the producing rules of interharmonic current injected in system and quantitative correlativity of interharmonic magnitude and effect factors. This model was verified by simulation test with Simulink.Because interharmonics always are produced in pairs, in this thesis, characteristics of fluctuation waveform and fluctuation index of voltage containing a pair of interharmonics were investigated. The factors of impact on characteristics of voltage fluctuation caused by a pair of interharmonics are confirmed. The conclusion that the characteristics of voltage both containing a single interharmonic and a pair of interharmonics are similar is reached. And an equivalent equation of relative RMS or peak deviations of voltages containing one or two interharmonics which can be used for simplifying the analysis of voltage flicker caused by a pair of interharmonics is derived and brings potential applications.Based on dynamic heat balance equation and radioluminescence theory of incandescent lamp, light flicker caused by amplitude modulated voltage and voltage containing interharmonics were researched. The relationships between fluctuation characteristics, deviation and frequency of luminous flux and amplitude modulated signal and interharmonic component are obtained. According to the voltage threshold values provided by IEC Flickermeter, luminous flux limit curve caused by amplitude modulated voltage was derived. Considering same luminous flux index resulting in same flicker effect, in lummminous flux view, an interharmonic flicker limit curve is presented which will be helpful for establishing interharmonic limit standard. Meanwhile, the limitations of IEC flickermeter employed to evaluate flicker caused by interharmonics were analyzed and an improved flickermeter model, which is suitable for any kind of voltage fluctuation, is developed and is proved by Matlab simulation test and small light test.