正弦脈寬調(diào)制畢業(yè)設(shè)計外文文獻及翻譯-全文預(yù)覽
【正文】 d theα?s required to achieve this objective,it is sufficient to set the corresponding h?s in the above equations to the desired values(0 for the n1 harmonics to be eliminated and the desired perunit ac magnitude for the fundamental)and solve for theα?s. Fig 4:A twolevel PWM waveform with odd and halfwave symm Equation 1 can be readily proved by finding the fourier coefficients of the waveform shown general,for a periodic waveform with period,the Fourier Cosine and Sine Coeffi cients are given by: Because of the halfcycle symmetry of the waveform of ,only odd order harmonics exist. Also,it is easy to see that the Fourier Cosine coefficients disappear with the choice of coordinate axes the quarter cycle symmetry,the Fourier Sine coefficients bee: Substituting the twovalued pwm waveform for,one obtains(see ): The following example illustrates the use of three chops per quarter cycle which allow for three degrees of may use these to eliminate two harmonics and control the magnitude of the fundamental to any desired value: Example: Selective Harmonic Elimination is applied with a view to controlling the fundamental ponent of voltage to 50V(rms)and eliminating the 3rd and 5th source voltage is 100 V. Calculate the required chopping angles. As three objectives are to be achieved,we need 3 fundamental,3rd and 5th harmonic magnitudes are given by: We require: 翻譯 電力電子 正弦脈寬調(diào)制 電壓源逆變器的開關(guān)（見圖 1）可以按要求打開和關(guān)閉。T=period of funda mental),the high frequency ponents do not propagate significantly in the ac work(or load) due the presence of the inductive ,a higher carrier frequency does result in a larger number of switchings per cycle and h
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