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【正文】 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（見圖 1）可以按要求打開和關閉。 Power Electronics Sinusoidal Pulse width modulation The switches in the voltage source inverter(See )can be turned on and off as the simplest approach,the top switch is turned on If turned on and off only once in each cycle,a square wave waveform ,if turned on several times in a cycle an improved har monic profile may be achieved. Fig 1:Simple Voltage Sourced In the most straightforward implementation,generation of the desired output voltage is achieved by paring the desired reference waveform(modulating signal)with a highfrequency triangu lar?carrier?wave as depicted schematically in on whether the signal voltage is larger or smaller than the carrier waveform,either the positive or negative dc bus voltage is applied at the that over the period of one triangle wave,the average voltage applied to the load is pro
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