Page 353 - Solutions Manual to accompany Electric Machinery Fundamentals
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(e) Comparing the spectra in (b) and (d), we can see that the frequencies of the first large sidelobes
doubled from about 900 Hz to about 1800 Hz when the reference frequency was doubled. This increase
in sidelobe frequency has two major advantages: it makes the harmonics easier to filter, and it also makes
it less necessary to filter them at all. Since large machines have their own internal inductances, they form
natural low-pass filters. If the contaminating sidelobes are at high enough frequencies, they will never
affect the operation of the machine. Thus, it is a good idea to design PWM modulators with a high
frequency reference signal and rapid switching.
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