Predicting the harmonic amplitude of a triac circuit from its waveform

A common problem in designing a triac phase-controlled circuit is predicting and controlling the amount of electrical noise it generates. The regulation of specific harmonics of triac waveforms has already been proposed in Europe, and may be proposed in the United States. This paper describes a method of using the shape of a triac power line waveform to predict its harmonic amplitude from its Fourier series. An APL computer program is used to calculate the Fourier series for the waveform. The program can immediately determine how the harmonic amplitude of the waveform changes as its shape changes. This feature is especially useful for determining, without a spectrum analyzer, if a waveform is below a given limit at a given frequency. Finally, examples show how the harmonic amplitude of the waveform varies as certain parameters, such as rise time and power line losses, are varied