Harmonics in power systems

The appearance of nonlinear currents and voltages in power distribution systems has accelerated in recent times due to the availability of economical and reliable adjustable speed drives. The most popular generator of harmonic currents and voltages appear to be three-phase six-pulse SCR power converters and three-phase six-pulse diode bridges, generally used with DC and AC motor drives. A more recent development in power electronics for AC to DC conversion is the voltage source converter (VSC). This is a transistor power converter that can be controlled to produce low distortion line currents and unity input power factors. The most popular and easily understandable method to analyze the nonlinear currents and voltages is to use the Fourier transform to calculate the amplitudes of sinusoidal functions with discrete frequencies. These amplitudes may be used to calculate other phenomena within the power system or component. This paper shows how complex waveforms are captured and then resolved into Fourier amplitude spectra that can used as a design aid