An effective computation algorithm of voltage flicker severity for electric arc furnaces

Effective and accurate calculation methods are presented to obtain the voltage flicker components and the 10-Hz equivalent value. By using the indirect demodulation method, the RMS values of a voltage waveform are calculated cycle by cycle to obtain the envelopment. Then the fast Fourier transform (FFT) is used to get the flicker components. The other method uses the instantaneous voltage vectors. After the voltage waveform of a phase is recorded, the discrete Fourier transform can be used to get the system frequency and magnitude. Then the other two phases are assumed perfectly sinusoidal to construct a virtual three-phase system. The instantaneous voltage vectors are calculated from the virtual three-phase voltages. Finally, the FFT is used to obtain the voltage flicker components from instantaneous voltage vectors. Some given waveforms and field measured waveforms of arc furnace loads with voltage flicker disturbances are used to show the goodness of these approaches.