Spectral analysis techniques for estimating power quality indices

This paper presents the theory, design and implementation of a real time virtual instrument to measure the power quality indices such as power factor, voltage harmonic distortion and current harmonic distortion as given by the IEEE standard. Windowing techniques offer an adjustable mechanism to detect low or high power harmonics as they have different leakage characteristics. Cross spectral density is a simple tool for finding phase angle differences among different voltage and current phases. The virtual instrument presented in this document integrates digital signal processing (DSP) methods such as windowing techniques, Welch power spectral density and cross-spectral density estimation to calculate voltage and current phasors. Simulation and experimental results under different waveforms are presented to show the accuracy and robustness of the virtual instrument. The real time experiment is carried out using a rectified AC waveform applied across an RL circuit.