A new fuzzy-wavelet based representative quality power factor for stationary and nonstationary power quality disturbances

Power factor is an important index for evaluating the transmission efficiency in electric power system (EPS) along with the quality of the transmitted power. Three different power factors currently exist in the standards to satisfy those requirements namely; displacement, transmission efficiency and oscillation power factors. Currently those three power factors are defined according to the fast Fourier transform (FFT) which produces inaccurate results in case of nonstationary (sinusoidal or nonsinusoidal) waveforms. Therefore in this paper, the three power factors are redefined in the time-frequency domain using the wavelet packet transform (WPT) that proves to be capable of accurately measuring and representing EPS waveforms especially under nonstationary disturbances. Then a new fuzzy-wavelet based representative quality power factor module is developed to amalgamate the three redefined power factors into one single index called fuzzy-wavelet representative quality power factor (FWRQPF). The advantage of the new index is to evaluate quantitatively, qualitatively and accurately the power transmission efficiency while benefiting from the advantages of fuzzy systems to be simple, easy to be used with no need for an expert since it contains its own knowledge base. The new index can be indicative for billing purposes, evaluating the PQ in deregulated markets, help deciding suitable PQ mitigation and power factor correction techniques for power factor improvements under stationary or nonstationary operating conditions.