Improved active impedance estimation technology by mobile window method

The active impedance estimation is addition a noncharacteristic harmonic disturbance voltage in the output voltage of the distributed generation. The variation in the impedance of the point of common coupling (PCC) is observed. The measured PCC voltage and current use a running sum DFT (discrete Fourier transform) method to isolate the noncharacteristic harmonic. A mobile window method is used in this paper to quickly calculate the running sum DFT or FFT, in order to reduce the time that is required to calculate the impedance and to reduce the detected time for islanding operation. The running sum DFT of using mobile window method is called the mobile window DFT. The method uses DSP and the voltage source inverter in an islanding test system. Matlab/Simulink is used to verify the experimental results. The time that is required to calculate both the mobile window DFT, and FFT using the mobile window method is compared. The proposed method to estimate the PCC impedance in detecting islanding operation is compared with the active reactive power variation (RPV) method, in order to verify the performance of the proposed method. The experimental results show that estimation of the impedance using the mobile window DFT to detect times is superior to the RPV method under various load conditions.