Research On The Harmonic And Inter-harmonic Detection Technology In HVDC

Compared with other power transmission mode, HVDC has obviously advantage in long distance and high capacity transmission. In the power system, because of the existing of the non-linear equipment, it will produce harmonics and inter-harmonics in the DC-side and AC-side. Harmonics and inter-harmonics can propagation in the grid, which will influence the system’s safe operation. Currently, the most commonly used harmonics and inter-harmonics detection algorithm is FFT in the HVDC. Thus, the research on harmonics and inter-harmonics detection algorithm which has high accuracy and real-time quality is very important.Firstly, this paper analyzed the FFT algorithm and finds its limations. In order to reduce the error, this paper proposes the windowed interpolation FFT algorithm to detection by using MATLAB. The results tells that the five-term-maximumsidelobe-decay(MSD)window is one of the window functions whose sidelobes decay faster, and it can alleviate spectral leakage and fence effect effectively.But when using it analyzes the inter-harmonics, its accuracy should be improved. The recursive filter algorithm which has a band pass frequency property can overcome the limitations of FFT in harmonic detection. The recursive band pass filter has two characteristic parameters which are scaling factor and central frequency, so this paper determined these parameters to apply to DSP. Considering all of the algorithm’s shortcomes and advantages, this paper proposed to combine the MSD windowed interpolation FFT and recursive band pass filter algorithm, which can reduce the computation and guarantee the accuracy meanwhile. This method uses MSD windowed interpolation FFT to detect the signal to find the frequency band first and then uses the recursive filter algorithm to analyze the band.This paper also designed online detection device which uses DSP and ARM as the core. The functions of the device are transformation of voltage and current, the acquisition of events, the analysis of the events, the display of the analysis results and the communication with the host computer etc. This paper transplant the algorithm to the device by using the CCS and it realized the software design of the windowed interpolation FFT and recursive band pass filter algorithm and the combination of the two algorithm Through the results of the measurement, it can conclude that the new algorithm is more accurate has better real-time feature.