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Harmonic Cancellation by Adaptive Notch Filter Based on Discrete Wavelet Packet Transform for an MMCC-STATCOM

This paper presents an adaptive harmonic current extraction scheme using notch filters combined with a modified discrete wavelet-packet transform (DWPT). The scheme is applied to an MMCC-STATCOM for mitigating current harmonics distortion in a power line. The modified DWPT incorporates a data expansion technique to overcome the limitations of boundary effect. It identifies the rms values of the dominant harmonic elements of the non-stationary current in real-time, these being used to update the order and stop-frequency of a notch filter chain. This adaptive notch filter is embedded in the current control system for the MMCC-STATCOM to generate reference current. The results have shown that the modified DWPT tracks harmonic changes faster and more accurately than the conventional method. The technique enables the STATCOM to adapt quickly to load current changes, hence giving accurate elimination of current harmonics in real-time.