Application of Wavelet transform in denoising synchronising signal in line synchronised power electronics converters

摘要

Line synchronised phase-controlled thyristor power converters produce notches in synchronising signals at the instant of turning on thyristors. These synchronising signals are derived from three-phase supply to generate gate pulses for a converter. The presence of notches leads to malfunctioning of the connected power converters whose operations decisively rely on the proper zero-crossing information of the synchronising signal. Denoising these notches is difficult because of the nonstationary pattern of the synchronising signal. The small drift of supply frequency is the main cause for this non-stationary pattern. A filtering technique based on wavelet transform (WT) is proposed in this work. The application of filtering banks using multi-resolution analysis (MRA) of discrete wavelet transform (DWT) with 'Daubechies1' as mother wavelet is found effective in denoising synchronising signals from such noises. The simulation study and the experimental results are presented to justify the proposed filter structure.