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

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 non-stationary 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.