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This paper presents a new variable-frequency phase-shift control method to improve the conversion efficiency for a high-power wide-range converter based on a phase-shifted full-bridge (PSFB) converter. The proposed converter can adjust the switching-frequency according to the load power to make the input impedance be inductive. The main switches of the converter can achieve zero voltage switching (ZVS) over a wide load range (500 W–50 kW) without any auxiliary circuit. The maximum switching-frequency of high-power insulated gate bipolar transistor (IGBT) is determined by analyzing the influence of collector current on IGBT switching time. The necessary condition for the proposed converter to realize ZVS is given according to the steady-state model of the full-bridge converter. This paper analyzed the influence of voltage, current and temperature on the switching time of high-power IGBT in detail, and obtained the relationship between the load current and the dead time of high-power IGBT. The optimal switching-frequency under different loads was determined by establishing a switching-frequency loss model of the proposed converter. A 50 kW prototype of the proposed converter was developed and the experimental and simulation results verify the effectiveness and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

To address the issue of white noise at partial discharge (PD) ultra high frequency (UHF) signal in gas insulated substation (GIS), this paper develops an external sensor and proposes new empirical mode decomposition (EMD) denoising method based on autocorrelation coefficient and similar wavelet soft threshold. Four types of typical GIS defects at the PD UHF signal were obtained through experiment. The autocorrelation coefficient of intrinsic mode functions (IMF) components at the PD UHF signal was computed, the cut-off point between the noise signal dominant mode and the UHF signal dominant mode was found. The similar wavelet soft threshold denoising was performed on the signal which is dominated by the noise signal, all the UHF signals were finally reconstructed. The signal-to-noise ratio computed by the proposed denoising method was compared with the one computed by the wavelet denoising method, the results shows that the proposed denoising method in this paper is more effective than the wavelet denoising method. [ABSTRACT FROM AUTHOR]