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An increase in the research of medium-voltage AFD (adjustable frequency drive) system for the save of electrical energy has been seen during recent years. There are various converters configuration for medium-voltage and control methods abroad, but the detail control methods are rarely seen on publications. This paper has described two novel control strategies for voltage-source (VS) AFD systems of medium-voltage, and analyzed output waveforms, RCMV (rectifier-common-mode voltage), ICMV (inverter-common-mode voltage) and output waveform spectrums as well. For every control strategy a good few conclusions have been attained through simulation analysis.
CVTs with passive ferro-resonance circuits have flat high-frequency characteristics which cover the frequency band from 10kHz to several hundreds kHz, the secondary voltages are directly used to extract voltage incident traveling-waves without the need of specially designed voltage traveling-wave transducers. And wavelet transform modulus sum based arrival detection of incident traveling-wave is proposed, simulation and experiment data are given to verify the schemes, which will be useful in applications of fault location and relay protection using incident voltage traveling-waves.
