Evaluating Voltage Notch Problems Arising from AC/DC Converter Operation

This paper analyzes the voltage notches in ac/dc converters and the problems that they create. Voltage notch disturbs the voltage´s waveform and excites the natural frequencies of the system. In some systems, these excisions create considerable high-frequency oscillations in the voltages of the converter and the adjacent buses; this can damage capacitor banks, create parallel resonance, and generate radio disturbances. This paper analyzes the effect of snubber circuits on the voltage oscillations that arise from commutation. It also presents the theoretical foundation and analytical derivation that are used to calculate notch depth and the frequency of oscillations. To achieve accurate and applicable results, various loads of the converter, the dc current ripple, and the characteristic impedance of the system are considered. Several experimental results are shown in order to illustrate the effects of changes in the system and converter parameters on the voltage waveform of the converter. Computer simulations and experimental results indicate the accuracy of the theoretical relations. The proposed equations make it possible to effectively study the harmonic and power quality in networks that include high-power converters.