Patent ID: 8385096

Claim:
An unbalanced voltage compensation method in power conversion for subjecting three-phase AC voltages to PWM conversion and outputting DC voltage, comprising, a centroid vector operation step for obtaining wye-phase voltages which are 120° out of phase with each other, from line voltages of the three-phase AC voltages, a symmetrical component calculation step for calculating symmetrical component voltages of a three-phase balanced system, from the wye-phase voltages that are obtained by the centroid vector operation step, and an unbalanced voltage compensation step for forming a compensation signal for compensating for unbalanced voltages of three-phase AC voltages, and subjecting the three-phase AC voltages to the PWM conversion to generate a control signal for outputting the DC voltage, wherein, the centroid vector operation step performs a vector operation as to all combinations of two line voltages which are selected from the line voltages, obtains centroid vector voltages which are directed to respective terminal voltages from a terminal-voltage centroid according to the vector operation, and renders the vector voltages respectively as the wye-phase voltages which are 120° out of phase with each other, and the unbalanced voltage compensation step generates the compensation signal for compensating for the unbalanced voltages of the three-phase AC voltages based on a zero-phase-sequence voltage of the symmetrical component voltages which are obtained in the symmetrical component calculation step, obtains wye-phase voltages based on the symmetrical component voltages and the compensation signal, the wye-phase voltages being 120° out of phase with each other as to which the unbalanced voltages have been compensated for, and subjects the three-phase AC voltages to the PWM conversion based on the wye-phase voltages to generate the control signal for outputting the DC voltage.