| 摘要 |
PROBLEM TO BE SOLVED: To estimate a residual voltage in a circuit connected to a three-phase system regardless of an accident aspect when a voltage drops.SOLUTION: A phase synchronization circuit 11 calculates a positive phase &thetas;and a negative phase &thetas;based on line-to-line voltages V, Vof a three-phase system. DQ conversion parts 12a, 12b perform rotation coordinate conversion on the line-to-line voltages V, Vby using the positive phase &thetas;and the negative phase &thetas;to calculate a positive-phase D-axis component V, a positive-phase Q-axis component V, a negative-phase D-axis component V, and a negative-phase Q-axis component V. Absolute value calculating parts 13a, 13b calculate a positive phase component absolute value Vbased on the positive-phase D-axis component Vand the positive-phase Q-axis component V, and calculate a negative phase component absolute value Vbased on the negative-phase D-axis component Vand the negative-phase Q-axis component V. A differentiator 14 calculates, from a difference between the positive phase component absolute value Vand the negative phase component absolute value V, an asymmetrical residual voltage V, which is a residual voltage independent of an accident aspect when a voltage drops. |
