| 摘要 |
PROBLEM TO BE SOLVED: To suppress the DC current component flowing out to an AC circuit and to prevent trouble such as the generation of DC biased magnetism and higher harmonics of a transformer and overloads on various equipment by controlling the ignition timing of a semiconductor switch so that the DC current component flowing out of a switch arm to the AC circuit is nearly zero. SOLUTION: A DC component suppressing circuit 204 calculates the difference between a DC current component Idab and a DC component reference Idref by a subtracting circuit, finds that the difference is larger than a specific value by a dead zone circuit, and inputs its output to an integrator. The integrator continues to integrate the difference until the DC current component Idab and DC component reference Idref become nearly equal to each other and outputs a control angular modulation signal Δα. The output of the DC component suppressing circuit 204 is inputted to an adding circuit 205 and the subtracting circuit 206 to modulate control angles υto αz of thyristor switches of respective phases, thereby controlling the DC current component Idab almost equanl to the DC component reference Idref. |
