Mechanism analysis and suppression of overvoltage on DC side of ASVG under driving pulses blocking operation

In order to enhance the operating reliability of ASVG (advanced static VAr generator), the "driving pulses blocking operation mode" is put into use which means that when blocking the conduction of switching components (GTO), the main switch connecting the ASVG to the power system keeps closed. For the configuration of large capacity ASVG based on multiple inverters, the mechanism of overvoltage on the DC side under driving pulses blocking operation mode is researched. With the help of a large amount of field tests and principal analysis, it is illustrated that overvoltage is caused mainly by the harmonic voltages on no-load transformers. The harmonic voltages are a result of harmonic magnetic flux caused by magnetic saturation of the transformer and complicated magnetizing circuit required by harmonic voltage elimination strategy. On the basis of mechanism research and circuit calculation, a simple countermeasure of suppressing overvoltage on the DC side is put forward. "Driving pulses blocking operation" is successful on a 300 kVAr ASVG.