SYSTEM FOR ESTIMATING SUB-MODULAR CAPACITOR OF MODULAR MULTILEVEL CONVERTER AND METHOD THEREOF

摘要

The present invention relates to a system and method for estimating capacitance of a sub-modular capacitor of a modular multilevel converter. The system for estimating capacitance of a sub-modular capacitor of a modular multilevel converter according to the present invention comprises: a modular multilevel converter having a plurality of modular multilevel converter sub-modules comprising the sub-modular capacitor which charges or discharges energy according to IGBT switching operation; an average voltage control unit to use a difference between an average voltage command value and an average voltage of the sub-modular capacitor to output a circuit current command value; a circuit current control unit to use the sum of the difference between a circuit current command value and a circuit current to output the average voltage control command value of the sub-modular capacitor; an individual voltage balance control unit which uses the difference between the average voltage command value and the measured value of a voltage of the sub-modular capacitor to output a voltage balance control command value; a calculation unit which uses the average voltage control command value and the voltage balance control command value to output a final voltage command value; a pulses adjustment unit to use the final voltage command value to adjust a pulse of the modular multilevel converter; and an estimation unit to use the voltage and a current of the sub-modular capacitor of the modular multilevel converter to estimate capacitance of the sub-modular capacitor. According to the present invention, a software controller and a software filter can be used without a hardware facility added to a converter circuit to estimate the deterioration state of a capacitor in real time. Additionally, the capacitance of the capacitor can be periodically estimated to determine the replacement time of the capacitor in advance to improve productivity.