Thin-film capacitance is required in DC side of H-bridge cascade STATCOM so as to reduce its capacitance which will help improve device’s power density. After the voltage stress of the device being taken into consideration

modulation output voltage range is one of the key factors that restrict STATCOM DC bus capacitance. For application in star connection H-bridge cascaded STATCOM

after the fluctuation dc voltage being taken into consideration

the range of capacitance under the modulation output voltage is analyzed. Based on the carrier modulation technology

the analytical relationship of dc capacitance

compensation current and modulation output range is derived. Based on the obtained results

with DC voltage peak value as a constraint

an equation of STATCOM modulated output voltage is established

and the value range of capacitive reactance is also analyzed. Furthermore

the influences of filter reactance on capacitance value and how to set the DC mean voltage reference are discussed. Compared with the traditional capacitance value selection method

the validity of theoretical analysis is verified by simulation and experiments. The analytical conclusion obtained in this paper can provide a theoretical reference for the research on reducing capacitance of STATCOM.