Theoretical Analysis and Comparison of Capacitor Requirement in Modular Converters for Grid Integration of High Power Solar PV

Recent studies use cascaded H-bridge (CHB) and modular multilevel converters (MMC) for large scale solar photovoltaic (PV) integration to a medium voltage (MV) grid. In these converters, electrolytic capacitors are normally preferred in order to obtain high capacitance in each module. This paper investigates the capacitance requirement of three modular converters for solar PV integration to an MV grid: a conventional half-bridge submodule (HBSM) based MMC, a full-bridge submodule (FBSM) based MMC and a delta connected CHB. A detailed analytical study is carried-out to derive the expressions of the capacitor ripple voltage and rms value of ripple current for these three converters. The analysis reveals that the total capacitance requirement in FBSM based MMC and delta connected CHB is 77% lower than that of the HBSM based MMC. Further, the total capacitor loss in the HBSM based MMC configuration is more than that in FBSM based MMC configuration. To verify the claims, simulation studies are carried out in MATLAB/Simulink for all the three configurations and the results are compared.