A Capacitor Voltage Balancing Scheme for a Single-Phase Cascaded H-Bridge STATCOM

Abstract

This paper investigates the individual DC capacitor voltage balancing algorithm of a single-phase cascaded H-bridge (CHB) STATCOM. The main purpose of STATCOM connected to the grid is to inject or absorb the reactive power but in the process, it draws active power also to meet the losses in the system. The losses accrued in the H-bridges are uneven because of asymmetries in the modules or because the switching and conduction losses are different in the H-bridges. The individual balancing algorithm equalizes reactive power among the H-bridges but the active power remains unequal in different H-bridges. A combination of PLL and Fourier series method is used to extract the phase information as well as coordinate transformations. The entire system is modeled by an MATLAB-SIMULINK environment with the switching losses represented by using a resistive load across the DC capacitors.