New current control algorithm incorporating multilevel SHE-PWM approach for STATCOM operation under unbalanced condition

This paper presents a new decoupling current control algorithm for Static Synchronous Compensator (STATCOM) system operating under unbalanced condition. The STATCOM is constructed using multilevel cascaded H-bridge inverter (CHI) employing new multilevel selective harmonic elimination pulse width modulation (MSHE-PWM) technique. The MSHE-PWM is based on variable DC voltage levels, which enables elimination of more harmonics as well as provides constant switching angles and linear pattern of DC voltage levels over the modulation index range. This further eases the implementation of the technique for dynamic systems such as STATCOM. For simplicity, the DC-DC buck converter is considered to provide the variable DC voltage levels. Current vector controllers based synchronous reference frame (SRF) are proposed in this work to separately regulate the required positive- and negative-sequence variables for correcting the power factor and balancing the three-phase source currents at the point of common coupling (PCC), respectively. The effectiveness and the theoretical analysis of the proposed approach are demonstrated and verified via various simulation studies using MATLAB/SIMULINK for both the dynamic and transient conditions.