Cascaded Packed U-Cell STATCOM With Low Capacitance And Its Third Harmonic Control

This paper proposes a novel STATCOM by cascading packed U-cell (CPUC) and using low capacitance. Compared to cascaded H-bridge, the CPUC-STATCOM can largely reduce switch counts and their related gate driver circuits. Then, skillfully utilizing the principle that the second-order harmonic component of capacitor voltage is in phase with the absolute value of grid voltage in capacitive mode, low capacitance is used in CPUC-STATCOM. It can reduce cost, weight and volume of system compared to usually using large capacitance to limit voltage ripple within 10% of nominal capacitor voltage. However, it has limited compensation capability in inductive mode by using low capacitance. Aiming at overcome the aforementioned drawback, a flexible third harmonic control method is proposed, which can reduce capacitor peak voltage and averaged voltage. Finally, the simulation results verified the performance of the proposed topology and control method.1