A Novel Submodule Voltage Balancing Scheme for Modular Multilevel Cascade Converter—Double-Star Chopper-Cells (MMCC-DSCC) Based STATCOM

Abstract

A novel capacitor voltage balancing scheme for modular multilevel cascade converter-double-star chopper-cells (MMCC-DSCC)-based STATCOM is proposed in this paper. Compared with the conventional software voltage balancing methods, the proposed scheme has three main advantages. First, only six voltage sensors are needed, and other voltage sensors have been removed. Then, the control framework can be simple without sort and select process, or some balancing control loops. Additional delay process caused by the sampling and control signals transmission is also mitigated. Finally, the faster capacitor balancing speed can be obtained. In addition, compared with some other hardware voltage balancing schemes, there are superior characteristics in terms of the reduced number of switches and only the popular power modules in the additional units are applied. For these additional modules, the parameters design guide of the proposed scheme has been discussed. Verified results from the 13-level simulated system and 9-level experimental platform for the MMCC-DSCC based STATCOM show the effectiveness of the proposed scheme. By the proposed scheme, both DC capacitor voltage balancing control and reactive power compensation are simultaneously realized for the MMCC-DSCC-based STATCOM even in balanced and unbalanced load.

Keywords

• Diode-clamped circuit
• double-star chopper-cell (DSCC)
• modular multilevel cascade converter (MMCC)
• voltage balancing
• STATCOM