Research On Cascaded Multi-level Converter-based STATCOM

Reactive power plays a vital role on the security and stability of power system, therefore, the reactive power compensation has a very wide range of application in power system. In recent years, static synchronous compensator has been rapid development, and another problem has been the research focus that how to get STATCOM been used in the power grid of high voltage.This paper obtained the typical advantages of cascaded multi-level converter through the comparison of a variety of large-capacity converter topologies.The analysis of operating principle and output characteristics of cascaded multi-level converter is given on the basis of H-bridge modules.In addition, the mathematical model of cascade multi-level STATCOM is established, and the detection and inner ring decoupling control methods of reactive current is studied in this paper as also as the carrier phase shift sinusoidal pulse width modulation strategy.It is a difficulty of outer ring stability control of DC bus voltage of devices with cascade structure. The hierarchical control theory is referenced in this paper and a hierarchical control method is proposed to control the balance of DC bus voltage from overall, each phase and each H-bridge modules, and simulation results have verified its good response rate and control effect of DC bus voltage.On the basis of these studies, a new main topology of cascade structure based hybrid reactive power compensation device is proposed, which consists of shunt capacitor and three-phase cascaded multi-level STATCOM. When working at the rate state, the shunt capacitor will compensate most of the reactive power, while the cascade STATCOM will provide fast dynamic regulation of reactive power, and the efficiency of the hybrid device increases. Simulation results have verified the typical advantages of the hybrid device.