Research On STATCOM Based On MMCC-SDBC

In the power system, reactive power is an important factor affecting the voltage stability, it relates to the security and stability of the entire power system. Because of the inability to fully meet the demand for reactive power from the generator, the reactive power compensation system is very important in the electrical grid. As one kind of Flexible Alternative Current Transmission Systems, static synchronous compensator or STATCOM becomes more and more important in reactive power compensation. With the increasing requirements for power quality, STATCOM has gradually a multi-module cascade development. A static synchronous compensator based on MMCC-SDBC (Modular Multilevel Cascade Converter with Single-Delta Bridge-Cells), as well as its application in negative sequence reactive power compensation, has been studied in this paper.The basic topology and basic working principle of STATCOM was firstly analyzed, as well as the time domain mathematical model. After comparing the three different reactive power detection methods based on Instantaneous Reactive Power Theory, dqO method was chosed, which can be used in imbalanced system. Carrier Phase-Shifted Sinusoidal Pulse Width Modulation (SPWM) was used in multi-module cascade STATCOM to achieve multi-level voltage output, thereby reducing harmonic content. Several structures of Modular Multilevel Cascade Converter (MMCC) are presented. STATCOM based on MMCC-SDBC could have a best performance in the compensation of positive sequence reactive power, negative sequence reactive power and low frequency active power at the same time, which makes it possible to be applied in flicker compensation for arc furnaces. The power control method was introduced, as well as dc-capacitor control method using the circulating current. The numerical modulation of STATCOM has been built and the simulation was executed in Matlab/Simulink. The simulation results correspond well to those of theoretical analysis. A600var STATCOM based on SDBC was designed and constructed. DSP was used as the control system. The experimental result was analyzed.