Design And Optimization Of Parameters For Cascaded Multilevel STATCOM

Electric power with high quality is under great requirement because of fast social and economic development. STATCOM, the Static Synchronous Compensator, has drawn people’s attention for years because of its unique advantages, and the research interest keeps growing. Driven by the new technology, for example, the FACTS control strategies,control strategy of STATCOM gets updated and developed. STATCOM acts greatly in compensating: it helps the electric system gain continuous and precious reactive power compensation.The topological structure of the cascaded STATCOM was first identified in this paper,and an equivalent circuit diagram was built on this structure. Then a transient mathematics model of STATCOM is constructed under the three-phase static coordinate system. The coordinate is then transformed, obtaining a model under the dq0 coordinate, and the normalized STATCOM mathematical model is finally completed comparing with the transformer reduction model. Stationary of the model is proved as well in the research process. The ip-iq current detection method under the voltage unbalance condition is optimized: an arithmetic operation of positive sequence voltage of A-phase is added prior to the phase-locked loop. The phase-locked loop can obtain grid voltage angle simultaneously with the time in the way, and STATCOM therefore obtains instruction current accurately.The traditional carrier phase-shifting SPWM modulation technology is refined, as well as the utilization rate of capacitor at the DC side. The optimization method is that, a zero sequence component is injected into the modulation wave, and combined with the optimal switching frequency PWM modulation technology. Because of the special advantage of Genetic Algorithm(GA) in solving the optimization problem, double closed ring PI controller is applied in outer loop parameter improvement in the off-line calculation in PI controller. MATLAB/Simulink is applied in simulation: model is built virtually in the software, and STATCOM operation characteristics are further improved with the help of simulation.