Design And Implementation Of Cascaded29-level STATCOM

With the fast development of the global economy, power consumers gradually increase thedemand for electrical energy, become more stringent for the power quality. Therefore, atpresent, an immediate and significant problem is how to ensure the stability and the security ofthe power system, run with little loss and guarantee the quality of power supply. During "the12th Five-Year", the national grid will begin to speed up the construction of a unified, strongand smart grid, and the construction of flexible AC transmission system is included.As an important one in the FACTS devices, STATCOM becomes the new direction ofdevelopment for reactive power compensation technology in the power system applications anda new generation of reactive power compensation device. Commonly, increasing the capacity ofthe main circuit is used to manufacture the STATCOM with large capacity, cascadedmulti-level structure has the advantages of being easy to modular and control, therefore, it iselected as the main circuit of the STATCOM, at the same time, the basic principle ofSTATCOM is introduced and a mathematical model of the STATCOM is established. The stepmodulation technique has a low switching frequency requirement for power devices and simplecontrol features, meanwhile, in order to reduce the harmonic content, the algorithm of specificharmonic elimination is applied to cooperate with the modulation method. The combinationcontrol of is used to realize the characteristics of the fast response to the reactive current,and cascaded multi-level STATCOM device is a typical non-linear system, thus a dual-inputand dual-output linearization control method is adopted, finally, the decoupling control of theoutput variable is realized. The imbalance of the DC side capacitor voltage will affect theoutput voltage harmonics characteristics of the STATCOM device and the safe operation, thereasons for the voltage unbalance and the common balance strategy are discussed, the methodof the pulse loop transposition is applied and the improvement measures is given.For the above control methods, this thesis uses MATLAB/Simulink to build simulationmodels to verify the feasibility of those, and the simulation results show that cascadedmulti-level STATCOM device has fast response to the reactive current and the goodcharacteristic of the output voltage harmonic.