Simulation Research Of Static Var Generator

With the rapid development of power network and electronic technology, the scale of power system is increasing, because more and more electrical equipment are come into use, the application of large quantities of nonlinear devices produce a large number of harmonics and reactive power, power quality has been affected badly, its stability is greatly damaged. Therefore, it becomes very important to suppress the harmonics and compensate reactive power. In many reactive power compensation devices, the static var generator(SVG) has excellent performance such as fast response, strong filtering ability and precise control, which has gradually become a hot spot in the field of reactive power compensation.This thesis first introduces the concept of physical reactive power, significance, influence of reactive power on the grid, reactive power compensation equipment and the development trend of SVG. Then it explains the structure of SVG system and internal loss of two different working principle. For the main circuit structure of SVG, it analyzes two kinds of multilevel structure, which is clamped and cascade. In reactive current detection, the traditional detection methods are briefly described, based on the instantaneous reactive power of p-q detection, ip-iq detection, id-iq detection method are analyzed in detail. Through the analysis, the high accuracy, rapid control, detection of a wide range of id-iq detection method is selected. Then the working principle of cascade multilevel circuit, cascade PWM control method, the star and triangle connection method of H bridge cascaded, the mathematical model of cascade SVG are discussed. In the control of SVG, the control strategy combined with direct current control and DC voltage balance control is adopted.In the topological structure of SVG, the cascade multilevel circuit is the most promising structure. In this thesis, it takes the cascade SVG as the research object, list its mathematical model according to the principle. Based on this model, a complete set of SVG system is designed by the above detection and control method. The control parameters of the circuit are calculated by the mathematical model of the whole system. In order to verify the compensation performance of the cascade SVG, the system simulation circuit is built on the MATLAB software platform. The simulation results show that the cascade SVG system is stable and has good dynamic compensation performance.Balancing problem of DC capacitor voltage of the cascade SVG system is directly related to the stability of the system, but also is one of the most difficult problems in SVG design. This thesis proposes a new two stage control method, the first stage is to use the phase-to-phase voltage to achieve the overall control of each phase voltage, the second stage is to achieve the balance control of each power unit by using the phase-to-phase voltage average. The simulation results show that the two stage control strategy has good voltage regulation and voltage sharing performance.