Research And Design Of Static Var Generator Technology Based On T-Type-Three-Level

Three-level Static Var Generator(SVG)has been widely used in the power grid for its accurate reactive power compensation and quick response,etc.This paper deeply studies the T type three-level SVG topology and the midpoint potential balance problem,then puts forward some feasible improvement design schemes.Firstly,the advantages and disadvantages of the T-type three-level topology and the diode-clamped topology are compared.The switching states and the commutation process of the T-type three-level topology are analyzed in detail.First,the mathematical models under various coordinate systems are established.Then a T-type three-level topology for SVG design is proposed.Finally the T-type three-level SVG is simulated to verify the feasibility of the T-type three-level converter on SVG.The three-level space vector modulation strategy is analyzed in detail.The four steps of judging the small area of the reference voltage vector,synthesizing the reference voltage vector method,calculating the time of each vector function and optimizing the switching sequence of the output vector are analyzed and the implementation method is given.The midpoint potential imbalance problem in T-type three-level topology is analyzed,and several commonly used methods to control midpoint potential balance are introduced.In addition,some improvements have been made for the distribution factor method.Finally,an improved distribution factor method is proposed to solve the problem of the midpoint potential imbalance.The reactive power compensation device based on T-type three-level is designed and manufactured to experimentally analyse the performance of the system under different loads.The experiment is respectively conducted with or without the control of the midpoint potential of the DC side capacitor.Experimental results show that T-type three-level SVG topology has good compensation function under different load conditions.The improved distribution factor method can effectively suppress the midpoint potential shift.