Research On Five Level SVG Control Technology Based On NPP Topology

The traditional transmission control equipment is difficult to be enough flexible and fast,and flexible AC transmission technology can effectively solve these problems.The use of flexible AC transmission technology to improve the transmission capacity of the power system,with low cost of investment,will be able to take full advantage of the potential of the line,thereby increasing the transmission capacity.With the continuous development of high power semiconductor devices,the concept of flexible AC transmission system controller is constantly updated,production costs continue to decrease and the use of flexible AC transmission technology widely has become the power industry's trend.Static var generator is an important part of FACTS system.Compared with the traditional reactive power compensation devices,such as SVC and synchronous compensator,SVG can adjust the reactive power quickly and flexibly.And because the instantaneous power of symmetrical three-phase load is equal with the total power,SVG required energy storage devices' capacity much smaller than the compensation capacity it provides,which greatly reduces the cost of reactive power compensation.The control strategy of NPP five-level topology in SVG application is researched in this paper.In order to simplify the calculation,the space vector modulation is carried out in 60 degree coordinate system.In order to verify the effectiveness of the five-level-NPP topology,a simulation model and an experimental prototype are built,and a resistance-inductance load are connected in order to verify the output level.It is verified that the topology can output phase voltage of the 5 levels and the line voltage of the 9 levels effectively.In addition,the SVG model in the rotating coordinate axis is analyzed,and the effective and reliable compensation control strategy is proposed.This paper proposes three control strategies for five-level-NPP topology.All of these methods are based on the space voltage vector modulation method,and can be used to ensure the accurate control of the capacitor voltage and the accurate compensation of the reactive current in the case of random selection of the redundant space vectors.The inductive current and capacitive current are compensated respectively in Matlab/Simulink to verify the effectiveness of each strategy.Then the control strategies are compared via reactive power compensation and capacitor voltage control.The most suitable control strategy for five-level-NPP topology SVG is found through those comparisons.