Research On Power Factor Correction Scheme Of Solid State Transformer

China's smart grid construction is still in the primary stage,which is part of the distribution network,especially the rural distribution network of network power factor is low,the loss is bigger,a lot of odd harmonic problems with the network side current,the power quality have caused a certain degree of influence on the electrical.Therefore,as a converter for power factor correction to reduce power loss and improve power quality harmonic removal to the entire distribution network is very necessary to use solid state transformer in smart grid in operation.Reasonably solid state transformer application requirements more stringent and high-tech industry are very sensitive to power quality of the production in the field of power quality,the complete power conversion work and provide high-quality electrical energy at the same time,can play a good role in reducing the energy loss.Firstly,features of the solid state transformer and traditional oil immersed transformer are compared,and the solid state transformer can power factor correction,can realize the reactive power compensation,has excellent performance in the new energy grid function are introduced.Starting from the history of the development of solid state transformer,the transformer from the solid single stage structure type for the development of the two stage structure type,and then to the current three stage(input stage,isolation stage and output stage)structure with each other,and in-depth study of the topological change in the process of the development of solid state transformer.On the basis of the wide application prospect of solid state transformer,the three stage solid state transformer with bidirectional power flow is determined as the main research object of this paper.Then from the working principle and the transform scheme of solid state transformer,combined with the control objective of power factor correction circuit topology,determine the solid state transformer input stage,isolation level and output level,in-depth study of the solid state transformer work at all levels according to the characteristics of mathematical model,determine the input level selection of three-phase voltage type PWM rectifier,with double isolation level active power converter,the output stage using three-phase full bridge inverter circuit.The determination of control and design is an important link to complete the simulation,with power factor correction and AC/DC transform as the control target,put forward the choice of double loop decoupling control strategy to control the solid state transformer input stage,and the control principle to carry out in-depth research;as the control target to two-way flow of energy at the same time as DC/DC transform.The proposed control method simplifies the control structure of the control scheme to control the solid state transformer isolation level;to achieve the DC/AC transform as the control target,and considering the effects of parameter,put forward to using the double loop control strategy to control the solid state transformer output stage.The whole control system is designed based on the control strategy.Including the overall structure of the solid state transformer control system,function module design and system software design.Finally make a simulation research on the transformation process of all solid state transformer by using MATLAB/Simulink simulation software.The simulation result proves that the implementation of accurate control and complete the conversion of electrical energy requirements at all levels control strategy can correct the power factor control at all levels,finally in the solid state transformer overall simulation,simulation results show that a large number of odd side in the net harmonics and three-phase voltage unbalance,solid state transformer can suppress harmonics effectively and will not affected by the network side voltage drop effect,continuous and stable output voltage and circuit,dynamic performance is good.