Research On Solid State Transformer Control Strategy And Its Application In New Energy

Electricity is the basic dynamic of a nation's economy,the development and utilization of new energy,such as solar energy and wind energy which are inextremely abundant deposit,can guarantee cheap and reliable suppliment of electricity.Solid state transformer,as a new type of power transformation equipment,is a blend of power electronic technology and high-frequency transformer technology,so the flexible control of original and vice side of the transformer is achieved.SST can control the input and output,adjust the power factor.When SST is applied to power system,it will improve the controll ability of the system,improve power quality,and facilitate new energy grid-connected,will push forward the construction of the future smart grid.The control strategy of the SST,which has three levels containing intermediate dc unit is the main research object.The mathematical model and control strategy of the input level,isolation level and output level is studied respectively,and the application of the three level SST inthe new energy power generation systemis analyzed.In this paper,the main work content is as follows:1.A kind of three levels SST topology with intermediate dc level is introduced in this paper.The mathematical model of voltage source converter,the core of SST is built.VSC's mathematical models in the three-phase static coordinate system and the two-phase synchronous rotating coordinate system are established.The voltage space vector pulse width modulation method is adopted in the voltage source converter modulation,the modulation principle and implementation process are introduced.For the realization of interconnecting the photovoltaic output low voltage direct current to the high voltage alternating current,a cascade inverter topology is proposed in this paper and its mathematical model is established.2.The corresponding control strategies for various levels' control objectives are proposed.The voltage and current double closed-loop feed-forward decoupling control and model predictive control are adopted in the input level.Single phase shift control is adopted in the intermediate isolation level.The voltage and current double closed-loop control and droop control are adopted in the output level.And the carrier phase shifting control is adopted in the cascade inverter.The simulation of the control strategies are carried out under the Matlab/Simulink environment and the simulation results indicate the correctness of the mathematical model built and the validity of control strategy used.3.The application in the solar energy and wind power grid-connected system is studied based on the excellent characteristics of SST,and SST's superiority and application value in the field of new energy area is analyzed.