Research On Control Strategy Of Power Conver-Sion System Under Non-ideal Power Grid

With the growing permeability of the distributed new energy generation such as wind and solar power in the micro grid,the negative impact of the intermittent and uncertainty of the output power is becoming more and more serious.Thus,the en-ergy storage system should be introduced to regulate the power fluctuation in the microgrid.Power Conversion System(PCS),as the interface between the microgrid system and the energy storage medium,plays a role in reducing the power fluctua-tion,cutting the peak and filling the valley,stabilizing the voltage and improving the power quality of the power grid in the microgrid.At the same time,the voltage im-balance of the power grid system and the voltage drop caused by short circuit are common,so it is very important to study the control of energy storage power con-verter under the condition of non-ideal power grid.Based on this,the main research work of this paper is as follows:(1)Analyzing and introducing the application background and significance of energy storage power converter.Researching the control strategies under some non-ideal power grids at home and abroad.Summarizing the topology of single stage and two-stage energy storage power converter,Comparing and researching the difference between the traditional DC/AC three-phase full bridge topology and T type three level topology and the difference between the multiplied DC/DC and the and single DC/DC.Considering the energy storage power converter studied in this paper,a two-level T type three level topology based on DC/DC dual structure is se-lected.(2)Deeply researching the working principle of the pre stage bidirectional Buck-Boost converter and the post stage T type three level converter.In order to fa-cilitate the design of the control system of the energy storage power converter,the mathematical model of the dual level T type three level energy storage power con-verter under the ideal and non-ideal power grid is established respectively.(3)Under the ideal grid,this paper gives the parallel and off network control strategy of the energy storage power converter,and fully validates the correctness of the strategy through the corresponding experiments.Under non-ideal conditions such as the unbalance voltage of the power grid,the voltage drop caused by short circuit,and the non-planned isolated island,the dual two order generalized integral phase locked loop is used to lock the voltage phase of the power grid accurately.This paper provides the active anti-island protection control strategy based on the frequency offset,the control strategy of restraining the negative sequential current,and the low voltage crossing control strategy based on birotation coordinate system.(4)At last,building the simulation of battery energy storage system in the Matlab/Simulink environment,verifying the control strategy under the non-ideal power grid,and building the experimental platform of the battery energy storage system.The experiment was completed on a dual level T type three level energy storage power converter prototype,and the feasibility of the control strategy was verified.