Research On Control Strategy Of Power Electronic Transformer Based On MMC Model

With the acceleration of the green transition of energy,renewable energy represented by new energy power generation technology has been more and more widely used,and in the face of the traditional distribution network with a single structure,its planning,construction and operation are proposed Higher requirements.Since the AC/DC hybrid distribution network has the advantages of both AC/DC distribution networks,it will receive more and more attention and research in the future renewable energy power generation technology.In order to realize the flexible connection of renewable energy power generation equipment and AC/DC loads,AC/DC hybrid distribution network interconnection equipment-power electronic transformers(PET)will play an important role.Because the modular multilevel converter(MMC)has a highly modular structure,considering the future medium and high voltage application scenarios of PET,the MMC-PET will have significant advantages,and it can set multiple AC and DC voltage level ports to facilitate multi voltage level interconnection of various types of loads and active consumption of renewable energy.Therefore,MMC-PET will be of great significance to the construction of the AC/DC hybrid distribution network in the future.This article mainly takes MMC-PET as the research object,and conducts in-depth research on its input stage,isolation stage,output stage and power coordinated control strategy.The specific research content is as follows:Firstly,the topology and working principle of MMC-PET are introduced,the mathematical model of MMC-PET is established,and the basic control strategy of mmc-pet is deeply studied.In the input stage,the modulation strategy,sub module equalization control strategy and circulating current suppression strategy of MMC are studied;The research focus of isolation stage is the current and voltage sharing control of multiple DAB connected by ISOP;The output stage mainly studies the sinusoidal pulse width modulation of VSC.In order to overcome the disadvantages of the traditional capacitor voltage sequencing method for modulation of MMC sub module in the input stage,such as large amount of calculation,high switching frequency and large loss,this paper proposes an algorithm for optimizing the capacitor voltage of the sub module.Secondly,according to the designed control strategy,simulation models at all levels are built on PSCAD / EMTDC platform to verify the rationality of the proposed control strategy;Then,the MMC-PET system simulation model is built to test and simulate the typical special conditions to verify the outstanding advantages of MMC-PET.Finally,an AC / DC hybrid distribution network with MMC-PET is constructed,and the power balance relationship between parallel and separate operation modes is analyzed in detail;Aiming at the application of MMC-PET in power coordination control of AC / DC hybrid distribution network,power coordination control strategies under parallel and off grid operation modes are designed respectively,and the correctness of the proposed control strategy is verified by simulation.