Research On Topology And Control Strategy Of Three Port Energy Delivery And Management System

It is difficult to meet the requirements of smart grid development for traditional power system equipment in the future,owing to the characteristics of inflexible power flow control,one-sided energy transmission and single power supply form.With the development of power electronics technology,solid-state transformers and other types of power electronic conversion device came into being,not only provide a rich internet interface for all types of renewable energy and energy storage systems,but also give flexibility control methods for the future power grid intelligent distribution management and multi-end energy conversion.This thesis studies a three-port energy delivery and management system(TPEDMS)for future smart grid applications.The contents are as follows.Firstly,this paper introduces the development history and the typical topology of solid state transformer,on the basis of above,the TPEDMS is proposed.Analysis the working principle of high voltage cascade rectifier and isolated DC-DC converter.The input stage is consist of three phase cascaded converter which adopts a three-level H-bridge module,and based on the switch equivalent circuit,the mathematical relation was derived.The middle stage adapts bidirectional half bridge three level DC-DC converter,and its operational principle was analyzed,as well as its power transmission under phase shift control strategy.Then,the DQ decoupling control strategy is studied for three-phase cascaded rectification based on the circuit analysis.Due to the existed problem of multi capacitor's voltage balance in three-level H-bridge multi-level module,the modulation technique of carrier phase-shifting among modules and reverse carrier disposition within modules,further more,add the redundancy switch,to form the satisfied module strategy.Also,the dual three-level phase shift control strategy is used in the intermediate three-level half-bridge DC-DC converter.The power transmission characteristics of different modes is derived and a control strategy of achieving high efficiency under light load circumstance for isolated DC-DC converter is researched.Thirdly,on the basis of the analysis above,a MATLAB/Simulink model for TPEDMS is built.The simulation shows the dynamic characteristics of input stage's booting and load change and the steady-state performance,such as the sinusoidal unit power factor operation of grid-side current.Also,the working principle of dual three-level control strategy and power transmission characteristics of the middle stage was analyzed.What's more,the current in MFT under the traditional phase-shifting control,single three-level control strategy and dual three-level control strategy under the condition of light load is compared.Through different parameter settings of TPEDMS simulation system,the power transmission characteristics between the two low-voltage output sides and the high-voltage input side is demonstrated.Finally,on the basis of theoretical research and simulation verification,a small power stage laboratory prototype composed of three-phase rectification and isolation DC-DC is constructed.The control program design is finished based on FPGA and the dynamic and static performance of the system is given.The correctness and feasibility of circuit topology and control strategy on three-phase cascade rectifier,isolated DC-DC converter and multi-port energy interaction are verified by the experimental results.