The Study Of Power Electronic Transformer With Energy Storage System

With the rapid development of economy, the requirement of the power supply andits quality and reliability in society gives a higher standard. Since its invention,traditional power transformer has been widely applied in power transmission anddistribution system, and it is seemed to be one of the basic equipment in power system.Although the traditional power transformer has the characteristic of simple productionprocess, high reliability, its disadvantages are also obvious, such as large volume, highno-load loss and threat to the environment, etc. Power Electronic Transformer (PET) isan entirely new class of transformer, not only has it the basic functions, such as voltagetransformation, energy transfer and so on, the magnitude and phase angle of voltage orcurrent in both the primary side and the secondary side of PET can be controlledflexibly by the power electronic and control technology. So, PET can meet many newrequirements of future power system. Therefore, the study of PET has extremelyimportant theory and application value.In this paper, the development and research status of PET are summarized and theapplication of energy storage system in PET is introduced firstly. The basic principle ofPET and its several kinds of typical physical structure scheme are analyzed in detail.Due to the PET does not have the function of energy storage, and also there is no specialenergy storage unit in it, the PET can not compensate for voltage interruption andhelpless in the depth of voltage sags, hence the scheme of super capacitor energystorage system applied in PET is proposed. In chapter3, the mathematical model ofPET and energy storage system is deduced and the control strategies of PET’s threestages and energy storage system are studied and analyzed.In chapter4, the parameters of PET’s main circuit and energy storage system areanalyzed and designed, and the simulation model of PET is established inMatlab/Simulink simulation software. There’s no energy storage system in PET and thePET with energy storage system are simulated respectively. Simulation results show thatthe PET has good input and output characteristics in different load cases, but its loadscan not operate well while the input voltage is interrupted or in deeply sags. However,after connected with energy storage system in PET, the loads can work normally andstably while the input voltage interrupted or in deeply sags of PET. Simulation resultsverify the scheme of PET with energy storage system is correct and effective. According to the characteristic of large charge and discharge currents in energystorage system, in Chapter5, a novel interleaved parallel bi-directional DC/DCconverter is proposed which can be used in energy storage system. In the paper, thebasic principle and the performance of this new converter are introduced and analyzed,then a small power experimental prototype is established, the experimental results showthat this new bi-directional DC/DC converter has the characteristics such as highvoltage conversion ratio, low input/output current ripple and low voltage stress, etc.Thus it can be applied in the energy storage system and has the significance of referenceand promotion.