Research On High-frequency Transformer’s Magnetic Coreand Winding Characteristic In Power Electronic Transformer

Power Electronic Transformer (PET) is a new type of transformer. Energy can beconverted and controlledwith power electronic devices and power electronic transformationtechnology, and the required volume and weight of traditional transformer arereduced.As aresult, raw material and power energy are saved. High-frequency transformer is the core ofPET. It can isolate circuit and transmit power, so its performance directly decides to theperformance of PET. The bad-performance transformer has large loss and low efficiency. Itwould influence the stability and reliability of the whole system, even cause the fault of thepower electronics device, eventually lead to the failure of energy conversion.In this dissertation, the equivalent circuit of high-frequency transformer was analyzedand the characteristic experiment of high frequency magnetic materials is achieved. Inaddition,10kVA high-frequency transformer prototypes employed different windingstructures were designed, then the correlative measurement and study, such aselectromagnetic parameters, no-load and short–circuit characteristic, were finished. Finallya high-frequency transformer which was applied to20kHz,10kVA photovoltaic inverterwas made and tested.Firstly, the equivalent circuit and parameter calculation of high-frequency transformerwere discussed and analyzed. According to the electromagnetic induction effect principle,the experimental platform which could test the characteristic of high frequency magneticmaterials was built. Based the test results, the magnetic properties of some materials onhigh frequency in sine wave were obtained，which were ferrite material, amorphous alloymaterial and nanocrystalline alloy.The magnetization curve and magnetic hysteresis curveswere drawnwith the experimental data. The core loss curves under various frequencyconditions were calculated and compared.Secondly, the traditional core loss model of the magnetic material was analyzed. Basedon the characteristic experiment results, the high frequency core loss model ofnanocrystalline alloy was achieved, that was the relation between high frequency coercivity,high frequency core loss and the maximum magnetic flux density, frequency. A method todetermine the high frequency core loss according to the Steinmetz coefficient was proposedby means of three dimension fitting. It paved the way to choose magnetic core material for high-frequency transformer.Finally, by use of finite element method, the high frequency effects of the high-frequencytransformer winding in different conditions were calculated, also the effects of differentwinding structures on high-frequency transformer electromagnetic parameter were studied.The high-frequency transformer prototypeswithtwo winding configurations (sandwichedand interleaved) were designed and finished. During measuring and analyzing theirelectromagnetic parameters and characteristic, it was found that the interleavedconfiguration could reduce the high-frequency transformer loss. Based on above study, ahigh-frequency transformer which was applied to20kHz,10kVA photovoltaic inverter wasdeveloped. This high-frequency transformer which employed the modified interleavedconfiguration was99.3%maximum efficiency developed.