Research On The Parallel Current Sharing Of The Low-voltage Inverter In The Electronic Power Transformer

After Europe and America, our country has launched the research and construction ofthe smart grid. Large enterprises, like the WISCO, are constructing the smart grid, in linewith China’s smart grid construction situation. Through the construction of its strong smartgrid, the WISCO can significantly improve the energy efficiency of its power grid andrealize our country’s requirements of energy conservation and emission reduction. One ofthe main parts of the smart grid in WISCO construction is to enhance the controllability ofpower grid.This main research object is the parallel current sharing control of the EPT’s low-voltage level converter. The study of how to realizethe electronic power transformer abroadhas made some progress. And a laboratory prototype has been made, confirming thefeasibility of controlled transformer. But on a large enterprise’s power grid, like WISCO, apractical prototype is also the first time. Such electronic power transformers have the samebasic functions with the normal transformers, such as transformation、 isolation andtransferring energy. But the electronic power transformer uses the power electronics’conversion technology and the electric energy’s conversion technology based on theelectromagnetic induction principle. It can complete the waveform control、power flowcontrol, and power quality adjustment, so it would be possible to resolve many of the oldand new issues in the electric power system.Because the DC/AC inverter control technology is the core technology of the wholeinverter circuits. And according to the design requirements of electronic power transformerof WISCO, the rated capacity is500kVA, while the output voltage’s effective value is only231V, but the output current’s effective value is723A. And now the capacity of electronicpower switching devices available on the market is limited, so in order to meet the high-current needs of the electronic power transformer in WISCO and increase the overloadcapacity, the low-voltage level is better to be in parallel. So this article focuses on theresearch of the low voltage converter’s output control of the EPT, as well as multi-channelparallel operation control of this kind ofconverter.This article uses four kinds of control schemes, including voltage and current doubleclosed-loop control、hysteresis current control、carrier phase shifted control, double loop and hysteresis combination control. And the simulation and experimental study on thesefour kinds of control schemes are separately carried on. Afterwards the results of thesimulations and tests are analyzed and compared. In order to more accurately reflect thereal time operation status of the power grid in this paper, the differences between the DCinput voltagesand the output filtering inductors are done when in simulation, analyzing theimpact on the parallel system under the various differences. Actually through running in theexperimental prototype, it is confirmed that double-loop and hysteresis current combinationcontrol scheme is better than the other three schemes used in this article.