Research On Power Electronic Transformer With Hybrid Energy Storage Device

Power electronic transformer has the basic functions of voltage level conversion and electrical isolation,as well as has the ability to connect the various distributed energy sources and the energy storage devices,and is bided fair to turn into an important equipment for building smart grid in the future.Focus on the issue that power electronic transformer is difficult to respond to voltage suspend and voltage fall/surge in electrified wire netting,a hybrid energy storage device is proposed to be applied to power electronic transformer.The low-voltage DC bus voltage of power electronic transformers can be stabilized by using its charging and discharging,so that power electronic transformer can effectively deal with the harsh working conditions of power grid.Firstly,by analyzing the working conditions that affect the power quality in the electrified wire netting,a three-phase four-wire power electronic transformer with the ability to improve the power quality is selected as the research object.The charging and discharging features of battery and super-capacitor in hybrid energy storage device are studied respectively,besides the fluctuation of low-voltage DC bus of power electronic transformer under bad working conditions is stabilized by using the complementary characteristics of these two energy storage elements.Combined with the common hybrid energy storage circuit structure,an active circuit structure consisted of a high-gain bidirectional DC/DC converter,a battery and a super-capacitor is proposed,which is connected to the low-voltage DC bus of the power electronic transformer to better deal with the bad working conditions of the power grid.Secondly,Corresponding control strategies are proposed for all levels of converters of power electronic transformer,and the performance of all levels of converters under the proposed control strategies are emulated and dissected.For purpose of enabling the battery and super-capacitor in hybrid energy storage device cooperate with each other in charge and discharge,so as to deal with the bad working conditions in the power grid and stabilize the low-voltage DC bus voltage of power electronic transformer,nine working modes are designed for hybrid energy storage device.In term of the realistic bad working conditions of the electrified wire netting,the capacity of hybrid energy storage device is configured.Finally,the main circuit and control system of power electronic transformer with hybrid energy storage device are contrived,and the contrived power electronic transformer is emulated.The power electronic transformer is simulated and compared with and without hybrid energy storage device under the working conditions of grid voltage drop,surge and interruption,respectively.The emulation consequences indicate that the power electronic transformer with hybrid energy storage device can keep the low-voltage DC bus voltage stable and make the three-phase voltage waveform at the output end complete.Therefore,the power electronic transformer with hybrid energy storage device has certain practical value in dealing with the harsh working conditions of power grid.Figure [92] Table [2] Reference [82]...