Research On Control Of High Frequency Isolated Interconnection Converter For AC/DC Hybrid Microgrid

Energy crisis and environmental pollution have become the two major problems of economic development.For this reason,the world has increased the research and utilization of new energy,and a series of new energy sources,such as solar,energy wind energy and water energy,have been widely used.In order to improve the efficiency of energy utilization,the microgrid emerges as the times require.Among them,AC/DC hybrid microgrid has become the new trend of the development of microgrid due to the common advantages of two DC microgrids and AC microgrids.In the research of AC/DC hybrid microgrid,the converter connected to DC microgrid and AC microgrid has become a research hotspot.At present,the research on AC/DC hybrid microgrid converters mainly focuses on the topology,converter control and PWM modulation of converters.Based on the analysis of the topology of high frequency isolated interconnected converters in AC/DC hybrid microgrid and the operation principle of the converter,this thesis studies the switch loss in the converter process.The existence of semiconductor switching loss is not conducive to the improvement of converter frequency and reduces the efficiency of converter operation.In this thesis,a converter control strategy is proposed.In the topology of the isolated AC/DC hybrid microgrid converter,the buffer capacitor in the DC side voltage source converter and a corresponding commutation algorithm can be used to effectively reduce the soft commutation of the semiconductor switch in the Zhou Bo converter and the voltage source converter.The switching loss of the two converters.In this converter control strategy,the converter of voltage source converter will be very long under the low load condition of the AC side,because the recharge process of the buffer capacitor becomes very slow when the current is low.When the voltage source converter is converted,a cycle transformer is used to short circuit the AC side of the transformer so as to start a resonant commutation.In this resonant process,the current in the voltage source converter is increased and the speed of the buffer capacitor recharging is accelerated,which effectively solves the current problem of voltage source converter in low load conditions.In this thesis,a high frequency isolated interconnected converter system of AC and DC hybrid microgrid is designed,and the converter control experiment platform is built.The simulation of PWM modulation and inverter is carried out on the Matlab/Simulink simulation platform.The DC side square wave voltage simulation is completed,and the three-phase inverter simulation circuit is designed,and three is completed.Phase inversion PWM waveform modulation,the corresponding PWM waveform and three-phase inverter voltage waveform are obtained,and the experimental results verify the correctness of the experimental scheme.Based on the analysis of converter operation principle,the saturation of magnetic core in converter is studied in this thesis.Because there are many non ideal factors in the actual circuit,such as the asymmetry of the IGBT control signal on the AC side,the difference of voltage drop at the opening of the IGBT and the different switching characteristics of the IGBT itself,there is a non zero DC voltage in the DC side of the converter,which leads to the saturation of the magnetic core of the converter.Based on the above theoretical analysis,a control strategy for restraining core saturation is proposed.An excitation current model is established,and a PI regulator is designed to regulate the excitation current in the converter.Finally,a simulation circuit model is built based on the PSIM platform.The simulation results verify the feasibility of the proposed strategy.