Research On Improvement Of Micro-Converter Performance And Circulation Suppression Method Of Multi-Converters Parallel Connection

DC micro grid is the development trend of future energy utilization technology.At present,more and more user equipment use DC power supply,which reduces AC-DC conversion link to improve reliability and work efficiency.With the continuous increase of load capacity,the number of power generation units in DC microgrid has also increased,and the application of multiple converters in parallel has appeared.For the structure of the grid-connected multiple converters in parallel,it is necessary to study the control method of converter and the circulating current suppression method of the multiple converters in parallel to improve the performance.For improving the working efficiency of bidirectional DC converter,improving the grid-connected current quality of flyback converter,the consistency coherent control and circulating current suppression method of the multiple converters in parallel,the dissertation carried out the following research work:(1)Bidirectional DC converter is the essential part of the connection between the energy storage system and DC bus.In order to eliminate reflow power of bidirectional DC converter and improve the working efficiency,it is studied from control strategy of bidirectional converter in the dissertation.By detecting the zero crossing of the inductor current in the topology,the current path is cut off to prevent reflow power.According to the above principles,the inductor current zero crossing control strategy is proposed.The hardware experimental results show that the proposed control can eliminate reflow power of the converter.(2)Micro flyback grid-connected converter delivers the surplus energy of the system of the multiple converters in parallel to AC grid.In order to improve the current quality of micro grid-connected converter,the control strategy of the grid-connected current of micro flyback grid-connected converter is studied in the dissertation.Because the small signal model of flyback grid-connected converter has nonlinear parameter time varying characteristics,the inverse system model is compensated before the small signal model according to the inverse system principle,and the inverse system control method of the grid-connected current is proposed.The hardware experimental results show that the proposed control strategy improves the current quality compared with proportional resonance integral control.(3)The point to the consistency coherent control of the multiple converters in parallel is the consistency method.In order to improve the speed of the consistency power coordinated control process of the multiple converters in parallel in the circulating current suppression,the consistency control method of the multiple converters in parallel with additional control law is proposed in the dissertation.The convergence of the consistency method of weight time varying undirected and directed topology with additional control law is studied.By the Getschgorin theorem,the convergence condition of additional control law consistency method is proved.The simulation results verify the correctness of the convergence conditions in MATLAB/Simulink.(4)In order to reduce the parallel circulating current of the multiple converters and improve the working efficiency,the circulating current suppression method of the multiple converters in parallel is studied in the dissertation.The characteristics of the circulating current and bus voltage of the multiple converters in parallel of DC micro grid are analyzed.By considering the suppression of circulating current,bus voltage compensation and the equivalent impedance of the line connected by the converter to bus,the control method of the multiple converters in parallel with the circulating current suppression is proposed in the dissertation.It includes adaptive droop control of converter,the consistency power coordinated control with additional control law and bus voltage compensation control.Finally,compared with the traditional droop control,the proposed method improves DC bus voltage quality while suppressing the circulating current by Matlab/Simulink simulation experiment of the grid-connected multiple converters in parallel structure.