Research On Isolated Grid Connected DC/DC Converter With Dual-DC-buses Supporting Mutually For Power

With the rapid development of photovoltaic power generation,wind power generation and other new energy power generation systems,as well as the emergence of DC microgrid,the operation structure of the power system has been enriched,and the diversified configuration of power energy in space has been realized,but it undoubtedly brings challenges to the stability of the existing mature power system.Nowadays,the research of DC microgrid has attracted wide attention.However,the structure of DC microgrid is still based on a single DC bus,and the bidirectional DC/DC converters used in it is usually the non-isolated type.Thus,in order to achieve the bi-directional power flow between the DC microgrid sub-module networks of multiple DC buses and the application requirements of isolated bidirectional DC/DC converters,this paper studies the application of interleaved parallel current source isolated bidirectional DC/DC converters to the isolated DC grid-connected system with dual DC buses as power supports,and at the same time,a current sharing control strategy of the converter is proposed to increase the power to meet the modular cascade expansion demand of the converter.Firstly,this paper analyzes the operation principle of interleaved current source isolated bidirectional DC/DC converter under SPS modulation mode,and analyzes the power and soft switching characteristics of the converter.Meanwhile,for the interleaved buck/boost structure at the low voltage side of the converter,small signal modeling reveals that it does not have the essential feature of automatic current sharing.Therefore,the current imbalance of the two inductors at the low voltage side will affect the soft switching state of the switching devices under dynamic conditions.In this paper,through the single-zero-double-pole compensation control structure and the analysis of the steady-state inductor current,the balanced compensation control of the inductor current is realized.Secondly,in view of the scalability of the isolated DC/DC converter in the isolated DC grid-connected system where the dual DC buses are mutually power-supported,based on the traditional master-slave current sharing method,a master-slave current sharing method control strategy based on average current feedforward is proposed and implemented.The stability analysis of the parallel system is carried out,the feasibility of the current-sharing control strategy is verified by simulation,and the correctness and effectiveness of the current-sharing control strategy are verified by experiments.Finally,the operating characteristics of the isolated DC grid-connected system with dual DC buses as power supports are analyzed,and the control strategy of the shared voltage outer loop is proposed.The DC bus voltage is simulated by the series droop resistance of the power supply to verify that the energy storage components of the converter are on and off grid.Time energy running state;and coordinated control of dual-DC bus solutions are given to ensure the stable operation of the DC bus voltage is-adjustable.Build a dual DC bus system simulated by the converter and simulate the faulty DC bus voltage to verify the correctness of the theoretical analysis.