Research On Dual Mode Seamless Transfer Control Strategy For DC Microgrid Based On DSP

In recent years,with the development of distributed new energy resources,the research of micro grid has become a hot spot,in which the DC microgrid has no frequency and other factors but voltage.The key point of this paper is how to realize the seamless transfer between the two operating states of the DC microgrid.This paper studies working principle and mathematical model of photovoltaic power generation,battery and super capacitor,three-phase converter,and also studied on the power electronic interface control methods,and the photovoltaic is connected to the bus by boost circuit,the control method of PV were introduced,combined with the advantage of their storage the advantages,selecting battery and super capacitor as the hybrid energy storage,and introduced the hybrid energy storage's structure connected with the bus,this paper uses the parallel structure,this structure can control charge and discharge more flexibly,to achieve bidirectional flow of energy,the power electronic interface adopts bidirectional DC/DC,this paper introduces the three-phase voltage converter used in the topology and the control strategythe mathematics,using the control method of feed-forward decoupling in this article.Secondly,it introduces the DC microgrid' s different control strategies,island,interconnection and seamless switching control strategy is studied in this paper,according to the DC microgrid operation state the photovoltaic power works at maximum power point tracking(Maximum Power Point Tracking,MPPT)or under constant voltage mode.using the fast dynamic response and high power density,the super capacitor can be compensated at first time,using the energy density of the battery,battery can be compensated for a long time,and it can be used as the backup energy of super capacitor.Energy storage is in the charging and discharging state in the case of off grid,Stop working when it is full when connected to the grid.This paper adopts bidirectional Bust circuit connected to three-phase converter as the improved AC/DC interface,The bidirectional Bust circuit can not only reduce the impact of the grid voltage side or the fault on the DC side,but also increase the DC voltage,this paper stables DC voltage by voltage loop and realize the power control and power flow and power factor by current loop,in order to solve the coupling between the two loop,feedforward decoupling double loop control strategy is introduced.In this paper,an improved software phase locked loop(PLL)control technique is used to capture the phase of three-phase voltage.in order to solve the voltage unbalance influence on the precision of PLL,this paper adopts a double rotating coordinate transformation phase locked loop,designing PI control module to realize phase pre synchronization,To avoid impulse current caused by voltage phase and amplitude deviation when connected to the grid.In addition,this paper studies the islanding effect,and selects the passive islanding detection method.When the islanding condition is detected,the corresponding processing is realized.This paper finally verified the correctness of the proposed control method through matlab/simulink simulation and hardware experiment.