Grid-Connection Strategy Of Photovoltaic Storage Converter Based On Improved Droop Control

DC microgrid plays an important role in large-scale access of renewable energy and promoting the transition from traditional power grid to smart grid.With the expansion of the scale of DC microgrid,the traditional DC microgrid structure needs multiple converters to run in parallel to expand the capacity,which will cause the loss of power and reduce the transmission efficiency of power.High-performance optical storage converter that three port converter integrate the photovoltaic power generation unit,battery energy storage unit and load unit into a converter,with low cost,high power density,high reliability and the characteristics of modularization,integration.Using this kind of converter in parallel to expand the capacity of the DC microgrid will save multiple converters,reduce the energy loss and improve the transmission efficiency of electricity.However,a large number of optical storage converters incorporated into the DC microgrid will cause the problems that uneven power distribution between converters and grid voltage instability,then,choosing an appropriate control strategy to solve the above problems is particularly important! The main research contents of this topic are as follows:Firstly,introducing the modulation and control method of the three-port converter and the current-balancing control strategy of the parallel converter in the DC microgrid.Analyzing the traditional droop control and pointting out the problems of bus drop and low accuracy of current balancing caused by it.To solve the above problems,proposing an improved droop control+PPAS control strategy suitable for three-port converters in parallel.On the basis of the traditional droop control algorithm,adding the current balancing loop and voltage lifting loop to compensate the droop coefficient and DC bus voltage,which makes up for the defects of the traditional droop control.Analyzing the proposed control strategy mathematically,and proving the truth that improved droop control can reduce the bus voltage deviation from theoretic,improve the accuracy of current distribution,and make the system have good dynamic and steady current balancing performance.Secondly,carring out the small signal modeling for the interleaved parallel Buck-Boost and DAB integrated three-port converter and converter parallel system studied in this paper,and PI compensation is carried out to make the compensated system have good stability.Finally,building a simulation model of the DC microgrid system with two three-port converters in parallel in PSIM,also comparing and analyzing the traditional droop control+PPAS control strategy and the improved droop control+PPAS control strategy.The simulation results confirm the superiority of the improved droop control in this system.In addition,building a small household DC microgrid system,and designing the high frequency transformer.Connecting two three-port converters in parallel to the DC microgrid system,and carring out the on-off and off-load experiments respectively to verify the feasibility and effectiveness of the proposed improved droop control+PPAS strategy.