Research On Adaptive Droop Control Strategy For DC Distribution Network With High Permeability Photovoltaic

With the increase of distributed PV permeability in DC distribution network,it is a hot research topic to ensure the friendly access of high proportion and large-scale distributed photovoltaic power.The photovoltaic DC distribution network with droop control has the characteristics of non communication,high reliability and flexible operation mode.However,in practice,the photovoltaic output power is greatly affected by environmental factors,which brings new challenges to the reliable operation of DC distribution network under droop control mode.In this thesis,the photovoltaic DC distribution network under the vertical control mode is the research object.Aiming at the problem that the droop control effect is worse due to the influence of the environment,the improvement scheme of droop control is proposed.The main work and achievements of this thesis are as follows:(1)This thesis introduces the structure of DC distribution network,establishes the mathematical model of photovoltaic unit,energy storage unit,grid connected converter and load unit,and analyzes its working principle and control strategy.Build a DC distribution network system including the above four parts to provide a theoretical basis for the follow-up research.(2)An adaptive droop control method for DC distribution network considering photovoltaic output power margin is proposed.By using the voltage signals of the input and output terminals of the PV converter,the system load change and the output power margin of the PV power supply are judged.On the basis of traditional droop control,the droop coefficient is modified based on the input voltage deviation of the photovoltaic side converter,so as to realize the reasonable distribution of unbalanced power among photovoltaic power sources with different output power margin.Theoretical analysis shows that the proposed adaptive droop control can effectively improve the stability of the system when multi PV parallel connected to DC distribution network.Simulation experiments based on MATLAB/Simulink platform verify the effectiveness of the proposed control method.(3)An adaptive subsection droop control method for the flexible output of photovoltaic converter in DC distribution network is proposed.Aiming at the problem that the photovoltaic output is seriously affected by environmental factors,which leads to the deterioration of the traditional droop control effect,this thesis adaptively adjusts the droop characteristic curve according to the change of photovoltaic output,so as to realize the accurate power distribution under heavy load conditions and realize the accurate power distribution under light load conditions Under this condition,the stable control of bus voltage is realized.The influence of the self-adaptive variation of droop coefficient on the circulation suppression ability and the average current of the system is analyzed.The simulation of photovoltaic DC distribution network is built in Matlab/Simulink.Theoretical analysis and simulation results show that the adaptive piecewise droop control strategy can dynamically adjust the power allocation task according to the output of photovoltaic power supply,improve the system power allocation accuracy under heavy load,and reduce the DC bus voltage bias under light load.