Research On Operation Coordination Control Technology Of Photovoltaic And Storage DC Microgrid

With the increasingly serious problems of environmental pollution and fossil energy consumption,people’s development and utilization of renewable energy is also gradually increasing.The microgrid composed of distributed power sources,energy storage units and loads not only effectively reduces the adverse impact of a large number of renewable distributed power sources on the power system caused by direct and disorderly grid connection,but also greatly improves the economic benefits of distributed power sources.Compared with the AC microgrid,the DC microgrid is favored by more and more researchers due to its advantages of fewer energy conversion links,flexible control,and low system loss.This paper mainly studies the operation coordination control technology of the photovoltaic and storage DC microgrid.Firstly,the structure of the photovoltaic storage DC microgrid system is introduced.The equivalent circuit models of photovoltaic arrays,lithium batteries and super capacitors are established respectively.And the Boost converter,bidirectional DC/DC converter and grid-connected converter are modeled,working principle analysis and parameter design.The above work lays a theoretical foundation for the subsequent operation control strategy design of each unit and the coordinated control of the microgrid system operation.Then,the control strategies of each unit of the system are studied respectively.Including the maximum power tracking control and constant voltage control of photovoltaic power generation units;the power distribution control based on low-pass filter and the power distribution control based on virtual impedance of the hybrid energy storage unit;the unit power factor voltage regulation control and reactive power compensation priority voltage regulation control of the grid-connected converter unit.Among them,a detailed analysis is made on the control principle,control target and control parameter design of power distribution control based on virtual impedance.Based on the study of the control strategy of each unit,taking into account factors such as the maximum utilization of solar resources,the extreme state of the hybrid energy storage unit,and the operation status of on-grid and off-grid.Taking the control of DC bus voltage stability as the primary purpose,a coordinated control strategy for multi-mode operation of the photovoltaic and storage DC microgrid system is presented.By analyzing the existing working modes of each unit of the system,the system is divided into eight operating modes,and the switching conditions between the operating modes are established.The flexible switching between the operating modes and the stability of the system operating are verified by simulation.Finally,the low voltage ride-through control strategy of DC microgrid is studied.When a three-phase short-circuit fault occurs at the grid-connected point,the coordinated control of source-grid-storage is realized by adjusting the control strategies of photovoltaic power generation unit,energy storage unit,and grid-connected unit.By providing reactive power support to the AC grid,it can ensure that the DC microgrid system does not off the grid during a fault,and at the same time,the output current of the grid-connected converter is not over current;during a fault,the hybrid energy storage unit is used to maintain the stability of the DC bus voltage.Construct simulation models,simulate faults and verify the correctness and effectiveness of the proposed control strategy.