| In order to cope with the energy crisis and environmental pressure,the development and utilization of new energy mainly based on clean renewable energy has increased rapidly.Compared with the traditional centralized power generation,the distributed utilization of new energy is more convenient and flexible,which plays an important role in the construction of new power system based on new energy.The microgrid effectively solves the problems of local utilization of distributed energy and high-quality grid connection.In order to improve the power supply capacity and system reliability of microgrid,the parallel operation mode of multiple distributed energy is generally adopted.As the interface between distributed energy and microgrid,the control mode of inverter is particularly important.In order to maximize the use of energy and reduce the system loss,the distributed generation should be made to output in proportion to its capacity,and in order to make the inverter cut in and cut out freely,more effective control strategies should be adopted to improve the stability of the system operation.In order to solve the problem of circulating current and uneven power distribution of multi-inverters,the droop control strategy is proposed under the condition of centralized communication and adjacent inverter communication.The main contents include:(1)This paper introduces the development status of distributed energy resources,summarizes the existing microgrid topology with distributed energy resources,puts forward the operation requirements and control strategy research status of multi parallel inverters,and summarizes the advantages and disadvantages of the existing control strategy.The mathematical models of the inverter in different coordinate systems are established.According to its structure,the droop control strategy based on voltage and current double closed loops is designed and verified by simulation.(2)This paper establishes the equivalent model of two parallel inverters,analyzes the causes of circulating current in parallel system taking two parallel inverters as an example,classifies the circulating current,and expounds the relationship between line impedance and reactive power.The droop characteristics of inverter with droop control strategy are analyzed when the capacity of distributed energy is the same or different,and the existing problems are verified by simulation model.(3)A new droop control algorithm based on communication is proposed.By acquiring the output reactive power information of other inverters,an integral controller is introduced,and the droop coefficient is modified to achieve the accurate distribution of reactive power while restraining the circulating current.Finally,a model is built on the simulation platform.Compared with the traditional droop control in four conditions,the effectiveness of the proposed control strategy is verified and the influence of communication fault on the control strategy is analyzed.(4)This paper introduces the related concepts of multi-agent system and consensus algorithm,which provides a theoretical basis for the subsequent control strategy.Aiming at the problem of control strategy failure caused by communication failure,a novel droop control strategy based on consensus algorithm is proposed by using adjacent communication to obtain the output reactive power information of inverter.The effectiveness of the control strategy is verified by simulation under four conditions.The actual circuit based on dSPACE is built,and the control strategy is further verified by experiments. |
