Control Strategy Considering Power Sharing Among Distributed Generations And Bus Voltage Quality Improvement In Microgrid

Microgrid is widely used because it integrates the advantages of renewable energy,low power generation cost,high power supply reliability,environmental protection and plug and play.Nonlinear loads and a large number of power electronic devices bring a lot of harmonics to the microgrid system.At the same time,because the line impedance of each distributed generation(DG)from the common bus is not consistent,the fundamental and harmonic circulation problems exist in the parallel DG system,which will affect the stable operation of the DG parallel system,and the existence of line impedance will affect the voltage quality of the common bus.The power sharing among parallel DGS and the improvement of microgrid voltage quality have become the research hotspot.Therefore,in this paper,the islanded microgrid with parallel DG is taken as the research object,and reasonable control strategy is designed to suppress the circulating current between DG and improve the voltage quality.Firstly,the mathematical model of DG parallel system in islanded microgrid is established.On the basis of expounding the basic principle of traditional control strategy,the equivalent model of the parallel system in fundamental and harmonic domain is derived.The fundamental circulating current,harmonic circulating current and the fundamental reasons affecting the bus voltage quality are analyzed.Secondly,on the basis of the equivalent model,the fundamental circulating current,harmonic circulating current and bus voltage quality are considered comprehensively,and the improved droop control based on integral link to solve the fundamental circulating current problem is adopted.Therefore,the difference of line impedance does not afect the distribution of active power,and then the fundamental circulating current is suppressed.Aiming the problems of harmonic circulating current and voltage quality,a harmonic power sharing strategy based on improving voltage quality is proposed,by which the equivalent impedance of the system in harmonic domain is reshaped and the equivalent impedance in harmonic domain is adjusted dynamically to suppress harmonic circulating current and improve bus voltage quality.The harmonic circulating current deviation analysis,voltage quality analysis and stability analysis are carried out.Finally,the simulation model of microgrid with DG parallel system based on PSIM simulation software and the experimental platform of two parallel single-phase inverters based on STM32F407ZG are built.The simulation and experimental comparison between the proposed strategy and the traditional harmonic power sharing strategies are carried out.The results verify the correctness and feasibility of the proposed strategy.