In the process of accessing distributed power sources in microgrid, there will be serious coupling between active power and reactive power, which will lead to significant changes in the inverter outlet voltage and impedance and increase the circulating current phenomenon. The generation of circulating current will accelerate the aging of devices, reduce the inverter efficiency, and threaten the stable operation of the system. In this paper, the mechanism of circulating current generation is analysed, the basic characteristics of circulating current are studied, and an inverter parallel circulating current suppression strategy with adaptive virtual composite impedance and droop control dynamic adjustment algorithm is proposed. The virtual impedance setting can weaken the influence of line difference on system stability, make the system equivalent output impedance resistive, weaken the inductive device characteristics and reduce the circulating current amplitude; the adaptive droop algorithm implantation dynamically correlates the control power with the droop coefficient, enhance the power decoupling accuracy and weaken the circulating current influenced by power changes. The simulation platform and experimental setup established by the large‐scale simulation software PSCAD/EMTDC are used to study the basic scenarios of the inverter under two conditions of equal and unequal capacity, and the rationality of the proposed control strategy is tested.

Aluminum tube collector is a new type of collector that can be popularized, which can absorb solar energy and air energy at the same time. By analyzing the heat transfer process of aluminum tube collector, its mathematical model is established, and iterative calculation is carried out in Visual Basic to obtain the relationship between collector efficiency and different parameters. Finally, it is concluded that the thermal efficiency of aluminum tube collector is about 1.5, which is much higher than that of traditional collector; In sunny days with high ambient temperature, aluminum tube collectors are preferred; When the fin width is about 28mm, the mass flow is 0.20kg/s-0.25kg/s, and the inlet temperature of the working medium of the collector is about 5-10°C lower than the ambient temperature, the performance of the collector is better.