An exponential-function-based droop control strategy for the distributed energy resources (DERs) is proposed to reduce the reactive power-sharing deviation, limit the minimum value of frequency/voltage, whilst improving the utilization rate of renewable energy. Both DERs and loads are interconnected to achieve a power exchange by converters, where the power management system should accurately share the active/reactive power demand. However, the proportional reactive power sharing often

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... tes due to its dependence on the line impedances. Thus, an exponential-function-based droop control is proposed to À prevent voltage and frequency from falling to the lower restraint,'achieve accurate reactive power sharing,´eliminate communication and improve the usage ratio of renewable energy. Furthermore, its stability is analyzed, and the application in islanded AC/DC hybrid microgrids is investigated to achieve the bidirectional power flow. The simulation and experimental results show that the reactive power sharing deviation can be reduced, and the utilization rate of renewable energy is improved by using the proposed method. Moreover, the simulation results illustrate that the system can maintain stable operation when the microgrid is switched from one supplied energy operation condition to another absorbed one. mismatch between the DERs and bus commonly causes the output voltages of inverters to be different [9] . Furthermore, frequency and voltage magnitude may fall to their lower limitation due to linear droop curve. Thus, the conventional droop control has intrinsic limitation so that the proportional reactive power sharing cannot be achieved, and frequency/voltage magnitude may fall to their lower limitation [10] [11] [12] . From the viewpoint of the limitation of frequency and voltage, the second level control was widely employed to achieve the frequency and voltage regulation [13] [14] [15] [16] . A novel distributed coordinated control strategy based on droop coefficient via a dynamic multi-agent consensus algorithm in our previous work [13] was applied to restore the system frequency. Furthermore, in order to deal with the voltage deviation caused by the droop controller, the dynamic consensus-based distributed controller in our previous work [14] was presented to regulate the output voltages of all the DERs. Nevertheless, the communication delay may impact the performance of the system. The novel secondary voltage and frequency restoration controller was employed in [15] to assess the impact of the communication delay. However, these methods need additional communication networks, which lose the advantage of droop control strategy. Thus, the local droop controller without communication networks was proposed to achieve the voltage regulation by combining with an event-driven operator of the parameter-varying filter [16] . Meanwhile, the control strategy without using sparse communication networks, which can achieve both frequency and voltage regulations, still remains a challenge. From the viewpoint of the reactive power sharing, there are two main approaches, i.e., droop controller with/without communication. On the side of the droop controller with communication, in [17] , an adaptive virtual impedance droop control strategy based on multi-agent was proposed to make equivalent output impedance of each converter be adjusted inversely to its rated capacity. In [18] , an adaptive droop coefficient control strategy was presented to realize accurate reactive power sharing. Thereinto, the excessive droop coefficients would cause the system instability, whereas low droop coefficients would affect the response speed of the system. Moreover, these above methods also need additional communication networks. Therefore, some methods without communication were developed one after another. The static virtual impedance concept was first presented to achieve reactive power sharing in the high R/X ratio low-voltage microgrids [19] . Nevertheless, the performance of the reactive power sharing was not ensured on account of uncertain line impedance parameters. Therefore, some scholars put forward some improved droop controllers by adjusting droop