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Abstract:In low-voltage converter-based alternating current (AC) microgrids with resistive distribution lines, the P-V droop with Q-f boost (VPD/FQB) is the most common method for load sharing. However, it cannot achieve the active power sharing proportionally. To overcome this drawback, the conventional P-ω/Q-V droop control is adopted in the low-voltage AC microgrid. As a result, the active power sharing among the distributed generators (DGs) is easily obtained without communication. More importantly, this study clears up the previous misunderstanding that conventional P-ω/Q-V droop control is only applicable to microgrids with highly inductive lines, and lays a foundation for the application of conventional droop control under different line impedances. Moreover, in order to guarantee the accurate reactive power sharing, a guide for designing Q-V droop gains is given, and virtual resistance is adopted to shape the desired output impedance. Finally, the effects of power sharing and transient response are verified through simulations and experiments in converter-based AC Microgrid.

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Operation efficiency is one of important concerns for power conversion system. Efficiency issue of microgrids with multiple paralleled inverters has been paid slightly concerns. Therefore, this paper presents an efficiency analysis method of microgrid in system level and an efficiency-prioritized droop control strategy to improve operation efficiency of microgrids under different load profiles. Efficiency model of microgrid is first established to reveal time-varying efficiency characteristic under different load profiles. Then, optimum solution of efficiency model is derived by Lagrange Multiplier Method, and optimum conditions to capture maximum efficiency are obtained. Furthermore, an efficiency-prioritized droop control strategy is proposed to improve operation efficiency according to the established efficiency model. In addition, stability analysis of the proposed droop controller is performed, from which the guideline for controller design is given. Simulation and experimental results are provided to validate the proposed efficiency-prioritized droop control strategy. The proposed droop control strategy is able to improve overall efficiency of microgrid under different load profiles, which also preserves advantages of conventional droop control strategy.