IET Power Electronics   2016 年 9 卷 5 期

2016.04.20

In a low-voltage microgrid, due to the effect of mainly resistive line impedance, the conventional P/w and Q/Edroop control is subject to the coupling and dynamic instability of the real and reactive power control. To address thisproblem, a novel virtual impedance composed of virtual negative resistor (VNR) and virtual inductor is employed tocontrol the interfaced inverters in this study. The virtual resistance is controlled to be negative to counteract the effectof the line resistance thus ensuring a mainly inductive system impedance. However, it is found in this study that, thegrid-connected inverter system may present non-fundamental instability if the line resistance drifts to be smaller thanthe value of VNR with the basic VNR method. To produce a more stable system when the line parameter drifts, animproved VNR form based on a proportional-resonant structure is proposed. Moreover, an interesting conclusion isobtained that, if the PI voltage regulator and the basic VNR are used, the grid-connected inverter becomes criticalstable when the virtual resistance is exactly equal to the line resistance. Experimental results of a low-voltagemicrogrid consisting of two 6-kW inverters are given to validate the control strategy.