Passivity Enhancement of Voltage-Controlled Inverters in Grid-Connected Microgrids Considering Negative Aspects of Control Delay and Grid Impedance Variations

With growing environmental concerns, the installation of distributed generation systems forming microgrids in power systems has received much attention recently. This panacea, however, has always some challenges with itself. The delay in digital control systems, grid impedance variations in weak grids, and the interaction between paralleled converters in a microgrid, which can threaten the expectable operation of microgrids, are notable examples. Thus, this paper formulates these challenges in microgrids and then addresses them so that guarantees the stable operation of the microgrid. To this end, this paper first offers a delay compensation method, and elaborates it so that the control system achieves a high robustness against grid impedance variations. Then, a feedforward loop is introduced to the control system that makes the system immune against the interaction of inverters in microgrids. Using these methods, the system can survive irrespective of the above-mentioned non-ideal conditions. The grid-forming control approach is selected as the operation mode of the microgrid in this paper, since it could be used for both grid-connected and islanded scenarios. The experimental results of a laboratory prototype show the correctness of the theoretical conclusions and confirm the efficiency of the suggested technique.