Stability Blind-Area-Free Control Design for Microgrid-Interfaced Voltage Source Inverters Under Dual-Mode Operation

Voltage-controlled voltage source inverters (VSIs) are generally adopted to achieve seamless transfer between islanded mode and grid-connected mode in microgrid applications. However, these two operation modes for VSIs feature different output filters, i.e.,
LC
filters for islanded mode while
LCL
filters for grid-connected mode, thus leading to different stability performance. In this article, the traditional control strategy based on an outer capacitor voltage loop cascaded with an inner capacitor current active damping loop is investigated in details. The analysis indicates that there exists an inevitable blind area of stability design, where the system cannot be stable under two operation modes at the same time. Therefore, in order to raise available space for system design, this article proposes a stability blind-area-free control design method. The analysis indicates that the proposed stability design is only affected by
LC
filter parameters under islanded mode. Therefore, the blind area of the traditional control method can be well eliminated, and meanwhile the system robustness against the grid impedance variation under grid-connected mode is improved. The detailed design method is also presented. Simulation and experimental results are finally provided to verify the effectiveness of the analyses and the feasibility of the method.