Coupled Problem of Transient Voltage/Angle Stability in Paralleled Synchronous and Virtual Synchronous Generators with Dynamic Loads

The interaction between two or more distributed generators (DGs) may cause transient angle instability of islanded microgrids, while the interaction between DGs and dynamic loads may cause transient voltage instability of islanded microgrids. However, with the increase of DGs and dynamic loads in islanded microgrids, the two interaction phenomena would simultaneously exist and are coupled to each other. That would lead to the interweaving of transient voltage/angle instability, which may make the transient instability mechanism more complicated. This paper focuses on the coupled problem of transient voltage/angle stability of paralleled synchronous and virtual synchronous generators with dynamic loads. Firstly, a coupling model of the system is derived, and then its mechanism is explored. It can be found that after the fault is cleared, the angle instability and voltage instability deteriorate each other, forming a vicious circle of angle-voltage instability, which eventually leads to serious transient instability problems in the paralleled system. Experimental results verify correctness of the theoretical results.