Virtual Inertia Limit Estimation Method for Power Systems With High Proportion of Renewable Energy Considering Time Delay

As the increasing capacity of renewable energy sources (RESs), power system with high RES penetration urgently need virtual inertia support from RESs. Current research has found that, due to inherent time delay, providing excessive virtual inertia from RESs may instead cause small-signal instability in the power system. Therefore, determining the upper limit of virtual inertia from RESs is critical to ensuring small-signal stability. However, current studies have only proposed methods for determining small-signal stability in power systems that consider VIC time delay, with limited discussion of the upper limit of virtual inertia. Therefore, a discrete system frequency response (SFR) model considering VIC time delay is established in this paper. It is found through analysis that the frequency sampling period affects the critical stability condition much more sensitively than the time delay length. Furthermore, a sufficient condition for small-signal stability is proposed, which describes the upper limit of the virtual inertia of RESs by the frequency sampling period and the system inertia time constant. Although this condition is a conservative estimation of the upper limit of virtual inertia, but the experiment on the test bench of wind-integrated power systems verifies that the sufficient condition is close to the critical condition. The sufficient condition is independent of the time delay length, making it more suitable for guiding practical engineering applications.