Analysis of the Impact of the Increasing Inverter-based Resources on Inter-area Modes of the U.S. Western Interconnection

The retirement of conventional synchronous generators and the integration of inverter-based renewable energy sources (RES) are transforming power systems in unprecedented ways. Understanding the impact and consequences of this resource mix transition is crucial to maintaining reliable grid operation. In this regard, this paper examines the impact of increased RESs on the oscillatory behavior of the U.S. Western Interconnection. From our analysis, we found that increasing RES penetration levels can have a significant impact on the system modes. However, no single trend could be identified that can correlate this impact to the RES penetration levels. This impact was, in fact, dependent on the group of synchronous generators that were replaced by the RES machine models; for instance, replacing synchronous generators in Alberta, that have high participation factors and significantly contribute to the damping of the NS-A mode, had the most impact on the NS-A mode while the impact on the NS-A mode by replacing synchronous generators in the rest of the WI was less.