Accept Uncertainty and Prepare to Adapt with Increased Penetration of Inverter Based Resources
As penetration of Inverter Based resources (IBRs) continue to grow, the industry is faced with new challenges/issues, some of which are understood but others are not understood well, and few are yet to emerge. This paper will discuss following emerging issues: 1. Is there a need to start modeling system loads in short circuit model? a. Inverter Based Resources are current limited devices, i.e., current injection during fault condition is comparable to facility current rating. b. Inverter Based Resources are voltage dependent current sources. The split between active and reactive current during a fault is dependent on inverter terminal voltage. The PSRC WG C24 has developed a model to represent voltage dependent current source, which calls for injection of active and reactive current during a fault. 2. The large transmission network is often represented with a small system equivalent for the purpose of sharing with neighbor utilities, network customers, distribution providers and generator owners. Developing system equivalents for a network dominated by synchronous machines (voltage sources) is well understood. IBRs are voltage dependent current sources. How to develop a system equivalent for a system dominated with IBRs? 3. IBR’s contribution to system faults is driven by its control system. This same control system dictates IBR’s performance during grid disturbances. When IBRs are connected in a weak grid environment, it may be preferred that IBR’s control system response is slow to avoid any control stability issues. This paper briefly discusses IBR’s response time to system faults. As well as, a need for standardization to return to pre-fault operation soon after the fault has cleared. 4. What is the impact of IBRs displacing traditional synchronous machines on system fault currents? Is the impact most near displaced generation or elsewhere on the system?