IBR Power Plant Frequency Control Design Consideration

Voltage control is often time provided at the plant-level control of inverter-based resources (IBR). Addition of energy storage systems in an IBR power plant makes it feasible to have frequency control at the power plant level. While frequency control appears as a simple frequency-power droop control to adjust real power commands to inverter-level controls with measured frequency as an input, care must be taken to avoid interactions among the plant frequency control with communication delays, inverter-level control effects, and the frequency sensor, usually a phase-locked-loop (PLL). This paper present two types of interaction scenarios that makes frequency control design challenging. The first interaction scenario may occur if the frequency control's gain is large, while the second interaction scenario may occur at a small control gain if the plant-level PLL lacks sufficient damping. We contribute to the fundamental understanding of the causation of stability issues due to plant frequency control through the derivation of a simplified feedback system focusing on the frequency and power relationship, and the follow-up frequency-domain analysis for gaining insights. For validation, we also design a data-driven approach to obtain models from data generated from an electromagnetic transient (EMT) simulation testbed. The findings from analysis have all been validated by EMT simulation. Finally, we contribute to mitigating strategies and also the understanding of the role of additional proportional integration power feedback control. This addition has been demonstrated as an efficient stability enhancement strategy to mitigate the effect of communication delay.