Traditional analytical approaches for stability assessment of inverter-based resources (IBRs)

often requiring detailed knowledge of IBR internals

become impractical due to IBRs' proprietary nature. Admittance measurements

relying on electromagnetic transient simulation or laboratory settings

are not only time-intensive but also operationally inflexible

since various non-linear control loops make IBRs' admittance models operating-point dependent. Therefore

such admittance measurements must be performed repeatedly when operating point changes. To avoid time-consuming and cumbersome measurements

admittance estimation for arbitrary operating points is highly desirable. However

existing admittance estimation algorithms usually face challenges in versatility

data demands

and accuracy. Addressing this challenge

this letter presents a simple and efficient admittance estimation method for black-boxed IBRs

by utilizing a minimal set of seven operating points to solve a homogeneous linear equation system. Case studies demonstrate this proposed method ensures high accuracy across various types of IBRs. Estimation accuracy is satisfying even when non-negligible measurement errors exist.