Although the model introduced in Chap. 2 is universally applicable, its complexity arises from the diversity of polytope models representing each DER’s feasible region, which can vary significantly. To address this, it is possible to standardize and normalize the shapes of the feasible regions for each DER. This chapter introduces a typical normalization model: the generalized virtual battery model, and a data-driven approximation method for its implementation. The approach employs a virtual battery model to represent the aggregate capabilities of a VPP. Model parameters are determined through an inverse optimization process using multi-scenario operation data generated by the original operational model. Numerical experiments validate the proposed method, demonstrating its accuracy and effectiveness. By standardizing and approximating DER flexibility with a generalized model, this approach enhances the ability to leverage DERs’ flexibility in a systematic and scalable manner.