## 1 Introduction
To address this challenge, a feasible solution is the coupling integration of RESs and TPUs at a close physical distance, which are connected to the main power grid at the point of common coupling (PCC). This form of coordination operates as an integrated coupling generation system (CGS) for better coordination without considering the grid structure [18]. The CGS can more efficiently utilize the flexibility of TPUs to participate in DPR auxiliary services and accommodate RESs. Research in [19] demonstrates that the TPUs in CGS can achieve a real-time frequency response to handle the dynamic operation states of RESs. In [20], the coupling effect of TPUs and RESs was analyzed to demonstrate that CGS can achieve better coordination between power sources. In [21], an optimal scheduling strategy that fully considers the contributions of WT farms, PV parks, and TPUs to determine economic benefits and an environmental impact equilibrium in a hybrid generation system under natural limitations was proposed. In [22], a day-ahead optimal dispatch model of the coupled system was established based on the operation characteristics of DPR auxiliary services and the ladder-type ramping of TPUs. In [23], an optimal scheduling approach of CGS was presented to demonstrate that coupling integration can improve the economic benefits of the system. The above CGS studies have predominantly concentrated on the economic benefits facilitated by coupling integration, overlooking the quantitative evaluation of enhancements in RES utilization after coupling integration compared to the scenario before coupling. Moreover, there has been limited attention to the detailed implementation scheme for the real-world CGS with TPUs and RESs. To sum up, previous studies [9; 10; 11] that conducted macroscopic evaluations on the impact of retrofitted TPUs for improving the accommodation capability of RES did not fully exploit their potential for detailed coordination at the time-step level. On the other hand, the optimal scheduling models for TPUs and RESs in previous studies [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23] lack the ability to quantitatively measure the improvements in RES accommodation of different coordination methods with TPUs. To address the aforementioned gaps, this paper proposes an evaluation framework to assess the enhanced accommodation capabilities of RESs following the coupling integration optimization of retrofitted TPUs with WT and PV. Firstly, the analysis of the flexibility of TPUs, the accommodation measures of RESs, and the coordination framework of coupling integration for TPUs and RESs is presented. The implementation strategy for integrating the power sources into CGS is given in detail. Based on the above, an optimal power-source scheduling model is established based on the operation characteristics before and after retrofitting, as well as the features of DPR services. Then, the indices for assessing the RES accommodation level and TPU regulation marginals are proposed to quantify the performance of power sources before and after coupling and retrofitting. Finally, through a real-world project, the effectiveness of the proposed method is validated, demonstrating that retrofitted TPUs in CGS can improve the system's regulation marginals while maximizing the accommodation of RESs.