## 2 Section Margin Allocation Model  
Many of the existing section margin allocation methods do not take into account the probability of the REG stations realizing the power delivery instructions given by the dispatch center after the section margin allocation. If the REG stations cannot meet the output command, the power delivered from the section will not reach the upper limit of transmittable power, thus reducing the renewable energy accommodation capacity of the grid. A conceptual diagram of the renewable energy delivery cross section is shown in Figure 1.  
When the method in this paper is applied to REG clusters, the main role of the REG cluster is to output power to the grid. Therefore, this paper only considers the case where the cross section is in the power delivery state, and does not consider the case where the REG cluster power is in the negative value for the time being. In this regard, the purpose of the proposed section margin allocation method in this paper is to achieve the full utilization of renewable energy by reasonably allocating the section margin so that the power delivered at the renewable energy delivery section reaches the upper limit of the power that can be delivered at the section as far as possible, provided that the relevant constraints are met. This paper introduces an output realization probability function for an REG station. The output realization probability function is used to describe the probability that, at a given moment, the active power output of an REG station can be no less than every power value within the rated power. The output realization probability function reflects the probability that the REG station can meet the dispatch instructions after the margin allocation. The output realization probability function for an REG station \(i\) at time \(t\) is defined as:  
\[Pr_{i,t}(P_{i,t}+P_{i,t}^{M,t}) \tag{1}\]  
Figure 1: Concept diagram of the renewable energy delivery cross section. where \(P_{i.t}\) is the active power emitted by REG station \(i\) at moment \(t\). \(P_{i.t}^{M.l}\) is the active power output of the REG station \(i\) at moment \(t\) adjusted to the section margin requirement, taking into account the generation cluster load rise space. The objective function of the proposed section margin allocation method is set as the probability that all REG stations in the REG cluster will be able to issue capacity orders after margin allocation, i.e., the product of the probability of achieving capacity at all REG stations. \[ \begin{split}\max\prod\limits_{i=1}^{N}\left[P_{i.t}(P_{i.t}+P _{i.t}^{M.l})\right]\\ s.t.\left\{\begin{array}{l}P_{\max}^{S}-(\sum\limits_{i=1}^{N}P_{i.t}-P_{t}^{L})=P_{t}^{SM}\\ P_{i.t}+P_{i.t}^{M}\leq P_{i.t}^{pre}\\ P_{i.t}^{pre}\leq P_{i}^{NN}\\ \sum\limits_{i=1}^{N}P_{i.t}^{M}=P_{i}^{SM}+P_{j.t}^{Lf}\end{array}\right.\end{split}  \tag{2}\]  
where \(P_{\max}^{S}\) is the upper limit of the transmission power of the REG section. \(P_{t}^{L}\) is the load power of the REG cluster at time \(t\). \(N\) is the number of REG stations in the REG cluster that can participate in cooperative control. \(P_{i.t}^{pre}\) is the predicted active power output of the REG station \(i\) at time \(t\) for the next period. \(P_{i}^{N}\) is the rated power of the REG station \(i\); \(P_{t}^{SM}\) is the margin of the section at time \(t\). \(P_{j.t}^{Lf}\) is the load rise space of the REG cluster under operation mode \(j\). The allocation of section margins should take full account of the potential for load uplift within the REG cluster and therefore take into account the potential for load uplift in advance when allocating section margins. However, in order to avoid section transmission power exceeding the limits when actually giving orders, it is necessary to multiply \(P_{i.t}^{M.l}\) by a factor.