1.School of Electrical Engineering, Zhejiang University, Hangzhou 310027, China;2.East China Branch of State Grid Corporation of China, Shanghai 200120, China

Establishing the thermal stability control limit is a significant work for the power dispatching and control center and an important means to guarantee the safe operation of power grids. In order to address the problem that it is gradually difficult to establish thermal stability control limit due to the high uncertainty of power flows after the large-scale grid-connection of renewable energy, the power flow transfer relations are calculated and the power grid security constraints are established based on contingency analysis. Then, a three-stage thermal stability control limit calculation method for power grids based on the formulaic control limit and maximization of minimum safety margin is proposed to achieve the automatic calculation of thermal stability control limit. In the first stage, control limits of transmission channels are initialized. In the second stage, formulaic control limit requirements are established for those channels that are prone to overload after a contingency happens according to the criteria that power flow of the bottleneck equipment does not exceed its short-term current-carrying capacity after a contingency happens. In the third stage, the channel control limit is calculated successively according to the maximization principle of minimum safety margin for the set of channels with coupled transfer relation constraints. Both formulaic control limit and channel control limit requirements for the channels with tight transfer capacity can reduce the conservatism and fully release the transfer capacity of the channel. The control requirements can be reduced and simplified by establishing only channel control limit requirements for the remaining channels. Taking the summer peak operation mode of a regional power grid in 2023 as a case, the automatic limit calculation results are in good agreement with the stability regulations, which verifies the effectiveness of the proposed method.