Study of Method for Grid-Forming Transformation of Electrochemical Energy Storage in the Electric Energy-Frequency Regulation-Inertia Joint Market

[Objective] In response to the high investment cost and long investment payback period when grid-forming energy storage is directly constructed in weak power systems， and in consideration of the value incentives of multiple markets， a decision-making method for the grid-forming transformation of electrochemical energy storage based on the existing grid-following electrochemical energy storage is proposed in the context of the electric energy-frequency regulation-inertia joint market. [Methods] Based on the trading framework of the electric energy-frequency regulation-inertia joint market which includes electrochemical energy storage， and from the perspective of electrochemical energy storage operators， a bilevel model for electrochemical energy storage integration in the joint market is established， taking into account the cost of grid-forming transformation of electrochemical energy storage. The upper-level model aims to maximize the revenue of energy storage for market trading and grid-forming transformation decisions. The lower-level model simulates the joint clearing process of the electric energy， frequency regulation， and inertia markets. To address the non-convexity of the lower-level market clearing caused by the start-up and shutdown states of thermal power units， the problem is relaxed and reconstructed using duality theory to transform it into a single-level mixed-integer programming problem for solution. [Results] The case study analysis indicates that， under the incentive of the value of multiple markets， the net revenue of electrochemical energy storage operators increased by 94 772.32 yuan after the grid-forming transformation， with an increase of as high as 73.5%， while the system operating cost decreased by about 0.2%. When the installed capacity of wind power in the system increased by 50%， the optimal proportion of grid-forming transformation of electrochemical energy storage operators increased from 29% to 64%， the increase in net revenue rose to 04，746.46 yuan， and the reduction in the total system operating cost increased to 85，667.39 yuan. [Conclusions] The method effectively incentivizes grid-following electrochemical energy storage systems to undergo grid-forming transformation， displacing high-marginal-cost thermal power units and thereby raising aggregate social welfare. As the share of renewable generation increases， the economic case for such transformation is further strengthened.