Modeling the Carbon–Electricity Coupled System with Multi-Entity Participation Under Carbon Emission Trading Market Coverage Expansion: A System Dynamics Approach

China’s carbon emission trading market (CETM), initially covering only power generators, is expanding to include key carbon emitters, like steel and cement enterprises. These high-energy-consuming industries also participate in the electricity market as major consumers. Current research lacks a systemic analysis of multi-market, multi-entity coupling under CETM coverage expansion. This study employs system dynamics to model coupling among steel, cement, thermal power, and renewable energy enterprises within both electricity and carbon markets. Multi-scenario analysis examines key indicator changes as the policy deepens. The results indicate that the impact of CETM coverage expansion unfolds in two phases: initial and deepening stages. Policy deepening will significantly influence key indicators, such as carbon prices and grid feed-in tariffs. Allowance tightening will lead to a pronounced rise in carbon prices, and the carbon trading costs for steel enterprises are significantly higher than those for cement enterprises. The increase in Renewable Portfolio Standards obligations will affect the supply–demand dynamics in the electricity market and contribute to reducing carbon trading costs for high-emission enterprises. All entities should tailor their strategies according to their specific characteristics to proactively adapt to the market changes induced by the CETM coverage expansion.