Low-Carbon Economic Dispatch of Electricity–Heat–Cooling–Gas Integrated Energy System Considering Ladder-Type Carbon Trading Mechanism and Demand Response

To address weak emission-reduction incentives under conventional carbon trading and unclear low-carbon benefits of different demand response modes, this paper proposes a low-carbon economic dispatch model for an electricity–heat–cooling–gas integrated energy system (IES) considering ladder-type carbon trading and demand response (DR). According to load regulation characteristics, IES loads are classified into fixed loads, transferable loads (TLs), and replaceable loads (RLs). The objective is to minimize the total cost, including energy purchase cost, operation and maintenance cost, and carbon trading cost. The effects of carbon trading are evaluated under three scenarios: no-carbon-cost, conventional carbon trading, and ladder-type carbon trading. Under the ladder-type carbon trading scenario, four DR strategies are further compared: no-DR, TL-only, RL-only, and combined TL-RL. The results show that the model achieves the lowest total cost while reducing carbon emissions by 20.88%. Sensitivity analyses indicate that DR does not necessarily reduce emissions; its low-carbon effect depends on carbon price, proportion of TLs and proportion of RLs. The combined TL-RL strategy yields the lowest cost at all carbon prices, but its synergistic emission-reduction effect occurs only within an appropriate carbon price range. Sensitivity analysis of load proportions further shows that TLs contribute to synergistic emission reduction with RLs only when the proportion of RLs reaches a certain level and the proportion of TLs remains moderate.