The issue of real-time deep down-regulation ancillary service has received increasing attention in the Northeast of China. Participation of combined heat and power plants with multitype units and flexible heating devices in the market is investigated. This paper establishes a model of feasible operating region and the coal consumption function for the combined heat and power plant. An internal optimal dispatch model and the minimum overall electric power output model for the plant satisfying a given heat load are presented. Furthermore, the models of total cost for down-regulation and average cost for deep down-regulation in two levels are established. These models are validated based on the realistic data of the plant in the Northeast of China. In case studies, the influence factors and change rules of the minimum electric power output, the total cost, and the average cost of plants are analyzed.

In view of the frequency regulation (FR) policy in Northeast China, a two-stage real-time rolling optimization model for power plants participating in FR ancillary services is established. The optimization object of the first stage is to maximize the overall profitability of the power plant and to obtain FR performance sub-indicators (K₁, K₂, K₃) and the electric power curve of combined heat and power (CHP) units with energy storage. The second stage of the model performs load distribution with the objective of minimizing operating cost, subject to the constraint of electric and heat power balance for CHP units and energy storage. Meanwhile, rolling optimization combined with dynamic correction is used to ensure the accuracy of the two-stage FR optimization model by updating the operating status of the CHP units and energy storage and reducing the prediction errors of the FR commands. The above models have been validated by actual case studies of a CHP plant in Northeast China. They can ensure the economic and sustainable operation of CHP units and energy storage, enabling the CHP plant to benefit in the FR ancillary services market. The models offer a useful reference for CHP enterprises in terms of FR.