Unlocking the Flexibility of CHP in District Heating Systems to Provide Frequency Response

Abstract

Combined heat and power (CHP) units can be operated flexibly to mitigate the impact of renewable resources. However, when used in district heating systems, the constraint governing heat and electricity outputs limits the capability of CHP in supporting the power grid. To addresses this issue, this paper presents a two-layer control system to coordinate CHP, district heating network and buildings. With this control system, CHP can meet the heat demand of local users and provide frequency response for the power grid simultaneously. The excess/deficit heat of CHP supply is balanced by heat stored in buildings and pipelines. The proposed method is tested in the GB Firm Frequency Response market. Numerical results show that the capability of CHP in providing frequency response is determined by the following factors: capacity and ramping rate of CHP, the restriction in the supply temperature of district heating network and the temperature of buildings.