Droop control for district heating networks: Solution for temperature control of multi-energy system with renewable power supply

In a district heating system, the flow of heated water transfers enthalpy from the generation side to the load side. It is thus critical to maintain the supply temperature at a desired level. However, with the rise of renewable energy sources in the district heating network, the temperature of the heated water tends to be disturbed. This calls for a deployment of thermal energy storage. To effectively exploit the flexibility of thermal energy storage, the relationship between the temperature of the district heating water and the power sharing with other thermal energy resources is considered in this paper. Based on this relationship, the concept and realization of a droop control for the district heating network is proposed. It is shown how the droop characteristic between the temperature of the heated water and the power sharing of the thermal energy storage for the district heating network is developed in analogy to the droop control used in an electrical dc network. The droop characteristic so supports the control of a district heating network. The theoretical considerations are complemented by application to a residential district heating network model to illustrate the functionality of the control. The studies are conducted with the program PSCAD, which is otherwise typically used for simulating electromagnetic transients.