Bi-level optimal configuration of renewable electricity based heating in substations of district heating systems

District heating systems (DHS) are the largest energy consumers in the building energy sector. Substituting electricity in DHS is a pivotal way to achieve its low-carbon development. Existing studies configure the electric heating equipment on the heat source or load side, ignoring the influence of the thermal characteristics of the heat network on the system design and scheduling operation. The impact of the configuration location of the electric heating equipment on system performance is also not emphasized. This paper proposes a new renewable electricity based heating mode in substations of DHS. A bi-level optimal configuration model based on thermal-electricity synergy is proposed to determine the ideal placement, capacity, and operational planning for these heating equipment. The results show that the proposed model reduces operational and environmental benefit costs by 13.31 % and 5.35 % during the heating season. Additionally, it lowers the annualized cost by 6.24 % and curtails the annual discarded wind/photovoltaic power output by 88.76 % through a bi-level optimal configuration model. This method realizes the integration of electrical and thermal energy, enhancing renewable energy consumption while concurrently diminishing operating expenses. Consequently, the heating system achieves superior economic and environmental performance.