Bidirectional Substation Control for Smart Thermal Grids: Experimental Evaluation of a Weighted Proportional-Integral Approach

When transforming district heating networks into smart thermal grids, a crucial part is the integration of distributed energy resources and prosumers, coordinated by an overarching management system. Central to this transformation are bidirectional substations that technically facilitate flexible energy exchange between prosumers and the network. Novel control approaches are required that are capable of meeting temperature requirements, implementing power setpoints from overarching management, and mitigating the mutual thermohydraulic influence among prosumers simultaneously. A recently proposed control strategy to mitigate those challenges is based on combined and weighted errors as inputs for proportional-integral controllers; However, it was tested only using simulations so far. In this paper, we experimentally test the control approach using a realistic hardware setup, where two bidirectional substations exchange heat between two emulated prosumers. The investigated control approach achieved the control objectives within a stabilization time of approximately six minutes after step changes in the power setpoints. The controller successfully reflects the application-specific prioritization of different temperature objectives, confirming simulation results from prior work. Minor performance issues arose from hardware limitations, particularly in power transfer capabilities due to actuator sizing, highlighting their significance for practical applications. Overall, our experiments demonstrate for the first time the suitability of a control approach for prosumer-based district heating contexts with realistic hardware, laying a foundation for the practical implementation of smart thermal grids and contributing to a sustainable transition in heat supply.