Design and verification of an effective state-of-charge estimator for thermal energy storage

Abstract

Thermal energy storage (TES) is widely used in district heating and cooling systems (DHCS) to act as a buffer between the supply and demand schedules. The adequate control of charging and discharging modes of TES may improve the overall performance of a DHCS and, to this end, an effective regulation of its state-of-charge (SoC) is required. However, the calculation of SoC depends on the availability and accuracy of temperature measurements. A model-based observer for the calculation of the SoC of water-based TES tanks is presented. A dynamic model of a one-dimensional stratified water tank is adopted to develop the observer. Its effectiveness is assessed through ‘model-in-the-loop’ cosimulations, with the observer and the feedback control system being implemented in MATLAB/Simulink and a high-fidelity water tank component available in Apros being used as the plant model. Simulation results considering three different system configurations demonstrate that the model-based observer accurately estimates the temperature distribution within the tank, leading to an effective SoC computation and control—even in the case of sensor failure or upon limited sensor availability.