1. Modeling and Control of Heat Networks with Storage:
the Single-Producer Multiple-Consumer Case
T. W. Scholten, C. De Persis, P. Tesi
01/2015
Introduction
Controller
In heat networks, energy storage is a viable approach to balance demand and supply. In such networks, a heat carrier is used in the form of water, where heat is injected and extracted through heat exchangers. The network can transport heated water and store it in a storage tank to shift loads in time.
Heat injection
Flow rates
Output regulation theory
Flow producer
Exo-system
Plant
Controller
Output
Asymptotic convergence
District heating
Causes plant to be time varying
Fixed flow consumers
Heat injection through heat exchanger
Volume deviation
Storage with stratified water tank
Existence is proven
Simulations
Thermocline with steep temperature gradient
Time varying
Demand
Heat extraction through heat exchangers
Increased demand
Store to 900 𝑚 3
Drain to 100 𝑚 3
Control problem
Control goal
Let volume 𝑉 𝑠 ℎ and temperature 𝑇 𝑠 ℎ converge to specified setpoints 𝑉 𝑠 ℎ ∗ and 𝑇 𝑠 ℎ ∗
Keep hot layer at 90 degrees
Control input
Flow rates 𝑞 & Heat injection 𝑃 𝑝
Low heat injection due to drainage
Demand
Unknown, Time varying, Generated by an exo-system
Conclusions
A model for a district heating system is derived and a controller regulating the flows and temperature is designed. It is proven that the volume converges exponentially fast to the desired volume and the temperature error converges asymptotically to zero. The proposed controller is therefore able to regulate the energy level to the desired energy level despite time varying demand. Furthermore the existence of such a controller is also proven. In a future investigation we would like to extend this setup to multiple producers, multiple storage devices with different operating temperatures.
References
Skogestad, S. (2009). Chemical and energy process engineering. CRC press Boca Raton.
Isidori, A. et al. (2003). Robust autonomous guidance: an internal model approach. Springer.
De Persis, C. et al. (2014). Output Regulation of Large-Scale Hydraulic Networks. Control Systems Technology, IEEE Transactions on.
Hangos, K. et al. (2004). Analysis and control of nonlinear process systems. Springer.