Structural Analysis and Control of a Model of Two-site Electricity and Heat Supply

TL;DR

This paper develops a nonlinear control approach for a two-site electricity and heat supply system, addressing the challenge of stabilizing energy flows despite non-minimum phase dynamics and physical constraints.

Contribution

It introduces a novel control method that stabilizes short-term energy regulation and long-term equilibrium in a complex CHP system with non-minimum phase behavior.

Findings

Successfully stabilizes energy flows in simulations

Achieves short-term regulation and long-term stabilization

Addresses non-minimum phase control challenges

Abstract

This paper introduces a control problem of regulation of energy flows in a two-site electricity and heat supply system, where two Combined Heat and Power (CHP) plants are interconnected via electricity and heat flows. The control problem is motivated by recent development of fast operation of CHP plants to provide ancillary services of power system on the order of tens of seconds to minutes. Due to the physical constraint that the responses of the heat subsystem are not necessary as fast as those of the electric subsystem, the target controlled state is not represented by any isolated equilibrium point, implying that stability of the system is lost in the long-term sense on the order of hours. In this paper, we first prove in the context of nonlinear control theory that the state-space model of the two-site system is non-minimum phase due to nonexistence of isolated equilibrium points of the associated zero dynamics.Instead, we locate a one-dimensional invariant manifold that represents the target controlled flows completely. Then, by utilizing a virtual output under which the state-space model becomes minimum phase, we synthesize a controller that achieves not only the regulation of energy flows in the short-term regime but also stabilization of an equilibrium point in the long-term regime. Effectiveness of the synthesized controller is established with numerical simulations with a practical set of model parameters.