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Complementarity-constrained predictive control for efficient gas-balanced hybrid power systems

Kiet Tuan Hoang, Brage Rugstad Knudsen, Lars Struen Imsland

Abstract

Controlling gas turbines (GTs) efficiently is vital as GTs are used to balance power in onshore/offshore hybrid power systems with variable renewable energy and energy storage. However, predictive control of GTs is non-trivial when formulated as a dynamic optimisation problem due to the semi-continuous operating regions of GTs, which must be included to ensure complete combustion and high fuel efficiency. This paper studies two approaches for handling the semi-continuous operating regions of GTs in hybrid power systems through predictive control, dynamic optimisation, and complementarity constraints. The proposed solutions are qualitatively investigated and compared with baseline controllers in a case study involving GTs, offshore wind, and batteries. While one of the baseline controllers considers fuel efficiency, it employs a continuous formulation, which results in lower efficiency than the two proposed approaches as it does not account for the semi-continuous operating regions of each GT.

Complementarity-constrained predictive control for efficient gas-balanced hybrid power systems

Abstract

Controlling gas turbines (GTs) efficiently is vital as GTs are used to balance power in onshore/offshore hybrid power systems with variable renewable energy and energy storage. However, predictive control of GTs is non-trivial when formulated as a dynamic optimisation problem due to the semi-continuous operating regions of GTs, which must be included to ensure complete combustion and high fuel efficiency. This paper studies two approaches for handling the semi-continuous operating regions of GTs in hybrid power systems through predictive control, dynamic optimisation, and complementarity constraints. The proposed solutions are qualitatively investigated and compared with baseline controllers in a case study involving GTs, offshore wind, and batteries. While one of the baseline controllers considers fuel efficiency, it employs a continuous formulation, which results in lower efficiency than the two proposed approaches as it does not account for the semi-continuous operating regions of each GT.
Paper Structure (14 sections, 21 equations, 4 figures, 4 tables)

This paper contains 14 sections, 21 equations, 4 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Offshore hybrid power systems
  3. Modeling of Offshore Hybrid Power System
  4. Control Objective
  5. Optimal control of gas turbines
  6. Control with economic cost
  7. Direct control with complementarity constraints
  8. Indirect control with complementarity constraints
  9. Simulation and Validation
  10. Simulation environment and variables
  11. Key performance indicators
  12. Simulation study results - Reference tracking
  13. Simulation study results - Effect of regularisation
  14. Concluding remark

Figures (4)

  • Figure 1: An illustration of offshore hybrid power systems.
  • Figure 2: The relationship between GTG efficiency $\eta^\text{gtg}$ and partial load as defined by \ref{['eq:2-gtg-efficiency']} and \ref{['eq:2-gtg-partial']}. A cut-off at 35% partial load based on GE:2022-factsheet in red illustrates the semi-continuous operating region of GTGs.
  • Figure 3: Time profiles of the total power $P_\text{total}$, GTG power $P_\text{gtg}$, WTG power $P_\text{wtg}$, battery power $P_\text{bat}$, and battery state of charge $\text{SOC}_\text{bat}$ from the different methods, given current wind speed $\text{v}_\text{wind}$. The stipulated black lines are the quantities given for this specific simulation study, such as the wind speed and the demand.
  • Figure 4: Time profiles of the second semi-continous variable $y_2$ given different values for $K^{\mathrm{d}y}_j$ in \ref{['eq:3-cost-function-proposed-ENMPC-second']}.