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Hierarchical Fuel-Cell Airpath Control: an Efficiency-Aware MIMO Control Approach Combined with a Novel Constraint-Enforcing Reference Governor

Eli Bacher-Chong, Mostafa Ali Ayubirad, Zeng Qiu, Hao Wang, Alireza Goshtasbi, Hamid R. Ossareh

Abstract

This paper presents a hierarchical multivariable control and constraint management approach for an air supply system for a proton exchange membrane fuel cell (PEMFC) system. The control objectives are to track desired compressor mass airflow and cathode inlet pressure, maintain a minimum oxygen excess ratio (OER), and run the system at maximum net efficiency. A multi-input multi-output (MIMO) internal model controller (IMC) is designed and simulated to track flow and pressure set-points, which showed high performance despite strongly coupled plant dynamics. A new set-point map is generated to compute the most efficient cathode inlet pressure from the stack current load. To enforce OER constraints, a novel reference governor (RG) with the ability to govern multiple references (the cascade RG) and the ability to speed up as well as slow down a reference signal (the cross-section RG) is developed and tested. Compared with a single-input single-output (SISO) air-flow control approach, the proposed MIMO control approach shows up to 7.36 percent lower hydrogen fuel consumption. Compared to a traditional load governor, the novel cascaded cross-section RG (CC-RG) shows up to 3.68 percent less mean absolute percent error (MAPE) on net power tracking and greatly improved worst-case OER on realistic drive-cycle simulations. Control development and validations were conducted on two fuel cell system (FCS) models, a nonlinear open-source model and a proprietary Ford high-fidelity model

Hierarchical Fuel-Cell Airpath Control: an Efficiency-Aware MIMO Control Approach Combined with a Novel Constraint-Enforcing Reference Governor

Abstract

This paper presents a hierarchical multivariable control and constraint management approach for an air supply system for a proton exchange membrane fuel cell (PEMFC) system. The control objectives are to track desired compressor mass airflow and cathode inlet pressure, maintain a minimum oxygen excess ratio (OER), and run the system at maximum net efficiency. A multi-input multi-output (MIMO) internal model controller (IMC) is designed and simulated to track flow and pressure set-points, which showed high performance despite strongly coupled plant dynamics. A new set-point map is generated to compute the most efficient cathode inlet pressure from the stack current load. To enforce OER constraints, a novel reference governor (RG) with the ability to govern multiple references (the cascade RG) and the ability to speed up as well as slow down a reference signal (the cross-section RG) is developed and tested. Compared with a single-input single-output (SISO) air-flow control approach, the proposed MIMO control approach shows up to 7.36 percent lower hydrogen fuel consumption. Compared to a traditional load governor, the novel cascaded cross-section RG (CC-RG) shows up to 3.68 percent less mean absolute percent error (MAPE) on net power tracking and greatly improved worst-case OER on realistic drive-cycle simulations. Control development and validations were conducted on two fuel cell system (FCS) models, a nonlinear open-source model and a proprietary Ford high-fidelity model
Paper Structure (21 sections, 32 equations, 27 figures, 6 tables)

This paper contains 21 sections, 32 equations, 27 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Fuel Cell System Modeling and Analysis
  3. Ninth-Order Plant Model
  4. High-Fidelity Model
  5. Third-Order Control-Oriented Model
  6. Relative Gain Array (RGA) Analysis
  7. Set-Point Maps
  8. Internal Model Control (IMC)
  9. Background and Baseline FCS Application of Reference Governors (RG)
  10. General RG Theory
  11. RG Applied to OER
  12. Load governor
  13. Performant RG for MIMO Systems with Application to FCS
  14. Cascade RG
  15. Cross-Section RG (CS-RG)
  16. ...and 6 more sections

Figures (27)

  • Figure 1: Block diagram of the proposed fuel cell air-path control system.
  • Figure 2: Superimposed bode plots of transfer functions of ninth-order model from compressor voltage (V) and throttle opening (unitless) to compressor mass airflow (g/s) linearized at various stack currents, evenly spaced by 12.5 A.
  • Figure 3: Superimposed bode plots of transfer functions of ninth-order model from compressor voltage (V) and throttle opening (unitless) to cathode supply manifold pressure (bar) linearized at various stack currents, evenly spaced by 12.5 A.
  • Figure 4: RGA magnitude of $G(s)$ showing degree of input-output interaction for varying frequencies.
  • Figure 5: Numerically generated FCS net efficiency map with optimal pressures shown.
  • ...and 22 more figures