Julia Helen Buckland

Humidity and Pressure Regulation in a PEM Fuel Cell Using a Gain-Scheduled Static Feedback Controller

In this paper, the pressure difference between the anode and cathode compartments of a polymer electrolyte membrane (PEM) fuel cell stack is regulated along with the anode and cathode humidities using an anode recirculation system. The pressure regulation requirement stems from membrane safety considerations. The regulation of average humidities in the two compartments is a necessary (although not a sufficient) requirement for stack water management. Two actuators in the anode recirculation system are considered, namely the dry hydrogen flow and the anode back pressure valve. These actuators are adjusted using a static output feedback controller that relies on pressure and humidity measurements on the anode side of the fuel cell stack. As the water mass dynamics and the characteristics of the water transport through the PEM are significantly different between subsaturated conditions (water is present only in vapor phase) and saturated conditions (liquid water along with water vapor), we show that the performance of the static output feedback controller with a fixed set of gains for subsaturated condition deteriorates significantly under a saturated condition. A gain-scheduled controller is therefore developed to compensate for a water-vapor saturated cathode condition. Analysis and simulation provide insights on some of the design and implementation issues for the gain-scheduled output feedback system.

Modeling and control of automotive powertrain systems: a tutorial

This tutorial presents an overview of key issues in electronic control of internal combustion engines for automotive passenger vehicles, and showcases the control oriented engine and aftertreatment system models that are useful in addressing these issues. Beginning with a discussion on electronic engine control systems and standard sensors and actuators, key engine control subsystems and their associated functionalities are outlined. Models for gasoline and diesel engines, lean aftertreatment systems, and turbochargers are described in more detail. Several representative control problems are elaborated through examples.

Reference and extended command governors for control of turbocharged gasoline engines based on linear models

In this paper, reference and extended command governors are developed for enforcing constraints in the air path of turbo-charged gasoline engines. These governors are add-on control schemes which protect the engine from violating pointwise-in-time state and control constraints, including compressor surge and actuator limits. Several design choices based on linear engine models at different operating points are compared in terms of response speed, sets of recoverable initial conditions, tolerance of disturbances, and computational complexity. The final design is implemented on the nonlinear engine model. Further, an approach to handle intake manifold pressure overshoot constraints, and a novel form of the extended command governor based on Laguerres sequences are presented.

Reduced order reference governor

Reference governors are add-on control schemes for enforcing constraints in closed-loop systems. This paper presents an approach to reducing the reference governor complexity for systems with states decomposable into “slow” and “fast” states. The reference governor design is based on the reduced order model for “slow” states, where constraints are tightened to ensure that the contribution of fast states does not cause constraint violation. The first of two examples demonstrates that a reference governor based on just two states can handle the surge constraint for a turbocharged downsized gasoline described by five dynamic states. The second example demonstrates that the tip deflection limits in an infinite-dimensional model of a flexible Euler-Bernoulli free-free beam can be handled based on just two modal coordinates.

Control analysis of an ejector based fuel cell anode recirculation system

An ejector based recirculation system is incorporated on the anode side of the fuel cell to address anode flooding. The objective of the recirculation system is to regulate anode humidity with recirculating flow, while safeguarding the membrane and supporting the electric load. These objectives can be achieved by a control system that uses two actuators, namely the fuel supplied from the fuel source and a back pressure valve placed in the recirculation path. For these actuators, the control analysis presented in this paper identifies anode pressure, along with either return manifold pressure or recirculation flow rate, as variables to be tracked in order to facilitate meeting of the control objectives, while assuring internal stability. Feedback regulation of these variables with a minimum number of pressure sensors is addressed by identifying appropriate sensor locations. The sensor selection and corresponding observer design for the system are treated from the points of view of the observability requirements and robustness to sensor noise. The performance of various sensor combinations shows that measurement of anode pressure is adequate for a full order observer based state feedback controller

Automotive emissions control

Local and global environmental concerns regarding automotive emissions motivate legislative action by governments throughout the world. Aggressive regulation of both tailpipe and evaporative emissions of passenger vehicles is the norm in most developed countries. These governmental regulations produce significant challenges and opportunities for control, particularly when combined with other system objectives such as fuel economy and performance. This tutorial presents an overview of the challenges related to emission control in the design and development of powertrain systems for modern passenger vehicles.

Practical observers for unmeasured states in turbocharged gasoline engines

Turbocharged gasoline engines are becoming more common in production vehicles as consumers demand improved fuel economy with uncompromised performance. Controlling this complex system to meet these and other competing objectives is a challenging task. Knowledge of exhaust manifold pressure and turbocharger speed can be important to success. Physical conditions of the system, however, make measurement impractical and costly, compelling manufacturers to implement some form of on-line estimation. Additional constraints imposed by computational resources and calibration processes limit application of a traditional state observer. In this paper, singular perturbation concepts are employed in concert with the reduced order observer to develop more practical estimates of exhaust manifold pressure and turbocharger speed. Simulation results show excellent observer performance with a significant reduction in calibration complexity.

Estimation of exhaust manifold pressure in turbocharged gasoline engines with variable valve timing

Feedforward A/F control in turbocharged gasoline engines with variable valve timing requires knowledge of exhaust manifold pressure, Pe . Physical conditions in the manifold make measurement costly, compelling manufacturers to implement some form of on-line estimation. Processor limitations and the calibration process, however, put constraints on estimator complexity. This paper assesses the feasibility of estimating Pe with an algorithm that is computationally efficient and relatively simple to calibrate. A traditional reduced order linear observer is found to perform well but has too many calibration parameters for practical implementation. Using the performance of the observer as a benchmark, static estimation is explored by parameterizing the equilibrium values of Pe with both the inputs and the outputs of the system. This nonlinear static estimate, combined with simple lead compensation, yields a practical observer implementation.Copyright

Reference feedforward in the idle speed control of a direct-injection spark-ignition engine

The direct-injection spark-ignition engine has emerged as a focus of research in improving fuel economy and controlling emissions. This engine can operate in multiple modes, including a stratified charge mode with an air-fuel ratio as large as 50:1. Operating in stratified mode results in improved fuel economy and reduced CO/sub 2/ emissions. The stratified charge mode is employed during low speed and load conditions, such as during engine idle. The idle speed control problem is cast as a two-input-two-output control problem and a baseline feedback controller is developed based on an existing topology from the literature. Significant delays, however, inhibit our ability to improve the transient response via feedback alone. An improved scheme employing reference feedforward is proposed and several potential topologies are presented. A reference feedforward algorithm is derived and nonlinear simulation results are shown in which the system transient responses are improved considerably.

Use of feedforward in idle speed control for a direct injection spark ignition engine during lean burn

The use of reference feedforward control is investigated in the idle speed problem for a direct-injection spark-ignition engine during lean burn. This additional control signal is added to improve the speed and air-fuel ratio transient responses due to large load torque disturbances. A baseline control design is given, and a feedforward algorithm is presented and added to the baseline controller. The design is illustrated through simulations of step responses due to disturbances in load torque. With feedforward in the air control loop, the maximum engine speed droop is decreased more than 20%, while also improving the setpoint control of air-fuel ratio.