Haluk Gorgun

A nonlinear observer design for fuel cell hydrogen estimation

We present an observer design to estimate the partial pressure of hydrogen in the anode channel of a fuel cell. A precise knowledge of this pressure is of importance to ensure reliable and efficient operation of the fuel cell power system. Our design makes use of a monotonic nonlinear growth property of the voltage output on hydrogen partial pressures at the inlet and at the exit of the channel. By treating the slowly varying inlet partial pressure as an unknown parameter, an adaptive observer is developed that employs a nonlinear voltage injection term. We then study the robustness of this observer against variations in the inlet partial pressure, and analyze its sensitivity to other modeling errors. We also prove a robustness property of the observer against the parameter estimation error, which means that it can be implemented with alternative parameter estimator designs.

A voltage-based observer design for membrane water content in PEM fuel cells

This paper presents a scheme for estimating membrane water content in polymer electrolyte membrane (PEM) fuel cells from voltage, current, temperature, and several pressure measurements. The approach is to exploit the resistive voltage drop which is closely associated with membrane water content. To distinguish this resistive drop from other voltage losses we make use of a well-developed fuel cell voltage model that characterizes each loss term, as well as the open circuit voltage. The unmeasured hydrogen and oxygen partial pressure values in the open-circuit model are estimated with a variant of the hydrogen and oxygen observers developed by M. Arcak et al. (2004). Preliminary experimental results, obtained at the Connecticut Global Fuel Cell Center, are presented and discussed.

An adaptive observer design for fuel cell hydrogen estimation

We present an observer design to estimate the partial pressure of hydrogen in the anode channel of a fuel cell. Our design makes use of a monotonic nonlinear growth property of the voltage output on hydrogen partial pressures at the inlet and at the exit of the channel. By treating the slowly-varying inlet partial pressure as an unknown parameter, an adaptive observer is developed that employs a nonlinear voltage injection term. We then prove robustness of this observer against variations in the inlet partial pressure, and analyze its sensitivity to measurement errors in the voltage.

Stabilisation of a class of 2-DOF underactuated mechanical systems via direct Lyapunov approach

This paper represents an alternative stabilisation procedure for a class of two degree-of-freedom underactuated mechanical systems based on a set of transformations and a Lyapunov function. After simplifying dynamic equations of the system via partial feedback linearisation and coordinate changes, the stability of the system is provided with Lyapunov’s direct method. Proposed control scheme is used on two different examples and asymptotic convergence for each system is proven by means of La Salle’s invariance principle. The designed controller is successfully illustrated through numerical simulations for each example.

A stabilizing controller for PVTOL aircraft

A stabilizing controller structure is proposed for planar vertical take off and landing (PVTOL) aircraft. In order to achieve almost global asymptotic stabilization, the coupling coefficient, ε, is assumed to be in the interval 0 ≤ ε <; 1. Stability analysis is performed based on a Lyapunov function and asymptotic convergence is proven by means of La Salles invariance principle. The proposed controller is implemented by numerical simulations on PVTOL aircraft and results are presented.

Exact Model Knowledge and Direct Adaptive Controllers on Ball and Beam

This paper presents analysis and implementation of Exact Model Knowledge (EMK) and Direct Adaptive control schemes on the 4th order ball and beam system in which the dynamics of the ball position and the dynamics of the beam angle are cascaded. For the controller analysis the error dynamic equations for ball position and the beam angle are derived for both cases. Following, experimental studies are conducted based on the proposed control approaches and it is presented that constant and sinusoidal references for the ball position are tracked asymptotically.

Pressure Drop on the Cathode Side of a PEM Fuel Cell as a Diagnostic Tool for Detection of Flooding and Drying Conditions

An increase in pressure drop on the cathode side of PEM fuel cell is a reliable indicator of PEM fuel cell flooding. Flooding, i.e., liquid water accumulation inside the cell causes a rather erratic cell potential behavior — steady voltage drops followed by sudden voltage increases. The pressure drop in this case behaves similarly, i.e., increases as the water accumulates, and drops as the water is expulsed from the cell, however with an obvious and detectable upward trend. In an opposite case of fuel cell drying, the cell potential steadily decreases as the ionic resistance increases, while the pressure drop initially decreases as the last of the liquid water is being expulsed, and thereafter remains constant. By monitoring both pressure drop and cell resistance in an operational fuel cell stack it was possible to reliably diagnose either flooding or drying conditions inside the stack, which were intentionally created by adjusting the humidification and stack temperatures. Pressure drop, therefore, may be used to define a control strategy, i.e. to make decisions on corrective actions. In most cases, the pressure drop is a linear function of flow rate when a single phase (gas) is flown through a fuel cell since the flow is well in the laminar regime. When the gas starts to carry water droplets, such as the case when the fuel cell operates with fully saturated gases, the pressure drop departs from linearity. In addition, slugs of water, possibly present inside the fuel cell passages, create unsteady conditions.Copyright

Multiple closed loop system control with digital PID controller using FPGA

PID (Proportional - Integral - Derivative) controllers are the most widely used closed loop controllers due to their simplicity, robustness, effectiveness and applicability for much kind of systems. With the rapid development of technology, implementation of PID controller has gone several steps from using analog components in hardware to using some software-based program to execute PID instructions digitally in some processor-based systems. And also, these developments have brought an alternative solution to implement PID instructions in Programmable Logic Devices (PLD). Field Programmable Logic Array (FPGA) is the most advanced members of PLDs. This paper presents the digital PID algorithm on FPGA. The controller algorithm is developed using VHDL and implemented using Altera DE0 Nano Board. As the controlled system, five axis robot arm is selected, which have five dc motor and four potentiometer to determine the positions of motors. The results show that digital PID controller and also multi-feedback control systems can be implemented successively using FPGA devices.

Stabilization of a Class of 2-DOF Underactuated Mechanical Systems Via Lyapunov's Direct Approach

Abstract We study a class of 2-DOF underactuated mechanical systems(UAMS) where the objective is to obtain a design framework for stabilization. We propose a stabilization procedure via Lyapunovs direct approach to a class of UAMS employing partial feedback linearization and a change of coordinates. Asymptotic stability of unstable equilibrium point has been achieved in a large region of attraction and we make use of La Salles theorem to prove it. Designed controller scheme has been successfully illustrated through simulations on two different UAMS namely the pendulum on a cart and the inertia wheel pendulum.

Disturbance observer based control of three phase UPS inverter

In this paper control of three phase UPS inverter with cascaded PI controller and load current estimation via disturbance observer are presented. Pure sinusoidal waveform with specified amplitude and frequency is required for UPS inverter under variety of loads. Load current acts as disturbance on the plant. To increase the disturbance rejection of the plant, the load current is adopted as feed forward loop to the voltage controller. Disturbance observer method is relatively simple method in comparison with Luenberger observer. The proposed algorithms are successfully presented with simulations and verified by experimentally.