An Analytical Study on Intermittent Air Humidification Control for Fuel Cell Vehicle
- Abstract
- Water management is important in proton exchange membrane fuel cell because the water balance has a significant impact on the overall fuel cell system performance. The flooding is one of the critical issues to put PEM fuel cell to practical use. When polymer electrolyte membrane (PEM) is not wet enough to have good ionic conductivity, the cell voltage decreases. Therefore, feed gases are humidified to prevent PEM from its dryness. On the other hand, flooding that is an excess of the liquid water in porous medium emerges in cell when the humidification of feed gases is excess.
In fuel cell vehicle, the vehicle's power demand is dynamic; therefore, the dynamic water management system is required. This present study proposes a method to control the humidity of the input air for the fuel cell vehicle. The method is an intermittent control with a constant interval and the magnitude of humidification is obtained from an optimization using genetic algorithm (GA) methods. This method is an improvement from the previous several methods. This proposed method uses fuel cell current as the control reference; therefore it does not wait the trigger to change the operating condition and has low deviation to the target of the flooding level. The simulation of this method using several driving cycles shows that this proposed intermittent air humidification control obtains a relatively good result. In this study case, the GA optimization provides 26 times faster than an optimization using the scanning system. The liquid saturation level is seen constant at the target level although still there are small deviations at driving cycles which having high power demands.
- Issued Date
- 2012
- Awarded Date
- 2012. 2
- Type
- Dissertation
- Publisher
- Pukyong National University
- Department
- 대학원 냉동공조공학과
- Advisor
- Prof. Choi Kwang Hwan
- Table Of Contents
- Summary i
Contents v
List of Figures ix
List of Table xiii
1.Introduction 1
1.1 Introduction to fuel cells 3
1.2 The operating principle of fuel cells 11
1.3 Motivation of the present work 15
1.4 Literature review 17
1.4.1 Studies of fuel cell modeling 18
1.4.2 Studies of water flooding mitigation on PEM fuel cell 19
1.4.2.1 Flow field design 20
1.4.2.2 Anode water removal 21
1.4.2.3 Operating condition control 21
1.4.2.4 Electro-osmotic pumping 22
1.4.2.5 MEA design 23
1.4.3 Studies of fuel cell water transportation 25
1.4.3.1. Mechanisms of water transport 26
1.4.3.2 Methods of humidification 30
1.4.3.3 Effect of reactant gas humidification 35
1.5 Contributions 41
2.Models 43
2.1 Fuel cell model 43
2.1.2 Fuel cell equilibrium voltage 47
2.1.3 Fuel cell losses 49
2.1.3.1 Activation over-potential 53
2.1.3.2 Diffusion over-potential 55
2.1.3.3 Electronic ohmic over-potential 56
2.1.3.4 Ionic over-potential 57
2.1.4 Membrane 57
2.1.5 Modeling fuel cell stacks 62
2.1.5.1 Fuel cell stack sizing 63
2.1.5.2 Number of cells 63
2.1.5.3 Fuel cell system design 64
2.2 Vehicle model 65
2.2.1 Vehicle movement 65
2.2.2 Vehicle resistance 66
2.2.2.1 Rolling resistance 67
2.2.2.2 Aerodynamic drag 72
2.2.3 Dynamic equation 74
2.3 Model of water liquid saturation level 75
2.3.1 Water balance 75
2.3.2 Water state in fuel cell process 76
2.3.3 Water state in convection process 78
2.3.4 Evaporation process 80
2.4 Experiment verification 82
2.4.1 Experiment apparatus 82
2.4.2 Apparatus components 83
2.4.3 The experiment result and the comparison to the model 88
3.Proposed Fuel Cell Humidification Control Method 93
3.1 Previous fuel cell control methods for input air humidification 93
3.1.1 Sensor as the control reference 94
3.1.2 Cell current as the control references 95
3.2 Proposed method 96
3.2.1 General concept 96
3.2.2 Comparison of proposed method with previous methods 97
3.3 Optimization in proposed method 97
3.3.1 Traditional 98
3.3.2 Non-traditional 99
3.4 Genetic Algorithms 101
3.4.1 Structures 104
3.4.2 Cycle 105
3.4.3 Elements 106
3.4.4 Genetic algorithm operations 107
3.4.4.1 Crossover 107
3.4.4.2 Mutation 109
3.4.5 Genetic algorithm for the proposed control 110
3.4.5.1 Generate population 112
3.4.5.2 Fitness function 112
3.4.5.3 Selection 112
4.Results and Discussions 115
4.1 Liquid saturation level of fuel cell vehicle with stationary power load and without humidification system 116
4.2 Power demand of fuel cell vehicle with different driving cycles 124
4.3 Simulation of the fuel cell vehicle model using dynamic power load but static humidification 127
4.4 Simulation of the fuel cell vehicle model using dynamic power load and using proposed humidification control method 130
5.Conclusions 135
References 137
Acknowledgment 147
Appendix 149
- Degree
- Doctor
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