On-line Parameter Estimation of the Polarization Curve of a Fuel Cell with Guaranteed Convergence Properties: Theoretical and Experimental Results

In this paper, we address the problem of online parameter estimation of a Proton Exchange Membrane Fuel Cell (PEMFC) polarization curve, that is the static relation between the voltage and the current of the PEMFC. The task of designing this estimator -- even off-line -- is complicated by the fact that the uncertain parameters enter the curve in a highly nonlinear fashion, namely in the form of nonseparable nonlinearities. We consider several scenarios for the model of the polarization curve, starting from the standard full model and including several popular simplifications to this complicated mathematical function. In all cases, we derive separable regression equations -- either linearly or nonlinearly parameterized -- which are instrumental for the implementation of the parameter estimators. We concentrate our attention on on-line estimation schemes for which, under suitable excitation conditions, global parameter convergence is ensured. Due to these global convergence properties, the estimators are robust to unavoidable additive noise and structural uncertainty. Moreover, their on-line nature endows the schemes with the ability to track (slow) parameter variations, that occur during the operation of the PEMFC. These two features -- unavailable in time-consuming off-line data-fitting procedures -- make the proposed estimators helpful for on-line time-saving characterization of a given PEMFC, and the implementation of fault-detection procedures and model-based adaptive control strategies. Simulation and experimental results that validate the theoretical claims are presented.Comment: 16 pages, 18 figures, requires IEEEtran.cls 2015/08/26 version V1.8

Input-parallel output-series DC-DC boost converter with a wide input voltage range, for fuel cell vehicles

An input-parallel, output-series DC-DC Boost converter with a wide input voltage range is proposed in this paper. An interleaved structure is adopted in the input side of this converter to reduce input current ripple. Two capacitors are connected in series on the output side to achieve a high voltage-gain. The operating principles and steady-state characteristics of the converter are presented and analyzed in this paper. A 400V/1.6kW prototype has been created which demonstrates that a wide range of voltage-gain can be achieved by this converter and it is shown that the maximum efficiency of the converter is 96.62%, and minimum efficiency is 94.14% The experimental results validate the feasibility of the proposed topology and its suitability for fuel cell vehicles

Converter based electrochemical impedance spectroscopy for fuel cell stacks

Fuel cells are important devices in a hydrogen-based chain of energy conversion. They have distinctive advantages over batteries with their higher energy density and faster refueling speed, which make them attractive in stationary power supplies and heavy-duty vehicles. However, the high cost and low durability associated with modern fuel cells are still hindering their wider commercialization. Besides developing more reliable and lower cost materials and advanced assemblies of cells and stacks, a practical and effective diagnostic tool is highly needed for fuel cells to identify any abnormal internal conditions and assist with maintenance scheduling or application of on-board mitigating schemes. Conventionally, linear instruments were used for fuel cell EIS, however, limited to single cells or short stacks only as a laboratory testing method. With recent developments, EIS enabled by switching power converters are capable of being applied to a high-power stack directly. This approach has the potential for practical field applications such as a servicing tool for fuel cell manufacturers or an on-board diagnostic tool of a moving vehicle. Previous works on converter based EIS have made a few different attempts at conceptually realizing this solution while several significant issues were not well recognized and resolved yet. As such, this thesis explores further on this topic to address the flexibility of EIS perturbation generation, the perturbation frequency range, and the linkage between fuel cell EIS requirements and the converter design to push for its readiness for practical implementations. Several new solutions are proposed and discussed in detail, including a total software approach for existing high-power converters to enable wide-frequency-range EIS, a redesign of the main dc/dc converter enabling wide-frequency-range perturbations, and a separate auxiliary converter as a standalone module for EIS operation. A detailed analysis of oscillations brought by converter based EIS in powertrains is also presented

복잡한 공학 시스템에 대한 오경보를 고려한 리질리언스 해석 및 설계 방법론 연구

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 기계항공공학부, 2018. 2. 윤병동.it estimates a healthy engineered to be faulty, resulting unnecessary system shutdown, inspection, and – in the case of incorrect inspection – unnecessary system repair or replacement. Although false alarms make a system unavailable with capital loss, it has not been considered in resilience engineering. To cope with false alarm problems, this research is elaborated to advance the resilience engineering considering false alarms. Specifically, this consists of three research thrusts: 1) resilience analysis considering false alarms, 2) resilience-driven system design considering false alarms (RDSD-FA), and 3) resilience-driven system design considering time-dependent false alarms (RDSD-TFA). In the first research thrust, a resilience measure is newly formulated considering false alarms. This enables the evaluation of resilience decrease due to false alarms, resulting in accurate analysis of system resilience. Based upon the new resilience measure, RDSD-FA is proposed in the second research thrust. This aims at designing a resilient system to satisfy a target resilience level while minimizing life-cycle cost. This is composed of three hierarchical tasks: resilience allocation problem, reliability-based design optimization (RBDO), and PHM design. The third research thrust presents RDSD-TFA that considers time-dependent variability of an engineered system. This makes one to estimate life-cycle cost in an accurate and rigorous manner, and to design an engineered system more precisely while minimizing its life-cycle cost. The framework of RDSD-TFA consists of four tasks: system analysis, PHM analysis, life-cycle simulation, and design optimization. Through theoretical analysis and case studies, the significance of false alarms in engineering resilience and the effectiveness of the proposed ideas are demonstrated.공학 시스템은 생애주기에 걸쳐 다양한 불확실성에 노출되며, 이로 인해 목표 성능을 충족시키지 못할 경우 사회적, 경계적, 인적 소실을 야기하게 된다. 이에 대한 해결 방안 중 하나로 리질리언스 주도 설계 기술 (resilience-driven system design이하 RDSD)이 개발되었다. RDSD는 건전성 예측 및 관리 기술 (prognostics & health management이하 PHM)을 설계에 도입함으로써 비용 효율적인 고장 예방을 가능케 하였다. 하지만, RDSD는 PHM의 고장 오경보 현상을 고려하지 않는 한계점을 갖는다. 고장 오경보는 건전한 시스템을 고장이라 추정하는 현상으로, 불필요한 시스템 정지 및 검사 비용을 야기하여, PHM과 RDSD의 기술적 효용성을 떨어트리게 된다. 따라서, RDSD의 기술적 약진과 실적용을 도모하기 위해서는 고장 오경보 현상을 해결해야 한다. 본 논문에서는 고장 오경보의 고려를 통해 리질리언스 해석 및 설계 방법론을 개선하고자 하며, 이를 위해 세 가지 연구 주제를 제안한다. 첫 번째 주제는 오경보를 고려한 리질리언스 분석으로, 공학 시스템의 리질리언스 시나리오 분석에 기반해 리질리언스 지수를 새롭게 정식화 한다. 이 지수는 고장 오경보로 인한 리질리언스의 저하를 분석함으로써, 정확한 리질리언스 추정을 가능케 한다. 두 번째 주제는 고장 오경보를 고려한 리질리언스 주도 설계 방법론이다. 이는 3단계의 계층적 요소로 구성된다. 먼저 목표 리질리언스 지수를 만족하면서 생애주기비용을 최소화하기 위해, 목표 신뢰도와 목표 오경보 및 유실경보율을 최적화한다. 이후 신뢰성 기반 최적 설계 (reliability-based design optimization)를 통해 목표 신뢰도를 확보하고, PHM 설계를 통해 할당된 목표 오경보 및 유실경보율을 충족시킨다. 세 번째 주제는 시변(時變) 오경보를 고려한 리질리언스 주도 설계 방법론이다. 기존의 설계 방법론들은 시스템의 건전성 상태를 시불변(時不變)하다 간주하였으나, 실제 시스템은 운행에 따라 점진적으로 건전성이 저하된다. 본 연구에서는 시변성을 분석하기 위해 시변 오경보율 및 유실경보율에 대한 개념을 새롭게 제안하였으며, 생애주기 시뮬레이션을 통한 총 유지보수 비용 분석 방법론을 개발하였다. 이를 통해 생애주기비용을 보다 엄밀하고 정확하게 추정할 수 있게 되었으며, 이를 최소화하는 방향으로 시스템과 PHM의 설계를 최적화였다. 본 연구에서 제안한 방법론들은 이론적 분석과 사례 연구를 통해 그 효용성을 입증하였다.Most engineered systems are designed with a passive and fixed design capacity and, therefore, may become unreliable in the presence of adverse events. In order to handle this issue, the resilience-driven system design (RDSD) has been proposed to make engineered systems adaptively reliable by incorporating the prognostics and health management (PHM) method. PHM tracks the health degradation of an engineered system, and provides health state information supporting decisions on condition-based maintenance. Meanwhile, one of the issues awaiting solution in the field of PHM, as well as in RDSD, is to address false alarms. A false alarm is an erroneous report on the health state of an engineered systemChapter 1. Introduction 1 1.1 Motivation 1 1.2 Research Scope and Overview 3 1.3 Dissertation Layout 6 Chapter 2. Literature Review 7 2.1 Resilience Engineering (Analysis and Design) 7 2.1.1 Resilience Analysis for Mechanical Systems 8 2.1.2 Resilience-Driven System Design (RDSD) for Mechanical Systems 15 2.2 False and Missed Alarms in Prognostics and Health Management 27 2.2.1 Definition of False and Missed Alarms 27 2.2.2 Quantification of False and Missed Alarms 32 2.3 Summary and Discussion 35 Chapter 3. Resilience Analysis Considering False Alarms 37 3.1 Resilience Measure Considering False Alarms 37 3.2 Case Studies 42 3.2.1 Numerical ample 42 3.2.2 Electro-Hydrtatic Actuator (EHA) 44 3.3 Summary and Discussion 53 Chapter 4. Resilience-Driven System Design Considering False Alarms (RDSD-FA) 55 4.1 Overview of RDSD-FA Framework 55 4.2 Resilience Allocation Problem Considering False Alarms 56 4.3 Prognostics and Health Management (PHM) Design Considering False Alarms 60 4.4 Case study: Electro-Hydrostatic Actuator (EHA) 61 4.4.1 Step 1: Resilience Allocation Considering False Alarms 61 4.4.2 Step 2: Reliability-Based Design Optimization 64 4.4.3 Step 3: PHM Design Considering False Alarms 68 4.4.4 Comparison of Design Results from RDSD and RDSD-FA 73 4.5 Summary and Discussion 75 Chapter 5. Resilience-Driven System Design Considering Time-Dependent False Alarms (RDSD-TFA) 77 5.1 Time-Dependent False and Missed Alarms in PHM 79 5.2 Resilience-Driven System Design Considering Time-Dependent False Alarms (RDSD-TFA) 83 5.2.1 Overview of RDSD-TFA Framework 83 5.2.2 Task 1: System Analysis 86 5.2.3 Task 2: PHM Analysis 89 5.2.4 Task 3: Life-Cycle Simulation 91 5.2.5 Task 4: Design Optimization 97 5.3 Case studies 98 5.3.1 Numerical Example of Life-Cycle Simulation 98 5.3.2 Electro-Hydrostatic Actuator (EHA) 107 5.4 Summary and Discussion 123 Chapter 6. Conclusions 126 6.1 Summary and Contributions 126 6.2 Suggestions for Future Research 129 References 132 Appendix 154 Abstract(Korean) 157Docto