Design and runtime optimizations of hybrid electrical energy storage systems

다국어 초록 (Multilingual Abstract)

Electrical energy storage (EES) systems provides various benefits of high energy efficiency, high reliability, low cost, and so on, by storing and retrieving energy on demand. The applications of the EES systems are wide, covering contingency service, load leveling, peak shaving, energy buffer for renewable power sources, and so on. Current EES systems mainly rely on a single type of energy storage technology, but no single type of EES element can fulfill all the desirable characteristics of an ideal electrical energy storage, such as high power/energy density, low cost, high cycle efficiency, and long cycle life. A hybrid electrical energy storage (HEES) system is composed of multiple, heterogeneous energy storage elements, aiming at exploiting the strengths of each energy storage element while hiding its weaknesses, which is a practical approach to improve the performance of EES systems. A HEES system may achieve the a combination of performance metrics that are superior to those for any of its individual energy storage elements with elaborated system design and control schemes.
This dissertation proposes high-level optimization approaches for HEES systems in order to maximize their energy efficiency. We propose new architectures for the HEES systems and systematic design optimization methods. The proposed networked charge transfer interconnect (CTI) architecture and bank reconfiguration architecture minimizes the power conversion loss and thus maximizes the charge transfer efficiency of the HEES system. We also point out the limitation of the conventional control schemes and propose a joint optimization design and control considering the power sources. The proposed maximum power transfer tracking (MPTT) operation and MPTT-aware design method effectively increases energy harvesting efficiency and actual available energy. We finally introduce a prototype of a HEES system implementation that physically proves the feasibility of the proposed HEES system.

국문 초록 (Abstract)

전기 에너지 저장 (electrical energy storage, EES) 시스템은 필요에 따라 에너지를 저장하였다가 사용함으로써 에너지 효율과 안정성을 높이고 에너지 단가를 낮추는 등의 기능을 한다. EES 시스템은 비상용 전기 공급, 부하 평준화, 첨두부하 분산, 재생에너지 발전을 위한 에너지 저장 등의 다양한 분야에서 응용할 수 있다. 현재 EES 시스템은 주로 단일 종류의 에너지 저장 기술을 사용하고 있는데, 아직까지 그 어떤 에너지 저장 기술도 높은 에너지 및 전력 밀도, 낮은 가격, 높은 충방전 효율, 긴 수명 등 이상적인 에너지 저장 기술의 모든 요건을 충족시키고 있지 못하고 있다. 하이브리드 전력 저장 (hybrid electrical energy storage, HEES) 시스템은 여러 다른 종류의 에너지 저장 소자를 이용하여 각각의 장점을 활용하여 단점을 보완하는 기법으로, EES 시스템의 성능을 개선시시키기 위한 실용적인 접근 방법 가운데 하나이다. HEES 시스템은 정교한 시스템 설계와 제어기법을 통해 각각의 에너지 저장 소자의 장점을 모두 합친 것과 같은 성능을 갖출 수 있다.
본 학위 논문은 HEES 시스템의 에너지 효율을 최대화하기 위한 고수준의 최적화 기법들을 소개한다. HEES 시스템의 새로운 구조들과 체계적인 최적 설계 기법들을 제시한다. 제안된 네트워크 전하 전송망 (charge transfer interconnect, CTI) 구조와 뱅크 (bank) 재구성 구조는 전력 변환 손실을 최소화하여 HEES 시스템의 전하 전송 효율을 최대화한다. 또한 기존의 제어 기법들이 가진 한계점을 지적하고, 이를 보완하기 위해 전력원을 동시에 고려하여 설계하고 제어하는 기법을 제시한다. 제안된 최대 전력 전달 추종 (maximum power transfer tracking, MPTT) 기법과 이를 고려한 설계 기법은 실직적인 에너지 수집량을 증가시키고 실제적으로 사용 가능한 에너지량을 증가시킨다. 마지막으로 제안된 기법의 실현 가능성을 검증하기 위한 HEES 시스템 프로토타입 구현을 소개한다.

목차 (Table of Contents)

• 1 Introduction
• 1.1 Motivations
• 1.2 Contribution and Significance
• 1.3 Organization of Dissertation
• 2 Background and Related Work
• 2.1 Electrical Energy Storage Elements
• 2.1.1 Performance Metrics
• 2.1.1.1 Power and Energy Density
• 2.1.1.2 Capital Cost
• 2.1.1.3 Cycle Efficiency
• 2.1.1.4 State-of-Health and Cycle Life
• 2.1.1.5 Self-Discharge Rate
• 2.1.1.6 Environmental Impacts
• 2.1.2 Energy Storage Elements
• 2.1.2.1 Lead-Acid Batteries
• 2.1.2.2 Lithium-Ion Batteries
• 2.1.2.3 Nickel-Metal Hydride Batteries
• 2.1.2.4 Supercapacitors
• 2.1.2.5 Other Energy Storage Elements
• 2.2 Homogeneous Electrical Energy Storage Systems
• 2.2.1 Energy Storage Systems
• 2.2.2 Applications of EES Systems
• 2.2.2.1 Grid Power Generation
• 2.2.2.2 Renewable Energy
• 2.2.3 Previous Homogeneous EES Systems
• 2.2.3.1 Battery EES Systems
• 2.2.3.2 Supercapacitor EES Systems
• 2.2.3.3 Other EES Systems
• 2.3 Hybrid Electrical Energy Storage Systems
• 2.3.1 Hybridization Architectures
• 2.3.2 Applications of HEES Systems
• 2.4 EES System Components Characteristics
• 2.4.1 Power Converter
• 2.4.2 Photovoltaic Cell
• 3 Hybrid Electrical Energy Storage Systems
• 3.1 Design Considerations of HEES Systems
• 3.2 HEES System Architecture
• 3.3 Charge Transfer and Charge Management
• 3.4 HEES System Components
• 3.4.1 Nodes
• 3.4.1.1 Energy Storage Banks
• 3.4.1.2 Power Sources and Load Devices
• 3.4.2 Charge Transfer Interconnect
• 3.4.3 System Control and Communication Network
• 4 System Level Design Optimization
• 4.1 Reconfigurable Storage Element Array
• 4.1.1 Cycle Efficiency and Capacity Utilization of EES Bank
• 4.1.2 General Bank Reconfiguration Architecture
• 4.1.3 Dynamic Reconfiguration Algorithm
• 4.1.3.1 Cycle Efficiency
• 4.1.3.2 Capacity Utilization
• 4.1.4 Cycle Efficiency and Capacity Utilization Improvement
• 4.2 Networked Charge Transfer Interconnect
• 4.2.1 Networked Charge Transfer Interconnect Architecture
• 4.2.1.1 Charge Transfer Conflicts
• 4.2.1.2 Networked CTI Architecture
• 4.2.2 Conventional Placement and Routing Problems
• 4.2.3 Placement and Routing Problems
• 4.2.4 Force-Directed Node Placement
• 4.2.5 Networked Charge Transfer Interconnect Routing
• 4.2.6 Energy Efficiency Improvement
• 4.2.6.1 Experimental Setup
• 4.2.6.2 Experimental Results
• 5 Joint Optimization with Power Sources
• 5.1 Maximum Power Transfer Tracking
• 5.1.1 Maximum Power Transfer Point
• 5.1.1.1 Sub-Optimality of Maximum Power Point Tracking
• 5.1.1.2 Maximum Power Transfer Tracking
• 5.1.2 MPTT-Aware Energy Harvesting System Design
• 5.1.2.1 Optimal System Design Problem
• 5.1.2.2 Design Optimization
• 5.1.2.3 Systematic Design Optimization
• 5.1.2.4 Energy Harvesting Improvement
• 5.2 Photovoltaic Emulation for MPTT
• 5.2.1 Model Parameter Extraction
• 5.2.2 Dual-Mode Power Regulator with Power Hybridization
• 5.2.2.1 PV Module I-V Characteristics
• 5.2.2.2 Modes of Operation
• 5.2.2.3 Circuit Design Principle
• 5.2.2.4 Dual-Mode Power Regulator Control
• 5.2.2.5 Implementation
• 5.2.2.6 Experiments
• 6 Experiments
• 6.1 HEV Application
• 6.1.1 Regenerative Brake
• 6.1.2 PV Modules
• 6.1.3 EES Bank Reconfiguration and Networked CTI
• 6.1.4 Overall Improvement and Cost Analysis
• 6.2 HEES Prototype Implementation
• 6.2.1 Design Specifications
• 6.2.1.1 Power Input and Output
• 6.2.1.2 Power and Energy Capacity
• 6.2.1.3 Voltage and Current Ratings
• 6.2.1.4 EES Elements
• 6.2.2 Implementation
• 6.2.2.1 Bank Module
• 6.2.2.2 Controller and Converter Module
• 6.2.2.3 Charge Transfer Interconnect Capacitor Module
• 6.2.2.4 Bidirectional Charger
• 6.2.2.5 Supervising Control Software
• 6.2.2.6 Component Assembly
• 6.2.3 Control Method
• 7 Conclusions and Future Directions