Table of Contents

1 Introduction -.. 1
1.1 Applications of Lithium-Ion Batteries - . . . . . 1
1.1.1 The Crucial Role of Batteries - . . . . . 1
1.1.2 Comparisons of Different Batteries - 4
1.2 Battery Inconsistency Phenomenon - . 5
1.3 Crucial Role of Cell Equalization - . . . 6
1.3.1 Voltage-Based Equalization - 7
1.3.2 SOC-Based Equalization - . . . 7
References - . . . . 10
2 Overview of Cell Equalization Systems - . . 13
2.1 Classification and Comparisons of Cell Equalization Systems . . . 13
2.1.1 Passive Cell Equalization Systems - . 13
2.1.2 Active Cell Equalization Systems - . 15
2.1.3 Comparisons of Cell Equalization Systems - . . . . . 16
2.2 Commercial Equalizers - . . . . . 17
2.2.1 Bidirectional Buck-Boost Converters - . . . . 17
2.2.2 Bidirectional Modified C？uk Converters - . . 19
2.3 Overview of Equalization Algorithms - . . . . . 21
2.3.1 Cell-to-Cell Equalization Algorithms - . . . . 21
2.3.2 Cell-to-Pack-to-Cell Equalization Algorithms - . . . 23
2.3.3 Charging Equalization Algorithms - 24
References - . . . . 25
3 Active Cell Equalization Topology - 29
3.1 Commonly Used Active Cell Equalization Topology - . . . . 29
3.1.1 Adjacent-Based Topology - . . 30
3.1.2 Non-adjacent-Based Topology - . . . . 35
3.1.3 Direct Cell-Cell Topology - . . 38
3.1.4 Mixed Topology - . . . . 40
3.2 Active Cell Equalization Topology Comparison - . . . 41
3.2.1 Performance Comparison - . . 41
3.2.2 Economic Comparison - . . . . 45
3.2.3 Discussions - . . 48
References - . . . . 49
4 Optimal Active Cell Equalizing Topology Design - . . . . . 55
4.1 Cell Equalizing System - . . . . . 55
4.1.1 Equalizing System Model - . . 56
4.1.2 Consensus-Based Cell Equalizing Algorithm Design . . . 57
4.2 Design of the Optimal Equalizing Topology - 59
4.2.1 Equalizing Time - . . . . 59
4.2.2 Traditional Cell Equalizing Topology - . . . . 61
4.2.3 Position Identification of the Added ICEs
for Reducing the Equalizing Time - . 62
4.3 Simulation Results - . . . 63
4.4 Experimental Results - . 67
References - . . . . 72
5 Neural Network-Based SOC Observer Design for Batteries - . 73
5.1 Battery Model - . 73
5.2 RBF Neural Network Observer - . . . . . 75
5.2.1 Neural Network Based Nonlinear Observer Design . . . . 75
5.2.2 Convergence Analysis - . . . . . 77
5.3 Experiments and Simulations - 79
5.3.1 Experiment for Parameter Extraction - . . . . 79
5.3.2 Experiment for SOC Estimation - . . 81
References - . . . . 86
6 Active Cell-to-Cell Equalization Control - . 89
6.1 Cell Equalizing System Model - . . . . . 89
6.1.1 Battery Cell Model - . . 89
6.1.2 Bidirectional Modified C？uk Converter Model - . . . 92
6.1.3 Cell Equalizing System Model - . . . . 93
6.2 Objective and Constraints of the Cell Equalizing Process - . 95
6.2.1 Cell Equalizing Objective - . . 95
6.2.2 Cell Equalizing Constraints - 96
6.3 SOC Estimation Based Quasi-Sliding Mode Control
for Cell Equalization - . . 97
6.3.1 Adaptive Quasi-sliding Mode Observer Design
for Cells’ SOC Estimation - . 97
6.3.2 Quasi-Sliding Mode-Based Cell Equalizing Control . . . 99
6.4 Experiments - . . . 102
6.4.1 Experimental Setup - . 102
6.4.2 Experimental Results - 105
References - . . . . 107
7 Module-Based Cell-to-Cell Equalization Control - . . . . . 109
7.1 Module-Based Cell-to-Cell Equalization Systems - . 109
7.1.1 Equalizing Currents - . 109
7.1.2 Cell Equalizing System Model - . . . . 112
7.1.3 Cell Equalizing Constraints - 113
7.2 Hierarchical Optimal Control Strategy - . . . . . 114
7.2.1 Cell Equalizing Task Formulation - . 115
7.2.2 Top Layer: Module-Level Equalizing Control - . . . 116
7.2.3 Bottom Layer: Cell-Level Equalizing Control - . . . 118
7.3 Results and Discussions - . . . . . 119
7.3.1 Cell Equalizing Results - . . . . 120
7.3.2 Tests of Different Weight Selections - . . . . . 121
7.3.3 Comparison With Decentralized Equalizing Control . . . 123
7.3.4 Tests for Different Cells’ Initial SOCs - . . . 124
References - . . . . 126
8 Module-Based Cell-to-Pack Equalization Control - . . . . 127
8.1 Improved Module-Based CPC Equalization System - . . . . . 127
8.1.1 Equalizing Current Formulation - . . . 128
8.1.2 Improved Module-Based CPC Equalization
System Model - 131
8.2 Two-Layer Model Predictive Control Strategy - . . . . 132
8.2.1 Cost Function Formulation - . 132
8.2.2 Constraints - . . 133
8.2.3 Centralized MPC Design - . . . 134
8.3 Two-Layer MPC for Cell Equalization - . . . . 134
8.3.1 Top-layer MPC: ML Equalizing Current Control - 135
8.3.2 Bottom-Layer MPC: CMC Equalizing
Current Control - . . . . . 136
8.3.3 Computational Complexity Comparison With
Centralized MPC - . . . 137
8.4 Results and Discussions - . . . . . 139
8.4.1 Equalization Results - 140
8.4.2 Comparison With the Centralized MPC - . . 140
8.4.3 Comparison With a Commercial CPC-Based
Equalization Structure - . . . . . 141
8.4.4 Tests of Different Cells’ Initial SOC Vectors - . . . . 142
References - . . . . 144
9 Optimal Hierarchical Charging Equalization for Battery Packs . . . . 147
9.1 Charging System Model - . . . . . 147
9.1.1 Battery Pack Model - . 147
9.1.2 Multi-module Charger Modeling - . . 148
9.1.3 Charging System Modeling - 149
9.2 Hierarchical Control for the Charging Equalization System . . . . . 150
9.2.1 Charging Equalization Objectives - . 151
9.2.2 Charging Constraints - 153
9.2.3 Top-Layer Control: Optimal Charging Current
Scheduling - . . . 153
9.2.4 Bottom-Layer Control: Charging Current Tracking . . . . 156
9.3 Simulation and Experimental Results - 158
9.3.1 Simulation Results - . . 159
9.3.2 Experimental Results - 163
References - . . . . 165
10 Simultaneous Charging Equalization Strategy for Battery Packs . . . 167
10.1 Charging Model - 167
10.1.1 Battery Pack Modeling - . . . . 167
10.1.2 Charging Objective - . 169
10.1.3 Charging Constraints - 170
10.2 Simultaneous Charging Development - . . . . . 171
10.3 Simulation and Experimental Results - 175
10.3.1 Simulation Results - . . 175
10.3.2 Experimental Results - 177
References - . . . . 181