DESIGN, MANAGEMENT AND CONTROL OF ENERGY STORAGE DC NANO-GRID TRAN DUONG NATIONAL UNIVERSITY OF SINGAPORE 2013 DESIGN, MANAGEMENT AND CONTROL OF ENERGY STORAGE DC NANO-GRID TRAN DUONG (B.Eng(Hons.), HUT, Hanoi, Vietnam) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2013 Acknowledgement First of all, I would like to express my sincere thanks to my research supervisor, Prof. Ashwin M Khambadkone, for his invaluable guidance and support throughout my research. He inspired and encouraged not only me but also his other research scholars via brain-storming discussions, and both self and mutual criticisms, which created a research group that can be trademarked by its own high research quality and strictness in following international research ethic. I always remember my first discussion with him towards the potential research topics, in which I recognized and learned the importance of practicability, applicability and fact indisputability in research. To be frank, until now, I am still unable to answer one of the simple but very fundamental questions that he asked during that discussion. But part of the answer is shown in this dissertation, which is related to energy and the worlds modern power system. His devotion to research and academic work with rigorous and professional attitudes has inspired all of us, who are lucky to have his supervision. Consequently, I always remind myself to reach and hold the level of world-class and state-of-the-art research that he has been motivating us to surpass. I also appreciate so much great technical support and help of lab officers: Mr. i Woo Ying Chee and Mr. Chandra from Electrical Machines and Drives Laboratory, and Mr. Seow Hung Cheng from Energy Management and Micro-grid Lab. I also would like to express my warmest thanks to Dr. Zhou Haihua, Dr. Tanmoy Bhattacharya and Mr. Terence Siew Tuck Sing for research discussions, and hardware design and development for the experiments. I would like to express many thanks to Dr. Kong Xin, Ms. Yu Xiaoxiao, Ms. Wang Huanhuan, Ms. Lim Shu Fan, Dr. Tan Yen Kheng, Mr. Souvik Dasgupta, Ms. Li Yanlin for research discussions to widen my research knowledge as well as to strengthen my research arguments. I am grateful to have research fellowship and accompany throughout my years of PhD at NUS with Mr. Hoang Duc Chinh, Mr. Parikshit Yadav, Mr. Sangit Sasidhar, Ms Htay Nwe Aung, and Mr. Abhra Roy Chowdhury. Finally, I would like to thank my wife Tran Nguyet Minh and my daughter Tran Ngoc Khanh for their understanding and encouragement. With their love and care, I have had an infinite support to overcome so many encountered nonresearch problems. I also would like to thank my parents and parents-in-law for supporting my family during my doctoral research. ii Contents Acknowledgement i Contents iii Summary xi List of Tables xiv List of Figures xvi Abbreviations xxvii Background and Problem Definitions 1.1 Evolution of modern power system . . . . . . . . . . . . . . . . . . 1.1.1 Evolution of modern power system . . . . . . . . . . . . . . 1.1.2 Micro-grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.3 Renewable Energy Plants . . . . . . . . . . . . . . . . . . . iii 1.2 1.3 1.4 Energy Storage DC Nano-grid . . . . . . . . . . . . . . . . . . . . . 1.2.1 Energy storage . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 DC technology . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.3 Energy storage DC nano-grid . . . . . . . . . . . . . . . . . 1.2.4 Related works . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Challenges in Energy Storage DC Nano-Grid . . . . . . . . . . . . . 11 1.3.1 Constraints of energy storage devices . . . . . . . . . . . . . 11 1.3.2 Intermittency of renewable energy sources . . . . . . . . . . 12 1.3.3 Instability caused by constant power load . . . . . . . . . . . 13 Content and Contributions of the Thesis . . . . . . . . . . . . . . . 14 Design of Energy Storage DC Nano-Grid 2.1 2.2 18 Review of energy storage technologies for power applications . . . . 18 2.1.1 Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.1.2 Ultra-capacitor . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1.3 Flywheel energy storage (FES) . . . . . . . . . . . . . . . . 23 2.1.4 Super-conducting magnetic energy storage (SMES) . . . . . 24 2.1.5 Flow battery . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.1.6 Compressed air energy storage (CAES) . . . . . . . . . . . . 29 2.1.7 Pumped hydro storage (PHS) . . . . . . . . . . . . . . . . . 30 Concept of energy storage DC nano-grid . . . . . . . . . . . . . . . 31 iv 2.2.1 Comparison of energy storage technologies for power applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.3 2.2.2 Packaging and integration of energy storage . . . . . . . . . 39 2.2.3 Energy storage DC nano-grid concept . . . . . . . . . . . . . 41 Selection of power interface for energy storage . . . . . . . . . . . . 46 2.3.1 Bidirectional DC-DC converters . . . . . . . . . . . . . . . . 46 2.3.2 Bidirectional DC-AC converters . . . . . . . . . . . . . . . . 55 2.3.3 Multi-port design for compact size 2.3.4 Modular design for high power and high flexibility . . . . . . 58 2.3.5 Soft-switching for increased efficiency . . . . . . . . . . . . . 60 2.3.6 Interface for power quality improvement . . . . . . . . . . . 60 . . . . . . . . . . . . . . 56 2.4 Sizing of of energy storage DC nano-grid . . . . . . . . . . . . . . . 61 2.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Energy Management in Energy Storage DC Nano-Grid 67 3.1 Roles of Energy Management in Energy Storage DC Nano-Grid . . 67 3.2 Related works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 3.3 Construction of Energy Manager . . . . . . . . . . . . . . . . . . . 73 3.3.1 Structure of Energy Manager . . . . . . . . . . . . . . . . . 73 3.3.2 Selection of algorithms for predictive model and optimizer . 74 v 3.3.3 Stochastic Dynamic Programming with time-cascade Markov chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.4 Energy Management for Energy Storage DC Nano-Grid in Residential Micro-Grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 3.5 3.6 3.4.1 Energy storage DC nano-grid in residential micro-grid . . . . 81 3.4.2 Objectives of Energy Manager . . . . . . . . . . . . . . . . . 83 3.4.3 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 3.4.4 Comparison and Discussion . . . . . . . . . . . . . . . . . . 92 Energy Management for Lifetime Extension . . . . . . . . . . . . . 97 3.5.1 Model of battery lifetime . . . . . . . . . . . . . . . . . . . . 98 3.5.2 Cost function for lifetime extension . . . . . . . . . . . . . . 101 3.5.3 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Dynamic Power Management of Energy Storage DC Nano-Grid for Wind Power Plant 113 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 4.2 Augmentation and location of energy storage DC nano-grid for wind power plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 4.2.1 Configurations of wind power plant . . . . . . . . . . . . . . 119 4.2.2 Augmentation and location of energy storage DC nano-grid for wind power plant . . . . . . . . . . . . . . . . . . . . . . 123 vi 4.3 4.4 Short-term power variation of wind energy . . . . . . . . . . . . . . 126 4.3.1 Power extraction from wind . . . . . . . . . . . . . . . . . . 126 4.3.2 Origins of short-term variations of wind power . . . . . . . . 127 Dynamic Power Management in energy storage DC nano-grid for wind power plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 4.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 4.4.2 Construction of Dynamic Power Manager . . . . . . . . . . . 129 4.4.3 Solving real-time optimization problem in Dynamic Power Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 4.5 4.4.4 Case study . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 4.4.5 Fast grouping of energy storage devices . . . . . . . . . . . . 152 4.4.6 Find optimal subset inside group of energy storage devices . 153 4.4.7 Comparison and Discussion . . . . . . . . . . . . . . . . . . 159 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Dynamic Control of Energy Storage DC Nano-Grid for Stable Operation of Wind Power Plant 163 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 5.2 Criteria for stable operation of wind power plant . . . . . . . . . . . 167 5.2.1 Small-signal stability criterion . . . . . . . . . . . . . . . . . 167 5.2.2 Large-signal stability criterion . . . . . . . . . . . . . . . . . 168 vii tions, IECON 2010 - 36th Annual Conference on IEEE Industrial Electronics Society, pp. 1818 1824, Nov. 2010. 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Khambadkone,Composite Energy Storage System Involving Battery and Ultracapacitor with Dynamic Energy Management in Micro-grid Applications, 275 IEEE Transactions on Power Electronics, vol. 26 , no. 3, pp. 923 - 930, 2011 5. Haihua Zhou, Tanmoy Bhattacharya, Duong Tran, Terence Siew and A.M. Khambadkone, Composite Energy Storage System Using Dynamic Energy Management in Micro-grid Applications, 2010 International Power Electronics Conference (IPEC), pp. 1163 - 1168, June 2010 6. Haihua Zhou, Tanmoy Bhattacharya, Duong Tran, Terence Siew and A.M. Khambadkone, Composite Energy Storage System with Flexible Energy Management Capability for Micro-grid Applications, IEEE Energy Conversion Congress and Expo (ECCE), pp. 2558 - 2563 Sep. 2010 7. Haihua Zhou, Duong Tran, Siew Tuck Sing and A.M. Khambadkone, Interleaved bi-directional Dual Active Bridge DC-DC converter for interfacing ultra-capacitor in micro-grid application, IEEE International Symposium on Industrial Electronics (ISIE), pp. 2229 - 2234, 2010 8. Duong Tran, Haihua Zhou and Ashwin M. Khambadkone, A simple design of DC power system with multiple source-side converters to operate stably under constant power load, 2nd IEEE International Symposium on Power Electronics for Distributed Generation Systems (PEDG), pp. 520 - 525, 2010 Patent Filed provisional patent application - number 61/523,872 - with the United States Patent & Trademark Office: SRC/P/06653/00/US; ILO ref. 11173A; VJP ref. 276 P105715 Dynamic Power Management for Energy Storage in Composite Storage Systems 277 Appendix A Output impedance and transfer function A.1 Relationship of open-circuit transfer function and output impedance with loaded transfer function Lemma A.1.1 Consider the system shown in Fig. A.1 in which the black-box has open-circuit voltage transfer function F (s)|Z , output impedance Zo . Voltage transfer function of the system under load Z is determined by: F (s)|Z = vo F (s)|Z = vs + ZZo 278 (A.1) v Black box F, Z + v Z Figure A.1: Relationship of open-circuit transfer function and output impedance with loaded transfer function Proof The result is derived directly from equation 6.1 with F (s)|Z FS and FL = 1. A.2 Equivalent output impedance and transfer function of L-C type input filter In practice, common experience to design input filter is to make output impedance of the input filter itself as small as possible. This can be done by techniques like parallel damping, series damping, multi-section of filters and so on. How to apply these techniques to improve equivalent output impedance of source sub-system and load-side converter input filter depends on specific structure of the input filter. Herein, relationship between equivalent output impedance of combined source subsystem and load-side converter input filter, and output impedance of input filter alone is shown for the L-C type input filter structure. The results can be applied for bus impedance analysis in later parts. Definition L-C type input filter is filter that has equivalent circuit diagram as shown in Fig. A.2. 279 Z Z Z Z Figure A.2: Equivalent circuit diagram of L-C type filter With the above definition, it is direct to obtain following results: Lemma A.2.1 For LC type input filter, we have: 1. Zisc = input impedance when output terminal it short-circuited. 2. Zp = Zioc Zisc where Zioc = input impedance when output terminal is open-circuited. Lemma A.2.2 For LC type input filter, we have: Zo = Zisc //Zp = F = Zp Zisc + Zp Zisc Zp Zisc + Zp (A.2) (A.3) where Zo is output impedance, F is voltage transfer function when output terminal is open-circuited. Based on the two above results, we have: Theorem A.2.3 Consider the system shown in Fig. A.3(a). Voltage source Vs has output impedance Zos . The filter is LC type filter with open-circuit transfer 280 function Ff , output impedance Zof . The equivalent output impedance and opencircuit transfer function from voltage source to output terminal then are determined by: Zo = F |Z = Zos Ff + Zof 1+ (A.4) Ff ) Ff 1+ Zos Ff (1 Zof (A.5) Ff ) Z Z V Zos Ff (1 Zof LC type Z F, Z V Z (a) Z Z v (b) Figure A.3: (a) System with voltage source, LC type filter and load (b) Equivalent circuit of the system Proof Because the filter is LC type, we have equivalent circuit of the system as shown in Fig. A.3(b). Then: Zo = (Zos + Zisc )//Zp = F |Z = (Zos + Zisc )Zp Zos + Zisc + Zp Zp vo |Z = Vs Zos + Zisc + Zp (A.6) (A.7) From Lemma A.2.2, we have: Zof Ff Zof = Ff Zisc = Zp 281 (A.8) (A.9) Substitute (A.8) and (A.9) to (A.6) (A.7), we obtain: Zo = F |Z = Zos Ff + Zof (Zos Ff + Zof )Zof = Z F Zos Ff (1 Ff ) + Zof + Zosof f (1 Ff ) Zof Ff = Zos Ff (1 Ff ) + Zof 1+ Ff Zos Ff (1 Zof Ff ) (A.10) (A.11) From results of Theorem A.2.3, we can calculate equivalent output impedance of the system based on source output impedance, filter output impedance and filter open-circuit transfer function. The transfer function from source to load Z can also be calculated by using Lemma A.1.1. When input filter of load-side converter is designed, it has to be taken into account both filtering characteristics and impedance, transfer function characteristics as mentioned in Theorem 6.2.1. 282 Appendix B Accurate model of DAB converter as current source under phase-shift modulation For DAB converter with phase-shift control, the output current at secondary side is known in literature as: iDAB = V1 2(1 2) 2Lk fs n (B.1) where V1 is input voltage at primary side, Lk is leakage inductance, fs is switching frequency, n is transformer turns ratio, is normalized phase-shift angle. Derivation of Eqn. (B.1) assumes that voltage source is ideal (with zero output impedance) and there is no loss over power devices. These assumptions are acceptable for design of controllers that does not require accurate model of the DAB converter. However, because feedback linearization that incorporates inverse 283 model of phase-to-current is used for DAB current control, a more accurate model that considers the non-ideality of source and power devices should be developed. Consider req as aggregate resistance for output impedance of source and power loss over components of the converter. The output current at secondary side is then derived as follows. iíịò rế Vẹ Sẹ Lé A iĩé B Sì Sỉ Sệ Sề S C D ẽ S ể Về S ễ Figure B.1: Dual Active Bridge DC-DC converter Let rs be source output impedance. Losses of power switches on two sides and loss of transformer are modeled as ron1 , ron2 , rT r respectively. The equivalent resistance is then: req = rs + 2ron1 + rT + 2ron2 n (B.2) Schematic diagram and waveforms of DAB with phase-shift control are shown in Fig. B.1 and Fig. B.2. 284 Vỏ Võó Tỡ tỗ tố tộ tở tờ Số, Sộ ọồổ ióỏ Iố Sờ, Sở Sớ, Sợ qộ qố Iộ Sù, S qờ -Iố iủũ > 0, V1 > V2 n t Figure B.2: Waveforms of DAB for phase-shift control We have: vLk V diLk V1 n2 req iLk = = Lk dt V V2 r i n during time interval [t1 , t2 ] (B.3) during time interval [t2 , t3 ] eq Lk where V2 is output voltage at secondary side. Solve the equations with approximation that ex + x + x2 2! + . for x 1, we have: V2 req V1 V1 (2 0.5) + + 2 2Lk fs 4nLk fs 4Lk fs V1 V2 V1 req = iLk (t2 ) = + 2 (4 1) + (4 1) 4Lk fs 4Lk fs 4nLk fs I1 = iLk (t1 ) = (B.4) I2 (B.5) Note that t1 +t2 +t3 = 0.5Ts , Ts = , fs the average current flow through leakage 285 inductance from t1 to t3 then is: V1 (1 2) (V1 V2 /n)req q1 + q2 + q3 (1 + 163 ) = + I13 = 0.5Ts Lk f s 16L2k fs2 V1 req ( 42 + 164 ) (B.6) 3 16Lk fs Neglect components of fs3 , we have output current from DAB: IDAB = I13 V1 2(1 2) (V1 V2 /n)req (1 + 163 ) = Fi () = + n 2Lk fs n 16L2k fs2 n 286 (B.7) [...]... challenge is how to control the overall energy storage DC nano- grid or energy storage system to ensure stability and improve performance of renewable power plants A specific control problem, for example, is then how to control energy storage DC nano- grid supporting the wind power plant so that the plant xii can contribute to grid frequency control Analysis and controller design are then provided and verified... chart of energy density and power density of different energy storage technologies (Electropaedia) 33 2.7 Efficiency and lifetime of different energy storage technologies 34 2.8 Energy density of different energy storage technologies 35 2.9 Power rating and discharge time of energy storage technologies 36 2.10 Cost of several energy storage technologies 37 2.11 Energy. .. 6.28 Management and control approach for energy storage DC nano- grid in low-dynamics applications 232 6.29 Current management for energy storage devices with slow or normal dynamics 234 6.30 Current management and dynamic control for energy storage devices in energy storage DC nano- grid 236 6.31 Experimental setup for verification of. .. and Future work 243 7.1 Conclusion 243 7.2 Future work 246 7.2.1 Contributive frequency regulation of wind power plant augmented with energy storage DC nano- grid 246 7.2.2 Contributive protection of energy storage DC nano- grid to DC electrical energy system 247 ix 7.2.3 Fault management in energy storage DC nano- grid. .. power load DC bus voltage is well regulated at 400VDC 227 6.25 Simulation result of energy storage DC nano- grid operation when overload occurs DC bus voltage is regulated back to 400VDC after overload ends 228 6.26 Hysteresis comparator for by-pass switch control 229 6.27 Management and control approach for energy storage DC nano- grid in high-dynamics... for infrastructure expansion and increasing vulnerability, transmission and distribution systems must have flexible configuration and smart management & control, which are of smart grid and micro -grid concepts To alleviate the problem of intermittency of renewable energy as well as to improve the controllability and smartness of transmission and distribution systems, energy storage plays an important role... 4.18 Impact of power deviation ∆P on RMS power ripple, P-P power ripple, energy loss and energy exchange 152 4.19 Find optimal subset inside group of energy storage devices 153 4.20 Labeling possible states and feasible range of power allocation to each energy storage device 156 4.21 Number of energy storage devices at ON state and number of energy storage devices... final challenge is how to control of multiple energy storage devices inside energy storage DC nano- grid The control is required to be compatible with upperlayered managers and at the same time, ensure that sufficient power and/ or energy are provided to meet load demands Possible dynamics interactions amongst energy storage devices are also needed to be taken care Theoretical analysis and experimental verification... of the abovementioned problems xiii List of Tables 2.1 Typical specifications of battery technologies 28 2.2 Quick summary of typical energy storage technologies 38 2.3 Large-scale lead-acid battery energy storage systems in operation (2001) 40 2.4 Levels of energy storage system and applications 44 2.5 Power and energy densities of energy. .. 15 1.6 Design, Management and Control of Energy Storage DC Nano- Grid 16 2.1 Battery cell 19 2.2 Flow battery in principle [2] 26 2.3 Compressed air energy storage (CAES) in principle (Source: SANDIA and [2]) 30 2.4 Pumped hydro storage (PHS) in principle (Source: TVA) 31 2.5 Several popular energy storage technologies . DESIGN, MANAGEMENT AND CONTROL OF ENERGY STORAGE DC NANO- GRID TRAN DUONG NATIONAL UNIVERSITY OF SINGAPORE 2013 DESIGN, MANAGEMENT AND CONTROL OF ENERGY STORAGE DC NANO- GRID TRAN DUONG (B.Eng(Hons.),. . . . . . . . . . . . . . . . . . . 66 3 Energy Management in Energy Storage DC Nano- Grid 67 3.1 Roles of Energy Mana gem ent in Energy Storage DC Nano- Grid . . 67 3.2 Related works . . . . configuration and smart management & control, which are of smart grid and micro -grid concepts. To alleviate the problem of intermittency of renewable energy as well as to improve the controllability and