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Research on Microgrid-based Power Flow Analysis and Flexible Control Technologies

Author: DuanYuBing
Tutor: LiQingMin;WangHui
School: Shandong University
Course: High Voltage and Insulation Technology
Keywords: Microgrid Power flow Analysis Flexible control Islanding detection Energy storage Power quality
CLC: TM727
Type: PhD thesis
Year: 2011
Downloads: 125
Quote: 0
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Executive Summary

Due to gradual depletion of the available coal resources as well as the pending environmental crises, new power generation technologies based on high efficiency and clean energy resources are nowadays developing very quickly. With a growing proportion in power systems, the distributed generation (DG) can meet various load demands, reduce environmental pollution and improve the overall efficiency of energy transfer and conversion, however, it may also lead to a series of emerging issues when DG sources are connected to the power systems. To counteract the problems such as the impact on power grids caused by interconnection of wind power and photovoltaic generation, as to fully explore the advantages of DGs, the concept of Microgrid has been proposed. Microgrid being a significant and indispensible component of smart grid, its optimal operation depends on the power flow analysis. Furthermore, to account for the specific operational conditions of Microgrid, such as smooth switch of the operation modes, intelligent detection of the islanding state as well as flexible compensation for the power quality issues, optimal and flexible control of the Microgrid voltages and currents needs to be achieved based on power electronic converters, with a view to guaranteeing safe, stable and reliable operation of the Microgrid. The thesis focuses on some key Microgrid issues including power flow analysis, islanding detection, flexible control strategy and power quality problems, the innovative research on which aspects present further development of the Microgrid technologies.Power flow analysis of the Microgrid is the foundation to realize power distribution and optimal operation. According to physical structure of the Microgrid and variety of the microsources, a method for node classification is proposed, and based on the backward-forward sweep scheme, deterministic power flow models are established with consideration of the transfer performance of the microsource converters. Futher, an effective calculation methodology for probabilistic power plows is also developed by incorporating the intermittent and random characteristics of the microsources, which presents a methodological basis for analysis, assessment and optimization of the Microgrid. The effectiveness of the proposed approach is verified by a computation case.Effective islanding detection is critical to ensure reliable and smooth switching between different operation modes of the Microgrid. Traditional islanding detection methods for distributed generation, either active or passive, is no longer applicable for the Microgrid, hence new islanding detection technologies must be further developed. Based on negative sequence harmonic and reactive current decomposition, a hybrid islanding detection methodology is established with combination of a harmonic current distortion rate and a random disturbance of reactive current, which can quickly identify the islanding state of the Microgrid without blind area, and the simulation results show effectiveness and accuracy of the proposed scheme without any side effect on power quality.Bottom-level control of the Microsources forms the base of optimized control strategy for the Microgrid. However, the asymmetrical nature of various system loads and faults may seriously affect the control behavior of the converters regarding different operation modes of the Microgrid. Based on orthogonal transformation in theα-βdomain, a dynamic mathematical model is developed as to eliminate the effects on converter output current control caused by various unsymmetrical factors. Further, with effective current decoupling of the inner controller, an adaptive discrete-time slide mode control strategy for converter output currents is established. Simulation results have verified the feasibility and effectiveness of the control strategy.Energy storage device can provide a backup boost for voltage and frequency stability of the Microgrid, as well as act an important technical scheme to ameliorate power qualities. Through analysis of the impacts of wind power generation on the Microgrid voltage stability, it shows the fluctuations of active and reactive power are the principal culprits to cause voltage instability of the Microgrid. Hence, a voltage stability control method is put forward based on an energy storage topology, and the simulation case verifies the validity and effectiveness of the proposed strategy. To improve the Microgrid power quality, a technical solution is presented with energy storage-based compensation devices. Both ip-iq and p-q methods are combined for detecting harmonics and reactive currents, further, based on tracing control of the Microsource currents, a new scheme with much preferable performance for harmonic and reactive power compensation is proposed. The novel scheme renders advantages of simple structure, easy realization and high reliability, and both simulation and experimental studies have verified its feasibility.The research achievements and outcomes in this thesis present references of significance for developing Microgrid-based key technologies.

Full-text Catalog

Summary     8-10
ABSTRACT     10-13
first chapter     13-29
1.1 micro grid background and significance     13-14
1.2 microgrid research progress and the main problems     14-27
1.2.1 microgrid development status     16-18
1.2. nbsp the microgrid key technology and research progress;   18-27
1.3 this study     27-29
second chapter of dollars and micro-power converter transmission characteristics microgrid trend calculated     29-43
2.1 micro power model and micro-grid the deterministic flow calculation method     29-35
2.1.1 microgrid component model     29-33
the 2.1.2 micro power node approach     33-35
the 2.2 the microgrid uncertainty Flow Algorithm achieve     the microgrid random 35
2.3 based on Monte Carlo simulation sexual power flow calculation method     35-37
2.3.1 Overview of the Monte Carlo method are found;   35-36
2.3.2 micro grid components probability model     36-37 < br /> 2.4 the microgrid random trend algorithm to achieve     37-41
2.4.1 probabilistic load flow algorithm flow     37-39
2.4.2 Algorithm Verification     39 - 41
2.5 Chapter Summary     41-43
Chapter disturbances negative sequence based on the harmonic distortion rate of the reactive current and reactive current microgrid islanding detection method     43-61
3.1 microgrid islanding detection method analysis     43-47
3.1.1 traditional islanding detection method     43-46
3.1.2 microgrid islanding detection of new requirements   the   46-47
3.2 hybrid islanding detection methods     the 47-57 3.2.1 harmonic current distortion rate of negative sequence reactive
strike     48-55
3.2.2 Intermittent reactive current disturbances strategy     55-56
3.2.3 hybrid islanding detection method to achieve     56-57
3.3 simulation     57-60
3.3.1 islanding detection methods application     the 58-59 3.3.2 pseudo silos
phenomenon of identification     59-60
3.4 Chapter Summary   60-61
Chapter of the   micro power inverter output current discrete sliding mode variable structure decoupling control method     61-83
4.1 micro power inverter topology and the output performance of the control system analysis   the   61-63
4.2 micro power inverter outer loop control methods     63-67
4.2.1 droop characteristics based on the V / f control     the 63-67 4.2.2 PQ control method
4.3 micro power inverter inner loop control method based on the principle of discrete sliding mode variable structure     67 -77
4.3.1 Variable Structure Control principle   the   68-72
4.3.2 three-phase current coupled to the impact of the current output of the inverter control     72-73 < br /> 4.3.3 α-β domain of micro power inverter discrete mathematical modeling     the Adaptive Sliding decoupling 73-75
4.3.4 inverter output current control strategy     the 75-77 4.4 Simulation Research
  the   77-82
4.4.1 standalone microgrid control strategy simulation     77-80
4.4.2 multi-machine the microgrid control policy simulation     80-82
4.5 Chapter Summary     82-83
Chapter based storage support micro-grid voltage stability and power quality control strategy     83-107 5.1 micro-grid voltage stability control strategy     83-93
5.1.1 wind turbines operating characteristics analysis     83-86

5.1.2 voltage stability of wind power on the access point mechanism     86-87
5.1.3 based storage support voltage stability control strategy     87-91
5.1.4 example verify     91-93
5.2 based storage support micro-grid power quality control strategy     93-102
5.2.1 detection of harmonic and reactive current based on the load side of compensation Control     95-98
5.2.2 Based on the output current of the power supply terminal directly tracking compensation control     98-102
the 5.3 experimental research     102-106
5.3.1 microgrid experiment platform physics     102-104
5.3.2 micro grid power quality control experiments     104-106
5.4 Chapter Summary     106-107
Chapter 6 Conclusions and Prospects     to References 107-109
thank the     120-121
PhD during have been published or accepted papers     121-123
Dissertation Table of reviewers and the respondent     123

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CLC: > Industrial Technology > Electrotechnical > Transmission and distribution engineering, power network and power system > Transmission and distribution technology > The power grid
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