Control and Operation of Power Distribution System for Optimal Accommodation of PV Generation

174 Pages·2014·0.77 MB·English

Control and Operation of Power Distribution System for
Optimal Accommodation of PV Generation
Mr.Yashodhan Prakash Agalgaonkar
Thesis submitted for the degree of
Doctor of Philosophy
Imperial College London
Control and Power Research Group
Department of Electrical and Electronic Engineering
March 2014
I hereby declare that all the work in this thesis is my own. The work of others has
been properly acknowledged.
Mr.Yashodhan P. Agalgaonkar.
20 March 2014
The copyright of this thesis rests with the author and is made available under a
Creative Common Attribution Non-Commercial No Derivatives licence. Researchers
are free to copy, distribute or transmit the thesis on the condition that they attribute
it, that they do not use it for commercial purposes and that they do not alter,
transform or build upon it. For any reuse or redistribution, researchers must make
clear to others the licence terms of this work.
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Abstract
The renewable policies in various countries are driving significant growth of grid
connected renewable generation sources such as the Photovoltaics (PVs). Typically
a PV generation is integrated into power systems at the low and the medium voltage
distribution level. The uptake of an intermittent power from the PVs is challenging
the power system operation and control. The network voltage control is one of the
major challenges during the operation of the distribution connected PVs. The active
power injection from a PV plant causes variable voltage rise. This forces the existing
voltage control devices such as on-load tap-changer (OLTC) and voltage regulator
(VR) to operate continuously. The consequence is the reduction of the operating life
of the voltage control mechanism. Also, the conventional non-coordinated reactive
power control results in the operation of the VR at its control limit (VR runaway
condition). This research focuses on the distribution voltage control in the presence
of PV generation and helps to establish detailed insights into the various associated
challenges.
Firstly, the typical grid integrated PV topologies are discussed. The existing
powersystemoperationalpracticesarepresentedandtheirlimitationsareidentified.
A voltage control methodology to tackle challenges such as over-voltage, excessive
tap counts and VR runaway is presented. These challenges are alleviated through
the coordinated reactive power control. The reactive power coordination is achieved
throughthedeterministicdistributionoptimalpowerflowsolvedthroughtheinterior
point technique. The irradiance and the load forecasting errors are another set of
challenges from the distribution network operators’ perspective. The stochastic
optimal voltage control strategy is proposed to tackle the element of randomness
associated with the forecast errors. The stochastic operational risks such as an over-
voltage and a VR runaway are defined through a chance constrained optimization
problem. The simulation study is performed using a realistic 95-bus UK generic
distribution network model and a practically measured irradiance to demonstrate
the effectiveness of the proposed control strategies. The thesis makes an effort to
offer an insight into the operational challenges and propose strategies to achieve a
seamless integration of the PVs into the power systems.
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Acknowledgements
The research presented in this thesis has been carried out under the supervision
of Prof. Bikash C. Pal at the Control and Power research group, Department of
Electrical and Electronic Engineering. I wish to thank Prof. Pal for his guidance
during the course of this research. I would also like to thank him for all the
encouragement and support. This work has been supported by a joint UK-India
initiativeinsolarenergythroughaprojectStabilityandPerformanceofPhotovoltaic
(STAPP) funded by Research Councils UK (RCUK) Energy Programme in UK
(contract no:EP/H040331/1) and by Department of Science and Technology (DST)
in India. I would like to thank the RCUK for funding this research. I would also
like to gratefully acknowledge Dr. R. A. Jabr from American University of Beirut,
Lebanon for his valuable suggestions during all stages of this research.
Thanks to Dr. Ravindra Singh from ABB Power Technologies, USA who helped me
in many ways. I would like to thank Dr.Tom Betts from Loughborough University,
UK for the solar irradiance data. Thanks to all my colleagues at the research lab
who created a friendly environment : Dr.Linash Kunjumuhammed, Dr.Dumisani
Simfukwe, Arif, Stefanie, Abhinav, Ankur, Georgios and Sara. Finally I wish to
express my deepest gratitude towards my mother Sandhya and my father Prakash.
I would like to thank my wife Sharayu for her support and understanding during my
Ph.D study. I am also thankful to my siblings. I take an opportunity to express my
respect towards my grandparents who will always remain my source of inspiration.
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Dedicated to my parents
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Contents
Declaration 2
Abstract 3
Acknowledgements 4
Abbreviations 15
1 Introduction 16
1.1 Global PV generation scenario . . . . . . . . . . . . . . . . . . . . . . 16
1.2 Grid integration challenges . . . . . . . . . . . . . . . . . . . . . . . . 23
1.2.1 Generation operation and control . . . . . . . . . . . . . . . . 23
1.2.2 Transmission operation and control . . . . . . . . . . . . . . . 26
1.2.3 Distribution operation and control . . . . . . . . . . . . . . . 26
1.3 Research objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
1.4 Contributions of the thesis . . . . . . . . . . . . . . . . . . . . . . . . 30
1.4.1 Research outcomes . . . . . . . . . . . . . . . . . . . . . . . . 30
1.4.2 Research dissemination . . . . . . . . . . . . . . . . . . . . . . 30
1.5 Organization of the thesis . . . . . . . . . . . . . . . . . . . . . . . . 33
2 PV Grid integration standards 35
2.1 Protection settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.1.1 Over/under voltage and over/under frequency . . . . . . . . . 36
2.1.2 Anti-islanding . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.1.3 Other settings . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.2 Power quality limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
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Harmonics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Unbalance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.3 Grid support features . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.3.1 Dynamic grid support . . . . . . . . . . . . . . . . . . . . . . 44
Dynamic voltage support . . . . . . . . . . . . . . . . . . . . . 44
Frequency support . . . . . . . . . . . . . . . . . . . . . . . . 47
2.3.2 Steady state voltage support . . . . . . . . . . . . . . . . . . . 48
pf(P) characteristic . . . . . . . . . . . . . . . . . . . . . . . . 49
Q(U) characteristic . . . . . . . . . . . . . . . . . . . . . . . . 49
2.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3 PV generation modeling 53
3.1 PV topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.2 PV generation dynamic model . . . . . . . . . . . . . . . . . . . . . . 54
3.2.1 PV power circuit . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.2.2 PV control structure . . . . . . . . . . . . . . . . . . . . . . . 59
Maximum power point tracking (MPPT) . . . . . . . . . . . . 59
DC link voltage control . . . . . . . . . . . . . . . . . . . . . . 63
Active and reactive power control . . . . . . . . . . . . . . . . 65
3.2.3 Case study : small signal stability analysis . . . . . . . . . . . 67
Single solar infinite bus model . . . . . . . . . . . . . . . . . . 67
Multi machine power system . . . . . . . . . . . . . . . . . . . 74
3.3 PV generation steady state model . . . . . . . . . . . . . . . . . . . . 77
3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4 Deterministic voltage control 79
4.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.2 Radial feeder voltage variation . . . . . . . . . . . . . . . . . . . . . . 81
4.3 Classical voltage control devices . . . . . . . . . . . . . . . . . . . . . 83
4.3.1 On-load tap changer . . . . . . . . . . . . . . . . . . . . . . . 83
4.3.2 Voltage regulator (VR) . . . . . . . . . . . . . . . . . . . . . . 84
Line drop compensation (LDC) . . . . . . . . . . . . . . . . . 86
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VR control settings . . . . . . . . . . . . . . . . . . . . . . . . 88
4.4 Feeder operational challenges . . . . . . . . . . . . . . . . . . . . . . 93
4.5 Optimal Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . 98
4.5.1 Control Strategy . . . . . . . . . . . . . . . . . . . . . . . . . 98
4.5.2 Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Objective function . . . . . . . . . . . . . . . . . . . . . . . . 99
Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
4.6 Case study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4.6.1 System model . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4.6.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
5 Stochastic voltage control 120
5.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5.2 Chance constrained optimization (CCO) . . . . . . . . . . . . . . . . 121
5.2.1 Optimization objective . . . . . . . . . . . . . . . . . . . . . . 122
5.2.2 Probabilistic constraints . . . . . . . . . . . . . . . . . . . . . 122
5.3 CCO solution strategy . . . . . . . . . . . . . . . . . . . . . . . . . . 124
5.4 Tap tail expectation(TTE) . . . . . . . . . . . . . . . . . . . . . . . . 127
5.5 Case study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
5.5.1 System model . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
5.5.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
5.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
6 Conclusions 139
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
6.2 Thesis contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
6.3 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
References 145
A PV model parameters 159
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B Multi machine system data 160
C UKGDS 95-bus system data 163
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List of Figures
1.1 Cumulative global capacity[GWp] during 2007-2013 . . . . . . . . . . 18
1.2 Country-wise cumulative capacity percentage in Europe . . . . . . . . 18
1.3 Region-wise cumulative capacity percentage in UK . . . . . . . . . . 19
1.4 Country-wise cumulative capacity percentage outside Europe . . . . . 20
1.5 Region-wise cumulative capacity percentage in USA . . . . . . . . . . 21
1.6 Region-wise cumulative capacity percentage in India . . . . . . . . . . 22
1.7 Power System operating reserves . . . . . . . . . . . . . . . . . . . . 24
1.8 PV inverter antiislanding . . . . . . . . . . . . . . . . . . . . . . . . . 27
1.9 PV as a DG connected near substation transformer. . . . . . . . . . . 28
2.1 Typical PV generator protection . . . . . . . . . . . . . . . . . . . . . 37
2.2 IEC61727 : Permissible PCC voltage and frequency variation . . . . . 38
2.3 PV plant ride through capability . . . . . . . . . . . . . . . . . . . . 45
2.4 PV plant reactive current injection . . . . . . . . . . . . . . . . . . . 46
2.5 Active power reduction during over-frequency . . . . . . . . . . . . . 47
2.6 Solar generation capacity curve . . . . . . . . . . . . . . . . . . . . . 48
2.7 pf(P) characteristic as per voltage support . . . . . . . . . . . . . . . 50
2.8 Q(U) characteristic for voltage support . . . . . . . . . . . . . . . . . 51
3.1 Generic grid integrated PV topology . . . . . . . . . . . . . . . . . . 54
3.2 Equivalent circuit of PV module . . . . . . . . . . . . . . . . . . . . . 55
3.3 Typical PWM strategy for a VSC . . . . . . . . . . . . . . . . . . . . 57
3.4 Converter circuit represented by voltage sources (average model) . . . 58
3.5 Power against voltage or current characteristics. . . . . . . . . . . . . 60
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