Modeling and Modern Control of Wind Power
Description
This book covers the modeling of wind power and application of modern control methods to the wind power control--specifically the models of type 3 and type 4 wind turbines. The modeling aspects will help readers to streamline the wind turbine and wind power plant modeling, and reduce the burden of power system simulations to investigate the impact of wind power on power systems. The use of modern control methods will help technology development, especially from the perspective of manufactures.
Chapter coverage includes: status of wind power development, grid code requirements for wind power integration; modeling and control of doubly fed induction generator (DFIG) wind turbine generator (WTG); optimal control strategy for load reduction of full scale converter (FSC) WTG; clustering based WTG model linearization; adaptive control of wind turbines for maximum power point tracking (MPPT); distributed model predictive active power control of wind power plants and energy storage systems; model predictive voltage control of wind power plants; control of wind power plant clusters; and fault ride-through capability enhancement of VSC HVDC connected offshore wind power plants. Modeling and Modern Control of Wind Power also features tables, illustrations, case studies, and an appendix showing a selection of typical test systems and the code of adaptive and distributed model predictive control.
* Analyzes the developments in control methods for wind turbines (focusing on type 3 and type 4 wind turbines)
* Provides an overview of the latest changes in grid code requirements for wind power integration
* Reviews the operation characteristics of the FSC and DFIG WTG
* Presents production efficiency improvement of WTG under uncertainties and disturbances with adaptive control
* Deals with model predictive active and reactive power control of wind power plants
* Describes enhanced control of VSC HVDC connected offshore wind power plants
Modeling and Modern Control of Wind Power is ideal for PhD students and researchers studying the field, but is also highly beneficial to engineers and transmission system operators (TSOs), wind turbine manufacturers, and consulting companies.
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Edited by
Qiuwei Wu, PhD, is an Associate Professor at the Technical University of Denmark (DTU). His research areas include wind power integration and wind turbine modeling, the standard modeling of wind power, VSC HVDC connection for offshore wind power integration, coordinated control of wind power and energy storage systems.
Yuanzhang Sun, PhD, is a Full Professor at Wuhan University, Hubei Province, China. His research interests are power system stability and control, operational reliability of power systems, smart grid, and renewable energy.
Content
List of Contributors xi
About the CompanionWebsite xiii
1 Status of Wind Power Technologies 1
Haoran Zhao and Qiuwei Wu
1.1 Wind Power Development 1
1.2 Wind Turbine Generator Technology 4
1.2.1 Type 1 4
1.2.2 Type 2 5
1.2.3 Type 3 5
1.2.4 Type 4 6
1.2.5 Comparison 7
1.2.6 Challenges withWind Power Integration 7
1.3 Conclusion 9
References 9
2 Grid Code Requirements for Wind Power Integration 11
Qiuwei Wu
2.1 Introduction 11
2.2 Steady-state Operational Requirements 12
2.2.1 Reactive Power and Power Factor Requirements 12
2.2.2 Continuous Voltage Operating Range 17
2.2.3 Frequency Operating Range and Frequency Response 18
2.2.4 Power Quality 24
2.3 Low-voltage Ride Through Requirement 26
2.3.1 LVRT Requirement in the UK 26
2.3.2 LVRT Requirement in Ireland 29
2.3.3 LVRT Requirement in Germany (Tennet TSO GmbH) 30
2.3.4 LVRT Requirement in Denmark 31
2.3.5 LVRT Requirement in Spain 31
2.3.6 LVRT Requirement in Sweden 32
2.3.7 LVRT Requirement in the USA 33
2.3.8 LVRT Requirement in Quebec and Alberta 34
2.4 Conclusion 36
References 36
3 Control of Doubly-fed Induction Generators for Wind Turbines 37
Guojie Li and Lijun Hang
3.1 Introduction 37
3.2 Principles of Doubly-fed Induction Generator 37
3.3 PQ Control of Doubly-fed Induction Generator 40
3.3.1 Grid-side Converter 41
3.3.2 Rotor-side converter 43
3.4 Direct Torque Control of Doubly-fed Induction Generators 46
3.4.1 Features of Direct Torque Control 47
3.4.2 Application of Direct Torque Control in DFIGs 49
3.4.3 Principle of Direct Torque Control in DFIG 50
3.5 Low-voltage Ride Through of DFIGs 58
3.6 Conclusions 61
References 61
4 Optimal Control Strategies of Wind Turbines for Load Reduction 63
Shuju Hu and Bin Song
4.1 Introduction 63
4.2 The Dynamic Model of aWind Turbine 64
4.2.1 Wind Conditions Model 64
4.2.2 Aerodynamic Model 64
4.2.3 Tower Model 66
4.2.4 DrivetrainModel 66
4.2.5 Electrical Control Model 67
4.2.6 Wind Turbine DynamicModel 67
4.3 Wind Turbine Individual Pitch Control 67
4.3.1 Control Implementation 68
4.3.2 Linearization of theWind Turbine Model 68
4.3.3 Controller Design 71
4.3.4 Simulation Analysis 73
4.4 Drivetrain Torsional Vibration Control 73
4.4.1 LQG Controller Design 73
4.4.2 Simulation Analysis 79
4.5 Conclusion 83
References 83
5 Modeling of Full-scale Converter Wind Turbine Generator 85
Yongning Chi, Chao Liu, Xinshou Tian, Lei Shi, and Haiyan Tang
5.1 Introduction 85
5.2 Operating Characteristics of FSC-WTGs 88
5.3 FSC-WTG Model 89
5.3.1 Shaft Model 89
5.3.2 Generator Model 91
5.3.3 Full-scale Converter Model 94
5.4 Full Scale Converter Control System 96
5.4.1 Control System of Generator-side Converter 97
5.4.2 Grid-side Converter Control System 101
5.5 Grid-connected FSC-WTG Stability Control 107
5.5.1 Transient Voltage Control of Grid-side Converter 108
5.5.2 Additional DC Voltage Coupling Controller 108
5.5.3 Simulations 109
5.6 Conclusion 114
References 114
6 Clustering-based Wind Turbine Generator Model Linearization 117
Haoran Zhao and Qiuwei Wu
6.1 Introduction 117
6.2 Operational Regions of Power-controlledWind Turbines 118
6.3 SimplifiedWind Turbine Model 119
6.3.1 Aerodynamics 119
6.3.2 Drivetrain 120
6.3.3 Generator 120
6.3.4 Tower 121
6.3.5 Pitch Actuator 121
6.4 Clustering-based IdentificationMethod 122
6.5 Discrete-time PWA Modeling ofWind Turbines 123
6.5.1 Identification of Aerodynamic Torque Ta 123
6.5.2 Identification of Generator Torque Tg 123
6.5.3 Identification of Thrust Force Ft 124
6.5.4 Identification of Correction Factor Kc 125
6.5.5 Formulation of A' d and B' d 126
6.5.6 Region Construction through Intersection 126
6.5.7 PWA Model of aWind Turbine 126
6.6 Case Study 127
6.6.1 LowWind Speed Case 128
6.6.2 HighWind Speed Case 129
6.7 Conclusion 131
References 131
7 Adaptive Control of Wind Turbines for Maximum Power Point Tracking 133
Haoran Zhao and Qiuwei Wu
7.1 Introduction 133
7.1.1 Hill-climbing Search Control 134
7.1.2 Power Signal Feedback Control 135
7.1.3 Tip-speed Ratio Control 135
7.2 Generator Control System forWECSs 135
7.2.1 Speed Reference Calculation 136
7.2.2 Generator Torque Control 138
7.2.3 Speed Control 139
7.3 Design of óD1 Adaptive Controller 140
7.3.1 Problem Formulation 140
7.3.2 Architecture of the óD1 Adaptive Controller 140
7.3.3 Closed-loop Reference System 142
7.3.4 Design of óD1 Adaptive Controller Parameters 142
7.4 Case Study 144
7.4.1 Wind Speed Estimation 144
7.4.2 MPPT Performance 144
7.5 Conclusion 147
References 148
8 Distributed Model Predictive Active Power Control of Wind Farms 151
Haoran Zhao and Qiuwei Wu
8.1 Introduction 151
8.2 Wind Farm without Energy Storage 152
8.2.1 Wind Farm Control Structure 152
8.2.2 Load Evaluation of theWind Turbine 154
8.2.3 MPC Problem Formulation 154
8.2.4 Standard QP Problem 156
8.2.5 Parallel Generalized Fast Dual Gradient Method 158
8.3 Wind Farm Equipped with Energy Storage 160
8.3.1 Wind Farm Control Structure 160
8.3.2 Modelling of ESS Unit 161
8.3.3 MPC Problem Formulation 162
8.4 Case Study 163
8.4.1 Wind Farm Control based on D-MPC without ESS 163
8.4.2 Wind Farm Control based on D-MPC with ESS 166
8.5 Conclusion 171
References 172
9 Model Predictive Voltage Control ofWind Power Plants 175
Haoran Zhao and Qiuwei Wu
9.1 Introduction 175
9.2 MPC-basedWFVC 176
9.3 Sensitivity Coefficient Calculation 178
9.3.1 Voltage Sensitivity to Reactive Power 178
9.3.2 Voltage Sensitivity to Tap Position 179
9.4 Modeling ofWTGs and SVCs/SVGs 180
9.4.1 WTG Modeling 180
9.4.2 SVC/SVG Modeling 181
9.4.3 General Composite Model 182
9.5 Coordination with OLTC 183
9.6 Formulation of MPC Problem forWFVC 184
9.6.1 Corrective Voltage Control Mode 184
9.6.2 Preventive Voltage Control Mode 186
9.7 Case Study 186
9.7.1 Scenario 1: Normal Operation 187
9.7.2 Scenario 2: Operation with Disturbances 187
9.8 Conclusion 190
References 191
10 Control of Wind Farm Clusters 193
Yan Li, Ningbo Wang, Linjun Wei, and Qiang Zhou
10.1 Introduction 193
10.2 Active Power and Frequency Control of Wind Farm Clusters 194
10.2.1 Active Power Control Mode of Wind Farms 194
10.2.2 Active Power Control Strategy of Wind Farm Cluster 198
10.2.3 AGC of Wind Farm Cluster 200
10.3 Reactive Power and Voltage Control of Wind Farms 200
10.3.1 Impact of Wind Farm on Reactive Power Margin of the System 200
10.3.2 Reactive Voltage Control Measures for Wind Farms 202
10.3.3 Reactive Voltage Control Strategy of Wind Farm Cluster 208
10.3.4 Wind Farm AVC Design Scheme 210
10.4 Conclusion 213
References 213
11 Fault Ride Through Enhancement of VSC-HVDC Connected Offshore Wind Power Plants 215
Ranjan Sharma, Qiuwei Wu, Kim Høj Jensen, Tony Wederberg Rasmussen, and Jacob Østergaard
11.1 Introduction 215
11.2 Modeling and Control of VSC-HVDC-connected Offshore WPPs 216
11.2.1 Modeling of VSC-HVDC-connected WPP with External Grid 217
11.2.2 Modeling of VSC-HVDC-connected WPP 217
11.2.3 Control of WPP-side VSC 220
11.3 Feedforward DC Voltage Control based FRT Technique for VSC-HVDC-connected WPP 222
11.4 Time-domain Simulation of FRT for VSC-HVDC-connected WPPs 223
11.4.1 Test System for Case Studies 224
11.4.2 Case Study 224
11.5 Conclusions 229
References 230
12 Power Oscillation Damping from VSC-HVDC-connected Offshore Wind Power Plants 233
Lorenzo Zeni
12.1 Introduction 233
12.1.1 HVDC Connection of Offshore WPPs 233
12.1.2 Power Oscillation Damping from Power Electronic Sources 234
12.2 Modelling for Simulation 235
12.2.1 HVDC System 235
12.2.2 Wind Power Plant 237
12.2.3 Power System 238
12.3 POD from Power Electronic Sources 238
12.3.1 Study Case 238
12.3.2 POD Controller 241
12.3.3 Practical Considerations for Parameter Tuning 241
12.4 Implementation on VSC-HVDC-connected WPPs 245
12.4.1 Realization of POD Control 245
12.4.2 Demonstration on Study Case 246
12.4.3 Practical Considerations on Limiting Factors 248
12.5 Conclusion 254
Acknowledgement 254
References 254
Index 257
Chapter 1
Status of Wind Power Technologies
Haoran Zhao and Qiuwei Wu
Technical University of Denmark
1.1 Wind Power Development
Although wind power has been utilized by humans for more than 3000 years, the history of wind power for electricity production is only 120 years long.
In July 1887, Professor James Blyth (1839-1906) of Anderson's College, Glasgow built the first windmill for the production of electricity at Marykirk in Kincardineshire, Scotland [1]. The windmill was 10 m high, and was used to charge accumulators to power the lighting in the cottage. Around the same period, a wind turbine was designed and constructed in the winter of 1887-1888 by Charles F. Brush (1849-1929) in Cleveland, USA [2]. The rotor of Brush's wind turbine was 17 m in diameter and had 144 blades. The rated power was 12 kW. It was used either to charge a bank of batteries or to operate up to 100 incandescent light bulbs and various motors in Brush's laboratory.
A pioneer of modern aerodynamics, Poul la Cour (1846-1908) of Askov, Denmark, built the world's first wind tunnels for the purpose of aerodynamic tests to identify the best shape of the blades for turbines. Based on his experiments, he realized that wind turbines with fewer rotor blades were more efficient for electricity production. He designed the first four-blade wind turbine in 1891 [3].
The developments in the 20th century can be divided into two periods. From 1900-1973, the prices of wind-powered electricity were not competitive. The gradual extension of electrical networks and the availability of low-cost fossil fuels lead to the abandonment of wind turbines. Wind turbine generators (WTGs) were mainly used in rural and remote areas. Although several wind turbines in the hundred-kilowatt class were manufactured and installed for testing, due to high capital costs and reliability problems, they were not widely adopted.
The two oil crises in 1973 and 1979, with supply problems and price fluctuations for fossil fuels, spurred the adoption of non-petroleum energy sources. As an alternative to fossil fuels, wind power was once again put on the agenda. European countries and US government started to invest in research into large commercial wind turbines. The world's first multi-megawatt wind turbine was constructed in 1978, and pioneered many technologies now used in modern wind turbines. From 1975 through to the mid-1980s, NASA developed 3.2 MW and 4 MW wind turbines. Although they were sold commercially, none of these were ever put into mass production. When oil prices declined, electricity generated by wind power became uneconomical and many manufacturers left the business.
At the beginning of the 21st century, although fossil fuels were still relatively cheap, concerns over energy security, global warming, and eventual fossil fuel depletion increased, and this led to an expansion of interest in renewable energy. The wind power industry has since achieved rapid development.
From the point of view of global capacity, according to statistics from the Global Wind Energy Council (GWEC), the global annual and cumulative installed wind capacities for the past ten years are as illustrated in Figures 1.1 and 1.2, respectively. In 2015, the global wind power industry installed 63.5 GW of capacity, representing annual market growth of 22%. By the end of 2015, the total installed capacity reached 432.4 GW, representing cumulative market growth of 17%. As estimated by International Energy Agency (IEA), that figure will reach 2016 GW by 2050, representing 12% of global electricity usage [5].
Figure 1.1 Global annual installed wind capacity 2005-2015 [4].
Figure 1.2 Global cumulative installed wind capacity 2005-2015 [4].
From the point of view of development in each country, more than 83 countries around the world were using wind power on a commercial basis by 2010. The top ten countries in terms of 2015-installed and cumulative wind power capacities at 2015 are illustrated in Figures 1.3 and 1.4, respectively. More than half of all new installed wind power was added outside the traditional markets of Europe and North America. Asia has been the world's largest regional market for new wind power development, with capacity additions of 33.9 GW. China maintained its leadership position. China accounted for nearly half of the installations (48.4%) and its total wind power reached 145.1 GW.
Figure 1.3 Newly installed capacity during 2015 [4].
Figure 1.4 Cumulative capacities at 2015 [4].
In many countries, relatively high levels of wind power penetration have been achieved. Figure 1.5 presents the estimated wind power penetration in leading wind markets [6]. The installed capacity is estimated to supply around 40% of Denmark's electricity demand, and between 20% to 30% in Portugal, Ireland, and Spain, respectively. Denmark has a even more ambitious target of 50% by 2020. In the United States, 5.6% of the nation's electricity demand is estimated to be covered by the wind power. On a global basis, the contribution of wind power is estimated to be around 4.3% [6].
Figure 1.5 Wind power penetration in leading wind markets in 20142015 [6].
1.2 Wind Turbine Generator Technology
As at 2015, the largest wind turbine is the 8 MW capacity Vestas V164, for offshore use. By 2014, over 240,000 commercial-sized wind turbines were operating in the world, and these met 4% of the world's electricity demand. WTG-based wind energy conversion systems (WECS) can be divided into the following four main types [7, 8].
1.2.1 Type 1
Type 1 generators are directly grid-connected induction generators (IGs) with fixed rotor resistance. An example is the squirrel cage induction generator (SCIG). As illustrated in Figure 1.6, the wind turbine rotor (WTR) is connected to the IG via a gearbox (GB). Most Type 1 WTGs are equipped with mechanically switched capacitor (MSC) banks, which provide reactive power compensation. As the protection device, the main circuit breaker (CB) disconnects the generator and capacitor from the grid in the event of a fault. Through a step-up transformer (TR), the WTG is connected to the grid.
Figure 1.6 Structure of Type 1 WTG [8]. Refer to main text for explanation of acronyms.
Because of the direct connection to the grid, the IG operates at its natural mechanical characteristic, with an accentuated slope (corresponding to a small slip, normally 1-2%) from the rotor resistance [7]. The rotational speed of the IG is close to the synchronous speed imposed by grid frequency, and is not affected significantly by wind variation.
1.2.2 Type 2
Type 2 generators are directly grid-connected IGs with variable rotor resistance (VRR).
Figure 1.7 illustrates the general structure of a Type 2 WTG. As an evolution of Type 1 WTGs, using regulation through power electronics, the total (internal plus external) rotor resistance is adjustable. In this way, the slip of the generator can be controlled, which affects the slope of the mechanical characteristic. The range of dynamic speed variation is decided by the additional resistance. Usually, the control range is up to 10% over the synchronous speed.
Figure 1.7 Structure of Type 2 WTG [8]. Refer to main text for explanation of acronyms.
1.2.3 Type 3
Type 3 generators are double-fed induction generators (DFIGs). As illustrated in Figure 1.8, the DFIG is an induction generator with the stator windings connected directly to the three-phase, constant-frequency grid and the rotor windings connected to back-to-back voltage source converters (VSCs), including a rotor-side converter (RSC) and grid-side converter (GSC) [9]. They are decoupled with a direct current (DC) link. Conventionally, the RSC controls the generator to regulate the active and reactive power, while the GSC controls the DC-link voltage to ensure DC voltage stability.
Figure 1.8 Structure of Type 3 WTG [8]. Refer to main text for explanation of acronyms.
The power flow of the stator is always from wind turbine to grid. However, the power flow of the rotor is dependent on the operating point:
- If the slip is negative (over-synchronous operation), it feeds power into the grid.
- If the slip is positive (sub-synchronous operation), it absorbs power from the grid.
In both cases, the power flow in the rotor is approximately proportional to the slip. By regulation of the generator behaviour through the GSC controller, the rotation speed is allowed to operate over a larger, but still restricted range (normally 40%).
1.2.4 Type 4
Type 4 WTGs have the wind turbine connected fully through a power converter. Figure 1.9 shows the general structure of Type 4 WTG. The generator type can be either an induction generator or a synchronous generator. Furthermore, the synchronous generator can be either a wound-rotor synchronous generator (WRSG) or a permanent-magnet synchronous generator (PMSG). Currently, the latter is widely used by the wind turbine industry. The back-to-back VSC configuration is used. The RSC ensures the rotational speed is adjusted within a large range, whereas the GSC transfers the active power to the grid and attempts to cancel the reactive power...
