Power electronic converters for microgrid

As concerns about climate change, energy prices, and energy security loom, regulatory and research communities have shown growing interest in alternative energy sources and their integration into distributed energy systems. However, many of the candidate microgeneration and associated storage systems cannot be readily interfaced to the 50/60 Hz grid. In Power Electronic Converters for Microgrids , Sharkh and Abu-Sara introduce the basics and practical concerns of analyzing and designing such micro-generation grid interface systems. Readers will become familiar with methods for stably feeding the larger grid, importing from the grid to charge on-site storage, disconnecting from the grid in case of grid failure, as well as connect multiple microgrids while sharing their loads appropriately. Sharkh and Abu-Sara introduce not only the larger context of the technology, but also present potential future applications, along with detailed case studies and tutorials to help the reader effectively engineer microgrid systems.

Author Notes

S. M. Sharkh is a Senior Lecturer at the School of Engineering Sciences, University of Southampton and the Managing Director of HiT Systems Ltd, which specializes in electromagnetic system analysis and design, control systems and web applications. He has approximately 17 years research experience in electrical and electromagnetic systems, and has been awarded numerous research grants leading to commercialized products in a number of related areas: grid connected PWM inverters, electric machines in harsh environments (high-speed, high temperature, high pressure, corrosive chemicals, submerged in liquids or underwater) PM machines (axial gap dc machines, VRPM transverse flux machines), characterization of and management of lithium ion batteries, sensorless control of PM machines, novel structurally integrated electric machines for marine thrusters and electromagnetic losses in high-speed machines, and microgrid intefaces. Sharkh has lectured on the subject of grid-connected inverters and their control to both undergraduate and postgraduate students, as well as companies. He holds a BEng and PhD in electrical engineering from the University of Southampton.

M. A. Abu-Sara works with Bowman Power Systems, where he is the lead engineer in designing and developing systems for micro-generation. He holds a PhD in Electrical Engineering from the University of Southampton.

About the Authors	p. xi
Preface	p. xiii
Acknowledgments	p. xv
1 Introduction	p. 1
1.1 Modes of Operation of Microgrid Converters	p. 2
1.1.1 Grid Connection Mode	p. 2
1.1.2 Stand-Alone Mode	p. 3
1.1.3 Battery Charging Mode	p. 3
1.2 Converter Topologies	p. 4
1.3 Modulation Strategies	p. 6
1.4 Control and System Issues	p. 7
1.5 Future Challenges and Solutions	p. 9
References	p. 10
2 Converter Topologies	p. 13
2.1 Topologies	p. 13
2.1.1 The Two-Level Converter	p. 13
2.1.2 The NPC Converter	p. 14
2.1.3 The CHB Converter	p. 15
2.2 Pulse Width Modulation Strategies	p. 16
2.2.1 Carrier-Based Strategies	p. 17
2.2.2 SVM Strategies	p. 22
2.3 Modeling	p. 27
References	p. 28
3 DC-Link Capacitor Current and Sizing in NPC and CHB Inverters	p. 29
3.1 Introduction	p. 29
3.2 Inverter DC-Link Capacitor Sizing	p. 30
3.3 Analytical Derivation of DC-Link Capacitor Current RMS Expressions	p. 32
3.3.1 NPC Inverter	p. 33
3.3.2 CHB Inverter	p. 36
3.4 Analytical Derivation of DC-Link Capacitor Current Harmonics	p. 37
3.4.1 NPC Inverter	p. 38
3.4.2 CHB Inverter	p. 39
3.5 Numerical Derivation of DC-Link Capacitor Current RMS Value and Voltage Ripple Amplitude	p. 41
3.6 Simulation Results	p. 42
3.7 Discussion	p. 45
3.7.1 Comparison of Capacitor Size for the NPC and CHB Inverters	p. 45
3.7.2 Comparison of Presented Methods for Analyzing DC-Link Capacitor Current	p. 46
3.7.3 Extension to Higher-Level Inverters	p. 48
3.8 Conclusion	p. 48
References	p. 48
4 Loss Comparison of Two- and Three-Level Inverter Topologies	p. 51
4.1 Introduction	p. 51
4.2 Selection of TGBT-Diode Modules	p. 53
4.3 Switching Losses	p. 54
4.3.1 Switching Losses in the Two-Level Inverters	p. 54
4.3.2 Switching Losses in the NPC Inverter	p. 57
4.3.3 Switching Losses in the CHB Inverter	p. 58
4.4 Conduction Losses	p. 58
4.4.1 Conduction Losses in the Two-Level Inverter	p. 60
4.4.2 Conduction Losses in the NPC Inverter	p. 61
4.4.3 Conduction Losses in the CHB Inverter	p. 63
4.5 DC-Link Capacitor RMS Current	p. 65
4.6 Results	p. 69
4.7 Conclusion	p. 70
References	p. 71
5 Minimization of Low-Frequency Neutral-Point Voltage Oscillations in NPC Converters	p. 73
5.1 Introduction	p. 73
5.2 NPC Converter Modulation Strategies	p. 74
5.3 Minimum NP Ripple Achievable by NV Strategies	p. 77
5.3.1 Locally Averaged NP Current	p. 78
5.3.2 Effect of Switching Constraints	p. 79
5.3.3 Zero-Ripple Region	p. 81
5.3.4 A Lower Boundary for the NP Voltage Ripple	p. 81
5.4 Proposed Band-NV Strategies	p. 83
5.4.1 Criterion Used by Conventional NV Strategies	p. 83
5.4.2 Proposed Criterion	p. 84
5.4.3 Regions of Operation	p. 85
5.4.4 Algorithm	p. 88
5.4.5 Switching Sequences - Conversion to Band-NV	p. 90
5.5 Performance of Band-NV Strategies	p. 91
5.5.1 NP Voltage Ripple	p. 91
5.5.2 Effective Switching Frequency - Output Voltage Hannonic Distortion	p. 93
5.6 Simulation of Band-NV Strategies	p. 94
5.7 Hybrid Modulation Strategies	p. 100
5.7.1 Proposed Hybrid Strategies	p. 101
5.7.2 Simulation Results	p. 102
5.8 Conclusions	p. 106
References	p. 107
6 Digital Control of a Three-Phase Two-Level Grid-Connected Inverter	p. 109
6.1 Introduction	p. 109
6.2 Control Strategy	p. 112
6.3 Digital Sampling Strategy	p. 113
6.4 Effect of Time Delay on Stability	p. 115
6.5 Capacitor Current Observer	p. 116
6.6 Design of Feedback Controllers	p. 119
6.7 Simulation Results	p. 121
6.8 Experimental Results	p. 123
6.9 Conclusions	p. 127
References	p. 128
7 Design and Control of a Grid-Connected Interleaved Inverter	p. 131
7.1 Introduction	p. 131
7.2 Ripple Cancellation	p. 135
7.3 Hardware Design	p. 137
7.3.1 Hardware Design Guidelines	p. 138
7.3.2 Application of the Design Guidelines	p. 145
7.4 Controller Structure	p. 146
7.5 System Analysis	p. 149
7.5.1 Effect of Passive Damping and Grid Impedance	p. 151
7.5.2 Effect of Computational Time Delay	p. 151
7.5.3 Grid Disturbance Rejection	p. 154
7.6 Controller Design	p. 154
7.7 Simulation and Practical Results	p. 158
7.8 Conclusions	p. 167
References	p. 167
8 Repetitive Current Control of an Interleaved Grid-Connected Inverter	p. 171
8.1 Introduction	p. 171
8.2 Proposed Controller and System Modeling	p. 172
8.3 System Analysis and Controller Design	p. 175
8.4 Simulation Results	p. 178
8.5 Experimental Results	p. 179
8.6 Conclusions	p. 182
References	p. 182
9 Line Interactive UPS	p. 185
9.1 Introduction	p. 185
9.2 System Overview	p. 188
9.3 Core Controller	p. 192
9.3.1 Virtual Impedance and Grid Harmonics Rejection	p. 193
9.4 Power Flow Controller	p. 195
9.4.1 Drooping Control Equations	p. 195
9.4.2 Small Signal Analysis	p. 196
9.4.3 Stability Analysis and Drooping Coefficients Selection	p. 200
9.5 DC Link Voltage Controller	p. 206
9.6 Experimental Results	p. 209
9.7 Conclusions	p. 217
References	p. 218
10 Microgrid Protection	p. 221
10.1 Introduction	p. 221
10.2 Key Protection Challenges	p. 221
10.2.1 Fault Current Level Modification	p. 221
10.2.2 Device Discrimination	p. 223
10.2.3 Reduction in Reach of Impedance Relays	p. 223
10.2.4 Bidirectionality and Voltage Profile Change	p. 224
10.2.5 Sympathetic Tripping	p. 224
10.2.6 Islanding	p. 224
10.2.7 Effect on Feeder Reclosure	p. 224
10.3 Possible Solutions to Key Protection Challenges	p. 225
10.3.1 Possible Solutions to Key Protection Challenges for an Islanded Microgrid Having IIDG Units	p. 225
10.4 Case Study	p. 229
10.4.1 Fault Level Modification	p. 231
10.4.2 Blinding of Protection	p. 232
10.4.3 Sympathetic Tripping	p. 233
10.4.4 Reduction in Reach of Distance Relay	p. 233
10.4.5 Discussion	p. 234
10.5 Conclusions	p. 235
References	p. 236
11 An Adaptive Relaying Scheme for Fuse Saving	p. 239
11.1 Introduction	p. 239
11.1.1 Preventive Solutions Proposed in the Literature	p. 240
11.1.2 Remedial Solutions Proposed in the Literature	p. 241
11.1.3 Contributions of the Chapter	p. 242
11.2 Case Study	p. 242
11.3 Simulation Results and Discussion	p. 245
11.4 Fuse Saving Strategy	p. 247
11.4.1 Options and Considerations for the Selection of lockup of the Element	p. 249
11.4.2 Adaptive Algorithm	p. 251
11.5 How Reclosing Will Be Applied	p. 252
11.6 Observations	p. 255
11.7 Conclusions	p. 257
References	p. 257
Appendix A SVM for the NPC Converter-MATLAB®-Simulink Models	p. 261
A.1 Calculation of Duty Cycles for Nearest Space Vectors	p. 261
A.2 Symmetric Modulation Strategy	p. 262
A.3 MATLAB®-Simulink Models	p. 263
References	p. 279
Appendix B DC-Link Capacitor Current Numerical Calculation	p. 281
Index	p. 285

Available:*

On Order

Summary

Summary

Author Notes

Table of Contents