Modular Multilevel Converter Modelling and Simulation for HVDC Systems : State of the Art and a Novel Approach

This book provides a comprehensive review of the models and approaches that can be employed to simulate modular multilevel converters (MMCs). Each solution is described in terms of operating principle, fields of applicability, advantages, and limitations. In addition, this work proposes a novel and efficient simulation approach for MMCs based on sub-circuit isomorphism. This technique, which has its roots in the electronics fields, can be profitably exploited to simulate MMCs regardless of the model used to describe its sub-modules, including the most accurate ones. Lastly, this book considers a well-known high voltage direct current (HVDC) benchmark system consisting of two MMCs. After describing the implementation details of each benchmark component, simulation results in several scenarios (ranging from normal operating conditions to faults in the AC and DC grid) are included to validate the proposed approach and showcase its key features. Due to its educational content, this book constitutes a useful guide for PhD students and researchers interested in the topic of MMCs and their simulation. It also serves as a starting platform for junior electrical engineers who work in the field of power electronic converters for HVDC systems. Preface 6 Contents 8 1 Introduction 10 1.1 Challenges of Renewables in Electric Power Systems 12 1.1.1 Distributed Energy Resources 14 1.1.2 Concentrated Energy Resources and the Role of hvdc systems 15 1.2 Rationale of the Book 16 1.3 Notation 18 References 18 2 Modular Multilevel Converters: Key Features, Control Strategies and Main Challenges 20 2.1 Converter Technologies for High Voltage and Power Applications 20 2.1.1 Two-Level Voltage Source Converters 21 2.1.2 Diode Clamped Converters 23 2.1.3 Active Neutral Point Clamped Converters 26 2.1.4 Flying Capacitor Converters 28 2.1.5 Cascaded H-bridge Converters 29 2.2 Modular Multilevel Converters 30 2.3 The mmc Control Strategy 37 2.3.1 Park Transformation 38 2.3.2 Phase-Locked Loop pll 41 2.3.3 Upper Level Controls 42 2.3.4 Lower Level Controls 46 2.3.5 Protections 51 2.4 Challenges 52 2.4.1 Power Flow 52 2.4.2 Initialization 53 2.4.3 Stability Analysis 54 2.4.4 Electromagnetic Transient Simulation 55 References 56 3 Modular Multilevel Converter Models and Simulation Approaches 60 3.1 Literature Review of mmc Models for Transient Simulations 61 3.1.1 Full Physics (fp) Model 63 3.1.2 Full Detailed (fd) Model 64 3.1.3 Bi-value Resistor (bvr) Model 65 3.1.4 Thévenin Equivalent Model (tem) 66 3.1.5 Switching Function Model (sfm) 72 3.1.6 Average Value Model (avm) 77 3.2 Isomorphism-Based Simulation Techniques 80 3.2.1 Principles of Isomorphism 82 3.2.2 Isomorphic Simulation of mmc 84 3.2.3 Main Features and Fields of Application of the Isomorphism-Based Simulation of mmcs 89 References 91 4 Validation of the Isomorphism-Based Approach 94 4.1 Simulation Setting 94 4.1.1 ac Grids and Transformers 94 4.1.2 dc Line 96 4.1.3 mmc Parameters 103 4.1.4 Details Concerning Full-Physics, Full-Detailed, and Bi-value Resistor Submodule Models 104 4.1.5 Simulated Scenarios 107 4.2 Simulation Results 108 4.2.1 Analysis of Simulation Accuracy 108 4.2.2 Analysis of Submodules Variables 114 4.2.3 Analysis of Simulation Speed 116 References 123 5 Conclusion 125