Planning en Beheer van Bipolaire HVDC Netwerken: Vermogensstroom en optimale vermogensmodellen voor ongebalanceerde werking

The ongoing shift towards sustainable energy solutions underscores the necessity for advanced electric power transmission technologies. High Voltage Direct Current (HVDC) is emerging as a pivotal component in future power systems. The development of multi-terminal and meshed HVDC networks, referred to as HVDC grids, is expected to enhance both the economic efficiency and security of power supply. With recent advancements in Voltage Source Converter (VSC) HVDC technology and DC protection, HVDC grids have emerged as a viable option. Therefore, research on the HVDC grid has evolved significantly in the last two decades. However, significant challenges remain to be addressed in the planning and operation of HVDC grids. The design of HVDC systems has evolved to have various configurations, i.e., symmetric and asymmetric monopolar, and bipolar configurations. A bipolar HVDC configuration is considered more economical and reliable due to its capability to operate at half of the rated capacity during single pole or conductor outages. However, such reduced capacity operation in bipolar converter stations or DC grid networks results in unbalanced operation. Therefore, it is crucial to study the economic and operational security implications of the unbalanced HVDC grid operation. Since existing models and tools for planning and operation predominantly focus on balanced HVDC grids, further research is required to analyze and understand the unbalanced operation. To address this research gap, this thesis presents a comprehensive multiconductor model for DC grids. The model separately represents the positive and negative poles of bipolar converter stations and includes detailed representations of each conductor, including metallic return paths. The multiconductor model of DC grids is further integrated into Optimal Power Flow (OPF), Power Flow (PF), and Security Constrained Optimal Power Flow (SCOPF) problems for the steady-state analysis of power systems. The OPF model demonstrates the economic operation of HVDC grids under unbalanced conditions while adhering to component constraints. The PF model incorporates various converter control modes and enables an assessment of the system's operating state during normal operation as well as contingencies. The SCOPF model includes single pole outages in security-constrained operation. The findings of this thesis reveal that unbalanced operation can significantly enhance the economic efficiency and operational security of bipolar HVDC grids, leveraging the controllability of VSC HVDC technology. In summary, this thesis advances the understanding of bipolar HVDC grids by developing power flow and optimal power flow models for planning and operation. The models and tools developed herein enable steady-state analysis of unbalanced HVDC grids, thereby removing barriers to unbalanced operation for enhancing the economy and security of supply in future power systems.