ENHANCED GRID-FORMING MODULAR MULTILEVEL CONVERTER CONTROL STRATEGIES FOR OPTIMAL POWER FLOW IN HIGH VOLTAGE DIRECT CURRENT (HVDC) POWER SYSTEMS

Date

2024-9

Author

Pierre, Twizeyimana

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This thesis presents an in-depth study of enhanced control strategies for Modular Multilevel Converters (MMC) applied to HVDC systems, with a major focus on optimizing power flow through integration of droop control technology with OPF formulation model. This research covers the evolution of power converters, modulation techniques, modeling and control strategies with the focus on the definitional grid forming and grid following inverters. Different methods of modulation technologies have been studied and discussed like Level Shifted PWM (LS-PWM), Phase Shifted PWM (PS-PWM), and Nearest Level Modulation (NLM) in conjunction with Third Harmonic Injection (THI) for getting better and enhanced energy transmission capabilities for modern power systems. The research model the integration of either LSPWM or NLM with droop control, and OPF to maintain the limit of the MMC’s power flow, transmission line limits, system security, and enhance the optimal power flow while minimizing the cost of the system. The effectiveness of these control strategies is verified mathematically and through Matlab/Simulink simulation results including the circulating current calculations, harmonic levels, capacitor voltage regulation and dynamic behavior under different conditions. Also, it highlights the benefits and possible drawbacks concerning the stability problems due to the application of OPF for setting inverter control points. The findings contribute to the ongoing development of GFM- MMCs as a key technology for modern energy transmission networks, offering insights into their potential for maximizing power transmission efficiency while maintaining system stability. Furthermore, future research could involve developing state-space equations for both LSPWM and NLM-based GFL and GFM-MMCs to analyze eigenvalues and optimize system design. This would facilitate the enhancement of modern controller designs in power transmission, leading to more optimized and resilient power systems.

Subject Keywords

Grid-Forming and Following Converters, Modular Multilevel Converters, Droop Control, Optimal Power Flow, HVDC system

URI

https://hdl.handle.net/11511/111600

Collections

Northern Cyprus Campus, Thesis