Intelligent techniques for optimization of multiple controllers for VSC-HVDC transmission system

This thesis investigates a novel approach of using Particle Swarm Optimization (PSO) and Harmony Search (HS) techniques in the design of robust controllers for Voltage Source Converter based High Voltage Direct Current (VSC-HVDC) systems.;Two design problems are examined. The first problem considers the stabilization and optimization of VSC-HVDC systems controllers for a single operating point. The second problem considers stabilizing the controllers over a wide range of operating conditions in order to achieve robustness. Using MATLAB as the main platform, a linear VSC transmission model based on previous research was developed. The linear model is a small-signal dynamic linear-continuous model that was previously used for dynamic studies and generic controller design. State-space domain was used to represent all components of the complex model.;Three different eigenvalue-based design cases were investigated for the stabilization and optimization of the linear VSC model controllers' parameters. The first case considers stabilizing the controllers by shifting all eigenvalues of the system to the left of the imaginary axis. In addition to stabilizing of the system, the second case considers limiting the overshoot of the system responses by placing the eigenvalues in a wedge-shape region in the left complex s-plane. The third case investigates the improvement of settling time as well as limiting the overshoot by placing the eigenvalues in a D-shape region in the left complex s-plane.;The design cases were converted to objective functions solved by PSO and HS. Eigenvalue analysis, simulations results and performance indices that reflect the overshoot and settling time of the system responses were used to assess the effectiveness of the designed controllers. The eigenvalue analysis confirmed that the PSO-based controllers and HS-based controllers placed the eigenvalues in the desired distinctive locations in each of the three cases. The simulation results and the performance indices showed that the controllers designed in case 3 give the best system responses in terms of overshoots, settling time and oscillations.;The design of robust controllers was accomplished using an approach that simultaneously places the eigenvalues of system that represent different operating points to the left of the imaginary axis. The design took into consideration multiple operating points where different elements of the system such as the capacitors, inductors, resistors, and magnitude of power transmitted were varied. The designed controllers were tested through means of eigenvalue analysis and simulation and it was found that it successfully stabilize the system for the range of operating points considered. Finally, areas for further research on this topic are suggested.