Keywords: voltage source converters, high voltage direct current, VSC HVDC, parallel AC lines, H-infinity control, robust control, feedback control, state-space modelling, AC transmission lines, converter control, simulation
H∞ controller for stability enhancement in VSC HVDC system with parallel AC lines
In this paper, a state-space model for a voltage source converter based high voltage direct current (VSC HVDC) transmission link in parallel with an AC transmission line is developed using dq-coordinate system. A robust H∞ control design for the converter and inverter of the VSC HVDC system is proposed to maintain the DC voltage and control the active and reactive power at the converter stations. The H∞ control for the converter control systems is realised using output feedback control obtained by measuring the converter side DC voltage and reactive power, and the inverter side active and reactive power and satisfying the H∞ norm of the closed loop transfer function matrix. Simulation results with a large number of disturbances like torque changes and three-phase short circuits at the converter and inverter buses demonstrate the effectiveness of the designed controller and robustness with respect to the variations of the system operating conditions.