Robust nonlinear control strategy for HVDC light transmission systems technology

In this study, two robust nonlinear control strategies are investigated to control the HVDC Light™ transmission systems. The controller’s design are based on the Sliding Mode Control (SMC) and Lyapunov’s control methodologies to deal with the nonlinearities introduced by requirements to power flow and line voltage. First, the steady state mathematical model of the HVDC Light system is developed and the decoupled relationship between the controlling variables is investigated. Then, the SMC and Lyapunov control techniques are resorted to govern the DC link voltage and to control the active and reactive powers. The main feature of this hypothesis is the robustness with respect to parameters’ variations. Saturation, sigmoid and hyperbolic functions are used to avoid the issue of “chattering” caused by imperfect switching in the SMC. Based on Lyapunov method, the controller guaranteeing convergence of the state trajectory is developed. The robust nonlinear controllers are demonstrated through simulation studies on HVDC Light transmission systems using MATLAB©-Simulink software. Dealing with systems of high power ratings up to 300 MW, the simulation results show that the controllers contribute significantly toward improving the dynamic behaviour, enhancing the system stability and damping the oscillations over a wide range of operating conditions and parameters uncertainties.