SYNCHRONIZING AND STABILIZATION OF WEAK GRIDS WITH VSC AND NONLINEAR POWER DAMPING CONTROL

This paper presents a new methodology for a weak grid is to make possible the addition of voltage source converters more effective. The controller is mainly composed of two parts, namely linear power damping and synchronizing controller and a supplementary nonlinear controller. The first part synchronizes a voltage source converter (VSC) to the grid by supplying damping and synchronizing power components automatically and injects full power under very weak grid conditions. The frequency and angle regulation of the linear controller are choosen from the cascaded angle, frequency and power loops. Inspite of stable and smooth operation of linear controller in various cases, the stability of the weak grids cannot be guaranteed under sudden large transients which quickly transfers system dynamics to nonlinear region. In order to succeed this problem, the second part i.e the supplementary nonlinear controller is designed along with the linear controller to intensify the performance of the system under certain large disturbances such as low power and high power injection, self -synchronization and fault- ride-through conditions in weak grids. Simulation results of the proposed controller were carried out in MATLAB/SIMULINK environment. Simulation results prove that the proposed nonlinear controller improves the performance of the system under abnormal disturbances and shows the effective working of the controller. By replacing the dc source of the controller with a photovoltaic system, improved profiles are obtained and the cost of operation of the entire system is reduced than before which are to be observed from the simulation results of the replaced controller.