The VSC-HVDC can enhance the performance of power systems and plays a major role in the dynamic stability of power systems. In addition VSC-HVDC controller can be utilized to mitigate torsional torque and prevent sub-synchronous resonance (SSR) effectively. In this paper a controller has been designed for VSC-HVDC to suppress sub-synchronous oscillations. The Control methodology that is employed as sub-synchronous damping controller is based on implemented direct power control (DPC). Reducing SSR and increasing dynamic stability of power system including VSC-HVDC are discussed through simulations. Digital simulation has been carried out via MATLAB software to analyze torsional torque of turbine generator shaft and rotor speed in the case system which consists of VSC-HVDC and series compensated line.

A two-level optimization method is presented to find the optimal number and location of conventional protective devices to be upgraded to remote-controlled switches (RCSs) for an existing distribution network (DN). The effect of distributed generation (DG) on this problem is considered. In the first level, a nonlinear binary program is proposed to maximize the restored customers subject to technical and topological constraints. All feasible interchanges between protective devices and ties involved in the restoration, when a fault occurs at all possible locations are found considering switching dependencies. In the second level, a nonlinear cost function, combining the expected cost of interruptions (ECOST) and the switch cost, is minimized with respect to the location of RCSs. The expected cost function is computed based on the optimum restoration policies obtained from the first level. The optimum placement of RCSs using the proposed algorithm is tested on a 4-feeder 1069-node test system and compared to the solution obtained with a genetic algorithm (GA) on the same system.

Study of the buck converter and cascaded system considering the voltage mode controller has been done. First the small signal analysis of a buck dc/dc converter is presented and its mathematical representation has been showed. Then, the cascaded converter model regarding close loop impedances and voltage gain has been studied. The controller for this converter is proposed to stabilize the performance of the plant. The effectiveness of the proposed controller has been tested on a typical buck converter.

A novel method for achieving a better performance using the combination of the available passive and active methods has been proposed. The algorithm detects the islanding in proper time by using harmonic detection, the average rate of change of voltage and shifting power generation. Harmonic detection in this method decreases process time and also differentiates between islanding and other power systems events. For harmonic detection, extended Kalman filter has been used. Besides, the reliability of the method increases using the average rate of change of the voltage. The proposed method uses a strategy for decreasing the non-detection zone. In this strategy, minimum and maximum average rates of change of voltage limits are defined to improve the security of the system. Therefore, three main specifications of a proper method, reliability, security and time of process are achievable by the combination of these passive and active methods. By applying different power system events under different power conditions, the proposed method has been verified in Simulink software.