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Recently, using a non-linear programming method authors have demonstrated that based on certain criteria if some non-significant selectivity constraints are relaxed, all remaining constraints happen to be feasible but the solution of coordination problem is not possible with the conventional objective function as optimization procedure leaves the solution space [20]. In coordination studies solution with the conventional objective function provides minimum relay operating times. The present paper describes an additional criterion so that the solution with the conventional objective function can be achieved. This paper also achieves the acceptable speed of the primary protection while attempting to coordinate the maximum relay pairs. Complete results are presented in this paper in this regard. This paper uses the non-linear Random Search Technique to solve the coordination problem, which has been successfully applied in many problem areas.

When two protective apparatus installed in series have characteristics, which provide a specified operating sequence, they are said to be coordinated or selective. The coordination of directional overcurrent relays poses serious problems in the modern complex power system networks, which are interconnected. Researchers have looked upon the problem of coordination from different considerations by making use of computer aids. Many efforts have been made to the automation of the coordination process in the area of relay coordination. This paper compiles the most of the significant developments in the area of time-overcurrent relay coordination using different techniques and methodologies. It is hoped that this work will be useful for future generation researchers to find the relevant references to advance the research work in future.

Multilevel inverters (MLIs) are developed to meet medium voltage and high power applications in flexible power systems. The conventional configuration of multilevel inverter requires more switches and has limitation to its wide range application. This paper reports the performed work on 1-phase 7-level reduced switch multilevel inverter (RS MLI) in photovoltaic (PV) system. RS MLI configuration integration with PV system which uses less number of switching components for specified number of voltage output levels as compared to that of conventional multilevel inverter topology. To performed enhanced operation of PV cells and maximize the solar energy extraction an incremental conductance based maximum power point tracking scheme is used. To improve the quality of RS MLI output parameters mainly total harmonic distortion and switching losses, selected harmonic elimination based genetic algorithm method is consider for control the gating pulse of PV based RS MLI. This work is performed using MATLAB/SIMULINK software. Keywords Reduced switch multilevel inverter (RS MLI) • Maximum power point tracking (MPPT) • Incremental conductance (IC) • Genetic algorithm (GA) • Total harmonic distortion (THD)