Despite of several formulations discussed for operation of Directional Over current Relays (DOCRs) in micro grids the coordination of DOCR is yet a great tasked to be solved. A micro grid is a group of generators preferably a renewable energy source and loads interconnected. The modes of micro grid operation, grid connected mode and autonomous mode are to be considered simultaneously to design an optimal protection scheme for the micro grid. Several conflicting objective functions that must be optimized simultaneously during the relay setting process make the coordination problem to be treated as multi-objective. In this work a multi-objective approach yielding better coordination is presented. There are two major objectives as follows; former is the synchronization period between the main and secondary relays, later is the relay operation time. The conventional Multi-Objective Evolutionary Algorithms (MOEAs) may take thousands of function evaluations, which is not practical for real-world problems. Hence surrogates are introduced in those MOEAs to approximate the fitness function. The relay coordination is devised as a constrained multi-objective problem. The Surrogate Assisted Particle Swarm Optimization (SAPSO) Algorithm is applied to accomplish better coordination between the relays. The scheme is validated using standard IEEE systems and the results are compared with the conventional Multi-Objective Particle Swarm Optimization (MOPSO). The optimal values of pickup current and Time Dial Settings are computed for both modes of micro grid operation. The sum of operating time of all relays and the synchronization period between the main and secondary relays are minimized. The Inverted Generation Distance (IGD) is employed as the parameter for computing the performance of the algorithm. Also the convergence characteristic is analyzed. From the results it is proved that SAPSO have good stability than MOPSO and offers better Pareto fronts, convergence and distribution.

尽管针对微电网中定向过流继电器 (DOCR) 的操作讨论了几种公式，但 DOCR 的协调仍然是一项需要解决的重大任务。微电网是一组发电机，最好是可再生能源和互连的负载。微电网运行模式、并网模式和自治模式应同时考虑，以设计出最佳的微电网保护方案。在继电器设置过程中必须同时优化的几个相互冲突的目标函数使得协调问题被视为多目标。在这项工作中，提出了一种产生更好协调的多目标方法。有以下两个主要目标；前者是主副继电器同步时间，后者是继电器动作时间。传统的多目标进化算法 (MOEA) 可能需要数千个函数评估，这对于现实世界的问题是不切实际的。因此，在这些 MOEA 中引入了代理来近似适应度函数。中继协调被设计为一个受约束的多目标问题。代理辅助粒子群优化 (SAPSO) 算法用于实现中继之间更好的协调。该方案使用标准 IEEE 系统进行验证，并将结果与​​传统的多目标粒子群优化 (MOPSO) 进行比较。为两种微电网运行模式计算启动电流和时间拨号设置的最佳值。所有继电器的工作时间之和以及主副继电器之间的同步周期被最小化。反向生成距离（IGD）被用作计算算法性能的参数。还分析了收敛特性。结果表明，SAPSO 比 MOPSO 具有更好的稳定性，并提供更好的帕累托前沿、收敛和分布。