# The Power System and Microgrid Protection--A Review
## 4 Future Trends of Protection Systems
### Artificial Intelligence Algorithms  
Artificial intelligence (AI) and related technologies are effective in solving complex system controls and decision problems [142]. These techniques, such as expert systems (ESs), GAs, fuzzy logic (FL), and ANNs, have emerged with the development of computers [143; 144]. These techniques have brought an advancing frontier in power engineering and power electronics. An intelligent or smart power system with future advanced electrical devices can integrate state-of-the-art power electronics, communication, computers, information, and cyber technologies. Over the past two decades, the application of AI techniques for protection systems has been studied [145]. As a branch of AI techniques, agents have been introduced into the protection system. The relay agents are classified into the concept of a cooperative protection system by their roles [97; 146]. The authors of Reference [147] have proposed an intelligent coordinated protection and control scheme for a distribution network with the integration of wind generation. In References [148; 149; 150; 151], several algorithms with AI technologies, such as genetic evolution, Tabu search, and fuzzy control principle were investigated to realize the fault-tolerance function of WAP systems. Several fault detection methods have been presented according to AI techniques such as the methods based on the expert system [149]. In Reference [152], a distribution harmonic state estimator was developed using a modified particle swarm optimization (PSO) algorithm. This method uses PMU data, line/DG parameters, pseudo measurements, and known uncertainties to estimate the harmonic phasors through the minimization of the error between PMU measurements and the estimated values. Reference [153] proposed an integrated impedance angle (IIA)-based protection scheme using wide-area positive sequence components of voltages and currents with PMUs. The IIA for the lines considers information from both ends of PMU, which is an important key to detect faults in the microgrid. A weighted least-squares algorithm is applied along with singular value decomposition to estimate the harmonics [154; 155]. In References [156], a new hybrid GA method was suggested that was successfully applied to solve DOC relays coordination problems. A DOC relay is usually adjustable with a fixed power system topology in an interconnected power system. The system may change the topologies due to the outages of the transmission lines, transformers, and generating units. Reference [157] investigated the problem of determining the optimum values of time multiplier setting (TMS) and plug setting of DOC relays in different topologies. The study introduces the method to improve the convergence of the GA, as a new hybrid method. In Reference [158], a hybrid method has been proposed to overcome the drawbacks of GA and nonlinear programming (NLP) method, and to determine the optimum settings of OC relays, TMS and plug setting (PS). In References [122; 123], a new method has proposed for optimal coordination of DOC relays in microgrids. The optimization method is based on multiple parameters, such as the upper limit of the plug setting multiplier (PSM) in the GA. In general, the future of protection systems tends towards smart or intelligent grids. A smart grid is a cyber-enabled electric power system that combines information and communication technologies with power engineering. Some of the benefits of smart grids are as follows [159]:  
1. Providing two-way power and information flows;
2. Developing a wide-area monitoring system and pervasive control capability over widespread utilities' assets;
3. Enabling energy efficiency and demand-side management;
4. Integrating intermittent renewable energy sources into the existing power grid;
5. Providing self-healing and resiliency against cyber and physical attacks or system anomalies. The main differences between smart and traditional power grids are the improvement in controlling, monitoring, and communication systems.