[1]. Today's grid is an aging infrastructure, combined with the growth of distributed energy resources (DERs), it is therefore more prone to outages and disturbances leading to poor reliability and power quality. These factors present a significant challenge for distributed renewable energy integration to the grid with unidirectional power flow [2]. The current grid is characterized by one‐directional electricity flow, lack of information exchange, centralized bulk generation, lack of flexibility to directly trade in electricity markets, inefficient monitoring and control of the power distribution networks, lack of flexibility and accessibility to new innovative solutions such as flexible loads, accommodating large scale of fluctuating energy resources, electric vehicles wide usage, etc. The SG is designed to tackle all these challenges by integrating and smartly utilizing the electricity, information, and communication infrastructures.
The SG is the solution to overcome the aforementioned challenges while also responding to the current and future humanity energy expectations. SG's implementation will not only have environmental benefits through high penetration of renewable sources, but will also have significant regional, national, and global impacts related to achieving a more reliable, efficient, and economic energy system. The SG paradigm integrates a variety of modern advanced technologies such as smart sensors and measurements, advanced communication and information, edge computing and control. This paradigm allows a flexible and reliable electricity system with bi‐directional power and information flows [3]. The structures of the SG anticipate and respond to electric system disturbances, optimize asset utilization, and operate efficiently. SG houses all generation and storage options, which hinders the dependency on peak demand back‐up power stations – thus, cutting significant costs related to the generation, transmission, and distribution. Furthermore, SG enables active participation of customers, new products, services, and markets – thus can support the uptake of new industries. SG functions resiliently against attacks and natural disasters, delivers power quality for the digital economy‐ thus, creating new jobs and regenerating the economy at a time of financial crisis. The SG is a power network that contains distributed nodes, which operate under the pervasive control of smart subsystems, so‐called smart microgrids. A microgrid is a small‐scale version of the electric grid, however possessing distributed generation and potentially energy storage (ES). Microgrids can operate in a grid‐connected mode, islanded mode, or in both modes which improve the grid's reliability, controllability, and efficiency. Widespread installations of microgrids enable a faster transformation to the SG paradigm from the current grid infrastructure [4].
1.2 Fundamentals of a Current Electric Power System
The two main characteristics of conventional electrical power systems are: centralized energy generation and unidirectional power delivery systems. This means that electric power is first produced by bulk power generation and then transmitted across the electricity grid to the distribution layer, and finally to the end users. The flow of electricity in the grid is from top (high‐voltage network) to bottom (low‐voltage network). Figure 1.1 shows the three main stages of generation, transmission, and distribution [5]. Those grid elements are briefly explained in the next sub‐sections.
1.2.1 Electrical Power Generation
Traditional power plants burn the fossil fuel to generate electricity therefore they contribute in significant amount of greenhouse gas emission to the environment. The crucial need to adopt power‐generation approaches that have fewer environmental impacts is an essential requirement for modern power grids, which means moving toward more renewable energy systems. Among renewable energies, sunlight (photovoltaics) is converted into electricity, wind kinetic energy is converted into electricity, water gravitational and kinetic energy is converted to electricity (hydro) [6]. Continuous technology development is used to convert renewable energies into electricity at increased efficiency and lower cost. Therefore, it is essential for the current power grid to efficiently accommodate a constant increase of fluctuating renewable energy sources.
Figure 1.1 The fundamentals of electric power system. Adapted from Ref Num [5].
1.2.2 Electric Power Transmission
The transmission system has the highest voltage rating and is used to transmit the energy from the bulk generation plant to the distribution networks through interconnecting substations. The transmission system may include overhead lines, underground and under water cables. This transmission system could be high voltage alternating current (HVAC) or high voltage direct current (HVDC). Traditionally, an HVAC system is mostly used, however, the HVDC is rapidly gaining popularity due to reduced losses and cost particularly over large distances. The electric power could also be transported and distributed via underground cables. Construction of an underground transmission system normally costs 4 to 10 times that of an equal distance overhead line [7]. The overall amount of power and distance that the power needs to be transported, overdetermine the essential design of the transmission and distribution systems. Hence, the greater the distance and the more power to be transferred, the higher the rated voltage is, and the higher the cost of the system will be as shown in Figure 1.2 [8]. This shows that distributed renewable energy generation allows for the reduction of the cost not only of the central power generation plants, but also of the transmission and distribution infrastructures. This is one of the drivers for the SG energy paradigm.
1.2.3 Electric Power Distribution
The distribution network is the last stage in electric power delivery responsible for carrying electricity from the transmission and sub‐transmission systems to end users. There are four main arrangements used in electric power distribution: radial, parallel feeders, ring main, and interconnected (mesh) systems as shown in Figure 1.3 [9]. Distribution networks typically have a radial topology “star network,” with merely a single power flow path between the distribution substation and a certain load (unidirectional power flow). Distribution networks rarely implement a ring or loop topology, with two power flow paths between the distribution substation and the load [10]. Moving toward renewable energy systems and introducing distributed generators (DGs) enforces the use of bidirectional power flows which causes many challenges for traditional distribution systems. A transformation to the SG paradigm includes smart elements to allow for bidirectional power flow and ES technologies. ES systems may include pumped hydro, compressed air, electrochemical batteries, flow batteries, compressed air, superconducting magnetic ES, supercapacitors, and flywheels.
Figure 1.2 Selection of rated voltage for three‐phase AC transmission line. Ref [8]. Reproduced with permission from John Wiley & Sons.
Figure 1.3 Main types used in electric power distribution, (a) Redial feeder system. (b) Ring main feeder. (c) Meshed system. (d) Parallel feeder system. Adapted from Ref Num [9].
1.3 Limitations of the Traditional Power Grid
The
