Conventional power system challenges

Today, electric power is mostly generated centrally in bulk by large generation plants linked by long transmission lines that bring electric power to the end users via the utility grid; for instance the AC and DC high voltage transmission systems of the US, UK, and Iraq transfer power across 157810, 5340, and 10855 miles respectively [17]–[19]. Recently, the utility grid has faced the challenges of a significant increase in demand, threats of climate change, and the security of the power flow. On the other hand, there is increasing pressure for cost reductions on all fronts and maximisation of profits for shareholders and stakeholders.

The centralized power system has been struggling with many issues which affect the efficiency of its functions. Some issues are regarding the growing political instability on the dependence on fossil fuel at the generation and transportation sections. Other issues are regarding the environment situation, such as increasing carbon dioxide and particulates emissions. These issues have led to the use of renewable energy in generation units and electrifying the transportation sector to reduce energy dependency on fossil fuels and achieve decarbonizing objectives. Electrification equipment causes rapid growth in the electrical demand, whereas the infrastructure of the power system that is used today is too old. The nature of the application changes from a single directional power flow to a bidirectional power flow that could connect to the distribution network at any time of a day, with a different number of loads and at various

Others, 6% Oil, 5% Nuclear, 11% Hydroelectric, 17% Gas, 22% Coal, 39%

capacities. At the same time, ensuring the security of supply, working at a high quality, and keeping the power system stable are vital matters in the electric power system operation. However, renewable energy sources are unpredictable and inconsistent due to the intermittency of usage of energy supply [20]–[25]. The power generation from renewable energy sources is much lower than from fossil fuel sources. The current capital cost of constructing renewable energy sources is far greater than the fossil fuel energy sources for the same capacity. Also, renewable energy relies on the weather. Thus, renewable sources construction concentrates on some geographic areas more than others. For example, the wind turbine requires wind to turn the blade; as the speed of the wind on the offshore is higher than onshore, it is normally accepted to install wind turbines in the coastal area. Photovoltaic cells require clear skies and sunshine to generate electricity; therefore, installing them in high strength sunshine areas has a higher efficiency than in a cloudy area. Currently, it is not possible to totally replace the centralised fossil fuel generation units with decentralised renewable generation units to meet total demand of the electricity network, as shown in Figure 1-6. Therefore, the best solution to operate the existing power system is by integrating small-scale renewable resources and distributing generators in distribution areas to work in a synergetic way with the current generation units. This solution could provide power near the load without required transmitting it for long distances using a transmission system. Therefore, the losses on the power system will be reduced significantly, and there would be no need to increase the fossil fuel driven generation unit. Higher utilisation of renewable energy sources can be integrated into the distribution network and could result in the use of fewer fossil fuel generation units, resulting in meeting the decarbonizing environment objectives.

Generating power by using renewable sources in the distribution network and electrifying the transportation sector makes each node in the distribution network capable of absorbing power or generating power in a different situation. Therefore, the power in the distribution network could flow into the node at a time and from the node at another. That means it is hard to anticipate the direction of power within the node because it becomes bidirectional, rather than single directional. At the same time, it is essential to maintain the frequency and voltage characteristics at predefined levels in order to achieve good levels of power system quality. To keep changing the direction of power could affect the waveform characteristics of the power system over or under the limit, leading to a loss in sections, or even all, of the system. Such a system requires precise management, control, and monitoring for each piece of equipment to reach a satisfactory range of operation. Faced with these challenges, the most efficient strategy to deal with these uncertainties has automated the system to maintain the robustness of operation and make it works as a smart grid [13], [26]–[30]. Utility operators have begun to adopt the concept of the smart grid since its first official definition in 2007 [31]. The smart grid is an electrical system that aims to distribute electric power from the producers to the consumers efficiently [12]. As producers and consumers are dominant, sophisticated players in terms of their behaviour in the supply/demand dynamics, the smart grid is a very complex system that deploys different communication protocols to deal with the nonlinearity of user/supplier, hardware, security and bidirectional power flow [32]. Despite recent advances in the modern technology of communication protocols and monitoring devices, supervision of a large complex system still remains very difficult [12], [13], [33]–[36].

The smart grid will enhance the complex monitoring of the system and connection with other components. It increases the interdependency on the power management of demand. A smart grid power infrastructure can be separated into many areas; each area operates either as connected or islanded modes [28], [37]. Its purpose is to reduce the physical and electrical distance between generation units and loads by adding small scale distributed generators, mainly depending on the renewable energy near the electricity demand area. Each island (microgrid) could work alone and cover all the user load requirements within the area, depending mainly on renewable energy sources and distributed generators. Each island area could be connected to the utility grid, in case the generation exceeds the demand, by a point of common coupling where the point of common coupling works as a switch based on the power electronic devices to separate a network into island mode [38], [39].

Figure 1-6 Estimated Renewable Energy Share of Global Final Energy Consumption, 2014 [1]