To accomplish feasible large-scale integration of distributed energy resources (DER) into the existing grid system, microgrid implementation has proven to be the most effective. This paper reviews the vital aspects of DER based microgrid and presents simulations to investigate the impacts of DER sources, electric vehicles (EV), and energy storage system (ESS) on practicable architectures resilient operation. The focus is primarily on the concept and definition of microgrid, comparison of control strategies (primary, secondary and tertiary strategies), energy management strategies, power quality issues associated with DER based microgrid, and state-of-the-art entities such as ESS and EV's applications towards microgrid reliability. Following discussion on the different attributes of DER sources based microgrid, simulations are performed to verify the results of the past works on the effects of solar, wind energy sources, ESS, and EVs on the microgrid frequency response. Additional simulations are conducted to assess the influences of DERs, ESS, EVs and their operational strategies on the microgrid reliability aspects.

This paper presents a new method to evaluate the reliability of a power system with high penetration of wind generation, considering the impact of not only the intermittence but also the low inertia characteristic of wind power. As wind generation gradually replaces conventional generation, the system stability and the reliability are negatively affected. Some of the measures employed to deal with the challenges resulting from increasing wind penetration include operating wind generators at lower levels than their available output and providing inertia so that wind generation is able to contribute to system frequency regulation. Apart from these measures, another factor that limits the amount of wind power that can be absorbed into the grid is the imposition of the frequency standard and this also affects the reliability of the system in the presence of wind penetration. The reliability evaluation approach proposed in this paper is developed using discrete convolution and implemented on an IEEE RTS-79 system with a suitable modification. Power system reliability with and without considering the impacts of wind intermittence and low inertia are compared to show the effectiveness of the proposed method.

The integration of wind power into the grid causes numerous stability and reliability issues due to its low inertia and intermittent nature. To ensure system stability, wind power production has to be restricted, which implies that the system cannot absorb the entire output available from wind generation, especially if the output is high. Consequently, the reliability of the integrated system is adversely affected. In order to improve the system reliability, energy storage can be used, which is emerging as a prominent solution for enhancing supply continuity. Complete utilization of an energy storage device can be achieved if it is properly coordinated with wind and conventional generation. This paper proposes a new method to coordinate energy storage with the existing system to improve the system reliability while maintaining the system frequency security. The effectiveness of the model is demonstrated on the IEEE RTS-79 system.

Optimal power flow (OPF) minimizes the production cost while satisfying the constraints of the system, including real and reactive power balance, equipment capability constraints, and voltage limits. This paper presents a method of including a frequency security constraint within the framework of the OPF problem. Increasing displacement of conventional generation by renewable resources that contribute little or no frequency regulation capability may necessitate the enforcement of such a constraint to meet frequency security requirements. The system frequency is required to be maintained within a safe limit, thus indicating the balance between generation and consumption. Hence, the solution for optimization of power flow should not only present a minimum cost of generation within the operating conditions, but also ensure frequency stability. In order to obtain this solution, the requirement of frequency stability is introduced as a new constraint of the power dispatch problem and is represented by the maximum frequency deviation limit. This new constraint is constructed as a non-linear function of system inertia and the frequency regulation constant, since frequency deviation is highly sensitive to these factors. It is shown that the inclusion of this constraint causes the OPF to preferentially select higher inertia generators as necessary, to satisfy the frequency security requirement. A genetic algorithm is utilized as the optimization tool in this work. The IEEE RTS-79 test system is used to demonstrate efficacy of the proposed method.

It is now widely recognized that energy storage enables increased integration of renewable resources. One of the uses of storage is to provide synthetic inertia, making up for some of the inertia lost from displaced conventional generation, thereby maintaining frequency stability. However, energy storage systems continue to be very expensive, and this motivates the development of innovative approaches to mitigate some of the challenges posed by renewable resources. This paper presents a novel method called “grid-scale virtual energy storage” that harvests free energy storage from properties inherent to control of multi-area power systems, thereby increasing the amount of renewable generation that a system can tolerate before its frequency stability is compromised. The concept of virtual energy storage proposed here is based on the surplus of necessary energy that is required to restore the system frequency to within a safe range of the nominal frequency. In a dynamic sense, virtual energy storage is very responsive and is not limited by the operation time and capacity. Moreover, it can be exchanged easily among control areas and does not require installation and implementation expenses as it takes advantage of the existing diversity of area control errors in interconnected systems and employs an appropriate frequency control method. It also helps in reducing the reserve requirement, regulation capacity, transmission loading, and wear and tear on power system by functioning as normal energy storage. In this paper, the proposed new approach is explained mathematically, and its operation is analyzed using a mathematical model and simulation in order to validate its effectiveness.

Due to their many advantages, renewable energy resources (RERs) are proliferating rapidly to satisfy a significant portion of the global energy demand. It is predicted that the importance of RER generation will continue to increase in the future of the energy industry. In spite of all their known benefits, the integration of RERs poses several challenges to system stability and reliability. Low inertia characteristics and the intermittent output of RERs introduces additional variation into an already variable grid frequency. System regulation capability and reliability are reduced as RERs gradually replace conventional generators. This paper reviews the challenges associated with RER integration on system frequency response and how these challenges affect system reliability. Advanced methods for mitigating challenges associated with increasing RER integration, while ensuring system security, are discussed, and the necessary mathematical background is provided in concise form. A model is developed for determining the maximum level of RER penetration based on stability constraints. Emerging methods to advance the integration of RERs are discussed.