Power System Voltage Stability Taylor Pdf 26

Abstract:Power systems are the most complex systems and have great importance in modern life. They have direct impacts on the modernization, economic, political and social aspects. To operate such systems in a stable mode, several control and protection techniques are required. However, modern systems are equipped with several protection schemes with the aim of avoiding the unpredicted events and power outages, power systems are still encountering emergency and mal-operation situations. The most severe emergencies put the whole or at least a part of the system in danger. If the emergency is not well managed, the power system is likely to have cascading failures that might lead to a blackout. Due to the consequences, many countries around the world have research and expert teams who work to avoid blackouts on their systems. In this paper, a comprehensive review on the major blackouts and cascading events that have occurred in the last decade are introduced. A particular focus is given on the US power system outages and their causes since it is one of the leading power producers in the world and it is also due to the ready availability of data for the past events. The paper also highlights the root causes of different blackouts around the globe. Furthermore, blackout and cascading analysis methods and the consequences of blackouts are surveyed. Moreover, the challenges in the existing protective schemes and research gaps in the topic of power system blackout and cascading events are marked out. Research directions and issues to be considered in future power system blackout studies are also proposed.Keywords: energy system security; power system emergency; power system blackout; power system cascading events; emergency management; power system stability; smart grids; frequency protection; power system protection; power outages

power system voltage stability taylor pdf 26

For frequency regulation services, most projects have been reported to have a nominal power of more than 1 MW and a power/energy ratio of approximately 1:1 [14]. Moreover, frequency regulation requires a fast response, high rate performance, and high power capability for the energy storage system, which is challenging for batteries. To provide stable and reliable power in large-scale deployment and islanded applications, the stability of the voltage and frequency should be considered. When there is a mismatch between power generation and utilization, energy storage systems can maintain the stability of the voltage and frequency of power supply for short-term and long-term applications. In terms of their high round-trip efficiency and energy density, LIBs exhibit considerable potential for application [51]. A LIB energy storage system has been constructed and operated commercially with a power of 8 MW/2 MWh in 2010, which is increased to 16 MW in 2011 in New York for frequency regulation services [52].

Given its abundance and wide distribution, renewable sources have become one of the most cost-effective choices for power generation in power grids in many regions [57]. In recent years, the substantial growth of variable renewable sources promotes the development of electrical energy storage systems and requires them to be more flexible. Battery energy storage systems can effectively store the generated electricity of renewable sources, contributing to grid system stability and reliability, which in turn promote the use of renewable energy sources [58].

Solar photovoltaic power farms can also benefit from the integrated LIBs for storing the electrical energy and smoothing the output power. One of the main challenges to solar photovoltaic power generation is intermittence during the night and during periods when sunlight is blocked. The combination with batteries forms a perfect operating system that can cope with high-gradient power spikes and steady-state power requirements. Figure 4 depicts a grid-connected photovoltaic system based on the integrated energy storage system [64]. The use of batteries in a solar photovoltaic field exhibited output power stability, particularly under partial shading and solar radiation [65, 66]. Recently, Zubi et al. [34] pointed out that there will be continued growth of the LIB market with the integration of power supply systems with solar photovoltaics and wind power, which will be increased to 2 GWh/year in 2020 and 30 GWh/year in 2030.

Generally, grid energy storage systems demand sufficient power and energy for their stable operation. To effectively drive the complex and wide-range devices in the grid, the number of power supplies should be large, in the order of hundreds and even thousands. Therefore, given the complex functionality and large-scale deployments of various devices in the grid, efficient power network management encounters serious challenges to ensure independent and cooperative work. The key hurdle is to design a power management system that can ensure long-term stability, reliable operation, work and storage safety, and cost-effectiveness. Moreover, when a large variety of batteries are packed in a stack, the power management service must balance the electrical characteristics (e.g., voltage and current) of each battery in the stack. The power management system is an essential contributor to the capability of the battery to satisfy the requirements of grid-level energy storage applications, which have a considerable effect on the operation of the overall battery stack and its safety and cost [12, 67].

Although LIBs exhibit high energy density, one cell is insufficient to satisfy the requirements of the power grid. Therefore, the batteries need to be assembled in parallel to increase the current capability or in series to increase the voltage, which poses serious challenges to the stability, voltage operation, safety, and cycle life. For example, with just a few cells in series, the charge current and voltage are divided nearly equally among the cells. However, to achieve a high voltage, many cells need to be connected in series, which will result in unevenly divided voltage among these cells, leading to unbalanced cells with some cells fully charged and others overcharged. LIBs do not deal well with overcharging, resulting in potential safety issues and limited cycle life of the system. Therefore, establishing a system monitor to prevent any cell from being overcharged and balance the batteries to maximize the performance of the entire system is essential.

To ensure safety, the LIB monitors must function as follows: (1) balance the circuit and prevent the voltage or current of any cell from exceeding the limit by stopping the charging current, which should be considered to address the safety issues and ensure the stability of the system, and (2) monitor the temperature and prevent the temperature of any cell from exceeding the limit by requesting that the system be stopped and cooled [67].

Establishing comprehensive assessment: An intelligent power grid integrates large-scale power sources and applications, which are distributed worldwide with different environmental conditions, temperatures, and geographical locations. The evaluation of battery performance should consider the technical properties (e.g., round-trip efficiency, lifetime, working voltage, and power and energy densities), cost, safety, and environmental impact. Moreover, using the same standards to evaluate and compare the performance of different battery technologies is important.