Stability and eigenvalue sensitivity analysis of a BESS model in a microgrid

Flexible ac transmission systems (FACTS) devices are commonly used in power systems to improve the dynamic and static performances of the system. Battery energy storage systems (BESS) are now increasingly being installed in modern power systems for energy arbitrage and ancillary services. This paper describes a technique to improve the transient stability limit of a simple power system using a BESS. A previously developed control strategy to improve stability using STATCOM is applied to control the BESS. The strategy is based on a combination of the maximum and continuous current control. The stability limit, and hence the critical clearing time, obtained using BESS is compared with that obtained using STATCOM. A classical model of the system has been implemented in Matlab Simulink and DIgSILENT PowerFactory software for the analysis. Further analysis has been conducted for a higher order machine model implemented in PowerFactory. The investigations revealed that the BESS is more effective in enhancing the stability limit of the system compared to a STATCOM of the same current rating for both classical and higher order machine models.

Optimal Design and Economic Evaluation of a Battery Energy Storage System for the Maximization of the Energy Generated by Wind Farms in Isolated Electric Grids

Distribution systems are being operated closer to their voltage and loading instability limits, during peak-demand hours. To increase loadability of the circuit, Battery Energy Storage System (BESS) has been introduced to effectively manage the voltage along the distribution feeder. In this paper, we have developed an algorithm to properly size BESS and mitigate voltage problem on a weak distribution circuit within the SCE territory. This circuit undergoes an expansion of agricultural loads and integration of a couple new large PV farms. The objective is to size a BESS to address expected under-voltage and voltage instability issues and to determine the new circuit operational limits. The solution has been developed based on an analytical approach, - using the CYME software for modeling and the power flow studies. Sensitivity analyses have been performed to determine the maximum loadability of a circuit under various active and reactive power injections into the circuit. The results provide the best size of a BESS to address load growth in the target circuit.

With more renewable resources integrated to the grid, energy storage is expected to rise to the challenge of the grid caused by the characteristics of the intermittent renewable sources. This paper presents an innovative battery energy storage system (BESS) combined with the decoupled PQ control and adaptive capacity-based droop control for both grid-connected operation and stand-alone operation. When the system is islanded, such BESS synchronizes to form a reliable frequency source which does not collapse when member BESS fail. The flexibility of the proposed control method enables the BESS to adjust the power output according to its available capacity respectively so that the decentralized autonomous frequency control with load sharing is achieved without violating the stability limit. The paper also highlights the significant role of the Phase Lock Loop for the proposed control principles.

Due to the ever-growing global concerns of climate changes and environmental issues, renewable energies along with the distributed energy resources (DERs) are becoming popular day by day for the sustainable operation of microgrids. Since a number of energy sources are connected to microgrids, multiple power electronic devices, such as inverters, are interfaced with those sources to support the DC–AC and AC–DC conversion. Multiple inverters installed with DERs are very effective in order to deliver adequate amount of energy from different sources to the end users. However, the control and management of multiple inverters adversely suffer from limited system stability due to the lack of proper coordination among different components of microgrids. Moreover, due to the requirements of sustainable operation of microgrids and intermittent characteristics of renewable energy, efficient coordinated control is still quite difficult to maintain the balance between the generations and demands. In order to deliver a reliable energy supply to microgrids, inverters need to be controlled in a more efficient way. Moreover, the integration of battery energy storage systems (BESSs) adds a new dimension to the reliable operation of microgrids which also possesses a difficulty to manage power sharing during the change in network configurations. In this chapter, a communication-assisted distributed multi-agent system (MAS)-based control scheme is proposed to effectively control and manage the inverter-dominated microgrids with solar photovoltaic (PV) systems and BESSs. The MAS establishes the coordination between the power sharing and energy management through agent communication and further ensures the sustainable operation of microgrids by effectively controlling the inverters.

The number of electronics used in outdoor environment is constantly growing. The humidity causes about 19 % of all electronics failures and, especially, moisture increases these problems due to the ongoing process of miniaturization and lower power consumption of electronic components. Moisture loads are still not understood well by design engineers, therefore this field has become one of the bottlenecks in the electronics system design. The objective of this paper is to model moisture ingress into an electronics enclosure under isothermal conditions. The moisture diffusion model is based on a 1D quasi-steady state (QSS) approximation for Fick’s second law. This QSS approach is also described with an electrical analogy which gives a fast tool in modelling of the moisture response. The same QSS method is applied to ambient water vapour variations. The obtained results are compared to an analytical solution and very good agreement is found.

Voltage instability is a major issue that attracts worldwide interest because of its consequence of voltage collapses. These days power systems operate closer to their stability limits, transferring large amounts of powers from long distance and an inadequate supply of reactive power contribute to system voltage instability and eventually lead to voltage collapse. So estimating the margin in the loadability of the power system is essential in the real time system for voltage stability assessment. This paper investigates the enhancement of voltage stability using Static Compensator (STATCOM) in a wind integrated power system with storage. Wind energy is gaining the most interest among a variety of renewable energy resources and this requires energy storage because it is necessary to get a smooth output from a wind turbine. A battery energy storage system is connected to the system which enhances the voltage levels in weak buses. The combined action of battery storage and STATCOM enhances the voltage stability of the entire system. The analysis is done with power system analysis toolbox (PSAT), a powerful toolbox in MATLAB for power system analysis.

Recently, use of the electric vehicle (EV) has begun to spread rapidly. Fortuitously, there is a possibility that the EV can be connected to a smart house in order to control charging and discharging operations. In this case, the smart house must perform optimal load sharing control according to the state of charge of the storage battery and the battery capacity. In this paper, voltage control is accomplished by the use of energy storage systems which are controlled using an original voltage stability criterion. The voltage stability criterion is made possible using the (P, Q)-V limits of voltage stability for the IEEE 5-bus system model. The effectiveness of the proposed method is verified by simulation results in the Matlab environment.

This paper examines, from the energetic point of view, the design process of a stand-alone house as a microgrid (MG) in Rome, which inhabited by a family of four people. The house is equipped with all the electrical devices necessary to ensure comfort conditions and to achieve a Nearly Zero Energy Building (NZEB). In the island mode, the electric current of the building is supplied by a photovoltaic (PV) system and a battery energy storage system (BESS). All the electrical users present in the house are characterized by a high energy class. In order to make the house working in island mode from an electric and thermal point of view, has been decided to install a heat pump, electrically driven, for the production of domestic hot water (DHW) to feed the radiators and for domestic uses. For this MG case study, a standard load profile and an optimized load profile have been analyzed. The comparison between the two different scenarios has been carried out by the optimization software. The results show an improvement of all the economic and technical parameters in the optimized case compared to the standard case, due to a better exploitation of the energy produced by the PV system. Furthermore, the size of the components with the installation of a Building Automation and Control System (BACS) in the optimized case, is slightly reduced leading to a lower cost of operation and investment.

Energy management in microgrids is typically formulated as a nonlinear optimization problem. Solving it in a centralized manner does not only require high computational capabilities at the microgrid central controller (MGCC), but may also infringe customer privacy. Existing distributed approaches, on the other hand, assume that all generations and loads are connected to one bus, and ignore the underlying power distribution network and the associated power flow and system operational constraints. Consequently, the schedules produced by those algorithms may violate those constraints and thus are not feasible in practice. Therefore, the focus of this paper is on the design of a distributed energy management strategy (EMS) for the optimal operation of microgrids with consideration of the distribution network and the associated constraints. Specifically, we formulate microgrid energy management as an optimal power flow problem, and propose a distributed EMS where the MGCC and the local controllers jointly compute an optimal schedule. We also provide an implementation of the proposed distributed EMS based on IEC 61850. As one demonstration, we apply the proposed distributed EMS to a real microgrid in Guangdong Province, China, consisting of photovoltaics, wind turbines, diesel generators, and a battery energy storage system. The simulation results demonstrate the effectiveness and fast convergence of the proposed distributed EMS.

The steady-state kinetics of parallel reaction networks

In this paper we demonstrate several series of experiments for the measurement of viscosity of neat glycerol and its aqueous solutions using a tank-tube viscometer. Measuring viscosity of highly viscous liquids with the tank-tube viscometer is easier than other types of viscometers. This inexpensive viscometer continuously generates numerous reproducible viscosity data of highly viscous neat glycerol and its aqueous solutions under given experimental conditions such as a desired temperature and a desired concentration of water in aqueous glycerol solutions. Fabricating the tank-tube viscometer is inexpensive, since this viscometer does not need sophisticated accessories such as a high-pressure liquid pump, a sensitive pressure sensor, and an accurate flow meter. The tank-tube viscometer consists of a large-diameter reservoir and a long, small-diameter, vertical tube. The viscosity equation was developed under the following assumptions. Both the quasi steady state approach and the negligible friction loss due to a sudden contraction between the reservoir tank and the tube are valid. The kinetic energy of the emerging stream from the bottom end of the vertical tube of the tank-tube viscometer also is assumed to be negligible. Very viscous glycerol and its aqueous solutions were used to test the viscometer by comparing viscosity values from the viscometer with those from literatures. The main objective of this study is to demonstrate effects of water as well as temperature on viscosity of aqueous glycerol solutions, applying experimental data of accumulated amounts of aqueous glycerol solutions at various drain durations to the newly-developed viscosity equation for the fabricated tank-tube viscometer.

Simulation of Three-dimensional Flow in Compression Resin Transfer Molding by the Control Volume/Finite Element Method

This work considers the gravitational instability of a saline boundary layer formed by an evaporation-induced flow through a fully saturated porous slab. Evaporation of saline waters can result in the formation of salt lakes as salt accumulates near the top surface. As gravitational instabilities can impede the accumulation of salt, establishing a relation between their occurrence and the value of physical parameters such as evaporation rate is crucial. One step toward determining when gravitational instabilities can arise is to compute the ground-state salinity. In this work, this ground state is analytically derived within the framework of Sturm–Liouville theory. Then, a linear stability analysis in conjunction with the quasi-steady state approach is employed to investigate the occurrence of instabilities. These instabilities can develop and grow over time depending on the Rayleigh number and the dimensionless height of the porous medium. To calculate the critical Rayleigh number, which is used to determine the stability of a particular system, the eigenvalues of the linear perturbation equations have to be computed. Here, a novel fundamental matrix method is proposed to solve this perturbation eigenvalue problem and shown to coincide with an established Chebyshev–Galerkin method in their shared range of applicability. Finally, a two-dimensional direct numerical simulation of the full equation system via the finite volume method is employed to validate the time of onset of convective instabilities predicted by the linear theory. Moreover, the fully nonlinear convection patterns are analyzed.

A tank-tube viscometer and its novel non-Newtonian viscosity equation were developed to determine flow characteristics of non-Newtonian fluids. The objective of this study is to test capabilities of the tank-tube viscometer and its novel non-Newtonian viscosity equation by characterizing rheological behaviors of dairy products. The rheological behavior of fluid milk such as simulated fluid milk and grocery fluid milk such as skim milk and whole milk were characterized with the viscometer, using water as a reference calibration fluid. The non-Newtonian viscosity equation was developed under the assumptions that a quasi-steady state approach is valid, and the friction loss due to a sudden contraction between the reservoir tank and the tube is negligible for laminar fluid flows, using L’Hospital’s rule. Simulated fluid milk was prepared by adding dry nonfat milk powder to water, whereas commercial fluid milk such as skim milk and whole milk was purchased from a grocery store. The only experimental data required is the mass of the fluid milk that drains from the viscometer at a given drain duration. The concentration of dry nonfat milk powder in simulated fluid milk ranges from 4 to 10 wt%. As the concentration of dry nonfat milk powder in simulated fluid milk increases, the flow behavior index of simulated fluid milk decreases. Raising the temperature from 12 to 26°C, the flow behavior index of simulated fluid milk containing 4 wt% dry milk powder increases from about 0.7 to 0.9. The apparent viscosity values of the 4 wt% simulated fluid milk exhibits Arrhenius behavior with respect to temperature.