Improve System Stability Research Articles

Active Stabilization of Slung Loads in High-Speed Flight Using Cable Angle Feedback

This paper addresses the problem of active stabilization of slung loads up to 130 kt. To demonstrate the method, simulations of a utility helicopter with a dynamic inversion controller (as its automatic flight control system) and a CONEX cargo container were used. An airspeed-scheduled controller utilizing cable angle feedback was designed for the nonlinear-coupled system by the classic root locus technique. Nonlinear simulations of straight and level flight at different airspeeds were used to validate the controller performance in stabilizing the load pendulum motions. Controller performance was also evaluated in complex maneuvers with different levels of turbulence. The results show that using cable angle feedback provides or improves system stability when turbulence is not included in the simulation. When light/moderate turbulence is present, sustained limit cycle oscillations are avoided by the use of the controller. For severe turbulence levels, the controller did not provide any significant improvement.

An Improved Method for Reconfiguring and Optimizing Electrical Active Distribution Network Using Evolutionary Particle Swarm Optimization

The presence of optimized distributed generation (DG) with suitable distribution network reconfiguration (DNR) in the electrical distribution network has an advantage for voltage support, power losses reduction, deferment of new transmission line and distribution structure and system stability improvement. However, installation of a DG unit at non-optimal size with non-optimal DNR may lead to higher power losses, power quality problem, voltage instability and incremental of operational cost. Thus, an appropriate DG and DNR planning are essential and are considered as an objective of this research. An effective heuristic optimization technique named as improved evolutionary particle swarm optimization (IEPSO) is proposed in this research. The objective function is formulated to minimize the total power losses (TPL) and to improve the voltage stability index (VSI). The voltage stability index is determined for three load demand levels namely light load, nominal load, and heavy load with proper optimal DNR and DG sizing. The performance of the proposed technique is compared with other optimization techniques, namely particle swarm optimization (PSO) and iteration particle swarm optimization (IPSO). Four case studies on IEEE 33-bus and IEEE 69-bus distribution systems have been conducted to validate the effectiveness of the proposed IEPSO. The optimization results show that, the best achievement is done by IEPSO technique with power losses reduction up to 79.26%, and 58.41% improvement in the voltage stability index. Moreover, IEPSO has the fastest computational time for all load conditions as compared to other algorithms.

Nonlinear dynamic analysis of an electromechanical coupling transmission system: A case study on shearers

The operation environment of an electromechanical coupling transmission system in shearers is significantly harsher than that of electromechanical coupling transmission system for general applications. Besides, under the combined action of electrical and mechanical factors, unstable phenomenon may appear when the complicated dynamic behaviors of electromechanical coupling transmission system of a shearer occur such as bifurcation and chaos. Therefore, to solve this problem, the stability, bifurcation, and chaotic characters of electromechanical coupling transmission system with various electromagnetism stiffnesses are investigated in this paper. Then, the nonlinear dynamic equation of electromechanical coupling transmission system of a shearer is set up by taking both air-gap field energy of permanent magnet synchronous motor and coupling impact of mechanical and electrical parameters. According to the established equations, the equilibrium point and eigenvalue of the system are discussed. Meanwhile, the parameters conditions of the system Hopf bifurcation and chaotic motion are analyzed, and the homoclinic orbit of the system is determined. The results show that bifurcation and chaotic motion can be controlled effectively when reasonable parameters are concerned, which is of great practical significance to further study the vibration of the mechanical-electromagnetic coupling transmission system and the improvement of system stability.

Analysis of Stability Improvements by Using Capacitors

The demand for electricity has increased substantially while the expansion of electricity generation, power transmission is very limited, due to environmental restrictions, consequently some transmission lines, limiting power factor. Power flow in the generation system, covering the area of North Sumatra and Aceh which is managed by PT. PLN (Persero), ETAP 4.0 (Electrical Transient Analizer Program) is a program that can display GUI (Graphical User Interface) with unlimited bus number, ETAP 4.0 is useful for Power flow study. The data required by ETAP 4.0 on a generation system is a one-line diagram, nominal kV, and generator, bus, transformer, transmission, and safety rating. The power flow approach method used is the Newton-Raphson method with maximum iteration of 99 and the accuracy of 0.000001. The problem of power flows under consideration is the normal state system, one transmission is disconnected, one of the plants is not operating. The results of the power flow study for each problem obtained the lowest bus voltage, the highest losses in the transmis. The largest power distributed in power plants, new in high voltage transmission, increases the power of power from power to load, changes in voltage problems and improves system stability. This paper aims to verify the capacitor's ability to improve voltage regulation (voltage stability) in electric power transmission systems, from this capacitor simulated using ETAP 4.0 included in Newton-Raphson model.

Current Error Based Compensations for VSC Current Control in Weak Grids for Wind Farm Applications

A novel current control strategy is proposed for voltage source converters connected to weak grids using conventional current vector control with additional current error based voltage angle and magnitude compensations. For connecting to very weak ac network, the combination of vector control and grid synchronization with a conventional phase-locked loop is proved to be unstable, whereas the proposed current error based compensations can significantly improve system stability. In this way, the proposed control can still benefit from the presence of closed-loop current control without the need for control switching during large ac voltage variations. A comprehensive frequency domain model is established to analyze stability performance. Comprehensive time domain simulations are further carried out to validate its effectiveness and robustness by demonstrating its current control performance during a three-phase fault, multiple-converter situation, and various grid strength conditions.

Design and Verification Test of an HTS Leakage Flux-Controlled Reactor

Controlled reactors can adjust the output capacity to stabilize system voltage, control reactive power, and improve system stability according to operating conditions. The design of reactance and control system determines whether a controlled reactor can meet the requirement of stable operation. In this paper, the operating principle of a high temperature superconducting leakage flux-controlled reactor (HTS-LFCR) is introduced. The design of the reactance and the optimal initial turn-on angle of the control system are discussed. An HTS-LFCR is fabricated and tested. The experimental results show that the reactance design values are basically consistent with the experimental tests; when the initial turn-on angle of the control system is 90°, the reactor can achieve a smooth transition from one operating mode to another.

Eigensolution of a BTA deep-hole drilling shaft system

A numerical investigation is conducted to obtain the eigensolution of a deep-hole drilling shaft system. The rotating drilling shaft is modeled as a Rayleigh beam that conveys cutting fluid and is subjected to torque, compressive axial force, and support constraints. The governing equation of the drilling shaft system for lateral vibration is obtained by considering fluid-structure interaction, rotational inertia, gyroscopic effect, effect of motion constraints, and frictional damping generated by the surrounding fluid. The influence of cutting fluid flow velocity, rotational angular velocity, torque, compressive axial force, and support constraints on the natural frequency and stability of the drilling shaft system is examined. Cutting fluid flow velocity, compressive axial force, and torque decrease the natural frequency of the system, whereas rotational angular velocity and support constraints improve system stability.

Comparison on Promotion Effect of Various Types of Surfactants on HCFC-141b Hydrate Induction Time

Cold storage in air conditioning based on refrigerant hydrate is a new-type energy saving technology to reduce initial investment and running cost of air conditioning equipments and improve system stability. Refrigerant hydrate is generated under critical temperature and pressure condition, while surfactant is an effective medium to promote its phase equilibrium. In this paper, in order to research such promotion effect, different type of surfactants with unique mechanism, SDS, Tween80 and Span80, n-BA were selected to compare the respective impact on HCFC141b hydrate induction time based on temperature curve. Experimental results showed that no obvious change had been discovered when no surfactant was added into pure water system, which coincided with phase equilibrium diagram of HCFC141b. All the four kinds of surfactants had realized promotion effect to various degrees. For each hydration system, a large gap existed between the longest and the shortest induction time in 6 groups of parallel experiments, meaning relatively poor system stability. Under the combined effect of Tween80 (2wt%), Span80 (0.1wt%) and n-BA (0.1wt%), average and the shortest induction time was 20.9min and 17.5min respectively, corresponding to the best promotion effect.

Monostable Dynamic Analysis of Microbeam-Based Resonators via an Improved One Degree of Freedom Model.

Monostable vibration can eliminate dynamic bifurcation and improve system stability, which is required in many microelectromechanical systems (MEMS) applications, such as microbeam-based and comb-driven resonators. This article aims to theoretically investigate the monostable vibration in size-effected MEMS via a low dimensional model. An improved single degree of freedom model to describe electrically actuated microbeam-based resonators is obtained by using modified couple stress theory and Nonlinear Galerkin method. Static displacement, pull-in voltage, resonant frequency and especially the monostable dynamic behaviors of the resonators are investigated in detail. Through perturbation analysis, an approximate average equation is derived by the application of the method of Multiple Scales. Theoretical expressions about parameter space and maximum amplitude of monostable vibration are then deduced. Results show that this improved model can describe the static behavior more accurately than that of single degree of freedom model via traditional Galerkin Method. This desired monostable large amplitude vibration is significantly affected by the ratio of the gap width to mircobeam thickness. The optimization design results show that reasonable decrease of this ratio can be beneficial to monostable vibration. All these analytical results are verified by numerical results via Differential Quadrature method, which show excellent agreement with each other. This analysis has the potential of improving dynamic performance in MEMS.

Improvement of Power System Stability using BBO Algorithm

Improvement of Power System Stability using BBO Algorithm

Microbiome analysis and -omics studies of microbial denitrification processes in wastewater treatment: recent advances.

Nitrogen pollution is an increasingly severe worldwide problem because of drainage of nitrogen-containing wastewater and intensive application of nitrogen-containing fertilizers. Denitrification, a key process in nitrogen cycles, is commonly employed for nitrogen removal in engineered wastewater treatment systems. Biological denitrification is performed by denitrifying microbes (bacteria) that use nitrate as terminal electron acceptor. Better understanding the functions of diverse microbial populations in denitrification-based wastewater treatment systems, and the interactions of these populations with operating environments, is essential for improving both treatment performance and system stability. Recent advances in "meta-omics" (e. g., genomics, transcriptomics, proteomics, metabolomics), other molecular biology tools, and microbiome analysis have greatly enhanced such understanding. This minireview summarizes recent findings regarding microbial community structure and composition, key functional microbes and their physiology, functional genes involved in nitrogen cycle, and responses of microbes and their genes to changes of environmental factors or operating parameters, in denitrification processes in wastewater treatment systems. Of particular interest are heterotrophic denitrification systems (which require alternative organic carbon sources) and the autotrophic denitrification systems (which do not require an external carbon source). Integrated microbiome and -omics approaches have great future potential for determination of optimal environmental and biotechnological parameters, novel process development, and improvement of nitrogen removal efficiency and system stability.

Optimized Interval Type-II Fuzzy Controller-Based STATCOM for Voltage Regulation in Power Systems With Photovoltaic Farm

The intermittent characteristics and high penetration of renewables (such as photovoltaic and wind powers) cause voltage and stability problems in power systems. The static synchronous compensator (STATCOM) has recently acquired attention on account of its ability to regulate system voltages and improve system stability. This paper presents a novel interval type-II fuzzy logic system (IT2 FLS)-based controller, which consists of current and voltage regulators, applied to the STATCOM, to mitigate bus voltage variations caused by large disturbances (such as intermittent generation of photovoltaic arrays). The current regulator is used to produce the phase angle at the voltage-source converter in the STATCOM while the voltage regulator outputs the current reference on the quadrature axis for the STATCOM. The parameters of the upper/lower membership functions and control gains are optimized by particle swarm optimization. A realistic 10-bus distribution system is used to demonstrate the effectiveness of the proposed method. Comparative studies reveal that the proposed method outperforms traditional PI and type-I FLS-based methods.

Behavior Rhythm: A New Model for Behavior Visualization and Its Application in System Security Management

The widespread use of social media, cloud computing, and Internet of Things generates massive behavior data recorded by system logs, and how to utilize these data to improve the stability and security of these systems becomes more and more difficult due to the increasing number of users and amount of data. In this paper, we propose a novel model named behavior rhythm (BR) to characterize and visualize the user’s behaviors from the massive logs and apply it to the system security management. Based on the BR model, we conduct the clustering analysis to mine the user clusters. Different management and access control policies can be applied to different clusters to improve the management efficiency. Then, we apply the non-negative matrix factorization method to analyze the BRs and perform abnormal detection, and employ the BR similarity calculation to perform fast potential anomaly tracking. The detection and tracing results can help the administrators to control the threats efficiently. Experimental results based on the datasets collected from the campus network center of Xi’an Jiaotong University verify the accuracy and efficiency of our method in user behavior profiling and security management, which lay a solid foundation for improving system stability and quality of service.

Real-Time Contingency Analysis on Massively Parallel Architectures With Compensation Method

Real-time contingency analysis (RTCA) is paramount for modern power systems as it forms the basis for important operator actions that help to improve system stability, optimize generator dispatch, manage disparate resources, prevent cascading outages, and enhance market operations. With increasing system size and the number of contingency scenarios, RTCA is faced with computational challenges. To alleviate this situation, massively parallel graphics processing units (GPUs) are introduced for the acceleration of RTCA solution in this paper, where the compensation method (CM) is utilized for the concurrent AC power flow solution. Strategies and principles on the data structure, kernel function, and memory management are provided. Five benchmark systems (ranging from 300- to 13,659-bus) are employed for case studies. Based on the sequential CM implemented on single-thread CPU, the performance analysis related to execution time and speedup is carried out for parallel CMs running on other architectures, including multi-thread CPU, single-GPU, and multi-GPUs. Results indicate that the parallel CM with multi-GPUs has sufficient accuracy, convergence, and scalability. Finally, the potential of the proposal for practical RTCA has been discussed with the reviewing of other state-of-the-art parallel computing methods reported in the literature.

Optimization of MV Distribution System Designs

This paper will present a new approach that is advantageous to medium-voltage (MV) distribution design configurations for large industrial and power distribution system configurations [specifically main-tie-main (MTM)] for large industrial and power station installations. Sixty years of traditional low-cost design approaches (typical MTM and operated with open tiebreaker) are re-evaluated to demonstrate that traditional low capital cost design may miss improvement opportunities. Those opportunities can be major capital expenditure reduction, power quality improvement, MV motor soft starter deletion, and improved system stability to name a few. Many designers may not have considered the component interrelationships and/or their tradeoffs when in an integrated system. The designer and/or user should consider the advantages of higher short-circuit capacity (SCC) systems by integrating fault current limiters and MV switchgear. Utilizing higher SCC systems permits power system designer optimization opportunities not possible before using conventional design methods. This paper will provide documentation of substantial savings of capital investment and energy under higher SCC conditions. The savings in one system component will offset another's increased cost. An obvious benefit of stiffer systems is ease of direct-on-line starting of large motor-driven compressor trains. The future need for motor soft starters minimizing system impact will be challenged. This paper may change fundamental system design methodology for system designers by removing several performance tradeoffs. This paper, in its original version, was previously presented at the 2010 IEEE/IAS/Petroleum Chemical Industry Conference. It was expanded with new sections for the 2017 IEEE/Industry Applications Society (IAS)/Pulp, Paper Forestry Industries Conference to include pre-emptive prefault adjustable power quality and multisourced networked power systems.

Dual-Loop Digital Control of a Three-Phase Power Supply Unit With Reduced Sensor Count

Widespread deployment of voltage source inverter units in high penetration applications such as distributed generation and stand-alone renewable energy conditioning imposes stringent demands on reliability and output voltage regulation. Reported literature provides numerous solutions for output voltage regulation, which includes twin aspects of command tracking and output impedance control. Most of these methods rely on the measurement of at least two separate variables per phase, which compromises overall reliability. This paper focuses on a dual-loop voltage regulation approach requiring only output voltage measurement. The outer loop of a control scheme is used to assure prompt tracking of the inverter output voltage, whereas the inner derivative feedback loop improves system stability by damping the output filter resonance. Digital realization of this derivative term is generally a challenge with many methods currently developed for resolving it. These methods are, however, still facing drawbacks, which have inclusively been explained in this paper. Subsequently, a new digital derivative is proposed whose performance is predicted analytically and then validated through experimental results with a 7.5-kVA inverter prototype.

An architecture based on computing with words to support runtime reconfiguration decisions of service-based systems

Service-based systems (SBSs) need to be reconfigured when there is evidence that the selected Web services configurations no further satisfy the specifications models and, thus the decision-related models will need to be updated accordingly. However, such updates need to be performed at the right pace. On the one hand, if the updates are not quickly enough, the reconfigurations that are required may not be detected due to the obsolescence of the specification models used at runtime, which were specified at design-time. On the other hand, the other extreme is to promote premature reconfiguration decisions that are based on models that may be highly sensitive to environmental fluctuations and which may affect the stability of these systems. To deal with the required trade-offs of this situation, this paper proposes the use of linguistic decision-making (LDM) models to represent specification models of SBSs and a dynamic computing-with-words (CWW) architecture to dynamically assess the models by using a multi-period multi-attribute decision making (MP-MADM) approach. The proposed solution allows systems under dynamic environments to offer improved system stability by better managing the trade-off between the potential obsolescence of the specification models, and the required dynamic sensitivity and update of these models.

Virtual synchronous generator model based control of PV for power system stability improvement in a large-scale power system with a massive integration of PVs

In this paper, virtual synchronous generator (VSG) model based control of photovoltaic power generations (PVs) for power system stability improvement is proposed. Different from other studies on VS...

Detailed dynamic refrigerant migration characteristics in room air-conditioner with R290

Propane (R290) as flammable refrigerant posed additional fire and explosion risk in room air conditioner (RAC), refrigerant migration and redistribution have been recognized as essential factors for leakage characteristics and charge optimization researches. Hence, a detailed understanding of the dynamic behavior of RAC systems is beneficial to future charge analysis and model-based control design, and then a system-level finite-volume dynamic model was developed in this paper. For the purpose of realistic modelling, dynamic lubricant solubility and absorption rate, finite-volume model integrated with geometry configuration and fin equivalent simplification were adopted. On the other hand, transient solver and public domain software YSMP were derived from SINDA/FLUINT (S/F) platform to make models converge and reduce the CPU time. From the initial state assumptions given in this paper, simulated results like dynamic mass, temperature and pressure distribution were validated by experiments; and they had good conformity. It was found that refrigerant migration process before equilibrium could be divided into dramatic change phase and smooth change phase. Dramatic change phase was dominated by mass transfer, while smooth change phase was dominated by heat transfer. Finally, the sensitivity of conditions and geometries to each component charged fraction was studied. Under reasonable charged circumstances, greater displacement, less mass charged and larger volume ratio of condenser to evaporator will be beneficial for improving system stability during startup.

Developing Busbar protection with new differential characteristics to solve the breakpoint settings of digital commercial relays

The current commercial characteristics of the digital differential relays have many breakpoint settings of time delay due to Current Transformer Saturation “CT-SAT” and error. This can decrease the sensitivity of the Merz-Price circulating current protection relays. However, to enhance the stability of this type of relays, the operating threshold boundary is increased. This will cause serious limitations for the relays during faults occurrence inside the Bus-bar zone. The protection characteristic of such relays is based on the phasor quantities, in such case the secondary current during the CT-SAT equals to zero. To improve the Merz-Price circulating current protection characteristic, the relay operation should depend on the features of the faulted instantaneous current rather than the phasor quantities. The paper develops new Merz-Price circulating current characteristic based on the wavelet transform of the noises generated by the fault. The captured noises have valuable information during the CT-SAT. The study shows the performance improvement in system sensitivity and stability of the new characteristic. All types of the faults are successfully detected due to current saturation, ratio mismatch, early and late saturation.