Improvement Of Stability Margin Research Articles

The Effect Pso/Abc, Abc/Bfo, Pso/Bfo and Cs/Bfo Hybrid Techniques on Power System Buses for Voltage Stability Margin Improvement

This paper presents and investigates new approaches inspired by nature to determine the optimal placement of UPFC for enhancing voltage stability margin of power system network. Voltage collapse phenomenon has remained an operational problem yet to be solved by power system engineers. To improve the voltage stability of the power system network, new optimisation techniques viz: PSO/ABC, ABC/BFO, PSO/BFO AND CS/BFO hybrids are investigated for their performance on power system buses for voltage stability improvement. The performance of the proposed hybrid methods are examined on the practical Nigerian 56 - bus network for voltage stability improvement. The simulation results has shown that ABC/BFO technique is better than BFO/PSO by 3.44 in improving voltage stability of margin of power system, gives additional improvement of 4.07, totalling 7.51% and lastly BFO/CS technique improved voltage stability margin of power system further by 5% totalling 12.51%. Also this research revealed that the smaller the gamma value the better the UPFC contribution to voltage stability enhancement. BFO/CS technique yielded the smallest gamma values of 0. 74532 and 0.830913 in both Nigerian practical network and IEEE – 14 bus network as shown in the analysis.

Influence of diversified dihedral stator on the thermodynamic performance and flow loss characteristics of a variable core driven fan stage

The Variable Cycle Engines (VCE) have emerged as the unequivocal choice for the next generation of aircraft power systems, with the core driven fan stage (CDFS) playing a crucial role in determining its performance. In this study, the variations in performance improvements of CDFS with different dihedral stator schemes are analyzed, and a weight-adjustable comprehensive improvement coefficient is defined. The results indicate that under different modes, a dihedral angle of 10° provides optimal improvements in peak efficiency and maximum pressure rise, while the optimal dihedral angle for stability margin improvement varies depending on the operating mode. The influence of dihedral height on performance is relatively minimal compared to the dihedral angle. By integrating flow field analysis and quantitative loss analysis, it is observed that the dihedral blade can effectively mitigates the interaction between the trailing edge recirculation vortex and other vortex in the stator, resulting in a significant reduction in secondary flow losses and wake losses. However, under near stall conditions, excessively large dihedral schemes in the stator intensify the interaction between secondary flow vortices, leading to premature flow instability.

PID-Based control of sepic power stage with QS bacterial-based search algorithm for renewable energy applications

In response to the growing need for efficient power conversion in renewable energy applications, this study addresses the issue of harmonic distortion and low Power Factor (PF) values caused by non-linear loads, such as electronic devices. Low PF results in reduced efficiency, increased energy consumption, and higher costs for both consumers and utilities. Active correction, typically involving an active circuit implemented using a power converter, provides an optimal solution by offering high performance, precise regulation, and low harmonic distortion. This research proposes a Power Factor Correction (PFC) solution utilizing an Interleaved DC-DC Single Ended Primary Inductance Converter (SEPIC) for the power stage and a Proportional Integral Derivative (PID) controller for the control block, tuned by a Quorum Sensing (QS) bacterial-based search algorithm. The PID controller parameters are derived using a frequency-domain approach, which presents advantages such as reduced design complexity, improved stability margins, and enhanced SEPIC performance. Simulation results indicate reduced overshoot, settling time, rise time, and Total Harmonic Distortion (THD) percentage, as well as increased efficiency and power factor nearing unity. The proposed scheme also demonstrates improved dynamic performance for variations in load, line, and reference voltage. Owing to its high efficiency, precise voltage regulation, and minimized impact on the electrical grid, this solution is well-suited for renewable energy applications, where optimizing energy conversion and ensuring stable operation are crucial for the overall performance of renewable energy systems.

Analysis and Design of Voltage-controller Based on Single-state Feedback Active Damping for Grid-forming Converters

This paper investigates the analysis and design of digital single-loop voltage-controller for grid-forming voltage source converters with LC-filters. Inspired by the structure diagram of the passive damping method, the virtual resistance concept based on only capacitor voltage feedback is used to realize active damping without the need of any current sensor, reducing thus the system costs. It is revealed from the controller closed-loop analysis that the insertion of an integrator in series with a proportional and resonant controller can significantly improve stability margin and dynamic performance of the system, then only the proportional controller need to be determined for system stability and the resonant controller is merely used for zero steady-state tracking error, which facilitates the controller parameter tuning. A systematic design based on the root contours in the discrete z-domain is proposed to optimize the parameters of the controller. The largest distance between the poles of the closed-loop system and the unit circle is achieved, which indicates the fastest dynamic performance under desired stability margins. Meanwhile, a simple differentiator constructed by backward-Euler plus lead-compensator is used to replace the noise-sensitive derivative term. In order to evaluate the proposed control approach performance, the system is tested in laboratory setup under different load conditions. The obtained results verify the effectiveness of the proposed design method and validate the analysis.

Statistical evaluation of stability margin of a multi-stage compressor with geometric variability using adaptive polynomial chaos-Kriging model

Compressed air energy storage systems must promptly adapt to power network demand fluctuations, necessitating a high surge margin in the compression system to ensure safety. It is challenging to completely eliminate blade geometric variations caused by limited machining precision, the important effects of which should be considered during aerodynamic shape design and production inspection. The present paper explores the uncertainty impact of geometric deviations on the stability margin of a multi-stage axial compressor at a low rotational speed. Initially, an adaptive polynomial chaos expansion-based universal Kriging model is introduced, and its superior response performance in addressing high-dimensional uncertainty quantification problems is validated through rigorous analytical and engineering tests. Then, this model is used to statistically evaluate the stability margin improvement (SMI) of the compressor due to the Gaussian and realistic geometric variabilities separately. The results show that the mean and standard deviation of SMI are −0.11% and 0.5% under the Gaussian geometric variability, while those are 0.33% and 0.39% under the realistic variability. For both the geometric variabilities, the stagger angle and maximum thickness deviations of the first-stage rotor are the most influential parameters controlling the uncertainty variations in the stability margin. Finally, the underlying impact mechanism of the influential geometric deviations is investigated. The variation in the stability margin caused by the geometric deviations primarily results from the alteration of inlet incidences, affecting the size of the tip leakage vortex blockage and boundary-layer separation regions near the blade tip of the first-stage rotor.

Investigation of the impact of PSO, ABC, BFO and Cuckoo search optimization techniques on UPFC device for sustainable voltage stability margin improvement

This paper investigates the enhancement of voltage stability margin using Unified Power Flow Control (UPFC) device tuned with Particle Swarm Optimization (PSO), Artificial Bee Colony (ABC), Bacterial Foraging Optimization (BFO) and Cuckoo Search techniques (CS) on Nigerian 330 kV 56-bus practical network. In order to have a voltage stable power system, it is good to keep voltages within the acceptable limits. This is achieved using continuation power flow embedded in Power System Analysis Toolbox (PSAT). The optimal location and tuning of the UPFC device is determined using line stability index and the met-heuristics techniques. The effects of UPFC and the proposed optimizing techniques on voltage stability margin are examined. The results so obtained for tuning PSO, ABC, BFO and Cuckoo Search with UPFC device are compared to know the technique that yields the best loading parameter for Nigerian 56- bus power system for voltage stability margin enhancement. It is found that UPFC tuned with Cuckoo Search outperforms the other techniques in terms of the increased loading parameter of the Nigerian power system with margin improvement of 86.6%, 90% and 88.6% for Adiabor (Bus 45), Jalingo (Bus 34) and Jos (Bus 13). The tuned UPFC device has proved beyond reasonable doubt that it can improve voltage stability margin of the entire Nigerian 330 kV Network as envisaged from results before and after optimization.

Adaptive Control of Grid-Connected Inverters With Nonlinear LC Filters

Distributed generation is an effective solution to clean, reliable, and cost-efficient energy supply. In this framework, inverters play a key role as energy converters. Accordingly, this article investigates the utilization of nonlinear inductive–capacitive (LC) filters for grid-connected inverters. Nonlinear LC filters are made of inductors with nonlinear B–H curves, which makes them have a smaller volume, less dissipation loss, and lower cost. The main drawback of using these filters, however, is their nonlinear current-dependent characteristics. To harness the undesirable impacts of nonlinear filters on the system performance, an adaptive observer-based control scheme is developed in this article. The proposed controller is based on a concurrent estimation of nonlinear inductor values, capacitor voltages, and grid-side currents. Based on its fast adaptation to plant changes, this scheme provides an improved stability margin and an inherent resonant damping characteristic under grid impedance uncertainty. Compared with the conventional approaches, this method requires no extra sensors. A comparative simulation and experimental analysis, based on a three-phase 7-kW inverter, is provided to validate the efficacy of the proposed control strategy.

A New Virtual Inductance Control Method for Frequency Stabilization of Grid-Forming Virtual Synchronous Generators

Frequency stabilization is the premise of guaranteeing grid-friendly integration of virtual synchronous generator (VSG). Based on that premise, this article, focused on frequency stability, establishes the small signal model of grid-forming VSG system. At first, the mechanism of frequency oscillation occurring in system of active- and reactive-power coupling is analyzed by the defined feedback effect factor in this article. Besides, a new dynamic model is established for identifying dynamic interaction of voltage magnitudes and frequency by means of feedback effect. The analytical results of established models agree with that of eigenvalue analysis. Furthermore, a new virtual inductance control strategy is proposed to mitigate the unstable oscillation of frequency and powers, enhance damping performance, and improve stability margins. Unlike the conventional virtual inductance control, which is reliable on dual-loop control framework, the proposed virtual inductance control in this article is based on principle of energy conservation and can be applicable for the grid-forming inverter without inner dual-loop control structure. Finally, the proposed modeling as well as virtual inductance control method is experimentally verified.

Data-driven IQC-Based Uncertainty Modelling for Robust Control Design

A new approach is presented in the paper for modelling uncertainty as an elliptical set for robust controller synthesis. The method involves finding the best linear nominal model and the corresponding elliptical uncertainty set that is consistent with a set of frequency response functions of linear time-invariant (LTI) single-input single-output (SISO) systems. The uncertainty set is then converted into an equivalent integral quadratic constraint (IQC) using a novel split representation of uncertainty. Finally, the IQC is integrated into a data-driven frequency-domain controller synthesis method through convex optimization. The simulation and experimental results demonstrate that the proposed method yields a “tighter” uncertainty set and improved stability margins compared to classical methods that use disk uncertainty.

추력편향방식 AUV의 직진안정성 개선을 위한 고정핀 설계

AUVs (Autonomous Underwater Vehicles) have been widely used for various underwater survey missions. In general, cruising type AUVs have torpedo-shaped hull forms for minimizing the hull resistances. It is necessary to ensure there are sufficient straight-line stabilities for a cruising type AUV in order to maintain its desired courses and depths with minimum controls during operations. In this study, vertical and horizontal plane straight-line stabilities of a designed AUV are analyzed based on the captive model tests. VPMM (Vertical Planar Motion Mechanism) tests are carried out to obtain hydrodynamic coefficients of the designed AUV. The AUV shows both vertical and horizontal plane instabilities, its stability margin indices are unsatisfying when compared with the recommended values. But the recommended vertical plane stability margins are subject to very high-speed conditions, so the characteristic equations of the AUV are reconsidered to investigate low-speed vertical plane stabilities in more detail. Next, a pair of horizontal and vertical fins are respectively designed to improve the vertical and horizontal plane stabilities of the AUV. The AUV with fixed fins shows improved stability margin indices within the recommended levels. In addition, the shape of the horizontal fins is properly modified for safe operations. The AUV with the designed vertical fins shows good horizontal plane stability in straight run simulations with step disturbances. And the effects of the horizontal fins are investigated through depth control simulations with biased random disturbances.

Comparative Study and Performance Analysis of PSO, ABC, BFO and Cuckoo Search Optimization Techniques on UPFC Device for Voltage Stability Margin Improvement

Comparative Study and Performance Analysis of PSO, ABC, BFO and Cuckoo Search Optimization Techniques on UPFC Device for Voltage Stability Margin Improvement

Bifurcation Analysis of Active Electrical Distribution Networks Considering Load Tap Changers and Power Converter Capacity Limits

The aim of this article is to analyze the parameter stability and power transfer limits of active distribution networks with power converters and load tap changers by using bifurcation theory.First, the nonlinear model of a representative distribution grid with mixed loads and power converters is derived. Frequently neglected effects of converter capacity limits and transformers with load tap changers are considered, and for this purpose, static and dynamic saturations are modeled by using approximations based on smooth functions. In addition, a solution based on an antiwindup scheme is provided to model load tap changers without numerical convergence problems. These methods allow their integration to the model in a comprehensive way. Results show the impact of converter parameters and its limits on system stability as well as the impact of weak grid conditions. Moreover, they show that these effects can destabilize the system under, seemingly, safe operating conditions. The results indicate that reactive power support from converters can improve stability margins and the performed analysis can help in the design of the converter control parameters. Experimental results obtained from the laboratory environment comprising two distributed generators and a grid emulator are used for the validation of the contributions of this article.

Dynamic performance and stability characteristics of a multi pad externally adjustable fluid film bearing

ABSTRACT Due to the recent advances in the development of smart rotating machineries, there is a high demand for automated support bearings with efficient integrated control systems. Existing research studies have indicated that high-end performance can be attained from automated bearings through effective control and modification of the bearing performance parameters. In this study, an innovative journal bearing geometry with multi-control operations is presented. The four controllable bearing pads enclosed in the bearing casing have a novel feature to translate radially and undergo controlled tilt motions. The multi-control bearing system with radial and tilt pad motions will significantly influence the stability responses of the rotorsystem, which is theoretically analysed in this study. To predict the variation in film thickness for varied pad adjustments, a modified film thickness equation is incorporated in the linearised perturbed model for dynamic analysis. A notable variation in dynamic coefficients and stability parameters are observed for negative radial adjustment and tilt angles. Results indicate that negatively adjusted radial and pad tilt motion can generate improved stability margins at higher eccentricities. Data generated on stability margins at specific pad adjustments will be helpful while developing the control system for the actuation mechanism in the experimental setup.

Impact of control system on the DC impedance characteristics of low-medium frequency bands and stability of modular multilevel converter based HVDC system

The resonance in modular multilevel converter based high voltage direct current (MMC-HVDC) system poses a potential threat to the safe and stable operation of the power grid. The mechanism of the resonance phenomenon is complicated, which is closely related to the impedance characteristics of MMC system. By establishing the DC impedance model of MMC-HVDC system at both ends, the influence of parameters of control system in converter stations on the DC impedance characteristics of MMC system was analyzed, revealing the main influencing frequency bands and effect of each control parameter. The DC impedance characteristics of low and medium frequency bands could be shaped in a targeted manner by adjusting the control parameters, the stability margin of the system will be improved as well. The correctness of the results was verified by time domain simulation. The analysis results of this article can provide reference for the selection of the parameters of control system and the improvement of stability margin of MMC-HVDC system.

Robust combustor design based on flame transfer function modification

Operation under stable conditions is an important prerequisite for gas turbine safety. While recent studies have focused primarily on acoustic design to avoid thermoacoustic instabilities, in the present study we shift the focus to improving stability margins by flame transfer function (FTF) modification. The flame transfer function of premixed flames is affected by various mechanisms such as variations in equivalence ratio, swirl fluctuations and shear layer instabilities. These mechanisms can be influenced by modifying parameters such as fuel distribution, injection location, swirl number or gas composition. Based on the Nyquist stability method we formulate criteria for how and at what frequencies the flame transfer function needs to be modified, in order to increase the stability margins of a thermoacoustic system. Gain and phase margin as well as the sensitivity function serve as measures of stability. The criteria are limited to single frequencies, which allows experimental FTF optimization with manageable effort. In the second part of this study it is shown that the Nyquist method can also be used as an efficient and compact way to determine whether the uncertainties of subsystems can affect the overall stability, without requiring eigenvalue calculations.

Assessment of the Static Stability Margin and Voltage Profile Improvement in the SOUTH-SNEL PowerNetwork using a SVC under MATLAB / PSAT Environment

The huge increase in the demand of electric power and the economic constraints to build new facilities, lead the power systems to operate near of their stability limits. Indeed, instability has become a major problem in the management of power systems. Unavoidable disturbances such as short circuits, momentary unavailability of transmission lines, generators as well as transformers can affect the stability of the power system at any time and bring it into a state of instability or collapse. These collapses become a major problem for energy consumers, because the lack of energy leads them to use backup energy sources that are relatively expensive and polluting. This situation lowers the productivity of the industry, and for the national electric company of the Congo, (SNEL), the time to get rid of the magnetization of the network and to take all the loads, can generate penalties, which is a loss of revenue for the company. This paper aims to assess the stability margin and to improve the quality of electrical energy in the south-SNEL transmission system.

Intelligent stability margin improvement using series and shunt controllers

Electric market always prefers to use full capacity of existing power system to control the costs. Flexible alternate current transmission system (FACTS) devices introduced by Electric Power Research Institute (EPRI) to increase the usable capacity of power system. Placement of FACTS controllers in power system is a critical issue to reach their maximum advantages. This article focused on the application of FACTS devices to increase the stability of power system using artificial intelligence. Five types of series and shunt FACTS controllers are considered in this study. Continuation power flow (CPF) analysis used to calculate the collapse point of power systems. Controlling parameters of FACTS devices including their locations are determined using real number representation based genetic algorithm (RNRGA) in order to improve the secure margin of operating condition of power system. The 14 and 118 buses IEEE standard test systems are utilized to verify the recommended method. The achieved results manifestly proved the effectiveness of proposed intelligent method to increase the stability of power system by determining the optimum location and size of each type of FACTS devices.

Numerical Investigation on a Axial Slot Casing Treatment of a Large Circumferential Interval and Small Opening Area

Axial slot casing treatment is a common method to extend the stall margin of a compressor. Based on the mechanism of unsteady flow control, this paper redesigns axial slots with large circumferential interval and small opening area. To test the effect of this axial slot structure, unsteady numerical simulations were carried out with different slot areas and circumferential intervals. The results show that this novel axial slot casing treatment can significantly improve compressor stall margin. Meanwhile, compared with the traditional axial slot, the efficiency loss is greatly reduced. The flow field analysis shows that the new axial slot structure proposed in this paper can suppress the development of tip leakage vortex and unsteadiness in the tip region at the near stall condition through decreasing the tip loading periodically. Moreover, we find that the slot area is proportional to the improvement of stability margin. Under the same slot area, an excessive number of slots is not conducive to the improvement of the stability margin.

Intelligent stability margin improvement using series and shunt controllers

Electric market always prefers to use full capacity of existing power system to control the costs. Flexible alternate current transmission system (FACTS) devices introduced by Electric Power Research Institute (EPRI) to increase the usable capacity of power system. Placement of FACTS controllers in power system is a critical issue to reach their maximum advantages. This article focused on the application of FACTS devices to increase the stability of power system using artificial intelligence. Five types of series and shunt FACTS controllers are considered in this study. Continuation power flow (CPF) analysis used to calculate the collapse point of power systems. Controlling parameters of FACTS devices including their locations are determined using real number representation based genetic algorithm (RNRGA) in order to improve the secure margin of operating condition of power system. The 14 and 118 buses IEEE standard test systems are utilized to verify the recommended method. The achieved results manifestly proved the effectiveness of proposed intelligent method to increase the stability of power system by determining the optimum location and size of each type of FACTS devices.

Adaptive negative impedance strategy for stability improvement in DC microgrid with constant power loads

This paper presents a novel adaptive-based negative impedance strategy to solve the stability issue of DC microgrids with constant power loads (CPL). It is well known that constant power loads produce negative resistance characteristics, and its significance increases due the high penetration of CPL connected to a DC microgrid. The stability of DC power system starts deteriorating. Also, the stability problem becomes more sever if line inductance is not negligible. Therefore, the proposed strategy designed negative impedance at the source side of the converters which adapt the changes in CPL and DC link voltage deviations to adjust the parameters of negative impedance during live operation. The objectives of the proposed strategy are to provide improved stability margin as compared to the existing virtual negative stabilizer and reduces the voltage drop occurs in DC link voltage due to the consideration of the negative impedance. The adaptive virtual impedance is proposed to counteract the effect of large line inductance and CPL virtual resistance, thus enhancing the damping effect of the DC power system. The DC microgrid system with proposed strategy is carefully modeled using small signal analysis. Matlab Simulation is used to validate the effectiveness and the stable operation of a DC microgrid prototype with the proposed strategy under the variable CPL and the line impedance.