Swing Curves Research Articles

Numerical simulation of optimizing the swing curve of a 3DOF biomimetic pectoral fin in drag mode

In response to the optimization problem of the motion law of the pectoral fins of biomimetic robotic fish, this paper uses computational fluid dynamics (CFD) methods to achieve the CFD optimization of two types of rigid biomimetic pectoral fins with three degrees of freedom (DOF): elliptical and 8-shaped swing curves. By analyzing the hydrodynamic characteristic curve of the pectoral fins, pressure distribution upstream and downstream of the fin surface, velocity vector of the surrounding flow field during pectoral fin swing, and three-dimensional vortex structure, it is found that when the pectoral fins are pushed forward in an elliptical swing curve, the resistance peak value decreases after two optimizations. However, at the same time, a certain amount of thrust is lost. When the pectoral fin advances in an 8-shaped swinging curve, after two optimizations, the pectoral fins resistance decreases while maintaining an enormous thrust, comprehensively improving the propulsive effect of the pectoral fin on the robotic fish. By substituting the optimized 8-shaped pattern into the robotic fish model, it is found that the flapping angle of 35° has better drag reduction performance, and the average swimming speed of the robotic fish is the fastest at this angle.

Application of Static Synchronous Compensator for Improvement of Power System Transient Stability

Transient stability is the power system’s ability to maintain synchronism when exposed to severe disturbances such as loss of generation, rapid load changes, transmission lines tripping, switching operations and faults. Transient instability causes cascading outages, system collapse and economical losses. This study employed static synchronous compensator (STATCOM) for power system transient stability improvement. The system’s steady state and transient responses were respectively modelled with Newton-Raphson power flow and modified-Euler linearized swing equations. A balanced three-phased short circuit fault was introduced on selected buses for transient stability analysis. The steady state and transient responses of the system were simulated with and without STATCOM. The critical fault clearing time (CFCT) was obtained from the generators’ swing curves. The IEEE 9-bus and 14-bus power networks were used as test cases. The voltage magnitudes of all buses in both networks fell within the specified 0.95 to 1.1 p.u. voltage limit with and without compensation. The total active line loss on IEEE 9-bus and 14-bus networks which were 4.641 and 13.514 MW without compensation reduced to 4.600 and 13.014 MW, respectively with STATCOM’s application. The total reactive line losses of both networks which were 92.160 and 31.393 MVAr without compensation decreased to 90.160 and 30.693 MVAr, respectively with STATCOM’ utilization. The CFCT for fault on bus 8 of the IEEE 9-bus system without compensation were 0.2100 and 0.2700 s for generators 2 and 3, respectively. The system’s stability was, however, extended beyond 0.2700 s due to compensation from STATCOM. In the case of IEEE 14-bus system, the CFCT for fault on bus 6 was 0.36364 s for generators 2, 3, 4 and 5, respectively without compensation. The STATCOM inclusion, however, enhanced the system’s stability beyond 0.36366 s where all the four had lost synchronism. This work established that the use of STATCOM on the considered networks appropriately extended the CFCT such that the stability of the systems was not lost in the event of fault application via robust compensation of reactive power.

Analysis of Power System Transient Stability of the Nigerian 330-kV Electricity Grid

Faults on power system are inevitable and can occur at any time resulting into transient instability. Transient instability can cause loss of synchronism and possible damage to power equipment and consumer loads. Therefore, this study analyzed the transient stability (TS) of the Nigerian 330-kV, 34-bus power network. Power flow and swing equations describing the system steady and transient states were respectively analyzed using Newton-Rahpson and Runge-Kutta, fourth order numerical techniques to provide linear solution due to their non-linearity. Simulations were done and swing curves for different fault conditions obtained. The critical clearing time at which the simulated faults were cleared was determined. The results of load flow analyses revealed that buses 6, 10, 13, 14, and 17 with respective voltage magnitude of 0.937, 0.921, 0.938, 0.829 and 0.780 per unit violated voltage tolerance limit of 0.95 to 1.05 p.u. The system total active and reactive power losses were 57.62 MW and -70.62 MVar respectively. The obtained swing curve showed that for fault on bus 11 [line 9-11] generators 2, 3 and 7 lost synchronism after 1.0 s but other generators retained their stability. Similarly, for fault on bus 13 [line 10-14] generators 3 and 7 lost synchronism but other generators retained stability after 0.4 s. These results indicate that faults occurrence on generating stations of power system is unavoidable, but the clearance time must be short (few seconds) to avert total system collapse and loss of synchronism.

Identification of coherent generators based on clustering methods

The identification of coherent generators is very important for the stability analysis and control of power system. So far, there are three main identification methods of coherent generators which have cetain disadvantages. In this paper, two new algorithms based on clustering are proposed for the identification of coherent generators. Algorithm 1 is the optimal classification of generators based on given swing curves. By introducing the validity index into the algorithm, the optimal classification of the given generator swing curves can be obtained. Algorithm 2 is identification of coherent generators under specific faults. This algorithm firstly calculates the critical clear time of the system. Since the swing curves obtained at the critical clear time(critical curves) contain the complete information reflecting the swing and oscillation between generators, they can be used as reliable samples for clustering. Examples show that the two algorithms are effective.

Transient Stability Analysis of a System of Two Machines Connected to an Infinite Bus

Abstract The term large disturbance is often used in place of system collapse. It is the process by which the series of events accompanying voltage instability, frequency instability, and transient instability leads to a blackout or abnormally low voltages in a significant part of the power system. Large disturbance may be due to tripping of the lines on an account of fault or increase in load than the available supply. Transient stability deals with the effect of large and sudden disturbances in the system, while steady-state Stability deals with the effect of small disturbances in the system. Small disturbance can be a change in the gain of the automatic voltage regulator in the excitation system of a large generating unit. This paper studies the effect of a large disturbance in a power system. The system is represented by a two-machine system connected to an infinite bus. This study involves the effects of the fault on the speed of the rotor of the synchronous generator. Two cases were investigated: firstly, when fault occurred on a bus, and secondly, when fault occurred on the middle of a line. The conditions of the network before, during and after the fault are established in this paper. The equal area criterion was applied to the swing curves obtained to predict the critical clearing time of the system. The critical clearing time was found to lie between 0.20s and 0.225s if the fault occurred on the bus, and lies between 0.245s and 0.355s if the fault occurred at the middle of a line. Thus the system is more transiently stable in the second case than in the first. Machine 1 was less stable in the first case, while machine 2 was less stable in the second case. The critical clearing time is essential to the design of proper relaying schemes for fault clearing.

Transient Stability Analysis of a System of Two Machines Connected to an Infinite Bus

Abstract The term large disturbance is often used in place of system collapse. It is the process by which the series of events accompanying voltage instability, frequency instability, and transient instability leads to a blackout or abnormally low voltages in a significant part of the power system. Large disturbance may be due to tripping of the lines on an account of fault or increase in load than the available supply. Transient stability deals with the effect of large and sudden disturbances in the system, while steady-state Stability deals with the effect of small disturbances in the system. Small disturbance can be a change in the gain of the automatic voltage regulator in the excitation system of a large generating unit. This paper studies the effect of a large disturbance in a power system. The system is represented by a two-machine system connected to an infinite bus. This study involves the effects of the fault on the speed of the rotor of the synchronous generator. Two cases were investigated: firstly, when fault occurred on a bus, and secondly, when fault occurred on the middle of a line. The conditions of the network before, during and after the fault are established in this paper. The equal area criterion was applied to the swing curves obtained to predict the critical clearing time of the system. The critical clearing time was found to lie between 0.20s and 0.225s if the fault occurred on the bus, and lies between 0.245s and 0.355s if the fault occurred at the middle of a line. Thus the system is more transiently stable in the second case than in the first. Machine 1 was less stable in the first case, while machine 2 was less stable in the second case. The critical clearing time is essential to the design of proper relaying schemes for fault clearing.

Parallel computing of multi-contingency optimal power flow with transient stability constraints

To deal with the high dimensionality and computational density of the Optimal Power Flow model with Transient Stability Constraints (OTS), a credible criterion to determine transient stability is proposed based on swing curves of generator rotor and the characteristics of transient stability. With this method, the swing curves of all generator rotors will be independent one another. Therefore, when a parallel computing approach based on the MATLAB parallel toolbox is used to handle multi-contingency cases, the calculation speed is improved significantly. Finally, numerical simulations on three test systems including the NE-39 system, the IEEE 300-bus system, and 703-bus systems, show the effectiveness of the proposed method in reducing the computing time of OTS calculation.

Hybrid algorithm for rotor angle security assessment in power systems

Transient rotor angle stability assessment and oscillatory rotor angle stability assessment subsequent to a contingency are integral components of dynamic security assessment (DSA) in power systems. This study proposes a hybrid algorithm to determine whether the post-fault power system is secure due to both transient rotor angle stability and oscillatory rotor angle stability subsequent to a set of known contingencies. The hybrid algorithm first uses a new security measure developed based on the concept of Lyapunov exponents (LEs) to determine the transient security of the post-fault power system. Later, the transient secure power swing curves are analysed using an improved Prony algorithm which extracts the dominant oscillatory modes and estimates their damping ratios. The damping ratio is a security measure about the oscillatory security of the post-fault power system subsequent to the contingency. The suitability of the proposed hybrid algorithm for DSA in power systems is illustrated using different contingencies of a 16-generator 68-bus test system and a 50-generator 470-bus test system. The accuracy of the stability conclusions and the acceptable computational burden indicate that the proposed hybrid algorithm is suitable for real-time security assessment with respect to both transient rotor angle stability and oscillatory rotor angle stability under multiple contingencies of the power system.

A Minimax Polynomial Approximation Objective Function Approach for Optimal Design of Power System Stabilizer by Embedding Particle Swarm Optimization

The paper presents a novel approach based on Minimax approximation and evolutionary tool Particle Swarm Optimization (PSO) to fabricate the parameters of Power System Stabilizers (PSSs) for multi machine power systems. The proposed approach employs PSO algorithm for find the setting of PSS parameters. The worth mentioning feature of this work is the formulation of objective function with the help of swing curves interpolation. A novel transformation known as minimax approximation is used for converting the objective into the polynomials of degree one, two and three. To construct the objective function based on interpolation second order sensitivity analysis is performed. The performance of the PSSs is tested under different topological changes, operating conditions and system configurations. Nonlinear simulation reveals that proposed PSSs are effectively deal with local and interarea modes of oscillations. PSS design obtained through lower order polynomial expression of objective function is able to deal with the oscillatory modes efficiently. DOI: http://dx.doi.org/10.11591/telkomnika.v14i2.7602

Influence of conditions of growth on the structural perfection of AlN layers obtained by the MOS-hydride Epitaxy Method

The influence of buffer layers formed at different temperatures and ratios of elements of groups V and III (V/III) on crystalline perfection of epitaxial layers AlN grown using the MOS-Hydride Epitaxy Method on the templates α-Al2O3 is considered. It is shown that the most efficient method to increase the structural perfection of epitaxial layers is use of the high-temperature buffer layer on a low V/III ratio. Further improvement of the quality of AlN layers is possible due to the reduction of parasitic reactions between ammonia and trimethylaluminum in the gas phase by means of optimization of the gas flow through the reactor. The specified values of the growth parameters permitted obtaining the AlN layers of the high crystalline perfection (half-width of X-ray swing curves for reflections (0002), (0004) and \((10\bar 13)\) made asec of 50, 97 and 202, respectively) with a good root-mean-square roughness of the surface of 0.7 nm applicable for the creation of instruments based thereon.

Competitiveness of negative tone resists for nanoimprint lithography

This paper presents a semi-analytical approach for the calculation of the mean relative intensity within photoresist layers of a given thickness on silicon – the mean intensity is the one obtained after a post exposure bake to remove standing wave effects. The approach is based on the handling of analytically determined intensity values in a matrix form. Transmission, reflection and absorption in an air/resist/substrate configuration are considered to calculate the intensity for a single wavelength or a multiple wavelength exposure. Swing curves of the mean relative intensity as a function of the total resist thickness indicate a novel application in the context of nanoimprint: a residual layer-free imprint can be obtained with residual layers of up to about 30nm, as such thin layers always remain underexposed. Thus, when a negative tone photoresist is imprinted and is flood exposed after the imprint, any thin residual layer will be removable in a simple development step, thus avoiding any breakthrough etch. This is of particular interest for a further use of the imprinted structures with lift-off.

IMPROVEMENT OF TRANSIENT STABILITY OF POWER SYSTEM USING SOLID STATE CIRCUIT BREAKER

The aim of this study is to use a solid state circuit breaker for the improvement of transient stability margin. Long distance AC transmission is often subject to stability problems, which limits the transmission capability. Interconnected power systems suffer from weakly damped swings between synchronous generator and sub systems. The development of modern power system has lead to an increasing complexity in the study of power system and also presents new challenges to power system stability and in particular to the aspects of transient stability and small signal stability. Transient stability control plays a significant role in ensuring the stable operation of power systems in the event of large disturbances and faults and is thus a significant area of research. This study investigates the improvement of transient stability of a two area system, using Solid State Circuit Breaker which is capable of fast switching in case of faults and thus controlling the real and reactive power flows in a faulted transmission line. Simulations are carried out in Matlab/Simulink environment for two area system model with Solid State Circuit Breaker to analyze the effects of SSCB on transient stability performance of the system. From the simulation results, swing curves of the three phase faulted power system without SSCB gets increases monotonically and thus the system can be considered as unstable whereas the swing curves of the system with an SSCB reaches to a steady state.

Optimum design of photoresist thickness for 90-nm critical dimension based on ArF laser lithography

In this work, a 90-nm critical dimension (CD) technological process in an ArF laser lithography system is simulated, and the swing curves of the CD linewidth changing with photoresist thickness are obtained in the absence and presence of bottom antireflection coating (BARC). By analysing the simulation result, it can be found that in the absence of BARC the CD swing curve effect is much bigger than that in the presence of BARC. So, the BARC should be needed for the 90-nm CD manufacture. The optimum resist thickness for 90-nm CD in the presence of BARC is obtained, and the optimizing process in this work can be used for reference in practice.

Static Synchronous Series Compensator Controller based on Fuzzy Logic Control for Power System Stabilization

Problem statement: Modern power system consists of the complicated network of transmission lines and carries heavy demand. Thus they cause in the stability problem. Approach: Static Synchronous Series Compensator (SSSC) is a power electronic based device that has the capability of controlling the power flow through a line. The series voltage injection model of SSSC is modeled into power flow equation and thus it is used to determine its control strategy. This study applies the fuzzy logic applies the SSSC to improve stability of power system. The mathematical model and control strategy of a SSSC are presented. The SSSC is represented by variable voltage injection with associate transformer leakage control to derive control strategy of SSSC. The swing curves of the three phase faulted power system without and with a SSSC is tested and compared in various cases. Results: The swing curve of the system with SSSC based fuzzy logic control has the less amplitude during the dynamic period. Conclusion: It was found from simulation results that SSSC can improve the power system oscillation after disturbance.

STATCOM Stabilizer based on Fuzzy Logic Control for Damping Power Oscillation

Problem statement: In power systems, there exists a continuous challenge to improve dynamic performance of power system. Approach: Static Synchronous Compensator (STATCOM) is a power electronic based device that has the capability of controlling the power flow through a line. This study applies the Static Synchronous Compensator (STATCOM) to control the power flow during dynamic period. To verify the effect of the STATCOM on dynamic performance, the mathematical model and control strategy of a STATCOM was needed to be presented. The converters of STATCOM were represented by variable voltage source with associate transformer leakage reactance and the voltage source and the reactance were transformed into current injection. The current injection model of STATCOM was modeled into power flow equation and thus it was used to determine control strategy. This study applies the fuzzy logic control to determine the control strategy of STATCOM. The swing curves of the three phase faulted power system without and with a STATCOM was tested and compared in various cases. Results: The swing curve of the system with STATCOM based fuzzy logic control had the less amplitude during the dynamic period. Conclusion: STATCOM can improve the dynamic performance of the system after disturbance.

Inter-Area Power Systems Stability Improvement by Static Synchronous Series Compensator

Problem statement: The inter-area power systems have special characteristic of the stability behavior. The improvement of inter-area power system is one of the important aspects in power system. Approach: This study applies the Static Synchronous Series Compensator (SSSC) to improve stability of inter-area systems. The SSSC is modeled and then is applied to be incorporated into the power system model for investigating stability improvement. The SSSC is modeled as the variable susceptance and is controlled during dynamic state. This presented SSSC model can be incorporated into susceptance matrix of power system model. The presented method is tested on sample inter-area power system with 3 phase fault distubrances. Results: The swing curve of inter-area power system without a SSSC gets increases monotonically and thus the system can be considered as unstable whereas the swing curves of system with a SSSC can be considered as stable. Conclusion: From the simulation results, the SSSC can enhance stability of inter-area power systems.

Coordination of Series and Shunt Flexible AC Transmission System Devices Based Voltage Source Converter for Improving Power System Stability

Problem Statement: Static Synchronous Compensator (STATCOM) and Static Synchronous Series Compensator (SSSC) have been individually applied to improve stability of power system. Approach: This study presents the coordination of a STATCOM and SSSC for improving power system stability. The swing curves of the three phase faulted power system with various cases are tested and compared. Results: The swing curve of system without FACTS devices has undamped oscillation. The system with a STATCOM or a SSSC can increase damping of power system whereas the system with coordination of a STATCOM and a SSSC provides the best results of stability improvement Conclusion: From the simulation results, the stability of power system can be much better improved by coordination control of a STATCOM and a SSSC.

Coordination of Series and Shunt Flexible Alternating Current Transmission Line System Devices Based Thyristor Controller for Improving Power System Stability

Problem statement: Thyristor Controlled Series Capacitor (TCSC) and Static Var Compensator (SVC) have been individually applied to improve stability of power system. Approach: This study presents the coordination of a TCSC and SVC for improving power system stability. The swing curves of the three phase faulted power system with various cases are tested and compared. Results: The swing curve of system without FACTS devices has undamped oscillation. The system with a TCSC or a SVC can increase damping of power system whereas the system with coordination of a TCSC and a SVC provides the best results of stability improvement Conclusion: From the simulation results, the stability of power system can be much better improved by coordination control of a TCSC and a SVC.

Improving Power System Transient Stability with Static Synchronous Series Compensator

Problem statement: Modern power system consists of the complicated network of transmission lines and carries heavy demand. Thus they cause in the stability problem. One of the major interests of power utilities is the improvement of power system transient behavior. Approach: Static Synchronous Series Compensator (SSSC) is a power electronic based device that has the capability of controlling the power flow through a line. This study applies the SSSC to improve transient stability of power system. To verify the effect of the SSSC on transient stability, the mathematical model and control strategy of a SSSC is presented. The SSSC is represented by variable voltage injection with associate transformer leakage reactance and the voltage source. The series voltage injection model of SSSC is modeled into power flow equation and thus it is used to determine its control strategy. This study uses machine speed deviation to control it. The swing curves of the three phase faulted power system without and with a SSSC is tested and compared in various cases. Results: The swing curve of system without a SSSC gets increases monotonically and thus the system can be considered as unstable whereas the swing curves of system with a SSSC can be considered as stable. Conclusion: SSSSC can improve transient stability of power system.

Application of Interline Power Flow Controller to Increase Transient Stability of Power System

Problem statement: The Interline Power Flow Controller (IPFC) is a novel device which can increase transient stability of power system. To verify the capability of the effect of IPFC on stability improvement of power system, the suitable mathematical model and control strategy of IPFC are needed to be presented. Approach: This study presented the mathematical model and control strategy of IPFC. The multi-series converters of IPFC are represented by multi-series voltage sources with associate transformer leakage reactance. The parameters of IPFC are modeled into power flow equation and thus it is used to determine control strategy. This study used Bang-Bang control strategy. The swing curves of the three phase faulted power system without and with an IPFC are tested and compared in various cases. Results: The swing curve of system without an IPFC get increased monotonically and thus the system can be considered as unstable whereas the swing curves of system with an IPFC can return to stable equilibrium point. Conclusion: The presented model of IPFC can help us to comprehend the effect of IPFC on transient stability improvement of power system. From simulation results, the IPFC can increase transient stability of power system.