Swing Stability Research Articles

Handling Qualities Assessment and Discussion for Helicopter with Slung Load Systems Utilizing Various Sling Configurations

Sling configurations significantly influence the coupled dynamics of the helicopter with slung load system (HSLS), resulting in alterations to handling qualities (HQs) that remain inadequately understood. This study introduces a computer-oriented, generalized method for constructing the HSLS model with various sling configurations. To evaluate the HQs of 1-point, 2-point, and 4-point sling configurations, both the stability and response criteria outlined in ADS-33E and a newly proposed criterion for slung loads towards the updated ADS-33F were employed. Modal analysis was conducted to elucidate the coupled mechanisms of the HSLS under different sling configurations. The findings reveal that the dynamics of the main rotor can attenuate the lateral swing motions of the load in the 4-point sling configuration. While multiple-point sling configurations can enhance the helicopter’s bandwidth, they also amplify the magnitude notch in the helicopter’s response. Nevertheless, when a larger hook distance is employed, the notch frequency is sufficiently distant from the load swing bandwidth, leading to a reduced degradation in HQs. A 4-point configuration with lateral and longitudinal hook distances equal to twice the width and length of the slung load is recommended in practice to achieve sufficient swing stability and mitigate HQ degradation.

Mechanical characteristics analysis of high dimensional vibration isolation systems based on high-static-low-dynamic stiffness technology

Large floating raft vibration isolation systems (FRVISs) based on high-static-low-dynamic stiffness (HSLDS) technology offer excellent low frequency vibration isolation performance with broad application prospects. However, the design process for these complex high-dimensional coupled nonlinear systems remains poorly developed, particularly when applied for ocean-going vessels that experience rolling and pitching motions. The present work addresses this issue by establishing a six-degree-of-freedom HSLDS vibration isolation model for FRVISs composed of eight isolators, and the model is applied to fully analyze the swing stability and multidimensional vibration isolation performance of these systems. The influence of nonlinearity on the mechanical properties of the vibration isolators is analyzed more clearly by assuming that each vibration isolator realizes nonlinear HSLDS characteristics in the z direction and linear characteristics in the x and y directions. The results demonstrate that the swing displacement responses of the system are greatly reduced under weak nonlinearity, which reflects the high static stiffness and high static stability characteristics of an HSLDS system. The multidimensional vibration isolation performance of the system is evaluated according to the impacts of nonlinearity, the installation height Hz of the isolators, and the relative position Dr of the two middle isolators. The results of analysis demonstrate that applying a value of Hz = 0 produces the best vibration isolation performance overall under strong nonlinearity by avoiding unnecessary secondary peaks in the force transmission rate under harmonic mechanical excitation and ensuring a maximum high-frequency vibration isolation effect. However, applying a weak nonlinearity is better than a strong nonlinearity if Hz is not zero. In contrast, Dr has little effect on the vibration isolation effect of the raft in the x, y, and z directions. Therefore, an equidistant installation with Dr = 0.5 would be considered ideal from the standpoint of installation stability.

Inertia Optimization Control and Transient Stability Analysis of Wind Power Grid-Connected System

The virtual inertia control effectively makes up for the insufficient inertia caused by the high penetration wind power grid connection. However, it has an impact on the mechanical part of the wind turbine and greatly increases the difficulty of the dynamic stability analysis of the system, resulting in limited engineering practicability. Therefore, the state equation of the wind power grid-connected system is established in this paper, and the influence of virtual inertia control on wind turbine shafting oscillation is analyzed based on the small-signal theory. Secondly, the nonlinear extended disturbance observer is designed as the compensation signal of inertia control to improve its dynamic stability supportability. Based on the integral manifold method, the shafting model of the wind turbine is reduced, and the transient energy function of shafting is established, which provided the basis for the design of the shafting stability controller. Finally, a grid-connected wind power system with high permeability is installed, and the results demonstrate that under the proposed control strategy, the swing stability of power angle is significantly improved, and the wind turbine shafting oscillation is suppressed.

A Unified Model of Voltage-Controlled Inverter for Transient Angle Stability Analysis

The safety of grid-connected voltage-controlled inverter is threatened by transient angle instability due to fault. The impact of different active power control (APC) and reactive power control (RPC) on the inverter's transient angle stability hasn't been fully investigated. To fill this gap, firstly, a unified model of the voltage-controlled inverter considering different APC and RPC is put forward. Based on the proposed unified model, the effect of different APC and RPC loops on the inverter's transient angle stability are qualitatively analyzed by using equal area criterion (EAC). Then, the TS multimodeling method which is based on the Lyapunov function is applied to evaluate the effect of control parameters on the inverter's transient angle stability quantificationally. Finally, the above analysis is verified based on an experiment. It is found that lowering inertia improves the inverter's global stability but decreases the inverter's first swing stability. Transient stability of the inverter can be improved by increasing damping component of the inverter. Transient angle stability of the inverter is influenced by the RPC loop. With the increase of the output voltage of the RPC loop, reference reactive power, and output voltage of the inverter, transient angle stability of the inverter can be improved.

Power Flow Control in Transmission Line by Using UPFC

The power transfer capacity of electrical transmission lines is typically constrained by the capacity of large signals. Economic considerations such as the high cost of long lines and the income from the supply of additional power make it possible to pursue both economically and technically viable ways to increase the stability cap intensively. On the other hand, the production of efficient ways to use the full thermal capacity of transmission systems. The power industry has already begun to be affected by fast development in the field of power electronics. This is one direct consequence of the idea of aspects of FACTS, which has become possible due to the progress realized in power electronic devices. In theory, the FACTS devices can provide rapid control of real and Var power through transmission line. The UPFC is a FACTS family member with very appealing characteristics. Many parameters can be independently controlled by this unit. An alternative means of minimizing transmission system oscillations is given by this unit. The choice of input signals and the adopted control strategy for this system in order to dampen power oscillations in an efficient and robust manner are an important issue. In order to achieve the maximum desire effect in solving the first swing stability problem, the UPFC parameters can be regulated. In bulky power transmission systems with long transmission lines, this problem arises. A MATLAB Simulink Model with UPFC to test the efficiency of the electrical transmission system is considered in this paper. The main purpose of this analysis paper is to research different studies performed in the past to minimize UPFC transmission line losses.

A first swing stability improvement approach in microgrids with synchronous distributed generators

A first swing stability improvement approach in microgrids with synchronous distributed generators

Excitation control method based on wide-area measurement system for improvement of transient stability in power systems

In this paper, we propose a novel excitation control method for synchronous generators (SGs) for improvement of transient stability in power systems. The proposed excitation system controls the excitation voltage based on a wide-area measurement system (WAMS). An energy function for the power system was adopted as a stability index, and we designed a control system to promote a decrease in the energy function after a disturbance. Numerical simulations were carried out for a multi-machine power system. The results show that the proposed WAMS-based stabilizer (WBS) improves the first swing stability and enhances the damping of the subsequent oscillation, whereas the conventional power system stabilizer (PSS) does not necessarily improve the first swing stability. It is also noteworthy that the WBS has few parameters that need to be tuned, unlike the PSS.

Transient stability constrained optimal power flow based on trajectory sensitivity for power dispatch of distributed synchronous generators

This paper is focused on the transient stability constrained optimal power flow (TSC-OPF) problem and its application for determining the optimal dispatch of active and reactive powers of distributed synchronous generators. In order to deal with uncertainties related to the actual active and reactive load values and the network topology configuration, this paper proposes a TSC- OPF formulation that incorporates a set of mathematical constraints based on the trajectory sensitivity analysis (TSA) that represents the impact of different load scenarios and network topologies on the transient stability of the system. The TSC-OPF is solved by an iterative algorithm based on the primal-dual interior point method and the concept of rotor angle first swing (FS) stability. The proposed TSC-OPF is applied for a distribution network constituted by nine buses and two distributed synchronous generators.

A Library of Second-Order Models for Synchronous Machines

This article presents a library of second-order models for synchronous machines that can be utilized in power system dynamic performance analysis and control design. The models have a similar structure to that of the so-called classical model in that they consist of two dynamic states, the power angle and the angular speed. However, unlike the classical model, they find applications beyond first swing stability analysis, i.e., they can be utilized for multi-swing transient stability analysis. The models are developed through a systematic reduction of a nineteenth-order model using singular perturbation techniques. They are validated by comparing their response with that of the high-order model from which they were derived, as well as that of other synchronous machine models existing in the literature, such as the so-called two-axis model and the so-called one-axis model.

Optimized virtual inertia of wind turbine for rotor angle stability in interconnected power systems

In the power system with virtual inertias, the current dynamic analysis of frequency stability is insufficient to ensure grid security because the virtual inertia control also has a significant effect on the first swing stability of the rotor angle. This paper investigates a novel virtual inertia control strategy for wind turbines to improve the first swing stability of the rotor angle in the interconnected power grid. The virtual energy provided by the virtual inertia control of the wind turbines is calculated. Considering that the rotor angle swings in the forward and backward directions, the effect of virtual energies in two different coherent generator groups on system transient energy conversion is evaluated. Moreover, a novel control method is proposed to provide more reliable inertia support. A typical two-area interconnected power system with a high wind penetration of 35%, which consists of four conventional power plants and two doubly fed induction generator (DFIG)-based wind farms, is simulated. The simulation results demonstrate that in the transient events, the rotor angle difference between the coherent generator groups can be reduced by regulating the variable inertias, significantly improving the reliability of the virtual inertia support of wind turbines.

Multi-objective virtual inertia control of renewable power generator for transient stability improvement in interconnected power system

In the power system with high penetration of renewable power generators (RPG), although frequency performance can be improved by introducing virtual inertia control, the swing stability of the rotor angle is likely to be reduced due to the changed inertia distribution. The motion equation of an interconnected power system with RPGs is established firstly, and the transient energy function is then derived to analyse the impacts of virtual inertias on transient energy conversion. In this paper, the transient process of the rotor angle after the disturbances is divided into two periods of first swing and multi-swing, and the effects of virtual inertia on the system stability are then analysed in the two periods, respectively. Under the virtual inertia control, the RPGs are utilized not only to share accelerating energy with synchronous generators (SG), but also to provide additional decelerating energy for the reduction of the rotor angle variation during the first swing period. In addition, based on the eigenvalues analysis, the effects of virtual inertias on system damping are evaluated theoretically, and the virtual energy of RPGs is then regulated to damp the oscillations during the subsequent multi-swing period. Experimental tests on a hardware-in-the-loop platform of a two-area interconnected power system with high wind power penetration are carried out to validate the proposed control strategy. The results demonstrate that in addition to the basic frequency support function, the swing stability of rotor angle is also improved, thus greatly improving the reliability of the virtual inertia support.

The effect of using Gait Exercise Assist Robot (GEAR) on gait pattern in stroke patients: a cross-sectional pilot study

ABSTRACTBackground: The Gait Exercise Assist Robot (GEAR) has been developed to support gait training for stroke patients. The GEAR can assist paretic lower limb swing and stance stability, which make it possible to practice walking without excessive compensation movements. However, there are no studies to-date that investigate the effect of the GEAR on gait pattern.Objectives: The purpose of this study was to clarify the effect of gait training on gait pattern using the GEAR for rehabilitation in stroke patients.Methods: Fifteen hemiplegic patients who received gait training using the GEAR were recruited (GEAR group). As a control group, hemiplegic patients who did not receive gait training using the GEAR were selected for each patient in the GEAR group from 114 cases in our hospital database. Primary outcomes were index values indicating the degree of 10 abnormal gait patterns. Secondary outcomes were spatiotemporal factors and comfortable overground gait velocity.Results: Index values for abnormal gait patterns were significantly lower in the GEAR group compared to the control group for insufficient knee flexion during the swing phase, hip hiking, and excessive lateral shift of the trunk over the unaffected-side (p < .05). The comfortable overground gait velocity, stride length, and unaffected-step length in the GEAR group were significantly better than in the control group (p < .05).Conclusions: Gait training using the GEAR had effects on reducing abnormal gait patterns and improving gait velocity, stride, and unaffected-side step length compared to conventional gait training alone in individuals recovering from stroke-induced hemiplegia.

The influence of damping resistance on first swing stability of turbine generator considering stator transient

Generally, the ignored stator transient of turbine generator result in the unidirectional electromagnetic torque caused by damping resistance is neglected. While, the unidirectional electromagnetic torque has a braking effect which can reduce the rotor acceleration following the disturbance and improve the stability of power system. With a 300 MW turbine generator as an example, the large disturbance characteristic and First Swing Stability (FSS) limit are calculated by Time-Step Finite Element Model (T-S FEM) and three practical models of turbine generator in this paper. The unidirectional electromagnetic torque caused by stator transient is investigated and its important role in FSS is analyzed. Since there are several material options for damping windings, the influence of damping resistance on the large disturbance characteristic and FSS limit are calculated and compared under different damping resistance. The result shows that the FSS limits calculated by the practical model with stator transient are increased than that without stator transient; the FSS limits of turbine generator with damping windings made from stainless steel are larger than that made from aluminum and beryllium bronze by the four kinds of generator models. The result provides theoretic basis of generator modeling for precise simulation of power systems.

Transient Stability Constrained Optimal Power Flow Based on Multi-time Scale Power System Models

This paper is focused on the transient stability constrained optimal power flow (TSC-OPF) problem and its application for determining the optimal dispatch of active and reactive powers of distributed synchronous generators. In order to relieve the mathematical complexity of the TSC-OPF problem with respect to its dimensionality, this paper proposes a decomposition of the power system model in a two-time scale model which is constituted by two smaller-order subsystems denoted by the fast and slow subsystems, where only the equations of the fast subsystem are transformed in algebraic equations by means of the implicit trapezoidal technique and incorporated in the TSC-OPF formulation. The TSC-OPF is then solved by considering in its formulation the lowest amount of time steps in post-fault period that guarantee the rotor angle first swing (FS) stability of the fast subsystem, and this aspect also contributes for reducing the dimensionality of the TSC-OPF problem. Tests were made for a 31-bus distribution network with two synchronous generators and for a 51-bus distribution network with nine synchronous generators.

Toward intelligent transient stability enhancement in inverter-based microgrids

Nowadays, the concept of multiple inverter-interfaced distributed generations (IIDGs)-based MG is recognized as a renowned notion. Encountering unexpected transient situations, the fast inflexible response of IIDG may contribute in serious concerns over its successful operation. Contemplating the transient stability paradigm, first swing stability of the investigated system is the mostly pinpointed matter. In the state-of-the-art indices in transient analysis of IIDG-based technologies, the current index is referred as the frequently deployed one. However, this index is capped within the switches’ twice rated current to afford the inverter’s physical constraints. To tackle this requirement, the ongoing study aims at devising an efficient transient current control loop (TCCL) embedded as a part of main control procedure. In this practice, the well-known simple proportional–integral (PI) controller, as the most persuasive industrial choice, is regarded as the supplementary TCCL key unit. The main functionality of the founded TCCL is deemed as a talented transient current limiter in IIDGs during the versatile possible short-circuit situations. In spite of this, the conventional fixed tuning of gains in PI controller would depreciate its safe and reliable operation encountering different contingencies. To rehabilitate this matter, fuzzy logic and artificial neural network concepts are deployed for realizing an adaptive PI controller capable of handling both the connected and autonomous modes of operation. Precise numerical studies are carried out to interrogate the performance of the proposed approach. Results are analyzed in depth.

Determining potential stability enhancements of flexible AC transmission system devices using corrected transient energy function

In this study, the calculations of flexible AC transmission system (FACTS) devices energy function and corrected transient energy function (CTEF) in presence of FACTS are formulated. The most versatile FACTS devices are modelled for transient-stability assessment using CTEF. Furthermore, the effects of FACTS devices on the corrected transient margin are evaluated by considering the corrected transient energy margin (CTEM), corrected transient kinetic energy (CTKE), and fault critical clearing time (CCT). The proven formulations are applied and compared on three different networks, 3-bus, 39-bus, and 145-bus test systems. All evaluations are compared with each other in the presence and absence of the FACTS devices, and the results of simulation and direct method are investigated. It is proven that by using the energy functions of static VAr compensator, thyristor-controlled series capacitor, and unified power flow controller, the results of the direct method and the simulation method are almost equal. Also, the efficient criteria in identifying first swing stability behavior are developed for the hybrid method to evaluate the CTEM. Test results do not show any irregular non-linearity on the variations of CTEM, CTKE, and CCT for both plant and inter-area mode disturbances.

Wide‐area control through aggregation of power systems

This study proposes a new method for stabilising disturbed power systems using wide-area measurement and controllable devices. A new control algorithm based on kinetic energy is proposed to be applied on the controllers to improve the first swing stability of power systems following large disturbances while also damping the subsequent inter-area oscillations. The wide-area controller is implemented by using the Kalman filter estimation of the area-based model of the system, to stabilise the inter-area dynamic and improve the stability margin of the system. The proposed approach is simulated on several test systems and the results show significant improvement in the first swing and damping stability of the test systems.

Effect of functional foot orthotics on golf swing stability and accuracy of shots

Effect of functional foot orthotics on golf swing stability and accuracy of shots

The influence of turbine generator rotor damping structure and material on first swing stability

In this paper, we study the influence of rotor damping structure and material on First Swing Stability (FSS) of turbine generator connected to power system after three-phase short circuit. Considering the complex rotor damping structure of turbine generator, we make crucial improvements in finite element discrete strategy reflecting skin effect of eddy current and establish field-circuit-network coupled time-step finite element model. We test this model by the experiment of 7.5kW model machine. Based on this model, we take a 300MW turbine generator as an example to study the influence of damping bar, rotor iron core and conductive slot wedge on FSS. We investigate the importance of the rotor damping structure to FSS and find its impact is not negligible. By comparing the FSS limits affected by three components of rotor damping structure respectively, we conclude that the effect of rotor slot wedge and iron core is not linear superposition but Coupling relationship. Since we have several rotor slot wedge materials to choose from and the conductivity of these materials is different, we establish the relationship between FSS limit and conductivity of rotor slot wedge. The result shows that the FSS limit gradually increases as the conductivity of rotor slot wedge changes from σal (conductivity of aluminum alloy) to 0.05σal.

Influence of Different Practical Models on the First Swing Stability of Turbine Generators

There are two popular practical models of synchronous generators used in power system simulation, both based on Park equations, defined as assumed A and assumed B respectively, according to the different assumptions. To study the influence of the different models on the first swing stability calculation precision, the physical essence of the two assumptions are revealed in theory, and it is obtained that assumed A takes account of the mutual leakage flux linkage between field and damping windings and neglects the self-leakage flux linkage of damping winding, the opposite of assumed B. Taking a 300-MW turbine generator as an example, first swing stability limits calculated by two practical models are compared; simulation results are verified by the time-step finite-element model. The influence of line reactance and excitation system on first swing stability limits is studied. Results show that the first swing stability limit calculated by the practical model with assumed A is closer to the result of the time-step finite-element model, since assumed A takes account of the larger mutual leakage flux linkage. Therefore, the practical model with assumed A is more accurate. The result provides reasonable reference to select synchronous generator models in power system simulation.